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Diffstat (limited to 'source/use_case/asr/src/Wav2LetterMfcc.cc')
-rw-r--r-- | source/use_case/asr/src/Wav2LetterMfcc.cc | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/source/use_case/asr/src/Wav2LetterMfcc.cc b/source/use_case/asr/src/Wav2LetterMfcc.cc new file mode 100644 index 0000000..92c91bc --- /dev/null +++ b/source/use_case/asr/src/Wav2LetterMfcc.cc @@ -0,0 +1,137 @@ +/* + * Copyright (c) 2021 Arm Limited. All rights reserved. + * SPDX-License-Identifier: Apache-2.0 + * + * 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 "Wav2LetterMfcc.hpp" + +#include "PlatformMath.hpp" + +#include <cfloat> + +namespace arm { +namespace app { +namespace audio { + + bool Wav2LetterMFCC::ApplyMelFilterBank( + std::vector<float>& fftVec, + std::vector<std::vector<float>>& melFilterBank, + std::vector<int32_t>& filterBankFilterFirst, + std::vector<int32_t>& filterBankFilterLast, + std::vector<float>& melEnergies) + { + const size_t numBanks = melEnergies.size(); + + if (numBanks != filterBankFilterFirst.size() || + numBanks != filterBankFilterLast.size()) { + printf_err("Unexpected filter bank lengths\n"); + return false; + } + + for (size_t bin = 0; bin < numBanks; ++bin) { + auto filterBankIter = melFilterBank[bin].begin(); + float melEnergy = 1e-10; /* Avoid log of zero at later stages, same value used in librosa. */ + const int32_t firstIndex = filterBankFilterFirst[bin]; + const int32_t lastIndex = filterBankFilterLast[bin]; + + for (int32_t i = firstIndex; i <= lastIndex; ++i) { + melEnergy += (*filterBankIter++ * fftVec[i]); + } + + melEnergies[bin] = melEnergy; + } + + return true; + } + + void Wav2LetterMFCC::ConvertToLogarithmicScale( + std::vector<float>& melEnergies) + { + float maxMelEnergy = -FLT_MAX; + + /* Container for natural logarithms of mel energies. */ + std::vector <float> vecLogEnergies(melEnergies.size(), 0.f); + + /* Because we are taking natural logs, we need to multiply by log10(e). + * Also, for wav2letter model, we scale our log10 values by 10. */ + constexpr float multiplier = 10.0 * /* Default scalar. */ + 0.4342944819032518; /* log10f(std::exp(1.0)) */ + + /* Take log of the whole vector. */ + math::MathUtils::VecLogarithmF32(melEnergies, vecLogEnergies); + + /* Scale the log values and get the max. */ + for (auto iterM = melEnergies.begin(), iterL = vecLogEnergies.begin(); + iterM != melEnergies.end(); ++iterM, ++iterL) { + + *iterM = *iterL * multiplier; + + /* Save the max mel energy. */ + if (*iterM > maxMelEnergy) { + maxMelEnergy = *iterM; + } + } + + /* Clamp the mel energies. */ + constexpr float maxDb = 80.0; + const float clampLevelLowdB = maxMelEnergy - maxDb; + for (auto iter = melEnergies.begin(); iter != melEnergies.end(); ++iter) { + *iter = std::max(*iter, clampLevelLowdB); + } + } + + std::vector<float> Wav2LetterMFCC::CreateDCTMatrix( + const int32_t inputLength, + const int32_t coefficientCount) + { + std::vector<float> dctMatix(inputLength * coefficientCount); + + /* Orthonormal normalization. */ + const float normalizerK0 = 2 * math::MathUtils::SqrtF32(1.0f / + static_cast<float>(4*inputLength)); + const float normalizer = 2 * math::MathUtils::SqrtF32(1.0f / + static_cast<float>(2*inputLength)); + + const float angleIncr = M_PI / inputLength; + float angle = angleIncr; /* We start using it at k = 1 loop. */ + + /* First row of DCT will use normalizer K0. */ + for (int32_t n = 0; n < inputLength; ++n) { + dctMatix[n] = normalizerK0 /* cos(0) = 1 */; + } + + /* Second row (index = 1) onwards, we use standard normalizer. */ + for (int32_t k = 1, m = inputLength; k < coefficientCount; ++k, m += inputLength) { + for (int32_t n = 0; n < inputLength; ++n) { + dctMatix[m+n] = normalizer * + math::MathUtils::CosineF32((n + 0.5f) * angle); + } + angle += angleIncr; + } + return dctMatix; + } + + float Wav2LetterMFCC::GetMelFilterBankNormaliser( + const float& leftMel, + const float& rightMel, + const bool useHTKMethod) + { + /* Slaney normalization for mel weights. */ + return (2.0f / (MFCC::InverseMelScale(rightMel, useHTKMethod) - + MFCC::InverseMelScale(leftMel, useHTKMethod))); + } + +} /* namespace audio */ +} /* namespace app */ +} /* namespace arm */ |