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 | #pragma once |
| 6 | |
| 7 | |
| 8 | #include <vector> |
| 9 | #include <cstdint> |
| 10 | #include <cmath> |
| 11 | #include <limits> |
| 12 | #include <string> |
| 13 | |
| 14 | /* MFCC's consolidated parameters */ |
| 15 | class MfccParams |
| 16 | { |
| 17 | public: |
| 18 | float m_samplingFreq; |
| 19 | int m_numFbankBins; |
| 20 | float m_melLoFreq; |
| 21 | float m_melHiFreq; |
| 22 | int m_numMfccFeatures; |
| 23 | int m_frameLen; |
| 24 | int m_frameLenPadded; |
| 25 | bool m_useHtkMethod; |
| 26 | int m_numMfccVectors; |
| 27 | /** @brief Constructor */ |
| 28 | MfccParams(const float samplingFreq, const int numFbankBins, |
| 29 | const float melLoFreq, const float melHiFreq, |
| 30 | const int numMfccFeats, const int frameLen, |
| 31 | const bool useHtkMethod, const int numMfccVectors); |
| 32 | /* Delete the default constructor */ |
| 33 | MfccParams() = delete; |
| 34 | /* Default destructor */ |
| 35 | ~MfccParams() = default; |
| 36 | /** @brief String representation of parameters */ |
| 37 | std::string Str(); |
| 38 | }; |
| 39 | |
| 40 | /** |
| 41 | * @brief Class for MFCC feature extraction. |
| 42 | * Based on https://github.com/ARM-software/ML-KWS-for-MCU/blob/master/Deployment/Source/MFCC/mfcc.cpp |
| 43 | * This class is designed to be generic and self-sufficient but |
| 44 | * certain calculation routines can be overridden to accommodate |
| 45 | * use-case specific requirements. |
| 46 | */ |
| 47 | class MFCC { |
| 48 | public: |
| 49 | /** |
| 50 | * @brief Constructor |
| 51 | * @param[in] params MFCC parameters |
| 52 | */ |
| 53 | explicit MFCC(const MfccParams& params); |
| 54 | |
| 55 | MFCC() = delete; |
| 56 | |
| 57 | ~MFCC() = default; |
| 58 | |
| 59 | /** |
| 60 | * @brief Extract MFCC features for one single small frame of |
| 61 | * audio data e.g. 640 samples. |
| 62 | * @param[in] audioData Vector of audio samples to calculate |
| 63 | * features for. |
| 64 | * @return Vector of extracted MFCC features. |
| 65 | **/ |
| 66 | std::vector<float> MfccCompute(const std::vector<float>& audioData); |
| 67 | |
| 68 | /** @brief Initialise. */ |
| 69 | void Init(); |
| 70 | |
| 71 | /** |
| 72 | * @brief Extract MFCC features and quantise for one single small |
| 73 | * frame of audio data e.g. 640 samples. |
| 74 | * @param[in] audioData Vector of audio samples to calculate |
| 75 | * features for. |
| 76 | * @param[in] quantScale Quantisation scale. |
| 77 | * @param[in] quantOffset Quantisation offset. |
| 78 | * @return Vector of extracted quantised MFCC features. |
| 79 | **/ |
| 80 | template<typename T> |
| 81 | std::vector<T> MfccComputeQuant(const std::vector<float>& audioData, |
| 82 | const float quantScale, |
| 83 | const int quantOffset) |
| 84 | { |
| 85 | this->MfccComputePreFeature(audioData); |
| 86 | float minVal = std::numeric_limits<T>::min(); |
| 87 | float maxVal = std::numeric_limits<T>::max(); |
| 88 | |
| 89 | std::vector<T> mfccOut(this->m_params.m_numMfccFeatures); |
| 90 | const size_t numFbankBins = this->m_params.m_numFbankBins; |
| 91 | |
| 92 | /* Take DCT. Uses matrix mul. */ |
| 93 | for (size_t i = 0, j = 0; i < mfccOut.size(); ++i, j += numFbankBins) |
| 94 | { |
| 95 | float sum = 0; |
| 96 | for (size_t k = 0; k < numFbankBins; ++k) |
| 97 | { |
| 98 | sum += this->m_dctMatrix[j + k] * this->m_melEnergies[k]; |
| 99 | } |
| 100 | /* Quantize to T. */ |
| 101 | sum = std::round((sum / quantScale) + quantOffset); |
| 102 | mfccOut[i] = static_cast<T>(std::min<float>(std::max<float>(sum, minVal), maxVal)); |
| 103 | } |
| 104 | |
| 105 | return mfccOut; |
| 106 | } |
| 107 | |
| 108 | MfccParams m_params; |
| 109 | |
| 110 | /* Constants */ |
| 111 | static constexpr float ms_logStep = /*logf(6.4)*/ 1.8562979903656 / 27.0; |
| 112 | static constexpr float ms_freqStep = 200.0 / 3; |
| 113 | static constexpr float ms_minLogHz = 1000.0; |
| 114 | static constexpr float ms_minLogMel = ms_minLogHz / ms_freqStep; |
| 115 | |
| 116 | protected: |
| 117 | /** |
| 118 | * @brief Project input frequency to Mel Scale. |
| 119 | * @param[in] freq Input frequency in floating point. |
| 120 | * @param[in] useHTKMethod bool to signal if HTK method is to be |
| 121 | * used for calculation. |
| 122 | * @return Mel transformed frequency in floating point. |
| 123 | **/ |
| 124 | static float MelScale(float freq, |
| 125 | bool useHTKMethod = true); |
| 126 | |
| 127 | /** |
| 128 | * @brief Inverse Mel transform - convert MEL warped frequency |
