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      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 CROSSOVER2_H_
      7 #define CROSSOVER2_H_
      8 
      9 #ifdef __cplusplus
     10 extern "C" {
     11 #endif
     12 
     13 /* "crossover2" is a two channel version of the "crossover" filter. It processes
     14  * two channels of data at once to increase performance. */
     15 
     16 /* An LR4 filter is two biquads with the same parameters connected in series:
     17  *
     18  * x -- [BIQUAD] -- y -- [BIQUAD] -- z
     19  *
     20  * Both biquad filter has the same parameter b[012] and a[12],
     21  * The variable [xyz][12][LR] keep the history values.
     22  */
     23 struct lr42 {
     24 	float b0, b1, b2;
     25 	float a1, a2;
     26 	float x1L, x1R, x2L, x2R;
     27 	float y1L, y1R, y2L, y2R;
     28 	float z1L, z1R, z2L, z2R;
     29 };
     30 
     31 /* Three bands crossover filter:
     32  *
     33  * INPUT --+-- lp0 --+-- lp1 --+---> LOW (0)
     34  *         |         |         |
     35  *         |         \-- hp1 --/
     36  *         |
     37  *         \-- hp0 --+-- lp2 ------> MID (1)
     38  *                   |
     39  *                   \-- hp2 ------> HIGH (2)
     40  *
     41  *            [f0]       [f1]
     42  *
     43  * Each lp or hp is an LR4 filter, which consists of two second-order
     44  * lowpass or highpass butterworth filters.
     45  */
     46 struct crossover2 {
     47 	struct lr42 lp[3], hp[3];
     48 };
     49 
     50 /* Initializes a crossover2 filter
     51  * Args:
     52  *    xo2 - The crossover2 filter we want to initialize.
     53  *    freq1 - The normalized frequency splits low and mid band.
     54  *    freq2 - The normalized frequency splits mid and high band.
     55  */
     56 void crossover2_init(struct crossover2 *xo2, float freq1, float freq2);
     57 
     58 /* Splits input samples to three bands.
     59  * Args:
     60  *    xo2 - The crossover2 filter to use.
     61  *    count - The number of input samples.
     62  *    data0L, data0R - The input samples, also the place to store low band
     63  *                     output.
     64  *    data1L, data1R - The place to store mid band output.
     65  *    data2L, data2R - The place to store high band output.
     66  */
     67 void crossover2_process(struct crossover2 *xo2, int count,
     68 			float *data0L, float *data0R,
     69 			float *data1L, float *data1R,
     70 			float *data2L, float *data2R);
     71 
     72 #ifdef __cplusplus
     73 } /* extern "C" */
     74 #endif
     75 
     76 #endif /* CROSSOVER2_H_ */
     77