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/*******************************************************************************
* Copyright 2009-2016 Jörg Müller
*
* 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.
******************************************************************************/
#include "fx/LowpassCalculator.h"
#include <cmath>
AUD_NAMESPACE_BEGIN
LowpassCalculator::LowpassCalculator(float frequency, float Q) :
m_frequency(frequency),
m_Q(Q)
{
}
void LowpassCalculator::recalculateCoefficients(SampleRate rate, std::vector<float> &b, std::vector<float> &a)
{
float w0 = 2 * M_PI * m_frequency / rate;
float alpha = std::sin(w0) / (2 * m_Q);
float norm = 1 + alpha;
float c = std::cos(w0);
a.push_back(1);
a.push_back(-2 * c / norm);
a.push_back((1 - alpha) / norm);
b.push_back((1 - c) / (2 * norm));
b.push_back((1 - c) / norm);
b.push_back(b[0]);
}
AUD_NAMESPACE_END
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