engines/gig/Engine.cpp

/***************************************************************************
 *                                                                         *
 *   LinuxSampler - modular, streaming capable sampler                     *
 *                                                                         *
 *   Copyright (C) 2003,2004 by Benno Senoner and Christian Schoenebeck   *
 *   Copyright (C) 2005-2007 Christian Schoenebeck                        *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
 *   GNU General Public License for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the Free Software           *
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston,                 *
 *   MA  02111-1307  USA                                                   *
 ***************************************************************************/

#include <sstream>
#include "DiskThread.h"
#include "Voice.h"
#include "EGADSR.h"
#include "../EngineFactory.h"

#include "Engine.h"

namespace LinuxSampler { namespace gig {

    InstrumentResourceManager Engine::instruments;

    std::map<AudioOutputDevice*,Engine*> Engine::engines;

    /**
     * Get a gig::Engine object for the given gig::EngineChannel and the
     * given AudioOutputDevice. All engine channels which are connected to
     * the same audio output device will use the same engine instance. This
     * method will be called by a gig::EngineChannel whenever it's
     * connecting to a audio output device.
     *
     * @param pChannel - engine channel which acquires an engine object
     * @param pDevice  - the audio output device \a pChannel is connected to
     */
    Engine* Engine::AcquireEngine(LinuxSampler::gig::EngineChannel* pChannel, AudioOutputDevice* pDevice) {
        Engine* pEngine = NULL;
        // check if there's already an engine for the given audio output device
        if (engines.count(pDevice)) {
            dmsg(4,("Using existing gig::Engine.\n"));
            pEngine = engines[pDevice];

            // Disable the engine while the new engine channel is
            // added and initialized. The engine will be enabled again
            // in EngineChannel::Connect.
            pEngine->DisableAndLock();
        } else { // create a new engine (and disk thread) instance for the given audio output device
            dmsg(4,("Creating new gig::Engine.\n"));
            pEngine = (Engine*) EngineFactory::Create("gig");
            pEngine->Connect(pDevice);
            engines[pDevice] = pEngine;
        }
        // register engine channel to the engine instance
        pEngine->engineChannels.add(pChannel);
        // remember index in the ArrayList
        pChannel->iEngineIndexSelf = pEngine->engineChannels.size() - 1;
        dmsg(4,("This gig::Engine has now %d EngineChannels.\n",pEngine->engineChannels.size()));
        return pEngine;
    }

    /**
     * Once an engine channel is disconnected from an audio output device,
     * it wil immediately call this method to unregister itself from the
     * engine instance and if that engine instance is not used by any other
     * engine channel anymore, then that engine instance will be destroyed.
     *
     * @param pChannel - engine channel which wants to disconnect from it's
     *                   engine instance
     * @param pDevice  - audio output device \a pChannel was connected to
     */
    void Engine::FreeEngine(LinuxSampler::gig::EngineChannel* pChannel, AudioOutputDevice* pDevice) {
        dmsg(4,("Disconnecting EngineChannel from gig::Engine.\n"));
        Engine* pEngine = engines[pDevice];
        // unregister EngineChannel from the Engine instance
        pEngine->engineChannels.remove(pChannel);
        // if the used Engine instance is not used anymore, then destroy it
        if (pEngine->engineChannels.empty()) {
            pDevice->Disconnect(pEngine);
            engines.erase(pDevice);
            delete pEngine;
            dmsg(4,("Destroying gig::Engine.\n"));
        }
        else dmsg(4,("This gig::Engine has now %d EngineChannels.\n",pEngine->engineChannels.size()));
    }

    /**
     * Constructor
     */
    Engine::Engine() {
        pAudioOutputDevice = NULL;
        pDiskThread        = NULL;
        pEventGenerator    = NULL;
        pSysexBuffer       = new RingBuffer<uint8_t,false>(CONFIG_SYSEX_BUFFER_SIZE, 0);
        pEventQueue        = new RingBuffer<Event,false>(CONFIG_MAX_EVENTS_PER_FRAGMENT, 0);
        pEventPool         = new Pool<Event>(CONFIG_MAX_EVENTS_PER_FRAGMENT);
        pVoicePool         = new Pool<Voice>(CONFIG_MAX_VOICES);
        pDimRegionsInUse   = new ::gig::DimensionRegion*[CONFIG_MAX_VOICES + 1];
        pVoiceStealingQueue = new RTList<Event>(pEventPool);
        pGlobalEvents      = new RTList<Event>(pEventPool);
        InstrumentChangeQueue      = new RingBuffer<instrument_change_command_t,false>(1, 0);
        InstrumentChangeReplyQueue = new RingBuffer<instrument_change_reply_t,false>(1, 0);

        for (RTList<Voice>::Iterator iterVoice = pVoicePool->allocAppend(); iterVoice == pVoicePool->last(); iterVoice = pVoicePool->allocAppend()) {
            iterVoice->SetEngine(this);
        }
        pVoicePool->clear();

        ResetInternal();
        ResetScaleTuning();
    }

    /**
     * Destructor
     */
    Engine::~Engine() {
        MidiInputPort::RemoveSysexListener(this);
        if (pDiskThread) {
            dmsg(1,("Stopping disk thread..."));
            pDiskThread->StopThread();
            delete pDiskThread;
            dmsg(1,("OK\n"));
        }
        if (pEventQueue) delete pEventQueue;
        if (pEventPool)  delete pEventPool;
        if (pVoicePool) {
            pVoicePool->clear();
            delete pVoicePool;
        }
        if (pEventGenerator) delete pEventGenerator;
        if (pVoiceStealingQueue) delete pVoiceStealingQueue;
        if (pSysexBuffer) delete pSysexBuffer;
        Unregister();
    }

    void Engine::Enable() {
        dmsg(3,("gig::Engine: enabling\n"));
        EngineDisabled.PushAndUnlock(false, 2); // set condition object 'EngineDisabled' to false (wait max. 2s)
        dmsg(3,("gig::Engine: enabled (val=%d)\n", EngineDisabled.GetUnsafe()));
    }

    void Engine::Disable() {
        dmsg(3,("gig::Engine: disabling\n"));
        bool* pWasDisabled = EngineDisabled.PushAndUnlock(true, 2); // wait max. 2s
        if (!pWasDisabled) dmsg(3,("gig::Engine warning: Timeout waiting to disable engine.\n"));
    }

    void Engine::DisableAndLock() {
        dmsg(3,("gig::Engine: disabling\n"));
        bool* pWasDisabled = EngineDisabled.Push(true, 2); // wait max. 2s
        if (!pWasDisabled) dmsg(3,("gig::Engine warning: Timeout waiting to disable engine.\n"));
    }

    /**
     *  Reset all voices and disk thread and clear input event queue and all
     *  control and status variables.
     */
    void Engine::Reset() {
        DisableAndLock();
        ResetInternal();
        ResetScaleTuning();
        Enable();
    }

    /**
     *  Reset all voices and disk thread and clear input event queue and all
     *  control and status variables. This method is protected by a mutex.
     */
    void Engine::ResetInternal() {
        ResetInternalMutex.Lock();

        // make sure that the engine does not get any sysex messages
        // while it's reseting
        bool sysexDisabled = MidiInputPort::RemoveSysexListener(this);
        ActiveVoiceCount    = 0;
        ActiveVoiceCountMax = 0;

        // reset voice stealing parameters
        pVoiceStealingQueue->clear();
        itLastStolenVoice          = RTList<Voice>::Iterator();
        itLastStolenVoiceGlobally  = RTList<Voice>::Iterator();
        iuiLastStolenKey           = RTList<uint>::Iterator();
        iuiLastStolenKeyGlobally   = RTList<uint>::Iterator();
        pLastStolenChannel         = NULL;

        // reset all voices
        for (RTList<Voice>::Iterator iterVoice = pVoicePool->allocAppend(); iterVoice == pVoicePool->last(); iterVoice = pVoicePool->allocAppend()) {
            iterVoice->Reset();
        }
        pVoicePool->clear();

        // reset disk thread
        if (pDiskThread) pDiskThread->Reset();

        // delete all input events
        pEventQueue->init();
        pSysexBuffer->init();
        if (sysexDisabled) MidiInputPort::AddSysexListener(this);
        ResetInternalMutex.Unlock();
    }

    /**
     * Reset to normal, chromatic scale (means equal tempered).
     */
    void Engine::ResetScaleTuning() {
        memset(&ScaleTuning[0], 0x00, 12);
    }

    /**
     * Connect this engine instance with the given audio output device.
     * This method will be called when an Engine instance is created.
     * All of the engine's data structures which are dependant to the used
     * audio output device / driver will be (re)allocated and / or
     * adjusted appropriately.
     *
     * @param pAudioOut - audio output device to connect to
     */
    void Engine::Connect(AudioOutputDevice* pAudioOut) {
        pAudioOutputDevice = pAudioOut;

        ResetInternal();

        // inform audio driver for the need of two channels
        try {
            pAudioOutputDevice->AcquireChannels(2); // gig engine only stereo
        }
        catch (AudioOutputException e) {
            String msg = "Audio output device unable to provide 2 audio channels, cause: " + e.Message();
            throw Exception(msg);
        }

        this->MaxSamplesPerCycle = pAudioOutputDevice->MaxSamplesPerCycle();
        this->SampleRate         = pAudioOutputDevice->SampleRate();

        // FIXME: audio drivers with varying fragment sizes might be a problem here
        MaxFadeOutPos = MaxSamplesPerCycle - int(double(SampleRate) * CONFIG_EG_MIN_RELEASE_TIME) - 1;
        if (MaxFadeOutPos < 0) {
            std::cerr << "gig::Engine: WARNING, CONFIG_EG_MIN_RELEASE_TIME "
                      << "too big for current audio fragment size & sampling rate! "
                      << "May lead to click sounds if voice stealing chimes in!\n" << std::flush;
            // force volume ramp downs at the beginning of each fragment
            MaxFadeOutPos = 0;
            // lower minimum release time
            const float minReleaseTime = (float) MaxSamplesPerCycle / (float) SampleRate;
            for (RTList<Voice>::Iterator iterVoice = pVoicePool->allocAppend(); iterVoice == pVoicePool->last(); iterVoice = pVoicePool->allocAppend()) {
                iterVoice->EG1.CalculateFadeOutCoeff(minReleaseTime, SampleRate);
            }
            pVoicePool->clear();
        }

