engines/common/BiquadFilter.h

/***************************************************************************
 *                                                                         *
 *   LinuxSampler - modular, streaming capable sampler                     *
 *                                                                         *
 *   Copyright (C) 2003, 2004 by Benno Senoner and 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                                                   *
 ***************************************************************************/

#ifndef __LS_BIQUADFILTER_H__
#define __LS_BIQUADFILTER_H__

#include <math.h>

/// ln(2) / 2
#define LN_2_2                  0.34657359f

#ifndef LIMIT
# define LIMIT(v,l,u)           (v < l ? l : (v > u ? u : v))
#endif

namespace LinuxSampler {

    typedef float bq_t;

    /**
     * Internal parameters of the biquad filter, which are actually the
     * final parameters of the filter's transfer function. This strucure is
     * only needed when these parameters should stored outside the
     * BiquadFilter class, e.g. to save calculation time by sharing them
     * between multiple filters.
     */
    struct biquad_param_t {
        bq_t a1;
        bq_t a2;
        bq_t b0;
        bq_t b1;
        bq_t b2;
    };

    /**
     * Bi-quadratic filter
     * (adapted from lisp code by Eli Brandt, http://www.cs.cmu.edu/~eli/)
     */
    class BiquadFilter {
        protected:
            // following five variables are only used if no external biquad_param_t reference is used
            bq_t a1;
            bq_t a2;
            bq_t b0;
            bq_t b1;
            bq_t b2;
            // following four variables are used to buffer the feedback
            bq_t x1;
            bq_t x2;
            bq_t y1;
            bq_t y2;

            /**
             * Prevent \a f from going into denormal mode which would slow down
             * subsequent floating point calculations, we achieve that by setting
             * \a f to zero when it falls under the denormal threshold value.
             */
            inline void KillDenormal(bq_t& f) {
                // TODO: this is a generic solution for 32bit floats, should be replaced by CPU specific asm code
                f += 1e-18f;
                f -= 1e-18f;
            }
        public:
            inline BiquadFilter() {
                x1 = 0.0f;
                x2 = 0.0f;
                y1 = 0.0f;
                y2 = 0.0f;
            }

            inline bq_t Apply(const bq_t x) {
                bq_t y;

                y = this->b0 * x + this->b1 * this->x1 + this->b2 * this->x2 +
                    this->a1 * this->y1 + this->a2 * this->y2;
                KillDenormal(y);
                this->x2 = this->x1;
                this->x1 = x;
                this->y2 = this->y1;
                this->y1 = y;

                return y;
            }

            inline bq_t Apply(biquad_param_t* param, const bq_t x) {
                bq_t y;

                y = param->b0 * x + param->b1 * this->x1 + param->b2 * this->x2 +
                    param->a1 * this->y1 + param->a2 * this->y2;
                KillDenormal(y);
                this->x2 = this->x1;
                this->x1 = x;
                this->y2 = this->y1;
                this->y1 = y;

                return y;
            }

            inline bq_t ApplyFB(bq_t x, const bq_t fb) {
                bq_t y;

                x += this->y1 * fb * 0.98;
                y = this->b0 * x + this->b1 * this->x1 + this->b2 * this->x2 +
                    this->a1 * this->y1 + this->a2 * this->y2;
                KillDenormal(y);
                this->x2 = this->x1;
                this->x1 = x;
                this->y2 = this->y1;
                this->y1 = y;

                return y;
            }

            inline bq_t ApplyFB(biquad_param_t* param, bq_t x, const bq_t fb) {
                bq_t y;

                x += this->y1 * fb * 0.98;
                y = param->b0 * x + param->b1 * this->x1 + param->b2 * this->x2 +
                    param->a1 * this->y1 + param->a2 * this->y2;
                KillDenormal(y);
                this->x2 = this->x1;
                this->x1 = x;
                this->y2 = this->y1;
                this->y1 = y;

                return y;
            }
    };

    class LowpassFilter : public BiquadFilter {
        public:
            inline LowpassFilter() : BiquadFilter() {}

            inline void SetParameters(bq_t fc, bq_t bw, bq_t fs) {
                bq_t omega = 2.0 * M_PI * fc / fs;
                bq_t sn    = sin(omega);
                bq_t cs    = cos(omega);
                bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);

