1 /* Copyright (c) 2013 The Chromium OS Authors. All rights reserved. 2 * Use of this source code is governed by a BSD-style license that can be 3 * found in the LICENSE file. 4 */ 5 6 #ifndef BIQUAD_H_ 7 #define BIQUAD_H_ 8 9 #ifdef __cplusplus 10 extern "C" { 11 #endif 12 13 /* The biquad filter parameters. The transfer function H(z) is (b0 + b1 * z^(-1) 14 * + b2 * z^(-2)) / (1 + a1 * z^(-1) + a2 * z^(-2)). The previous two inputs 15 * are stored in x1 and x2, and the previous two outputs are stored in y1 and 16 * y2. 17 * 18 * We use double during the coefficients calculation for better accurary, but 19 * float is used during the actual filtering for faster computation. 20 */ 21 struct biquad { 22 float b0, b1, b2; 23 float a1, a2; 24 float x1, x2; 25 float y1, y2; 26 }; 27 28 /* The type of the biquad filters */ 29 enum biquad_type { 30 BQ_NONE, 31 BQ_LOWPASS, 32 BQ_HIGHPASS, 33 BQ_BANDPASS, 34 BQ_LOWSHELF, 35 BQ_HIGHSHELF, 36 BQ_PEAKING, 37 BQ_NOTCH, 38 BQ_ALLPASS 39 }; 40 41 /* Initialize a biquad filter parameters from its type and parameters. 42 * Args: 43 * bq - The biquad filter we want to set. 44 * type - The type of the biquad filter. 45 * frequency - The value should be in the range [0, 1]. It is relative to 46 * half of the sampling rate. 47 * Q - Quality factor. See Web Audio API for details. 48 * gain - The value is in dB. See Web Audio API for details. 49 */ 50 void biquad_set(struct biquad *bq, enum biquad_type type, double freq, double Q, 51 double gain); 52 53 #ifdef __cplusplus 54 } /* extern "C" */ 55 #endif 56 57 #endif /* BIQUAD_H_ */ 58