        // (re)create disk thread
        if (this->pDiskThread) {
            dmsg(1,("Stopping disk thread..."));
            this->pDiskThread->StopThread();
            delete this->pDiskThread;
            dmsg(1,("OK\n"));
        }
        this->pDiskThread = new DiskThread(((pAudioOut->MaxSamplesPerCycle() << CONFIG_MAX_PITCH) << 1) + 6, //FIXME: assuming stereo
                                           &instruments);
        if (!pDiskThread) {
            dmsg(0,("gig::Engine  new diskthread = NULL\n"));
            exit(EXIT_FAILURE);
        }

        for (RTList<Voice>::Iterator iterVoice = pVoicePool->allocAppend(); iterVoice == pVoicePool->last(); iterVoice = pVoicePool->allocAppend()) {
            iterVoice->pDiskThread = this->pDiskThread;
            dmsg(3,("d"));
        }
        pVoicePool->clear();

        // (re)create event generator
        if (pEventGenerator) delete pEventGenerator;
        pEventGenerator = new EventGenerator(pAudioOut->SampleRate());

        dmsg(1,("Starting disk thread..."));
        pDiskThread->StartThread();
        dmsg(1,("OK\n"));

        for (RTList<Voice>::Iterator iterVoice = pVoicePool->allocAppend(); iterVoice == pVoicePool->last(); iterVoice = pVoicePool->allocAppend()) {
            if (!iterVoice->pDiskThread) {
                dmsg(0,("Engine -> voice::trigger: !pDiskThread\n"));
                exit(EXIT_FAILURE);
            }
        }
    }

    /**
     * Clear all engine global event lists.
     */
    void Engine::ClearEventLists() {
        pGlobalEvents->clear();
    }

    /**
     * Copy all events from the engine's global input queue buffer to the
     * engine's internal event list. This will be done at the beginning of
     * each audio cycle (that is each RenderAudio() call) to distinguish
     * all global events which have to be processed in the current audio
     * cycle. These events are usually just SysEx messages. Every
     * EngineChannel has it's own input event queue buffer and event list
     * to handle common events like NoteOn, NoteOff and ControlChange
     * events.
     *
     * @param Samples - number of sample points to be processed in the
     *                  current audio cycle
     */
    void Engine::ImportEvents(uint Samples) {
        RingBuffer<Event,false>::NonVolatileReader eventQueueReader = pEventQueue->get_non_volatile_reader();
        Event* pEvent;
        while (true) {
            // get next event from input event queue
            if (!(pEvent = eventQueueReader.pop())) break;
            // if younger event reached, ignore that and all subsequent ones for now
            if (pEvent->FragmentPos() >= Samples) {
                eventQueueReader--;
                dmsg(2,("Younger Event, pos=%d ,Samples=%d!\n",pEvent->FragmentPos(),Samples));
                pEvent->ResetFragmentPos();
                break;
            }
            // copy event to internal event list
            if (pGlobalEvents->poolIsEmpty()) {
                dmsg(1,("Event pool emtpy!\n"));
                break;
            }
            *pGlobalEvents->allocAppend() = *pEvent;
        }
        eventQueueReader.free(); // free all copied events from input queue
    }

    /**
     * Let this engine proceed to render the given amount of sample points.
     * The engine will iterate through all engine channels and render audio
     * for each engine channel independently. The calculated audio data of
     * all voices of each engine channel will be placed into the audio sum
     * buffers of the respective audio output device, connected to the
     * respective engine channel.
     *
     *  @param Samples - number of sample points to be rendered
     *  @returns       0 on success
     */
    int Engine::RenderAudio(uint Samples) {
        dmsg(7,("RenderAudio(Samples=%d)\n", Samples));

        // return if engine disabled
        if (EngineDisabled.Pop()) {
            dmsg(5,("gig::Engine: engine disabled (val=%d)\n",EngineDisabled.GetUnsafe()));
            return 0;
        }

        // update time of start and end of this audio fragment (as events' time stamps relate to this)
        pEventGenerator->UpdateFragmentTime(Samples);

        // We only allow a maximum of CONFIG_MAX_VOICES voices to be spawned
        // in each audio fragment. All subsequent request for spawning new
        // voices in the same audio fragment will be ignored.
        VoiceSpawnsLeft = CONFIG_MAX_VOICES;

        // get all events from the engine's global input event queue which belong to the current fragment
        // (these are usually just SysEx messages)
        ImportEvents(Samples);

        // process engine global events (these are currently only MIDI System Exclusive messages)
        {
            RTList<Event>::Iterator itEvent = pGlobalEvents->first();
            RTList<Event>::Iterator end     = pGlobalEvents->end();
            for (; itEvent != end; ++itEvent) {
                switch (itEvent->Type) {
                    case Event::type_sysex:
                        dmsg(5,("Engine: Sysex received\n"));
                        ProcessSysex(itEvent);
                        break;
                }
            }
        }

        // reset internal voice counter (just for statistic of active voices)
        ActiveVoiceCountTemp = 0;

        // handle instrument change commands
        instrument_change_command_t command;
        if (InstrumentChangeQueue->pop(&command) > 0) {
            EngineChannel* pEngineChannel = command.pEngineChannel;
            pEngineChannel->pInstrument = command.pInstrument;

            // iterate through all active voices and mark their
            // dimension regions as "in use". The instrument resource
            // manager may delete all of the instrument except the
            // dimension regions and samples that are in use.
            int i = 0;
            RTList<uint>::Iterator iuiKey = pEngineChannel->pActiveKeys->first();
            RTList<uint>::Iterator end    = pEngineChannel->pActiveKeys->end();
            while (iuiKey != end) { // iterate through all active keys
                midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[*iuiKey];
                ++iuiKey;

                RTList<Voice>::Iterator itVoice     = pKey->pActiveVoices->first();
                RTList<Voice>::Iterator itVoicesEnd = pKey->pActiveVoices->end();
                for (; itVoice != itVoicesEnd; ++itVoice) { // iterate through all voices on this key
                    if (!itVoice->Orphan) {
                        itVoice->Orphan = true;
                        pDimRegionsInUse[i++] = itVoice->pDimRgn;
                    }
                }
            }
            pDimRegionsInUse[i] = 0; // end of list

            // send a reply to the calling thread, which is waiting
            instrument_change_reply_t reply;
            InstrumentChangeReplyQueue->push(&reply);
        }

        // handle events on all engine channels
        for (int i = 0; i < engineChannels.size(); i++) {
            ProcessEvents(engineChannels[i], Samples);
        }

        // render all 'normal', active voices on all engine channels
        for (int i = 0; i < engineChannels.size(); i++) {
            RenderActiveVoices(engineChannels[i], Samples);
        }

        // now that all ordinary voices on ALL engine channels are rendered, render new stolen voices
        RenderStolenVoices(Samples);

        // handle audio routing for engine channels with FX sends
        for (int i = 0; i < engineChannels.size(); i++) {
            if (engineChannels[i]->fxSends.empty()) continue; // ignore if no FX sends
            RouteAudio(engineChannels[i], Samples);
        }

        // handle cleanup on all engine channels for the next audio fragment
        for (int i = 0; i < engineChannels.size(); i++) {
            PostProcess(engineChannels[i]);
        }


        // empty the engine's event list for the next audio fragment
        ClearEventLists();

        // reset voice stealing for the next audio fragment
        pVoiceStealingQueue->clear();

        // just some statistics about this engine instance
        ActiveVoiceCount = ActiveVoiceCountTemp;
        if (ActiveVoiceCount > ActiveVoiceCountMax) ActiveVoiceCountMax = ActiveVoiceCount;

        FrameTime += Samples;

        return 0;
    }

    /**
     * Dispatch and handle all events in this audio fragment for the given
     * engine channel.
     *
     * @param pEngineChannel - engine channel on which events should be
     *                         processed
     * @param Samples        - amount of sample points to be processed in
     *                         this audio fragment cycle
     */
    void Engine::ProcessEvents(EngineChannel* pEngineChannel, uint Samples) {
        // get all events from the engine channels's input event queue which belong to the current fragment
        // (these are the common events like NoteOn, NoteOff, ControlChange, etc.)
        pEngineChannel->ImportEvents(Samples);

        // process events
        {
            RTList<Event>::Iterator itEvent = pEngineChannel->pEvents->first();
            RTList<Event>::Iterator end     = pEngineChannel->pEvents->end();
            for (; itEvent != end; ++itEvent) {
                switch (itEvent->Type) {
                    case Event::type_note_on:
                        dmsg(5,("Engine: Note on received\n"));
                        ProcessNoteOn((EngineChannel*)itEvent->pEngineChannel, itEvent);
                        break;
                    case Event::type_note_off:
                        dmsg(5,("Engine: Note off received\n"));
                        ProcessNoteOff((EngineChannel*)itEvent->pEngineChannel, itEvent);
                        break;
                    case Event::type_control_change:
                        dmsg(5,("Engine: MIDI CC received\n"));
                        ProcessControlChange((EngineChannel*)itEvent->pEngineChannel, itEvent);
                        break;
                    case Event::type_pitchbend:
                        dmsg(5,("Engine: Pitchbend received\n"));
                        ProcessPitchbend((EngineChannel*)itEvent->pEngineChannel, itEvent);
                        break;
                }
            }
        }

        // reset voice stealing for the next engine channel (or next audio fragment)
        itLastStolenVoice         = RTList<Voice>::Iterator();
        itLastStolenVoiceGlobally = RTList<Voice>::Iterator();
        iuiLastStolenKey          = RTList<uint>::Iterator();
        iuiLastStolenKeyGlobally  = RTList<uint>::Iterator();
        pLastStolenChannel        = NULL;
    }