                const float a0r = 1.0 / (1.0 + alpha);
                this->b0 = a0r * (1.0 - cs) * 0.5;
                this->b1 = a0r * (1.0 - cs);
                this->b2 = a0r * (1.0 - cs) * 0.5;
                this->a1 = a0r * (2.0 * cs);
                this->a2 = a0r * (alpha - 1.0);
            }

            inline void SetParameters(biquad_param_t* param, bq_t fc, bq_t bw, bq_t fs) {
                bq_t omega = 2.0 * M_PI * fc / fs;
                bq_t sn    = sin(omega);
                bq_t cs    = cos(omega);
                bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);

                const float a0r = 1.0 / (1.0 + alpha);
                param->b0 = a0r * (1.0 - cs) * 0.5;
                param->b1 = a0r * (1.0 - cs);
                param->b2 = a0r * (1.0 - cs) * 0.5;
                param->a1 = a0r * (2.0 * cs);
                param->a2 = a0r * (alpha - 1.0);
            }
    };

    class BandpassFilter : public BiquadFilter {
        public:
            inline BandpassFilter() : BiquadFilter() {}

            inline void SetParameters(bq_t fc, bq_t bw, bq_t fs) {
                bq_t omega = 2.0 * M_PI * fc / fs;
                bq_t sn    = sin(omega);
                bq_t cs    = cos(omega);
                bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);

                const float a0r = 1.0 / (1.0 + alpha);
                this->b0 = a0r * alpha;
                this->b1 = 0.0;
                this->b2 = a0r * -alpha;
                this->a1 = a0r * (2.0 * cs);
                this->a2 = a0r * (alpha - 1.0);
            }

            inline void SetParameters(biquad_param_t* param, bq_t fc, bq_t bw, bq_t fs) {
                bq_t omega = 2.0 * M_PI * fc / fs;
                bq_t sn    = sin(omega);
                bq_t cs    = cos(omega);
                bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);

                const float a0r = 1.0 / (1.0 + alpha);
                param->b0 = a0r * alpha;
                param->b1 = 0.0;
                param->b2 = a0r * -alpha;
                param->a1 = a0r * (2.0 * cs);
                param->a2 = a0r * (alpha - 1.0);
            }
    };

    class HighpassFilter : public BiquadFilter {
        public:
            inline HighpassFilter() : BiquadFilter() {}

            inline void SetParameters(bq_t fc, bq_t bw, bq_t fs) {
                bq_t omega = 2.0 * M_PI * fc / fs;
                bq_t sn    = sin(omega);
                bq_t cs    = cos(omega);
                bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);

                const float a0r = 1.0 / (1.0 + alpha);
                this->b0 = a0r * (1.0 + cs) * 0.5;
                this->b1 = a0r * -(1.0 + cs);
                this->b2 = a0r * (1.0 + cs) * 0.5;
                this->a1 = a0r * (2.0 * cs);
                this->a2 = a0r * (alpha - 1.0);
            }

            inline void SetParameters(biquad_param_t* param, bq_t fc, bq_t bw, bq_t fs) {
                bq_t omega = 2.0 * M_PI * fc / fs;
                bq_t sn    = sin(omega);
                bq_t cs    = cos(omega);
                bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);

                const float a0r = 1.0 / (1.0 + alpha);
                param->b0 = a0r * (1.0 + cs) * 0.5;
                param->b1 = a0r * -(1.0 + cs);
                param->b2 = a0r * (1.0 + cs) * 0.5;
                param->a1 = a0r * (2.0 * cs);
                param->a2 = a0r * (alpha - 1.0);
            }
    };

