ebiten/audio/internal/oboe/oboe_flowgraph_resampler_HyperbolicCosineWindow_android.h

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/*
* Copyright 2019 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 RESAMPLER_HYPERBOLIC_COSINE_WINDOW_H
#define RESAMPLER_HYPERBOLIC_COSINE_WINDOW_H
#include <math.h>
namespace resampler {
/**
* Calculate a HyperbolicCosineWindow window centered at 0.
* This can be used in place of a Kaiser window.
*
* The code is based on an anonymous contribution by "a concerned citizen":
* https://dsp.stackexchange.com/questions/37714/kaiser-window-approximation
*/
class HyperbolicCosineWindow {
public:
HyperbolicCosineWindow() {
setStopBandAttenuation(60);
}
/**
* @param attenuation typical values range from 30 to 90 dB
* @return beta
*/
double setStopBandAttenuation(double attenuation) {
double alpha = ((-325.1e-6 * attenuation + 0.1677) * attenuation) - 3.149;
setAlpha(alpha);
return alpha;
}
void setAlpha(double alpha) {
mAlpha = alpha;
mInverseCoshAlpha = 1.0 / cosh(alpha);
}
/**
* @param x ranges from -1.0 to +1.0
*/
double operator()(double x) {
double x2 = x * x;
if (x2 >= 1.0) return 0.0;
double w = mAlpha * sqrt(1.0 - x2);
return cosh(w) * mInverseCoshAlpha;
}
private:
double mAlpha = 0.0;
double mInverseCoshAlpha = 1.0;
};
} // namespace resampler
#endif //RESAMPLER_HYPERBOLIC_COSINE_WINDOW_H