    /**
     * Render all 'normal' voices (that is voices which were not stolen in
     * this fragment) on the given engine channel.
     *
     * @param pEngineChannel - engine channel on which audio should be
     *                         rendered
     * @param Samples        - amount of sample points to be rendered in
     *                         this audio fragment cycle
     */
    void Engine::RenderActiveVoices(EngineChannel* pEngineChannel, uint Samples) {
        #if !CONFIG_PROCESS_MUTED_CHANNELS
        if (pEngineChannel->GetMute()) return; // skip if sampler channel is muted
        #endif

        RTList<uint>::Iterator iuiKey = pEngineChannel->pActiveKeys->first();
        RTList<uint>::Iterator end    = pEngineChannel->pActiveKeys->end();
        while (iuiKey != end) { // iterate through all active keys
            midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[*iuiKey];
            ++iuiKey;

            RTList<Voice>::Iterator itVoice     = pKey->pActiveVoices->first();
            RTList<Voice>::Iterator itVoicesEnd = pKey->pActiveVoices->end();
            for (; itVoice != itVoicesEnd; ++itVoice) { // iterate through all voices on this key
                // now render current voice
                itVoice->Render(Samples);
                if (itVoice->IsActive()) ActiveVoiceCountTemp++; // still active
                else { // voice reached end, is now inactive
                    FreeVoice(pEngineChannel, itVoice); // remove voice from the list of active voices
                }
            }
        }
    }

    /**
     * Render all stolen voices (only voices which were stolen in this
     * fragment) on the given engine channel. Stolen voices are rendered
     * after all normal voices have been rendered; this is needed to render
     * audio of those voices which were selected for voice stealing until
     * the point were the stealing (that is the take over of the voice)
     * actually happened.
     *
     * @param pEngineChannel - engine channel on which audio should be
     *                         rendered
     * @param Samples        - amount of sample points to be rendered in
     *                         this audio fragment cycle
     */
    void Engine::RenderStolenVoices(uint Samples) {
        RTList<Event>::Iterator itVoiceStealEvent = pVoiceStealingQueue->first();
        RTList<Event>::Iterator end               = pVoiceStealingQueue->end();
        for (; itVoiceStealEvent != end; ++itVoiceStealEvent) {
            EngineChannel* pEngineChannel = (EngineChannel*) itVoiceStealEvent->pEngineChannel;
            if (!pEngineChannel->pInstrument) continue; // ignore if no instrument loaded
            Pool<Voice>::Iterator itNewVoice =
                LaunchVoice(pEngineChannel, itVoiceStealEvent, itVoiceStealEvent->Param.Note.Layer, itVoiceStealEvent->Param.Note.ReleaseTrigger, false, false);
            if (itNewVoice) {
                itNewVoice->Render(Samples);
                if (itNewVoice->IsActive()) ActiveVoiceCountTemp++; // still active
                else { // voice reached end, is now inactive
                    FreeVoice(pEngineChannel, itNewVoice); // remove voice from the list of active voices
                }
            }
            else dmsg(1,("gig::Engine: ERROR, voice stealing didn't work out!\n"));

            // we need to clear the key's event list explicitly here in case key was never active
            midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[itVoiceStealEvent->Param.Note.Key];
            pKey->VoiceTheftsQueued--;
            if (!pKey->Active && !pKey->VoiceTheftsQueued) pKey->pEvents->clear();
        }
    }

    /**
     * Will be called in case the respective engine channel sports FX send
     * channels. In this particular case, engine channel local buffers are
     * used to render and mix all voices to. This method is responsible for
     * copying the audio data from those local buffers to the master audio
     * output channels as well as to the FX send audio output channels with
     * their respective FX send levels.
     *
     * @param pEngineChannel - engine channel from which audio should be
     *                         routed
     * @param Samples        - amount of sample points to be routed in
     *                         this audio fragment cycle
     */
    void Engine::RouteAudio(EngineChannel* pEngineChannel, uint Samples) {
        // route master signal
        {
            AudioChannel* pDstL = pAudioOutputDevice->Channel(pEngineChannel->AudioDeviceChannelLeft);
            AudioChannel* pDstR = pAudioOutputDevice->Channel(pEngineChannel->AudioDeviceChannelRight);
            pEngineChannel->pChannelLeft->MixTo(pDstL, Samples);
            pEngineChannel->pChannelRight->MixTo(pDstR, Samples);
        }
        // route FX send signal
        {
            for (int iFxSend = 0; iFxSend < pEngineChannel->GetFxSendCount(); iFxSend++) {
                FxSend* pFxSend = pEngineChannel->GetFxSend(iFxSend);
                // left channel
                const int iDstL = pFxSend->DestinationChannel(0);
                if (iDstL < 0) {
                    dmsg(1,("Engine::RouteAudio() Error: invalid FX send (L) destination channel"));
                } else {
                    AudioChannel* pDstL = pAudioOutputDevice->Channel(iDstL);
                    if (!pDstL) {
                        dmsg(1,("Engine::RouteAudio() Error: invalid FX send (L) destination channel"));
                    } else pEngineChannel->pChannelLeft->MixTo(pDstL, Samples, pFxSend->Level());
                }
                // right channel
                const int iDstR = pFxSend->DestinationChannel(1);
                if (iDstR < 0) {
                    dmsg(1,("Engine::RouteAudio() Error: invalid FX send (R) destination channel"));
                } else {
                    AudioChannel* pDstR = pAudioOutputDevice->Channel(iDstR);
                    if (!pDstR) {
                        dmsg(1,("Engine::RouteAudio() Error: invalid FX send (R) destination channel"));
                    } else pEngineChannel->pChannelRight->MixTo(pDstR, Samples, pFxSend->Level());
                }
            }
        }
        // reset buffers with silence (zero out) for the next audio cycle
        pEngineChannel->pChannelLeft->Clear();
        pEngineChannel->pChannelRight->Clear();
    }

    /**
     * Free all keys which have turned inactive in this audio fragment, from
     * the list of active keys and clear all event lists on that engine
     * channel.
     *
     * @param pEngineChannel - engine channel to cleanup
     */
    void Engine::PostProcess(EngineChannel* pEngineChannel) {
        // free all keys which have no active voices left
        {
            RTList<uint>::Iterator iuiKey = pEngineChannel->pActiveKeys->first();
            RTList<uint>::Iterator end    = pEngineChannel->pActiveKeys->end();
            while (iuiKey != end) { // iterate through all active keys
                midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[*iuiKey];
                ++iuiKey;
                if (pKey->pActiveVoices->isEmpty()) FreeKey(pEngineChannel, pKey);
                #if CONFIG_DEVMODE
                else { // just a sanity check for debugging
                    RTList<Voice>::Iterator itVoice     = pKey->pActiveVoices->first();
                    RTList<Voice>::Iterator itVoicesEnd = pKey->pActiveVoices->end();
                    for (; itVoice != itVoicesEnd; ++itVoice) { // iterate through all voices on this key
                        if (itVoice->itKillEvent) {
                            dmsg(1,("gig::Engine: ERROR, killed voice survived !!!\n"));
                        }
                    }
                }
                #endif // CONFIG_DEVMODE
            }
        }

        // empty the engine channel's own event lists
        pEngineChannel->ClearEventLists();
    }

    /**
     *  Will be called by the MIDI input device whenever a MIDI system
     *  exclusive message has arrived.
     *
     *  @param pData - pointer to sysex data
     *  @param Size  - lenght of sysex data (in bytes)
     */
    void Engine::SendSysex(void* pData, uint Size) {
        Event event             = pEventGenerator->CreateEvent();
        event.Type              = Event::type_sysex;
        event.Param.Sysex.Size  = Size;
        event.pEngineChannel    = NULL; // as Engine global event
        if (pEventQueue->write_space() > 0) {
            if (pSysexBuffer->write_space() >= Size) {
                // copy sysex data to input buffer
                uint toWrite = Size;
                uint8_t* pPos = (uint8_t*) pData;
                while (toWrite) {
                    const uint writeNow = RTMath::Min(toWrite, pSysexBuffer->write_space_to_end());
                    pSysexBuffer->write(pPos, writeNow);
                    toWrite -= writeNow;
                    pPos    += writeNow;

                }
                // finally place sysex event into input event queue
                pEventQueue->push(&event);
            }
            else dmsg(1,("Engine: Sysex message too large (%d byte) for input buffer (%d byte)!",Size,CONFIG_SYSEX_BUFFER_SIZE));
        }
        else dmsg(1,("Engine: Input event queue full!"));
    }

    /**
     *  Assigns and triggers a new voice for the respective MIDI key.
     *
     *  @param pEngineChannel - engine channel on which this event occured on
     *  @param itNoteOnEvent - key, velocity and time stamp of the event
     */
    void Engine::ProcessNoteOn(EngineChannel* pEngineChannel, Pool<Event>::Iterator& itNoteOnEvent) {
        #if !CONFIG_PROCESS_MUTED_CHANNELS
        if (pEngineChannel->GetMute()) return; // skip if sampler channel is muted
        #endif

        if (!pEngineChannel->pInstrument) return; // ignore if no instrument loaded

        //HACK: we should better add the transpose value only to the most mandatory places (like for retrieving the region and calculating the tuning), because otherwise voices will unintendedly survive when changing transpose while playing
        itNoteOnEvent->Param.Note.Key += pEngineChannel->GlobalTranspose;

        const int key = itNoteOnEvent->Param.Note.Key;
        midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[key];

        // move note on event to the key's own event list
        RTList<Event>::Iterator itNoteOnEventOnKeyList = itNoteOnEvent.moveToEndOf(pKey->pEvents);

