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__

/// 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	schoenebeck	53	/***************************************************************************
2			* *
3			* LinuxSampler - modular, streaming capable sampler *
4			* *
5	schoenebeck	56	* Copyright (C) 2003, 2004 by Benno Senoner and Christian Schoenebeck *
6	schoenebeck	53	* *
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			/// ln(2) / 2
27			#define LN_2_2 0.34657359f
28
29			#ifndef LIMIT
30			# define LIMIT(v,l,u) (v < l ? l : (v > u ? u : v))
31			#endif
32
33			namespace LinuxSampler {
34
35			typedef float bq_t;
36
37			/**
38	schoenebeck	80	* Internal parameters of the biquad filter, which are actually the
39			* final parameters of the filter's transfer function. This strucure is
40			* only needed when these parameters should stored outside the
41			* BiquadFilter class, e.g. to save calculation time by sharing them
42			* between multiple filters.
43			*/
44			struct biquad_param_t {
45			bq_t a1;
46			bq_t a2;
47			bq_t b0;
48			bq_t b1;
49			bq_t b2;
50			};
51
52			/**
53			* Bi-quadratic filter
54			* (adapted from lisp code by Eli Brandt, http://www.cs.cmu.edu/~eli/)
55			*/
56	schoenebeck	53	class BiquadFilter {
57			protected:
58	schoenebeck	80	// following five variables are only used if no external biquad_param_t reference is used
59	schoenebeck	53	bq_t a1;
60			bq_t a2;
61			bq_t b0;
62			bq_t b1;
63			bq_t b2;
64	schoenebeck	80	// following four variables are used to buffer the feedback
65	schoenebeck	53	bq_t x1;
66			bq_t x2;
67			bq_t y1;
68			bq_t y2;
69
70			/**
71	schoenebeck	80	* Prevent \a f from going into denormal mode which would slow down
72			* subsequent floating point calculations, we achieve that by setting
73			* \a f to zero when it falls under the denormal threshold value.
74			*/
75			inline void KillDenormal(bq_t& f) {
76	schoenebeck	53	// TODO: this is a generic solution for 32bit floats, should be replaced by CPU specific asm code
77			f += 1e-18f;
78			f -= 1e-18f;
79			}
80			public:
81			inline BiquadFilter() {
82			x1 = 0.0f;
83			x2 = 0.0f;
84			y1 = 0.0f;
85			y2 = 0.0f;
86			}
87
88			inline bq_t Apply(const bq_t x) {
89			bq_t y;
90
91			y = this->b0 * x + this->b1 * this->x1 + this->b2 * this->x2 +
92			this->a1 * this->y1 + this->a2 * this->y2;
93			KillDenormal(y);
94			this->x2 = this->x1;
95			this->x1 = x;
96			this->y2 = this->y1;
97			this->y1 = y;
98
99			return y;
100			}
101
102	schoenebeck	80	inline bq_t Apply(biquad_param_t* param, const bq_t x) {
103			bq_t y;
104
105			y = param->b0 * x + param->b1 * this->x1 + param->b2 * this->x2 +
106			param->a1 * this->y1 + param->a2 * this->y2;
107			KillDenormal(y);
108			this->x2 = this->x1;
109			this->x1 = x;
110			this->y2 = this->y1;
111			this->y1 = y;
112
113			return y;
114			}
115
116	schoenebeck	53	inline bq_t ApplyFB(bq_t x, const bq_t fb) {
117			bq_t y;
118
119			x += this->y1 * fb * 0.98;
120			y = this->b0 * x + this->b1 * this->x1 + this->b2 * this->x2 +
121			this->a1 * this->y1 + this->a2 * this->y2;
122			KillDenormal(y);
123			this->x2 = this->x1;
124			this->x1 = x;
125			this->y2 = this->y1;
126			this->y1 = y;
127
128			return y;
129			}
130	schoenebeck	80
131			inline bq_t ApplyFB(biquad_param_t* param, bq_t x, const bq_t fb) {
132			bq_t y;
133
134			x += this->y1 * fb * 0.98;
135			y = param->b0 * x + param->b1 * this->x1 + param->b2 * this->x2 +
136			param->a1 * this->y1 + param->a2 * this->y2;
137			KillDenormal(y);
