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/* Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef BIQUAD_H_
#define BIQUAD_H_
#ifdef __cplusplus
extern "C" {
#endif
/* The biquad filter parameters. The transfer function H(z) is (b0 + b1 * z^(-1)
* + b2 * z^(-2)) / (1 + a1 * z^(-1) + a2 * z^(-2)). The previous two inputs
* are stored in x1 and x2, and the previous two outputs are stored in y1 and
* y2.
*
* We use double during the coefficients calculation for better accuracy, but
* float is used during the actual filtering for faster computation.
*/
struct biquad {
float b0, b1, b2;
float a1, a2;
};
/* The type of the biquad filters */
enum biquad_type {
BQ_LOWPASS,
BQ_HIGHPASS,
};
/* Initialize a biquad filter parameters from its type and parameters.
* Args:
* bq - The biquad filter we want to set.
* type - The type of the biquad filter.
* frequency - The value should be in the range [0, 1]. It is relative to
* half of the sampling rate.
*/
void biquad_set(struct biquad *bq, enum biquad_type type, double freq);
#ifdef __cplusplus
} /* extern "C" */
#endif
#endif /* BIQUAD_H_ */
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