        // if Solo Mode then kill all already active voices
        if (pEngineChannel->SoloMode) {
            Pool<uint>::Iterator itYoungestKey = pEngineChannel->pActiveKeys->last();
            if (itYoungestKey) {
                const int iYoungestKey = *itYoungestKey;
                const midi_key_info_t* pOtherKey = &pEngineChannel->pMIDIKeyInfo[iYoungestKey];
                if (pOtherKey->Active) {
                    // get final portamento position of currently active voice
                    if (pEngineChannel->PortamentoMode) {
                        RTList<Voice>::Iterator itVoice = pOtherKey->pActiveVoices->last();
                        if (itVoice) itVoice->UpdatePortamentoPos(itNoteOnEventOnKeyList);
                    }
                    // kill all voices on the (other) key
                    RTList<Voice>::Iterator itVoiceToBeKilled = pOtherKey->pActiveVoices->first();
                    RTList<Voice>::Iterator end               = pOtherKey->pActiveVoices->end();
                    for (; itVoiceToBeKilled != end; ++itVoiceToBeKilled) {
                        if (itVoiceToBeKilled->Type != Voice::type_release_trigger)
                            itVoiceToBeKilled->Kill(itNoteOnEventOnKeyList);
                    }
                }
            }
            // set this key as 'currently active solo key'
            pEngineChannel->SoloKey = key;
        }

        // Change key dimension value if key is in keyswitching area
        {
            const ::gig::Instrument* pInstrument = pEngineChannel->pInstrument;
            if (key >= pInstrument->DimensionKeyRange.low && key <= pInstrument->DimensionKeyRange.high)
                pEngineChannel->CurrentKeyDimension = float(key - pInstrument->DimensionKeyRange.low) /
                    (pInstrument->DimensionKeyRange.high - pInstrument->DimensionKeyRange.low + 1);
        }

        pKey->KeyPressed = true; // the MIDI key was now pressed down
        pKey->Velocity   = itNoteOnEventOnKeyList->Param.Note.Velocity;
        pKey->NoteOnTime = FrameTime + itNoteOnEventOnKeyList->FragmentPos(); // will be used to calculate note length

        // cancel release process of voices on this key if needed
        if (pKey->Active && !pEngineChannel->SustainPedal) {
            RTList<Event>::Iterator itCancelReleaseEvent = pKey->pEvents->allocAppend();
            if (itCancelReleaseEvent) {
                *itCancelReleaseEvent = *itNoteOnEventOnKeyList;         // copy event
                itCancelReleaseEvent->Type = Event::type_cancel_release; // transform event type
            }
            else dmsg(1,("Event pool emtpy!\n"));
        }

        // allocate and trigger new voice(s) for the key
        {
            // first, get total amount of required voices (dependant on amount of layers)
            ::gig::Region* pRegion = pEngineChannel->pInstrument->GetRegion(itNoteOnEventOnKeyList->Param.Note.Key);
            if (pRegion) {
                int voicesRequired = pRegion->Layers;
                // now launch the required amount of voices
                for (int i = 0; i < voicesRequired; i++)
                    LaunchVoice(pEngineChannel, itNoteOnEventOnKeyList, i, false, true, true);
            }
        }

        // if neither a voice was spawned or postponed then remove note on event from key again
        if (!pKey->Active && !pKey->VoiceTheftsQueued)
            pKey->pEvents->free(itNoteOnEventOnKeyList);

        if (!pEngineChannel->SoloMode || pEngineChannel->PortamentoPos < 0.0f) pEngineChannel->PortamentoPos = (float) key;
        pKey->RoundRobinIndex++;
    }

    /**
     *  Releases the voices on the given key if sustain pedal is not pressed.
     *  If sustain is pressed, the release of the note will be postponed until
     *  sustain pedal will be released or voice turned inactive by itself (e.g.
     *  due to completion of sample playback).
     *
     *  @param pEngineChannel - engine channel on which this event occured on
     *  @param itNoteOffEvent - key, velocity and time stamp of the event
     */
    void Engine::ProcessNoteOff(EngineChannel* pEngineChannel, Pool<Event>::Iterator& itNoteOffEvent) {
        #if !CONFIG_PROCESS_MUTED_CHANNELS
        if (pEngineChannel->GetMute()) return; // skip if sampler channel is muted
        #endif

        //HACK: we should better add the transpose value only to the most mandatory places (like for retrieving the region and calculating the tuning), because otherwise voices will unintendedly survive when changing transpose while playing
        itNoteOffEvent->Param.Note.Key += pEngineChannel->GlobalTranspose;

        const int iKey = itNoteOffEvent->Param.Note.Key;
        midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[iKey];
        pKey->KeyPressed = false; // the MIDI key was now released

        // move event to the key's own event list
        RTList<Event>::Iterator itNoteOffEventOnKeyList = itNoteOffEvent.moveToEndOf(pKey->pEvents);

        bool bShouldRelease = pKey->Active && ShouldReleaseVoice(pEngineChannel, itNoteOffEventOnKeyList->Param.Note.Key);

        // in case Solo Mode is enabled, kill all voices on this key and respawn a voice on the highest pressed key (if any)
        if (pEngineChannel->SoloMode && pEngineChannel->pInstrument) { //TODO: this feels like too much code just for handling solo mode :P
            bool bOtherKeysPressed = false;
            if (iKey == pEngineChannel->SoloKey) {
                pEngineChannel->SoloKey = -1;
                // if there's still a key pressed down, respawn a voice (group) on the highest key
                for (int i = 127; i > 0; i--) {
                    midi_key_info_t* pOtherKey = &pEngineChannel->pMIDIKeyInfo[i];
                    if (pOtherKey->KeyPressed) {
                        bOtherKeysPressed = true;
                        // make the other key the new 'currently active solo key'
                        pEngineChannel->SoloKey = i;
                        // get final portamento position of currently active voice
                        if (pEngineChannel->PortamentoMode) {
                            RTList<Voice>::Iterator itVoice = pKey->pActiveVoices->first();
                            if (itVoice) itVoice->UpdatePortamentoPos(itNoteOffEventOnKeyList);
                        }
                        // create a pseudo note on event
                        RTList<Event>::Iterator itPseudoNoteOnEvent = pOtherKey->pEvents->allocAppend();
                        if (itPseudoNoteOnEvent) {
                            // copy event
                            *itPseudoNoteOnEvent = *itNoteOffEventOnKeyList;
                            // transform event to a note on event
                            itPseudoNoteOnEvent->Type                = Event::type_note_on;
                            itPseudoNoteOnEvent->Param.Note.Key      = i;
                            itPseudoNoteOnEvent->Param.Note.Velocity = pOtherKey->Velocity;
                            // allocate and trigger new voice(s) for the other key
                            {
                                // first, get total amount of required voices (dependant on amount of layers)
                                ::gig::Region* pRegion = pEngineChannel->pInstrument->GetRegion(i);
                                if (pRegion) {
                                    int voicesRequired = pRegion->Layers;
                                    // now launch the required amount of voices
                                    for (int iLayer = 0; iLayer < voicesRequired; iLayer++)
                                        LaunchVoice(pEngineChannel, itPseudoNoteOnEvent, iLayer, false, true, false);
                                }
                            }
                            // if neither a voice was spawned or postponed then remove note on event from key again
                            if (!pOtherKey->Active && !pOtherKey->VoiceTheftsQueued)
                                pOtherKey->pEvents->free(itPseudoNoteOnEvent);

                        } else dmsg(1,("Could not respawn voice, no free event left\n"));
                        break; // done
                    }
                }
            }
            if (bOtherKeysPressed) {
                if (pKey->Active) { // kill all voices on this key
                    bShouldRelease = false; // no need to release, as we kill it here
                    RTList<Voice>::Iterator itVoiceToBeKilled = pKey->pActiveVoices->first();
                    RTList<Voice>::Iterator end               = pKey->pActiveVoices->end();
                    for (; itVoiceToBeKilled != end; ++itVoiceToBeKilled) {
                        if (itVoiceToBeKilled->Type != Voice::type_release_trigger)
                            itVoiceToBeKilled->Kill(itNoteOffEventOnKeyList);
                    }
                }
            } else pEngineChannel->PortamentoPos = -1.0f;
        }

        // if no solo mode (the usual case) or if solo mode and no other key pressed, then release voices on this key if needed
        if (bShouldRelease) {
            itNoteOffEventOnKeyList->Type = Event::type_release; // transform event type

            // spawn release triggered voice(s) if needed
            if (pKey->ReleaseTrigger && pEngineChannel->pInstrument) {
                // first, get total amount of required voices (dependant on amount of layers)
                ::gig::Region* pRegion = pEngineChannel->pInstrument->GetRegion(itNoteOffEventOnKeyList->Param.Note.Key);
                if (pRegion) {
                    int voicesRequired = pRegion->Layers;

                    // MIDI note-on velocity is used instead of note-off velocity
                    itNoteOffEventOnKeyList->Param.Note.Velocity = pKey->Velocity;

                    // now launch the required amount of voices
                    for (int i = 0; i < voicesRequired; i++)
                        LaunchVoice(pEngineChannel, itNoteOffEventOnKeyList, i, true, false, false); //FIXME: for the moment we don't perform voice stealing for release triggered samples
                }
                pKey->ReleaseTrigger = false;
            }
        }

        // if neither a voice was spawned or postponed on this key then remove note off event from key again
        if (!pKey->Active && !pKey->VoiceTheftsQueued)
            pKey->pEvents->free(itNoteOffEventOnKeyList);
    }

    /**
     *  Moves pitchbend event from the general (input) event list to the engine
     *  channel's event list. It will actually processed later by the
     *  respective voice.
     *
     *  @param pEngineChannel - engine channel on which this event occured on
     *  @param itPitchbendEvent - absolute pitch value and time stamp of the event
     */
    void Engine::ProcessPitchbend(EngineChannel* pEngineChannel, Pool<Event>::Iterator& itPitchbendEvent) {
        pEngineChannel->Pitch = itPitchbendEvent->Param.Pitch.Pitch; // store current pitch value
    }