| 129 | * back to normal frequency. |
| 130 | * @param[in] melFreq Mel frequency in floating point. |
| 131 | * @param[in] useHTKMethod bool to signal if HTK method is to be |
| 132 | * used for calculation. |
| 133 | * @return Real world frequency in floating point. |
| 134 | **/ |
| 135 | static float InverseMelScale(float melFreq, |
| 136 | bool useHTKMethod = true); |
| 137 | |
| 138 | /** |
| 139 | * @brief Populates MEL energies after applying the MEL filter |
| 140 | * bank weights and adding them up to be placed into |
| 141 | * bins, according to the filter bank's first and last |
| 142 | * indices (pre-computed for each filter bank element |
| 143 | * by CreateMelFilterBank function). |
| 144 | * @param[in] fftVec Vector populated with FFT magnitudes. |
| 145 | * @param[in] melFilterBank 2D Vector with filter bank weights. |
| 146 | * @param[in] filterBankFilterFirst Vector containing the first indices of filter bank |
| 147 | * to be used for each bin. |
| 148 | * @param[in] filterBankFilterLast Vector containing the last indices of filter bank |
| 149 | * to be used for each bin. |
| 150 | * @param[out] melEnergies Pre-allocated vector of MEL energies to be |
| 151 | * populated. |
| 152 | * @return true if successful, false otherwise. |
| 153 | */ |
| 154 | virtual bool ApplyMelFilterBank( |
| 155 | std::vector<float>& fftVec, |
| 156 | std::vector<std::vector<float>>& melFilterBank, |
| 157 | std::vector<uint32_t>& filterBankFilterFirst, |
| 158 | std::vector<uint32_t>& filterBankFilterLast, |
| 159 | std::vector<float>& melEnergies); |
| 160 | |
| 161 | /** |
| 162 | * @brief Converts the Mel energies for logarithmic scale. |
| 163 | * @param[in,out] melEnergies 1D vector of Mel energies. |
| 164 | **/ |
| 165 | virtual void ConvertToLogarithmicScale(std::vector<float>& melEnergies); |
| 166 | |
| 167 | /** |
| 168 | * @brief Create a matrix used to calculate Discrete Cosine |
| 169 | * Transform. |
| 170 | * @param[in] inputLength Input length of the buffer on which |
| 171 | * DCT will be performed. |
| 172 | * @param[in] coefficientCount Total coefficients per input length. |
| 173 | * @return 1D vector with inputLength x coefficientCount elements |
| 174 | * populated with DCT coefficients. |
| 175 | */ |
| 176 | virtual std::vector<float> CreateDCTMatrix( |
| 177 | int32_t inputLength, |
| 178 | int32_t coefficientCount); |
| 179 | |
| 180 | /** |
| 181 | * @brief Given the low and high Mel values, get the normaliser |
| 182 | * for weights to be applied when populating the filter |
| 183 | * bank. |
| 184 | * @param[in] leftMel Low Mel frequency value. |
| 185 | * @param[in] rightMel High Mel frequency value. |
| 186 | * @param[in] useHTKMethod bool to signal if HTK method is to be |
| 187 | * used for calculation. |
| 188 | * @return Value to use for normalizing. |
| 189 | */ |
| 190 | virtual float GetMelFilterBankNormaliser( |
| 191 | const float& leftMel, |
| 192 | const float& rightMel, |
| 193 | bool useHTKMethod); |
| 194 | |
| 195 | private: |
| 196 | |
| 197 | std::vector<float> m_frame; |
| 198 | std::vector<float> m_buffer; |
| 199 | std::vector<float> m_melEnergies; |
| 200 | std::vector<float> m_windowFunc; |
| 201 | std::vector<std::vector<float>> m_melFilterBank; |
| 202 | std::vector<float> m_dctMatrix; |
| 203 | std::vector<uint32_t> m_filterBankFilterFirst; |
| 204 | std::vector<uint32_t> m_filterBankFilterLast; |
| 205 | bool m_filterBankInitialised; |
| 206 | |
| 207 | /** |
| 208 | * @brief Initialises the filter banks and the DCT matrix. **/ |
| 209 | void InitMelFilterBank(); |
| 210 | |
| 211 | /** |
| 212 | * @brief Signals whether the instance of MFCC has had its |
| 213 | * required buffers initialised. |
| 214 | * @return true if initialised, false otherwise. |
| 215 | **/ |
| 216 | bool IsMelFilterBankInited() const; |
| 217 | |
| 218 | /** |
| 219 | * @brief Create mel filter banks for MFCC calculation. |
| 220 | * @return 2D vector of floats. |
| 221 | **/ |
| 222 | std::vector<std::vector<float>> CreateMelFilterBank(); |
| 223 | |
| 224 | /** |
| 225 | * @brief Computes and populates internal memeber buffers used |
| 226 | * in MFCC feature calculation |
| 227 | * @param[in] audioData 1D vector of 16-bit audio data. |
| 228 | */ |
| 229 | void MfccComputePreFeature(const std::vector<float>& audioData); |
| 230 | |
| 231 | /** @brief Computes the magnitude from an interleaved complex array. */ |
| 232 | void ConvertToPowerSpectrum(); |
| 233 | |
| 234 | }; |