diff options
Diffstat (limited to 'extern/audaspace/src/fx/ButterworthCalculator.cpp')
| -rw-r--r-- | extern/audaspace/src/fx/ButterworthCalculator.cpp | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/extern/audaspace/src/fx/ButterworthCalculator.cpp b/extern/audaspace/src/fx/ButterworthCalculator.cpp new file mode 100644 index 00000000000..f249fd45f15 --- /dev/null +++ b/extern/audaspace/src/fx/ButterworthCalculator.cpp @@ -0,0 +1,54 @@ +/******************************************************************************* + * 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/ButterworthCalculator.h" + +#include <cmath> + +#define BWPB41 0.76536686473 +#define BWPB42 1.84775906502 + +AUD_NAMESPACE_BEGIN + +ButterworthCalculator::ButterworthCalculator(float frequency) : + m_frequency(frequency) +{ +} + +void ButterworthCalculator::recalculateCoefficients(SampleRate rate, std::vector<float> &b, std::vector<float> &a) +{ + float omega = 2 * std::tan(m_frequency * M_PI / rate); + float o2 = omega * omega; + float o4 = o2 * o2; + float x1 = o2 + 2.0f * (float)BWPB41 * omega + 4.0f; + float x2 = o2 + 2.0f * (float)BWPB42 * omega + 4.0f; + float y1 = o2 - 2.0f * (float)BWPB41 * omega + 4.0f; + float y2 = o2 - 2.0f * (float)BWPB42 * omega + 4.0f; + float o228 = 2.0f * o2 - 8.0f; + float norm = x1 * x2; + a.push_back(1); + a.push_back((x1 + x2) * o228 / norm); + a.push_back((x1 * y2 + x2 * y1 + o228 * o228) / norm); + a.push_back((y1 + y2) * o228 / norm); + a.push_back(y1 * y2 / norm); + b.push_back(o4 / norm); + b.push_back(4 * o4 / norm); + b.push_back(6 * o4 / norm); + b.push_back(b[1]); + b.push_back(b[0]); +} + +AUD_NAMESPACE_END |