    /**
     *  Allocates and triggers a new voice. This method will usually be
     *  called by the ProcessNoteOn() method and by the voices itself
     *  (e.g. to spawn further voices on the same key for layered sounds).
     *
     *  @param pEngineChannel      - engine channel on which this event occured on
     *  @param itNoteOnEvent       - key, velocity and time stamp of the event
     *  @param iLayer              - layer index for the new voice (optional - only
     *                               in case of layered sounds of course)
     *  @param ReleaseTriggerVoice - if new voice is a release triggered voice
     *                               (optional, default = false)
     *  @param VoiceStealing       - if voice stealing should be performed
     *                               when there is no free voice
     *                               (optional, default = true)
     *  @param HandleKeyGroupConflicts - if voices should be killed due to a
     *                                   key group conflict
     *  @returns pointer to new voice or NULL if there was no free voice or
     *           if the voice wasn't triggered (for example when no region is
     *           defined for the given key).
     */
    Pool<Voice>::Iterator Engine::LaunchVoice(EngineChannel* pEngineChannel, Pool<Event>::Iterator& itNoteOnEvent, int iLayer, bool ReleaseTriggerVoice, bool VoiceStealing, bool HandleKeyGroupConflicts) {
        int MIDIKey            = itNoteOnEvent->Param.Note.Key;
        midi_key_info_t* pKey  = &pEngineChannel->pMIDIKeyInfo[MIDIKey];
        ::gig::Region* pRegion = pEngineChannel->pInstrument->GetRegion(MIDIKey);

        // if nothing defined for this key
        if (!pRegion) return Pool<Voice>::Iterator(); // nothing to do

        // only mark the first voice of a layered voice (group) to be in a
        // key group, so the layered voices won't kill each other
        int iKeyGroup = (iLayer == 0 && !ReleaseTriggerVoice) ? pRegion->KeyGroup : 0;

        // handle key group (a.k.a. exclusive group) conflicts
        if (HandleKeyGroupConflicts) {
            if (iKeyGroup) { // if this voice / key belongs to a key group
                uint** ppKeyGroup = &pEngineChannel->ActiveKeyGroups[iKeyGroup];
                if (*ppKeyGroup) { // if there's already an active key in that key group
                    midi_key_info_t* pOtherKey = &pEngineChannel->pMIDIKeyInfo[**ppKeyGroup];
                    // kill all voices on the (other) key
                    RTList<Voice>::Iterator itVoiceToBeKilled = pOtherKey->pActiveVoices->first();
                    RTList<Voice>::Iterator end               = pOtherKey->pActiveVoices->end();
                    for (; itVoiceToBeKilled != end; ++itVoiceToBeKilled) {
                        if (itVoiceToBeKilled->Type != Voice::type_release_trigger) {
                            itVoiceToBeKilled->Kill(itNoteOnEvent);
                            --VoiceSpawnsLeft; //FIXME: just a hack, we should better check in StealVoice() if the voice was killed due to key conflict
                        }
                    }
                }
            }
        }

        Voice::type_t VoiceType = Voice::type_normal;

        // get current dimension values to select the right dimension region
        //TODO: for stolen voices this dimension region selection block is processed twice, this should be changed
        //FIXME: controller values for selecting the dimension region here are currently not sample accurate
        uint DimValues[8] = { 0 };
        for (int i = pRegion->Dimensions - 1; i >= 0; i--) {
            switch (pRegion->pDimensionDefinitions[i].dimension) {
                case ::gig::dimension_samplechannel:
                    DimValues[i] = 0; //TODO: we currently ignore this dimension
                    break;
                case ::gig::dimension_layer:
                    DimValues[i] = iLayer;
                    break;
                case ::gig::dimension_velocity:
                    DimValues[i] = itNoteOnEvent->Param.Note.Velocity;
                    break;
                case ::gig::dimension_channelaftertouch:
                    DimValues[i] = pEngineChannel->ControllerTable[128];
                    break;
                case ::gig::dimension_releasetrigger:
                    VoiceType = (ReleaseTriggerVoice) ? Voice::type_release_trigger : (!iLayer) ? Voice::type_release_trigger_required : Voice::type_normal;
                    DimValues[i] = (uint) ReleaseTriggerVoice;
                    break;
                case ::gig::dimension_keyboard:
                    DimValues[i] = (uint) (pEngineChannel->CurrentKeyDimension * pRegion->pDimensionDefinitions[i].zones);
                    break;
                case ::gig::dimension_roundrobin:
                    DimValues[i] = (uint) pEngineChannel->pMIDIKeyInfo[MIDIKey].RoundRobinIndex; // incremented for each note on
                    break;
                case ::gig::dimension_random:
                    RandomSeed   = RandomSeed * 1103515245 + 12345; // classic pseudo random number generator
                    DimValues[i] = (uint) RandomSeed >> (32 - pRegion->pDimensionDefinitions[i].bits); // highest bits are most random
                    break;
                case ::gig::dimension_modwheel:
                    DimValues[i] = pEngineChannel->ControllerTable[1];
                    break;
                case ::gig::dimension_breath:
                    DimValues[i] = pEngineChannel->ControllerTable[2];
                    break;
                case ::gig::dimension_foot:
                    DimValues[i] = pEngineChannel->ControllerTable[4];
                    break;
                case ::gig::dimension_portamentotime:
                    DimValues[i] = pEngineChannel->ControllerTable[5];
                    break;
                case ::gig::dimension_effect1:
                    DimValues[i] = pEngineChannel->ControllerTable[12];
                    break;
                case ::gig::dimension_effect2:
                    DimValues[i] = pEngineChannel->ControllerTable[13];
                    break;
                case ::gig::dimension_genpurpose1:
                    DimValues[i] = pEngineChannel->ControllerTable[16];
                    break;
                case ::gig::dimension_genpurpose2:
                    DimValues[i] = pEngineChannel->ControllerTable[17];
                    break;
                case ::gig::dimension_genpurpose3:
                    DimValues[i] = pEngineChannel->ControllerTable[18];
                    break;
                case ::gig::dimension_genpurpose4:
                    DimValues[i] = pEngineChannel->ControllerTable[19];
                    break;
                case ::gig::dimension_sustainpedal:
                    DimValues[i] = pEngineChannel->ControllerTable[64];
                    break;
                case ::gig::dimension_portamento:
                    DimValues[i] = pEngineChannel->ControllerTable[65];
                    break;
                case ::gig::dimension_sostenutopedal:
                    DimValues[i] = pEngineChannel->ControllerTable[66];
                    break;
                case ::gig::dimension_softpedal:
                    DimValues[i] = pEngineChannel->ControllerTable[67];
                    break;
                case ::gig::dimension_genpurpose5:
                    DimValues[i] = pEngineChannel->ControllerTable[80];
                    break;
                case ::gig::dimension_genpurpose6:
                    DimValues[i] = pEngineChannel->ControllerTable[81];
                    break;
                case ::gig::dimension_genpurpose7:
                    DimValues[i] = pEngineChannel->ControllerTable[82];
                    break;
                case ::gig::dimension_genpurpose8:
                    DimValues[i] = pEngineChannel->ControllerTable[83];
                    break;
                case ::gig::dimension_effect1depth:
                    DimValues[i] = pEngineChannel->ControllerTable[91];
                    break;
                case ::gig::dimension_effect2depth:
                    DimValues[i] = pEngineChannel->ControllerTable[92];
                    break;
                case ::gig::dimension_effect3depth:
                    DimValues[i] = pEngineChannel->ControllerTable[93];
                    break;
                case ::gig::dimension_effect4depth:
                    DimValues[i] = pEngineChannel->ControllerTable[94];
                    break;
                case ::gig::dimension_effect5depth:
                    DimValues[i] = pEngineChannel->ControllerTable[95];
                    break;
                case ::gig::dimension_none:
                    std::cerr << "gig::Engine::LaunchVoice() Error: dimension=none\n" << std::flush;
                    break;
                default:
                    std::cerr << "gig::Engine::LaunchVoice() Error: Unknown dimension\n" << std::flush;
            }
        }

        // return if this is a release triggered voice and there is no
        // releasetrigger dimension (could happen if an instrument
        // change has occured between note on and off)
        if (ReleaseTriggerVoice && VoiceType != Voice::type_release_trigger) return Pool<Voice>::Iterator();

        ::gig::DimensionRegion* pDimRgn = pRegion->GetDimensionRegionByValue(DimValues);

        // no need to continue if sample is silent
        if (!pDimRgn->pSample || !pDimRgn->pSample->SamplesTotal) return Pool<Voice>::Iterator();