} // namespace LinuxSampler

#endif // __LS_BIQUADFILTER_H__
1	/***************************************************************************
2	* *
3	* LinuxSampler - modular, streaming capable sampler *
4	* *
5	* Copyright (C) 2003, 2004 by Benno Senoner and Christian Schoenebeck *
6	* *
7	* This program is free software; you can redistribute it and/or modify *
8	* it under the terms of the GNU General Public License as published by *
9	* the Free Software Foundation; either version 2 of the License, or *
10	* (at your option) any later version. *
11	* *
12	* This program is distributed in the hope that it will be useful, *
13	* but WITHOUT ANY WARRANTY; without even the implied warranty of *
14	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
15	* GNU General Public License for more details. *
16	* *
17	* You should have received a copy of the GNU General Public License *
18	* along with this program; if not, write to the Free Software *
19	* Foundation, Inc., 59 Temple Place, Suite 330, Boston, *
20	* MA 02111-1307 USA *
21	***************************************************************************/
22
23	#ifndef __LS_BIQUADFILTER_H__
24	#define __LS_BIQUADFILTER_H__
25
26	#include <math.h>
27
28	/// ln(2) / 2
29	#define LN_2_2 0.34657359f
30
31	#ifndef LIMIT
32	# define LIMIT(v,l,u) (v < l ? l : (v > u ? u : v))
33	#endif
34
35	namespace LinuxSampler {
36
37	typedef float bq_t;
38
39	/**
40	* Internal parameters of the biquad filter, which are actually the
41	* final parameters of the filter's transfer function. This strucure is
42	* only needed when these parameters should stored outside the
43	* BiquadFilter class, e.g. to save calculation time by sharing them
44	* between multiple filters.
45	*/
46	struct biquad_param_t {
47	bq_t a1;
48	bq_t a2;
49	bq_t b0;
50	bq_t b1;
51	bq_t b2;
52	};
53
54	/**
55	* Bi-quadratic filter
56	* (adapted from lisp code by Eli Brandt, http://www.cs.cmu.edu/~eli/)
57	*/
58	class BiquadFilter {
59	protected:
60	// following five variables are only used if no external biquad_param_t reference is used
61	bq_t a1;
62	bq_t a2;
63	bq_t b0;
64	bq_t b1;
65	bq_t b2;
66	// following four variables are used to buffer the feedback
67	bq_t x1;
68	bq_t x2;
69	bq_t y1;
70	bq_t y2;
71
72	/**
73	* Prevent \a f from going into denormal mode which would slow down
74	* subsequent floating point calculations, we achieve that by setting
75	* \a f to zero when it falls under the denormal threshold value.
76	*/
77	inline void KillDenormal(bq_t& f) {
78	// TODO: this is a generic solution for 32bit floats, should be replaced by CPU specific asm code
79	f += 1e-18f;
80	f -= 1e-18f;
81	}
82	public:
83	inline BiquadFilter() {
84	x1 = 0.0f;
85	x2 = 0.0f;
86	y1 = 0.0f;
87	y2 = 0.0f;
88	}
89
90	inline bq_t Apply(const bq_t x) {
91	bq_t y;
92
93	y = this->b0 * x + this->b1 * this->x1 + this->b2 * this->x2 +
94	this->a1 * this->y1 + this->a2 * this->y2;
95	KillDenormal(y);
96	this->x2 = this->x1;
97	this->x1 = x;
98	this->y2 = this->y1;
99	this->y1 = y;
100
101	return y;
102	}
103
104	inline bq_t Apply(biquad_param_t* param, const bq_t x) {
105	bq_t y;
106
107	y = param->b0 * x + param->b1 * this->x1 + param->b2 * this->x2 +
108	param->a1 * this->y1 + param->a2 * this->y2;
109	KillDenormal(y);
110	this->x2 = this->x1;
111	this->x1 = x;
112	this->y2 = this->y1;
113	this->y1 = y;
114
115	return y;
116	}
117
118	inline bq_t ApplyFB(bq_t x, const bq_t fb) {
119	bq_t y;
120
121	x += this->y1 * fb * 0.98;
122	y = this->b0 * x + this->b1 * this->x1 + this->b2 * this->x2 +
123	this->a1 * this->y1 + this->a2 * this->y2;
124	KillDenormal(y);
