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/*
* Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef MODULES_AUDIO_PROCESSING_AGC2_BIQUAD_FILTER_H_
#define MODULES_AUDIO_PROCESSING_AGC2_BIQUAD_FILTER_H_
#include "api/array_view.h"
namespace webrtc {
// Transposed direct form I implementation of a bi-quad filter.
// b[0] + b[1] • z^(-1) + b[2] • z^(-2)
// H(z) = ------------------------------------
// 1 + a[1] • z^(-1) + a[2] • z^(-2)
class BiQuadFilter {
public:
// Normalized filter coefficients.
// Computed as `[b, a] = scipy.signal.butter(N=2, Wn, btype)`.
struct Config {
float b[3]; // b[0], b[1], b[2].
float a[2]; // a[1], a[2].
};
explicit BiQuadFilter(const Config& config);
BiQuadFilter(const BiQuadFilter&) = delete;
BiQuadFilter& operator=(const BiQuadFilter&) = delete;
~BiQuadFilter();
// Sets the filter configuration and resets the internal state.
void SetConfig(const Config& config);
// Zeroes the filter state.
void Reset();
// Filters `x` and writes the output in `y`, which must have the same length
// of `x`. In-place processing is supported.
void Process(rtc::ArrayView<const float> x, rtc::ArrayView<float> y);
private:
Config config_;
struct State {
float b[2];
float a[2];
} state_;
};
} // namespace webrtc
#endif // MODULES_AUDIO_PROCESSING_AGC2_BIQUAD_FILTER_H_
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