        // allocate a new voice for the key
        Pool<Voice>::Iterator itNewVoice = pKey->pActiveVoices->allocAppend();
        if (itNewVoice) {
            // launch the new voice
            if (itNewVoice->Trigger(pEngineChannel, itNoteOnEvent, pEngineChannel->Pitch, pDimRgn, VoiceType, iKeyGroup) < 0) {
                dmsg(4,("Voice not triggered\n"));
                pKey->pActiveVoices->free(itNewVoice);
            }
            else { // on success
                --VoiceSpawnsLeft;
                if (!pKey->Active) { // mark as active key
                    pKey->Active = true;
                    pKey->itSelf = pEngineChannel->pActiveKeys->allocAppend();
                    *pKey->itSelf = itNoteOnEvent->Param.Note.Key;
                }
                if (itNewVoice->KeyGroup) {
                    uint** ppKeyGroup = &pEngineChannel->ActiveKeyGroups[itNewVoice->KeyGroup];
                    *ppKeyGroup = &*pKey->itSelf; // put key as the (new) active key to its key group
                }
                if (itNewVoice->Type == Voice::type_release_trigger_required) pKey->ReleaseTrigger = true; // mark key for the need of release triggered voice(s)
                return itNewVoice; // success
            }
        }
        else if (VoiceStealing) {
            // try to steal one voice
            int result = StealVoice(pEngineChannel, itNoteOnEvent);
            if (!result) { // voice stolen successfully
                // put note-on event into voice-stealing queue, so it will be reprocessed after killed voice died
                RTList<Event>::Iterator itStealEvent = pVoiceStealingQueue->allocAppend();
                if (itStealEvent) {
                    *itStealEvent = *itNoteOnEvent; // copy event
                    itStealEvent->Param.Note.Layer = iLayer;
                    itStealEvent->Param.Note.ReleaseTrigger = ReleaseTriggerVoice;
                    pKey->VoiceTheftsQueued++;
                }
                else dmsg(1,("Voice stealing queue full!\n"));
            }
        }

        return Pool<Voice>::Iterator(); // no free voice or error
    }

    /**
     *  Will be called by LaunchVoice() method in case there are no free
     *  voices left. This method will select and kill one old voice for
     *  voice stealing and postpone the note-on event until the selected
     *  voice actually died.
     *
     *  @param pEngineChannel - engine channel on which this event occured on
     *  @param itNoteOnEvent - key, velocity and time stamp of the event
     *  @returns 0 on success, a value < 0 if no active voice could be picked for voice stealing
     */
    int Engine::StealVoice(EngineChannel* pEngineChannel, Pool<Event>::Iterator& itNoteOnEvent) {
        if (VoiceSpawnsLeft <= 0) {
            dmsg(1,("Max. voice thefts per audio fragment reached (you may raise CONFIG_MAX_VOICES).\n"));
            return -1;
        }
        if (!pEventPool->poolIsEmpty()) {

            RTList<Voice>::Iterator itSelectedVoice;

            // Select one voice for voice stealing
            switch (CONFIG_VOICE_STEAL_ALGO) {

                // try to pick the oldest voice on the key where the new
                // voice should be spawned, if there is no voice on that
                // key, or no voice left to kill, then procceed with
                // 'oldestkey' algorithm
                case voice_steal_algo_oldestvoiceonkey: {
                    midi_key_info_t* pSelectedKey = &pEngineChannel->pMIDIKeyInfo[itNoteOnEvent->Param.Note.Key];
                    itSelectedVoice = pSelectedKey->pActiveVoices->first();
                    // proceed iterating if voice was created in this fragment cycle
                    while (itSelectedVoice && !itSelectedVoice->IsStealable()) ++itSelectedVoice;
                    // if we haven't found a voice then proceed with algorithm 'oldestkey'
                    if (itSelectedVoice && itSelectedVoice->IsStealable()) break;
                } // no break - intentional !

                // try to pick the oldest voice on the oldest active key
                // from the same engine channel
                // (caution: must stay after 'oldestvoiceonkey' algorithm !)
                case voice_steal_algo_oldestkey: {
                    // if we already stole in this fragment, try to proceed on same key
                    if (this->itLastStolenVoice) {
                        itSelectedVoice = this->itLastStolenVoice;
                        do {
                            ++itSelectedVoice;
                        } while (itSelectedVoice && !itSelectedVoice->IsStealable()); // proceed iterating if voice was created in this fragment cycle
                        // found a "stealable" voice ?
                        if (itSelectedVoice && itSelectedVoice->IsStealable()) {
                            // remember which voice we stole, so we can simply proceed on next voice stealing
                            this->itLastStolenVoice = itSelectedVoice;
                            break; // selection succeeded
                        }
                    }
                    // get (next) oldest key
                    RTList<uint>::Iterator iuiSelectedKey = (this->iuiLastStolenKey) ? ++this->iuiLastStolenKey : pEngineChannel->pActiveKeys->first();
                    while (iuiSelectedKey) {
                        midi_key_info_t* pSelectedKey = &pEngineChannel->pMIDIKeyInfo[*iuiSelectedKey];
                        itSelectedVoice = pSelectedKey->pActiveVoices->first();
                        // proceed iterating if voice was created in this fragment cycle
                        while (itSelectedVoice && !itSelectedVoice->IsStealable()) ++itSelectedVoice;
                        // found a "stealable" voice ?
                        if (itSelectedVoice && itSelectedVoice->IsStealable()) {
                            // remember which voice on which key we stole, so we can simply proceed on next voice stealing
                            this->iuiLastStolenKey  = iuiSelectedKey;
                            this->itLastStolenVoice = itSelectedVoice;
                            break; // selection succeeded
                        }
                        ++iuiSelectedKey; // get next oldest key
                    }
                    break;
                }

                // don't steal anything
                case voice_steal_algo_none:
                default: {
                    dmsg(1,("No free voice (voice stealing disabled)!\n"));
                    return -1;
                }
            }

            // if we couldn't steal a voice from the same engine channel then
            // steal oldest voice on the oldest key from any other engine channel
            // (the smaller engine channel number, the higher priority)
            if (!itSelectedVoice || !itSelectedVoice->IsStealable()) {
                EngineChannel* pSelectedChannel;
                int            iChannelIndex;
                // select engine channel
                if (pLastStolenChannel) {
                    pSelectedChannel = pLastStolenChannel;
                    iChannelIndex    = pSelectedChannel->iEngineIndexSelf;
                } else { // pick the engine channel followed by this engine channel
                    iChannelIndex    = (pEngineChannel->iEngineIndexSelf + 1) % engineChannels.size();
                    pSelectedChannel = engineChannels[iChannelIndex];
                }

                // if we already stole in this fragment, try to proceed on same key
                if (this->itLastStolenVoiceGlobally) {
                    itSelectedVoice = this->itLastStolenVoiceGlobally;
                    do {
                        ++itSelectedVoice;
                    } while (itSelectedVoice && !itSelectedVoice->IsStealable()); // proceed iterating if voice was created in this fragment cycle
                }

                #if CONFIG_DEVMODE
                EngineChannel* pBegin = pSelectedChannel; // to detect endless loop
                #endif // CONFIG_DEVMODE

                // did we find a 'stealable' voice?
                if (itSelectedVoice && itSelectedVoice->IsStealable()) {
                    // remember which voice we stole, so we can simply proceed on next voice stealing
                    this->itLastStolenVoiceGlobally = itSelectedVoice;
                } else while (true) { // iterate through engine channels
                    // get (next) oldest key
                    RTList<uint>::Iterator iuiSelectedKey = (this->iuiLastStolenKeyGlobally) ? ++this->iuiLastStolenKeyGlobally : pSelectedChannel->pActiveKeys->first();
                    this->iuiLastStolenKeyGlobally = RTList<uint>::Iterator(); // to prevent endless loop (see line above)
                    while (iuiSelectedKey) {
                        midi_key_info_t* pSelectedKey = &pSelectedChannel->pMIDIKeyInfo[*iuiSelectedKey];
                        itSelectedVoice = pSelectedKey->pActiveVoices->first();
                        // proceed iterating if voice was created in this fragment cycle
                        while (itSelectedVoice && !itSelectedVoice->IsStealable()) ++itSelectedVoice;
                        // found a "stealable" voice ?
                        if (itSelectedVoice && itSelectedVoice->IsStealable()) {
                            // remember which voice on which key on which engine channel we stole, so we can simply proceed on next voice stealing
                            this->iuiLastStolenKeyGlobally  = iuiSelectedKey;
                            this->itLastStolenVoiceGlobally = itSelectedVoice;
                            this->pLastStolenChannel        = pSelectedChannel;
                            goto stealable_voice_found; // selection succeeded
                        }
                        ++iuiSelectedKey; // get next key on current engine channel
                    }
                    // get next engine channel
                    iChannelIndex    = (iChannelIndex + 1) % engineChannels.size();
                    pSelectedChannel = engineChannels[iChannelIndex];

                    #if CONFIG_DEVMODE
                    if (pSelectedChannel == pBegin) {
                        dmsg(1,("FATAL ERROR: voice stealing endless loop!\n"));
                        dmsg(1,("VoiceSpawnsLeft=%d.\n", VoiceSpawnsLeft));
                        dmsg(1,("Exiting.\n"));
                        exit(-1);
                    }
                    #endif // CONFIG_DEVMODE
                }
            }

            // jump point if a 'stealable' voice was found
            stealable_voice_found:

            #if CONFIG_DEVMODE
            if (!itSelectedVoice->IsActive()) {
                dmsg(1,("gig::Engine: ERROR, tried to steal a voice which was not active !!!\n"));
                return -1;
            }
            #endif // CONFIG_DEVMODE

            // now kill the selected voice
            itSelectedVoice->Kill(itNoteOnEvent);

            --VoiceSpawnsLeft;

            return 0; // success
        }
        else {
            dmsg(1,("Event pool emtpy!\n"));
            return -1;
        }
    }

    /**
     *  Removes the given voice from the MIDI key's list of active voices.
     *  This method will be called when a voice went inactive, e.g. because
     *  it finished to playback its sample, finished its release stage or
     *  just was killed.
     *
     *  @param pEngineChannel - engine channel on which this event occured on
     *  @param itVoice - points to the voice to be freed
     */
    void Engine::FreeVoice(EngineChannel* pEngineChannel, Pool<Voice>::Iterator& itVoice) {
        if (itVoice) {
            midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[itVoice->MIDIKey];

            uint keygroup = itVoice->KeyGroup;

            // if the sample and dimension region belong to an
            // instrument that is unloaded, tell the disk thread to
            // release them
            if (itVoice->Orphan) {
                pDiskThread->OrderDeletionOfDimreg(itVoice->pDimRgn);
            }

            // free the voice object
            pVoicePool->free(itVoice);

            // if no other voices left and member of a key group, remove from key group
            if (pKey->pActiveVoices->isEmpty() && keygroup) {
                uint** ppKeyGroup = &pEngineChannel->ActiveKeyGroups[keygroup];
                if (*ppKeyGroup == &*pKey->itSelf) *ppKeyGroup = NULL; // remove key from key group
            }
        }
        else std::cerr << "Couldn't release voice! (!itVoice)\n" << std::flush;
    }