138			this->x2 = this->x1;
139			this->x1 = x;
140			this->y2 = this->y1;
141			this->y1 = y;
142
143			return y;
144			}
145	schoenebeck	53	};
146
147			class LowpassFilter : public BiquadFilter {
148			public:
149			inline LowpassFilter() : BiquadFilter() {}
150
151			inline void SetParameters(bq_t fc, bq_t bw, bq_t fs) {
152			bq_t omega = 2.0 * M_PI * fc / fs;
153			bq_t sn = sin(omega);
154			bq_t cs = cos(omega);
155			bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
156
157			const float a0r = 1.0 / (1.0 + alpha);
158			this->b0 = a0r * (1.0 - cs) * 0.5;
159			this->b1 = a0r * (1.0 - cs);
160			this->b2 = a0r * (1.0 - cs) * 0.5;
161			this->a1 = a0r * (2.0 * cs);
162			this->a2 = a0r * (alpha - 1.0);
163			}
164	schoenebeck	80
165			inline void SetParameters(biquad_param_t* param, bq_t fc, bq_t bw, bq_t fs) {
166			bq_t omega = 2.0 * M_PI * fc / fs;
167			bq_t sn = sin(omega);
168			bq_t cs = cos(omega);
169			bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
170
171			const float a0r = 1.0 / (1.0 + alpha);
172			param->b0 = a0r * (1.0 - cs) * 0.5;
173			param->b1 = a0r * (1.0 - cs);
174			param->b2 = a0r * (1.0 - cs) * 0.5;
175			param->a1 = a0r * (2.0 * cs);
176			param->a2 = a0r * (alpha - 1.0);
177			}
178	schoenebeck	53	};
179
180			class BandpassFilter : public BiquadFilter {
181			public:
182			inline BandpassFilter() : BiquadFilter() {}
183
184			inline void SetParameters(bq_t fc, bq_t bw, bq_t fs) {
185			bq_t omega = 2.0 * M_PI * fc / fs;
186			bq_t sn = sin(omega);
187			bq_t cs = cos(omega);
188			bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
189
190			const float a0r = 1.0 / (1.0 + alpha);
191			this->b0 = a0r * alpha;
192			this->b1 = 0.0;
193			this->b2 = a0r * -alpha;
194			this->a1 = a0r * (2.0 * cs);
195			this->a2 = a0r * (alpha - 1.0);
196			}
197	schoenebeck	80
198			inline void SetParameters(biquad_param_t* param, bq_t fc, bq_t bw, bq_t fs) {
199			bq_t omega = 2.0 * M_PI * fc / fs;
200			bq_t sn = sin(omega);
201			bq_t cs = cos(omega);
202			bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
203
204			const float a0r = 1.0 / (1.0 + alpha);
205			param->b0 = a0r * alpha;
206			param->b1 = 0.0;
207			param->b2 = a0r * -alpha;
208			param->a1 = a0r * (2.0 * cs);
209			param->a2 = a0r * (alpha - 1.0);
210			}
211	schoenebeck	53	};
212
213			class HighpassFilter : public BiquadFilter {
214			public:
215			inline HighpassFilter() : BiquadFilter() {}
216
217			inline void SetParameters(bq_t fc, bq_t bw, bq_t fs) {
218			bq_t omega = 2.0 * M_PI * fc / fs;
219			bq_t sn = sin(omega);
220			bq_t cs = cos(omega);
221			bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
222
223			const float a0r = 1.0 / (1.0 + alpha);
224			this->b0 = a0r * (1.0 + cs) * 0.5;
225			this->b1 = a0r * -(1.0 + cs);
226			this->b2 = a0r * (1.0 + cs) * 0.5;
227			this->a1 = a0r * (2.0 * cs);
228			this->a2 = a0r * (alpha - 1.0);
229			}
230	schoenebeck	80
231			inline void SetParameters(biquad_param_t* param, bq_t fc, bq_t bw, bq_t fs) {
232			bq_t omega = 2.0 * M_PI * fc / fs;
233			bq_t sn = sin(omega);
234			bq_t cs = cos(omega);
235			bq_t alpha = sn * sinh(M_LN2 / 2.0 * bw * omega / sn);
236
237			const float a0r = 1.0 / (1.0 + alpha);
238			param->b0 = a0r * (1.0 + cs) * 0.5;
239			param->b1 = a0r * -(1.0 + cs);
240			param->b2 = a0r * (1.0 + cs) * 0.5;
241			param->a1 = a0r * (2.0 * cs);
242			param->a2 = a0r * (alpha - 1.0);
243			}
244	schoenebeck	53	};
245
246			} // namespace LinuxSampler
247
248			#endif // __LS_BIQUADFILTER_H__