George Gekov | 23c2627 | 2021-08-16 11:32:10 +0100 | [diff] [blame] | 1 | // |
| 2 | // Copyright © 2020 Arm Ltd and Contributors. All rights reserved. |
| 3 | // SPDX-License-Identifier: MIT |
| 4 | // |
| 5 | #include "Wav2LetterMFCC.hpp" |
| 6 | #include "MathUtils.hpp" |
| 7 | |
| 8 | #include <cfloat> |
| 9 | |
| 10 | bool Wav2LetterMFCC::ApplyMelFilterBank( |
| 11 | std::vector<float>& fftVec, |
| 12 | std::vector<std::vector<float>>& melFilterBank, |
| 13 | std::vector<uint32_t>& filterBankFilterFirst, |
| 14 | std::vector<uint32_t>& filterBankFilterLast, |
| 15 | std::vector<float>& melEnergies) |
| 16 | { |
| 17 | const size_t numBanks = melEnergies.size(); |
| 18 | |
| 19 | if (numBanks != filterBankFilterFirst.size() || |
| 20 | numBanks != filterBankFilterLast.size()) |
| 21 | { |
| 22 | printf("Unexpected filter bank lengths\n"); |
| 23 | return false; |
| 24 | } |
| 25 | |
| 26 | for (size_t bin = 0; bin < numBanks; ++bin) |
| 27 | { |
| 28 | auto filterBankIter = melFilterBank[bin].begin(); |
| 29 | auto end = melFilterBank[bin].end(); |
| 30 | // Avoid log of zero at later stages, same value used in librosa. |
| 31 | // The number was used during our default wav2letter model training. |
| 32 | float melEnergy = 1e-10; |
| 33 | const uint32_t firstIndex = filterBankFilterFirst[bin]; |
| 34 | const uint32_t lastIndex = std::min<uint32_t>(filterBankFilterLast[bin], fftVec.size() - 1); |
| 35 | |
| 36 | for (uint32_t i = firstIndex; i <= lastIndex && filterBankIter != end; ++i) |
| 37 | { |
| 38 | melEnergy += (*filterBankIter++ * fftVec[i]); |
| 39 | } |
| 40 | |
| 41 | melEnergies[bin] = melEnergy; |
| 42 | } |
| 43 | |
| 44 | return true; |
| 45 | } |
| 46 | |
| 47 | void Wav2LetterMFCC::ConvertToLogarithmicScale(std::vector<float>& melEnergies) |
| 48 | { |
| 49 | float maxMelEnergy = -FLT_MAX; |
| 50 | |
| 51 | // Container for natural logarithms of mel energies. |
| 52 | std::vector <float> vecLogEnergies(melEnergies.size(), 0.f); |
| 53 | |
| 54 | // Because we are taking natural logs, we need to multiply by log10(e). |
| 55 | // Also, for wav2letter model, we scale our log10 values by 10. |
| 56 | constexpr float multiplier = 10.0 * // Default scalar. |
| 57 | 0.4342944819032518; // log10f(std::exp(1.0)) |
| 58 | |
| 59 | // Take log of the whole vector. |
| 60 | MathUtils::VecLogarithmF32(melEnergies, vecLogEnergies); |
| 61 | |
| 62 | // Scale the log values and get the max. |
| 63 | for (auto iterM = melEnergies.begin(), iterL = vecLogEnergies.begin(); |
| 64 | iterM != melEnergies.end() && iterL != vecLogEnergies.end(); ++iterM, ++iterL) |
| 65 | { |
| 66 | |
| 67 | *iterM = *iterL * multiplier; |
| 68 | |
| 69 | // Save the max mel energy. |
| 70 | if (*iterM > maxMelEnergy) |
| 71 | { |
| 72 | maxMelEnergy = *iterM; |
| 73 | } |
| 74 | } |
| 75 | |
| 76 | // Clamp the mel energies. |
| 77 | constexpr float maxDb = 80.0; |
| 78 | const float clampLevelLowdB = maxMelEnergy - maxDb; |
| 79 | for (float& melEnergy : melEnergies) |
| 80 | { |
| 81 | melEnergy = std::max(melEnergy, clampLevelLowdB); |
| 82 | } |
| 83 | } |
| 84 | |
| 85 | std::vector<float> Wav2LetterMFCC::CreateDCTMatrix( |
| 86 | const int32_t inputLength, |
| 87 | const int32_t coefficientCount) |
| 88 | { |
| 89 | std::vector<float> dctMatix(inputLength * coefficientCount); |
| 90 | |
| 91 | // Orthonormal normalization. |
| 92 | const float normalizerK0 = 2 * sqrtf(1.0f / |
| 93 | static_cast<float>(4 * inputLength)); |
| 94 | const float normalizer = 2 * sqrtf(1.0f / |
| 95 | static_cast<float>(2 * inputLength)); |
| 96 | |
| 97 | const float angleIncr = M_PI / inputLength; |
| 98 | float angle = angleIncr; // We start using it at k = 1 loop. |
| 99 | |
| 100 | // First row of DCT will use normalizer K0. |
| 101 | for (int32_t n = 0; n < inputLength; ++n) |
| 102 | { |
| 103 | dctMatix[n] = normalizerK0; // cos(0) = 1 |
| 104 | } |
| 105 | |
| 106 | // Second row (index = 1) onwards, we use standard normalizer. |
| 107 | for (int32_t k = 1, m = inputLength; k < coefficientCount; ++k, m += inputLength) |
| 108 | { |
| 109 | for (int32_t n = 0; n < inputLength; ++n) |
| 110 | { |
| 111 | dctMatix[m+n] = normalizer * cosf((n + 0.5f) * angle); |
| 112 | } |
| 113 | angle += angleIncr; |
| 114 | } |
| 115 | return dctMatix; |
| 116 | } |
| 117 | |
| 118 | float Wav2LetterMFCC::GetMelFilterBankNormaliser( |
| 119 | const float& leftMel, |
| 120 | const float& rightMel, |
| 121 | const bool useHTKMethod) |
| 122 | { |
| 123 | // Slaney normalization for mel weights. |
| 124 | return (2.0f / (MFCC::InverseMelScale(rightMel, useHTKMethod) - |
| 125 | MFCC::InverseMelScale(leftMel, useHTKMethod))); |
| 126 | } |