    /**
     *  Called when there's no more voice left on a key, this call will
     *  update the key info respectively.
     *
     *  @param pEngineChannel - engine channel on which this event occured on
     *  @param pKey - key which is now inactive
     */
    void Engine::FreeKey(EngineChannel* pEngineChannel, midi_key_info_t* pKey) {
        if (pKey->pActiveVoices->isEmpty()) {
            pKey->Active = false;
            pEngineChannel->pActiveKeys->free(pKey->itSelf); // remove key from list of active keys
            pKey->itSelf = RTList<uint>::Iterator();
            pKey->ReleaseTrigger = false;
            pKey->pEvents->clear();
            dmsg(3,("Key has no more voices now\n"));
        }
        else dmsg(1,("gig::Engine: Oops, tried to free a key which contains voices.\n"));
    }

    /**
     *  Reacts on supported control change commands (e.g. pitch bend wheel,
     *  modulation wheel, aftertouch).
     *
     *  @param pEngineChannel - engine channel on which this event occured on
     *  @param itControlChangeEvent - controller, value and time stamp of the event
     */
    void Engine::ProcessControlChange(EngineChannel* pEngineChannel, Pool<Event>::Iterator& itControlChangeEvent) {
        dmsg(4,("Engine::ContinuousController cc=%d v=%d\n", itControlChangeEvent->Param.CC.Controller, itControlChangeEvent->Param.CC.Value));

        // update controller value in the engine channel's controller table
        pEngineChannel->ControllerTable[itControlChangeEvent->Param.CC.Controller] = itControlChangeEvent->Param.CC.Value;

        // handle hard coded MIDI controllers
        switch (itControlChangeEvent->Param.CC.Controller) {
            case 5: { // portamento time
                pEngineChannel->PortamentoTime = (float) itControlChangeEvent->Param.CC.Value / 127.0f * (float) CONFIG_PORTAMENTO_TIME_MAX + (float) CONFIG_PORTAMENTO_TIME_MIN;
                break;
            }
            case 6: { // data entry (currently only used for RPN controllers)
                if (pEngineChannel->GetMidiRpnController() == 2) { // coarse tuning in half tones
                    int transpose = (int) itControlChangeEvent->Param.CC.Value - 64;
                    // limit to +- two octaves for now
                    transpose = RTMath::Min(transpose,  24);
                    transpose = RTMath::Max(transpose, -24);
                    pEngineChannel->GlobalTranspose = transpose;
                    // workaround, so we won't have hanging notes
                    ReleaseAllVoices(pEngineChannel, itControlChangeEvent);
                }
                // to avoid other MIDI CC #6 messages to be misenterpreted as RPN controller data
                pEngineChannel->ResetMidiRpnController();
                break;
            }
            case 7: { // volume
                //TODO: not sample accurate yet
                pEngineChannel->MidiVolume = VolumeCurve[itControlChangeEvent->Param.CC.Value];
                pEngineChannel->bStatusChanged = true; // engine channel status has changed, so set notify flag
                break;
            }
            case 10: { // panpot
                //TODO: not sample accurate yet
                pEngineChannel->GlobalPanLeft  = PanCurve[128 - itControlChangeEvent->Param.CC.Value];
                pEngineChannel->GlobalPanRight = PanCurve[itControlChangeEvent->Param.CC.Value];
                break;
            }
            case 64: { // sustain
                if (itControlChangeEvent->Param.CC.Value >= 64 && !pEngineChannel->SustainPedal) {
                    dmsg(4,("DAMPER (RIGHT) PEDAL DOWN\n"));
                    pEngineChannel->SustainPedal = true;

                    #if !CONFIG_PROCESS_MUTED_CHANNELS
                    if (pEngineChannel->GetMute()) return; // skip if sampler channel is muted
                    #endif

                    // cancel release process of voices if necessary
                    RTList<uint>::Iterator iuiKey = pEngineChannel->pActiveKeys->first();
                    for (; iuiKey; ++iuiKey) {
                        midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[*iuiKey];
                        if (!pKey->KeyPressed) {
                            RTList<Event>::Iterator itNewEvent = pKey->pEvents->allocAppend();
                            if (itNewEvent) {
                                *itNewEvent = *itControlChangeEvent; // copy event to the key's own event list
                                itNewEvent->Type = Event::type_cancel_release; // transform event type
                            }
                            else dmsg(1,("Event pool emtpy!\n"));
                        }
                    }
                }
                if (itControlChangeEvent->Param.CC.Value < 64 && pEngineChannel->SustainPedal) {
                    dmsg(4,("DAMPER (RIGHT) PEDAL UP\n"));
                    pEngineChannel->SustainPedal = false;

                    #if !CONFIG_PROCESS_MUTED_CHANNELS
                    if (pEngineChannel->GetMute()) return; // skip if sampler channel is muted
                    #endif

                    // release voices if their respective key is not pressed
                    RTList<uint>::Iterator iuiKey = pEngineChannel->pActiveKeys->first();
                    for (; iuiKey; ++iuiKey) {
                        midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[*iuiKey];
                        if (!pKey->KeyPressed && ShouldReleaseVoice(pEngineChannel, *iuiKey)) {
                            RTList<Event>::Iterator itNewEvent = pKey->pEvents->allocAppend();
                            if (itNewEvent) {
                                *itNewEvent = *itControlChangeEvent; // copy event to the key's own event list
                                itNewEvent->Type = Event::type_release; // transform event type
                            }
                            else dmsg(1,("Event pool emtpy!\n"));
                        }
                    }
                }
                break;
            }
            case 65: { // portamento on / off
                KillAllVoices(pEngineChannel, itControlChangeEvent);
                pEngineChannel->PortamentoMode = itControlChangeEvent->Param.CC.Value >= 64;
                break;
            }
            case 66: { // sostenuto
                if (itControlChangeEvent->Param.CC.Value >= 64 && !pEngineChannel->SostenutoPedal) {
                    dmsg(4,("SOSTENUTO (CENTER) PEDAL DOWN\n"));
                    pEngineChannel->SostenutoPedal = true;

                    #if !CONFIG_PROCESS_MUTED_CHANNELS
                    if (pEngineChannel->GetMute()) return; // skip if sampler channel is muted
                    #endif

                    SostenutoKeyCount = 0;
                    // Remeber the pressed keys
                    RTList<uint>::Iterator iuiKey = pEngineChannel->pActiveKeys->first();
                    for (; iuiKey; ++iuiKey) {
                        midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[*iuiKey];
                        if (pKey->KeyPressed && SostenutoKeyCount < 128) SostenutoKeys[SostenutoKeyCount++] = *iuiKey;
                    }
                }
                if (itControlChangeEvent->Param.CC.Value < 64 && pEngineChannel->SostenutoPedal) {
                    dmsg(4,("SOSTENUTO (CENTER) PEDAL UP\n"));
                    pEngineChannel->SostenutoPedal = false;

                    #if !CONFIG_PROCESS_MUTED_CHANNELS
                    if (pEngineChannel->GetMute()) return; // skip if sampler channel is muted
                    #endif

                    // release voices if the damper pedal is up and their respective key is not pressed
                    for (int i = 0; i < SostenutoKeyCount; i++) {
                        midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[SostenutoKeys[i]];
                        if (!pKey->KeyPressed && !pEngineChannel->SustainPedal) {
                            RTList<Event>::Iterator itNewEvent = pKey->pEvents->allocAppend();
                            if (itNewEvent) {
                                *itNewEvent = *itControlChangeEvent; // copy event to the key's own event list
                                itNewEvent->Type = Event::type_release; // transform event type
                            }
                            else dmsg(1,("Event pool emtpy!\n"));
                        }
                    }
                }
                break;
            }
            case 100: { // RPN controller LSB
                pEngineChannel->SetMidiRpnControllerLsb(itControlChangeEvent->Param.CC.Value);
                break;
            }
            case 101: { // RPN controller MSB
                pEngineChannel->SetMidiRpnControllerMsb(itControlChangeEvent->Param.CC.Value);
                break;
            }


            // Channel Mode Messages

            case 120: { // all sound off
                KillAllVoices(pEngineChannel, itControlChangeEvent);
                break;
            }
            case 121: { // reset all controllers
                pEngineChannel->ResetControllers();
                break;
            }
            case 123: { // all notes off
                #if CONFIG_PROCESS_ALL_NOTES_OFF
                ReleaseAllVoices(pEngineChannel, itControlChangeEvent);
                #endif // CONFIG_PROCESS_ALL_NOTES_OFF
                break;
            }
            case 126: { // mono mode on
                KillAllVoices(pEngineChannel, itControlChangeEvent);
                pEngineChannel->SoloMode = true;
                break;
            }
            case 127: { // poly mode on
                KillAllVoices(pEngineChannel, itControlChangeEvent);
                pEngineChannel->SoloMode = false;
                break;
            }
        }

        // handle FX send controllers
        if (!pEngineChannel->fxSends.empty()) {
            for (int iFxSend = 0; iFxSend < pEngineChannel->GetFxSendCount(); iFxSend++) {
                FxSend* pFxSend = pEngineChannel->GetFxSend(iFxSend);
                if (pFxSend->MidiController() == itControlChangeEvent->Param.CC.Controller)
                    pFxSend->SetLevel(itControlChangeEvent->Param.CC.Value);
            }
        }
    }

    /**
     *  Reacts on MIDI system exclusive messages.
     *
     *  @param itSysexEvent - sysex data size and time stamp of the sysex event
     */
    void Engine::ProcessSysex(Pool<Event>::Iterator& itSysexEvent) {
        RingBuffer<uint8_t,false>::NonVolatileReader reader = pSysexBuffer->get_non_volatile_reader();

        uint8_t exclusive_status, id;
        if (!reader.pop(&exclusive_status)) goto free_sysex_data;
        if (!reader.pop(&id))               goto free_sysex_data;
        if (exclusive_status != 0xF0)       goto free_sysex_data;

        switch (id) {
            case 0x41: { // Roland
                dmsg(3,("Roland Sysex\n"));
                uint8_t device_id, model_id, cmd_id;
                if (!reader.pop(&device_id)) goto free_sysex_data;
                if (!reader.pop(&model_id))  goto free_sysex_data;
                if (!reader.pop(&cmd_id))    goto free_sysex_data;
                if (model_id != 0x42 /*GS*/) goto free_sysex_data;
                if (cmd_id != 0x12 /*DT1*/)  goto free_sysex_data;

