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/*
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ANDROID_SECOND_ORDER_LOW_PASS_FILTER_H
#define ANDROID_SECOND_ORDER_LOW_PASS_FILTER_H
#include <stdint.h>
#include <sys/types.h>
// ---------------------------------------------------------------------------
namespace android {
// ---------------------------------------------------------------------------
class BiquadFilter;
/*
* State of a 2nd order low-pass IIR filter
*/
class SecondOrderLowPassFilter {
friend class BiquadFilter;
float iQ, fc;
float K, iD;
float a0, a1;
float b1, b2;
public:
SecondOrderLowPassFilter(float Q, float fc);
void setSamplingPeriod(float dT);
};
/*
* Implements a Biquad IIR filter
*/
class BiquadFilter {
float x1, x2;
float y1, y2;
const SecondOrderLowPassFilter& s;
public:
BiquadFilter(const SecondOrderLowPassFilter& s);
float init(float in);
float operator()(float in);
};
/*
* Two cascaded biquad IIR filters
* (4-poles IIR)
*/
class CascadedBiquadFilter {
BiquadFilter mA;
BiquadFilter mB;
public:
CascadedBiquadFilter(const SecondOrderLowPassFilter& s);
float init(float in);
float operator()(float in);
};
// ---------------------------------------------------------------------------
}; // namespace android
#endif // ANDROID_SECOND_ORDER_LOW_PASS_FILTER_H
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