125	this->x2 = this->x1;
126	this->x1 = x;
127	this->y2 = this->y1;
128	this->y1 = y;
129
130	return y;
131	}
132
133	inline bq_t ApplyFB(biquad_param_t* param, bq_t x, const bq_t fb) {
134	bq_t y;
135
136	x += this->y1 * fb * 0.98;
137	y = param->b0 * x + param->b1 * this->x1 + param->b2 * this->x2 +
138	param->a1 * this->y1 + param->a2 * this->y2;
139	KillDenormal(y);
140	this->x2 = this->x1;
141	this->x1 = x;
142	this->y2 = this->y1;
143	this->y1 = y;
144
145	return y;
146	}
147	};
148
149	class LowpassFilter : public BiquadFilter {
150	public:
151	inline LowpassFilter() : BiquadFilter() {}
152
153	inline void SetParameters(bq_t fc, bq_t bw, bq_t fs) {
154	bq_t omega = 2.0 * M_PI * fc / fs;
155	bq_t sn = sin(omega);
156	bq_t cs = cos(omega);
157	bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
158
159	const float a0r = 1.0 / (1.0 + alpha);
160	this->b0 = a0r * (1.0 - cs) * 0.5;
161	this->b1 = a0r * (1.0 - cs);
162	this->b2 = a0r * (1.0 - cs) * 0.5;
163	this->a1 = a0r * (2.0 * cs);
164	this->a2 = a0r * (alpha - 1.0);
165	}
166
167	inline void SetParameters(biquad_param_t* param, bq_t fc, bq_t bw, bq_t fs) {
168	bq_t omega = 2.0 * M_PI * fc / fs;
169	bq_t sn = sin(omega);
170	bq_t cs = cos(omega);
171	bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
172
173	const float a0r = 1.0 / (1.0 + alpha);
174	param->b0 = a0r * (1.0 - cs) * 0.5;
175	param->b1 = a0r * (1.0 - cs);
176	param->b2 = a0r * (1.0 - cs) * 0.5;
177	param->a1 = a0r * (2.0 * cs);
178	param->a2 = a0r * (alpha - 1.0);
179	}
180	};
181
182	class BandpassFilter : public BiquadFilter {
183	public:
184	inline BandpassFilter() : BiquadFilter() {}
185
186	inline void SetParameters(bq_t fc, bq_t bw, bq_t fs) {
187	bq_t omega = 2.0 * M_PI * fc / fs;
188	bq_t sn = sin(omega);
189	bq_t cs = cos(omega);
190	bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
191
192	const float a0r = 1.0 / (1.0 + alpha);
193	this->b0 = a0r * alpha;
194	this->b1 = 0.0;
195	this->b2 = a0r * -alpha;
196	this->a1 = a0r * (2.0 * cs);
197	this->a2 = a0r * (alpha - 1.0);
198	}
199
200	inline void SetParameters(biquad_param_t* param, bq_t fc, bq_t bw, bq_t fs) {
201	bq_t omega = 2.0 * M_PI * fc / fs;
202	bq_t sn = sin(omega);
203	bq_t cs = cos(omega);
204	bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
205
206	const float a0r = 1.0 / (1.0 + alpha);
207	param->b0 = a0r * alpha;
208	param->b1 = 0.0;
209	param->b2 = a0r * -alpha;
210	param->a1 = a0r * (2.0 * cs);
211	param->a2 = a0r * (alpha - 1.0);
212	}
213	};
214
215	class HighpassFilter : public BiquadFilter {
216	public:
217	inline HighpassFilter() : BiquadFilter() {}
218
219	inline void SetParameters(bq_t fc, bq_t bw, bq_t fs) {
220	bq_t omega = 2.0 * M_PI * fc / fs;
221	bq_t sn = sin(omega);
222	bq_t cs = cos(omega);
223	bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
224
225	const float a0r = 1.0 / (1.0 + alpha);
226	this->b0 = a0r * (1.0 + cs) * 0.5;
227	this->b1 = a0r * -(1.0 + cs);
228	this->b2 = a0r * (1.0 + cs) * 0.5;
229	this->a1 = a0r * (2.0 * cs);
230	this->a2 = a0r * (alpha - 1.0);
231	}
232
233	inline void SetParameters(biquad_param_t* param, bq_t fc, bq_t bw, bq_t fs) {
234	bq_t omega = 2.0 * M_PI * fc / fs;
235	bq_t sn = sin(omega);
236	bq_t cs = cos(omega);
237	bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
238
239	const float a0r = 1.0 / (1.0 + alpha);
240	param->b0 = a0r * (1.0 + cs) * 0.5;
241	param->b1 = a0r * -(1.0 + cs);
242	param->b2 = a0r * (1.0 + cs) * 0.5;
243	param->a1 = a0r * (2.0 * cs);
244	param->a2 = a0r * (alpha - 1.0);
245	}
246	};
247
248	} // namespace LinuxSampler
249
250	#endif // __LS_BIQUADFILTER_H__