                // command address
                uint8_t addr[3]; // 2 byte addr MSB, followed by 1 byte addr LSB)
                const RingBuffer<uint8_t,false>::NonVolatileReader checksum_reader = reader; // so we can calculate the check sum later
                if (reader.read(&addr[0], 3) != 3) goto free_sysex_data;
                if (addr[0] == 0x40 && addr[1] == 0x00) { // System Parameters
                    dmsg(3,("\tSystem Parameter\n"));
                }
                else if (addr[0] == 0x40 && addr[1] == 0x01) { // Common Parameters
                    dmsg(3,("\tCommon Parameter\n"));
                }
                else if (addr[0] == 0x40 && (addr[1] & 0xf0) == 0x10) { // Part Parameters (1)
                    dmsg(3,("\tPart Parameter\n"));
                    switch (addr[2]) {
                        case 0x40: { // scale tuning
                            dmsg(3,("\t\tScale Tuning\n"));
                            uint8_t scale_tunes[12]; // detuning of all 12 semitones of an octave
                            if (reader.read(&scale_tunes[0], 12) != 12) goto free_sysex_data;
                            uint8_t checksum;
                            if (!reader.pop(&checksum)) goto free_sysex_data;
                            #if CONFIG_ASSERT_GS_SYSEX_CHECKSUM
                            if (GSCheckSum(checksum_reader, 12)) goto free_sysex_data;
                            #endif // CONFIG_ASSERT_GS_SYSEX_CHECKSUM
                            for (int i = 0; i < 12; i++) scale_tunes[i] -= 64;
                            AdjustScale((int8_t*) scale_tunes);
                            dmsg(3,("\t\t\tNew scale applied.\n"));
                            break;
                        }
                    }
                }
                else if (addr[0] == 0x40 && (addr[1] & 0xf0) == 0x20) { // Part Parameters (2)
                }
                else if (addr[0] == 0x41) { // Drum Setup Parameters
                }
                break;
            }
        }

        free_sysex_data: // finally free sysex data
        pSysexBuffer->increment_read_ptr(itSysexEvent->Param.Sysex.Size);
    }

    /**
     * Calculates the Roland GS sysex check sum.
     *
     * @param AddrReader - reader which currently points to the first GS
     *                     command address byte of the GS sysex message in
     *                     question
     * @param DataSize   - size of the GS message data (in bytes)
     */
    uint8_t Engine::GSCheckSum(const RingBuffer<uint8_t,false>::NonVolatileReader AddrReader, uint DataSize) {
        RingBuffer<uint8_t,false>::NonVolatileReader reader = AddrReader;
        uint bytes = 3 /*addr*/ + DataSize;
        uint8_t addr_and_data[bytes];
        reader.read(&addr_and_data[0], bytes);
        uint8_t sum = 0;
        for (uint i = 0; i < bytes; i++) sum += addr_and_data[i];
        return 128 - sum % 128;
    }

    /**
     * Allows to tune each of the twelve semitones of an octave.
     *
     * @param ScaleTunes - detuning of all twelve semitones (in cents)
     */
    void Engine::AdjustScale(int8_t ScaleTunes[12]) {
        memcpy(&this->ScaleTuning[0], &ScaleTunes[0], 12); //TODO: currently not sample accurate
    }

    /**
     * Releases all voices on an engine channel. All voices will go into
     * the release stage and thus it might take some time (e.g. dependant to
     * their envelope release time) until they actually die.
     *
     * @param pEngineChannel - engine channel on which all voices should be released
     * @param itReleaseEvent - event which caused this releasing of all voices
     */
    void Engine::ReleaseAllVoices(EngineChannel* pEngineChannel, Pool<Event>::Iterator& itReleaseEvent) {
        RTList<uint>::Iterator iuiKey = pEngineChannel->pActiveKeys->first();
        while (iuiKey) {
            midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[*iuiKey];
            ++iuiKey;
            // append a 'release' event to the key's own event list
            RTList<Event>::Iterator itNewEvent = pKey->pEvents->allocAppend();
            if (itNewEvent) {
                *itNewEvent = *itReleaseEvent; // copy original event (to the key's event list)
                itNewEvent->Type = Event::type_release; // transform event type
            }
            else dmsg(1,("Event pool emtpy!\n"));
        }
    }

    /**
     * Kills all voices on an engine channel as soon as possible. Voices
     * won't get into release state, their volume level will be ramped down
     * as fast as possible.
     *
     * @param pEngineChannel - engine channel on which all voices should be killed
     * @param itKillEvent    - event which caused this killing of all voices
     */
    void Engine::KillAllVoices(EngineChannel* pEngineChannel, Pool<Event>::Iterator& itKillEvent) {
        RTList<uint>::Iterator iuiKey = pEngineChannel->pActiveKeys->first();
        RTList<uint>::Iterator end    = pEngineChannel->pActiveKeys->end();
        while (iuiKey != end) { // iterate through all active keys
            midi_key_info_t* pKey = &pEngineChannel->pMIDIKeyInfo[*iuiKey];
            ++iuiKey;
            RTList<Voice>::Iterator itVoice     = pKey->pActiveVoices->first();
            RTList<Voice>::Iterator itVoicesEnd = pKey->pActiveVoices->end();
            for (; itVoice != itVoicesEnd; ++itVoice) { // iterate through all voices on this key
                itVoice->Kill(itKillEvent);
                --VoiceSpawnsLeft; //FIXME: just a temporary workaround, we should check the cause in StealVoice() instead
            }
        }
    }

    /**
     * Determines whether the specified voice should be released.
     *
     * @param pEngineChannel - The engine channel on which the voice should be checked
     * @param Key - The key number
     * @returns true if the specified should be released, false otherwise.
     */
    bool Engine::ShouldReleaseVoice(EngineChannel* pEngineChannel, int Key) {
        if (pEngineChannel->SustainPedal) return false;

        if (pEngineChannel->SostenutoPedal) {
            for (int i = 0; i < SostenutoKeyCount; i++)
                if (Key == SostenutoKeys[i]) return false;
        }

        return true;
    }

    uint Engine::VoiceCount() {
        return ActiveVoiceCount;
    }

    uint Engine::VoiceCountMax() {
        return ActiveVoiceCountMax;
    }

    bool Engine::DiskStreamSupported() {
        return true;
    }

    uint Engine::DiskStreamCount() {
        return (pDiskThread) ? pDiskThread->ActiveStreamCount : 0;
    }

    uint Engine::DiskStreamCountMax() {
        return (pDiskThread) ? pDiskThread->ActiveStreamCountMax : 0;
    }

    String Engine::DiskStreamBufferFillBytes() {
        return pDiskThread->GetBufferFillBytes();
    }

    String Engine::DiskStreamBufferFillPercentage() {
        return pDiskThread->GetBufferFillPercentage();
    }

    String Engine::EngineName() {
        return LS_GIG_ENGINE_NAME;
    }

    String Engine::Description() {
        return "Gigasampler Engine";
    }

    String Engine::Version() {
        String s = "$Revision: 1.75 $";
        return s.substr(11, s.size() - 13); // cut dollar signs, spaces and CVS macro keyword
    }

    InstrumentManager* Engine::GetInstrumentManager() {
        return &instruments;
    }

    // static constant initializers
    const float* Engine::VolumeCurve(InitVolumeCurve());
    const float* Engine::PanCurve(InitPanCurve());
    const float* Engine::CrossfadeCurve(InitCrossfadeCurve());

    float* Engine::InitVolumeCurve() {
        // line-segment approximation
        const float segments[] = {
            0, 0, 2, 0.0046, 16, 0.016, 31, 0.051, 45, 0.115, 54.5, 0.2,
            64.5, 0.39, 74, 0.74, 92, 1.03, 114, 1.94, 119.2, 2.2, 127, 2.2
        };
        return InitCurve(segments);
    }

    float* Engine::InitPanCurve() {
        // line-segment approximation
        const float segments[] = {
            0, 0, 1, 0,
            2, 0.05, 31.5, 0.7, 51, 0.851, 74.5, 1.12,
            127, 1.41, 128, 1.41
        };
        return InitCurve(segments, 129);
    }

    float* Engine::InitCrossfadeCurve() {
        // line-segment approximation
        const float segments[] = {
            0, 0, 1, 0.03, 10, 0.1, 51, 0.58, 127, 1
        };
        return InitCurve(segments);
    }

    float* Engine::InitCurve(const float* segments, int size) {
        float* y = new float[size];
        for (int x = 0 ; x < size ; x++) {
            if (x > segments[2]) segments += 2;
            y[x] = segments[1] + (x - segments[0]) *
                (segments[3] - segments[1]) / (segments[2] - segments[0]);
        }
        return y;
    }

    /**
     * Changes the instrument for an engine channel.
     *
     * @param pEngineChannel - engine channel on which the instrument
     *                         should be changed
     * @param pInstrument - new instrument
     * @returns a list of dimension regions from the old instrument
     *          that are still in use
     */
    ::gig::DimensionRegion** Engine::ChangeInstrument(EngineChannel* pEngineChannel, ::gig::Instrument* pInstrument) {
        instrument_change_command_t command;
        command.pEngineChannel = pEngineChannel;
        command.pInstrument = pInstrument;
        InstrumentChangeQueue->push(&command);

        // wait for the audio thread to confirm that the instrument
        // change has been done
        instrument_change_reply_t reply;
        while (InstrumentChangeReplyQueue->pop(&reply) == 0) {
            usleep(10000);
        }
        return pDimRegionsInUse;
    }

}} // namespace LinuxSampler::gig