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Diffstat (limited to 'source/application/main/include/Mfcc.hpp')
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diff --git a/source/application/main/include/Mfcc.hpp b/source/application/main/include/Mfcc.hpp new file mode 100644 index 0000000..6379fab --- /dev/null +++ b/source/application/main/include/Mfcc.hpp @@ -0,0 +1,255 @@ +/* + * 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. + */ +#ifndef MFCC_HPP +#define MFCC_HPP + +#include "PlatformMath.hpp" + +#include <vector> +#include <cstdint> +#include <cmath> +#include <limits> +#include <string> + +namespace arm { +namespace app { +namespace audio { + + /* MFCC's consolidated parameters. */ + class MfccParams { + public: + float m_samplingFreq; + uint32_t m_numFbankBins; + float m_melLoFreq; + float m_melHiFreq; + uint32_t m_numMfccFeatures; + uint32_t m_frameLen; + uint32_t m_frameLenPadded; + bool m_useHtkMethod; + + /** @brief Constructor */ + MfccParams(float samplingFreq, uint32_t numFbankBins, + float melLoFreq, float melHiFreq, + uint32_t numMfccFeats, uint32_t frameLen, + bool useHtkMethod); + + MfccParams() = delete; + + ~MfccParams() = default; + + /** @brief String representation of parameters */ + std::string Str(); + }; + + /** + * @brief Class for MFCC feature extraction. + * Based on https://github.com/ARM-software/ML-KWS-for-MCU/blob/master/Deployment/Source/MFCC/mfcc.cpp + * This class is designed to be generic and self-sufficient but + * certain calculation routines can be overridden to accommodate + * use-case specific requirements. + */ + class MFCC { + public: + /** + * @brief Constructor + * @param[in] params MFCC parameters + */ + explicit MFCC(const MfccParams& params); + + MFCC() = delete; + + ~MFCC() = default; + + /** + * @brief Extract MFCC features for one single small frame of + * audio data e.g. 640 samples. + * @param[in] audioData Vector of audio samples to calculate + * features for. + * @return Vector of extracted MFCC features. + **/ + std::vector<float> MfccCompute(const std::vector<int16_t>& audioData); + + /** @brief Initialise. */ + void Init(); + + /** + * @brief Extract MFCC features and quantise for one single small + * frame of audio data e.g. 640 samples. + * @param[in] audioData Vector of audio samples to calculate + * features for. + * @param[in] quantScale Quantisation scale. + * @param[in] quantOffset Quantisation offset. + * @return Vector of extracted quantised MFCC features. + **/ + template<typename T> + std::vector<T> MfccComputeQuant(const std::vector<int16_t>& audioData, + const float quantScale, + const int quantOffset) + { + this->_MfccComputePreFeature(audioData); + float minVal = std::numeric_limits<T>::min(); + float maxVal = std::numeric_limits<T>::max(); + + std::vector<T> mfccOut(this->_m_params.m_numMfccFeatures); + const size_t numFbankBins = this->_m_params.m_numFbankBins; + + /* Take DCT. Uses matrix mul. */ + for (size_t i = 0, j = 0; i < mfccOut.size(); ++i, j += numFbankBins) { + float sum = 0; + for (size_t k = 0; k < numFbankBins; ++k) { + sum += this->_m_dctMatrix[j + k] * this->_m_melEnergies[k]; + } + /* Quantize to T. */ + sum = std::round((sum / quantScale) + quantOffset); + mfccOut[i] = static_cast<T>(std::min<float>(std::max<float>(sum, minVal), maxVal)); + } + + return mfccOut; + } + + /* Constants */ + static constexpr float ms_logStep = /*logf(6.4)*/ 1.8562979903656 / 27.0; + static constexpr float ms_freqStep = 200.0 / 3; + static constexpr float ms_minLogHz = 1000.0; + static constexpr float ms_minLogMel = ms_minLogHz / ms_freqStep; + + protected: + /** + * @brief Project input frequency to Mel Scale. + * @param[in] freq Input frequency in floating point. + * @param[in] useHTKmethod bool to signal if HTK method is to be + * used for calculation. + * @return Mel transformed frequency in floating point. + **/ + static float MelScale(float freq, + bool useHTKMethod = true); + + /** + * @brief Inverse Mel transform - convert MEL warped frequency + * back to normal frequency. + * @param[in] freq Mel frequency in floating point. + * @param[in] useHTKmethod bool to signal if HTK method is to be + * used for calculation. + * @return Real world frequency in floating point. + **/ + static float InverseMelScale(float melFreq, + bool useHTKMethod = true); + + /** + * @brief Populates MEL energies after applying the MEL filter + * bank weights and adding them up to be placed into + * bins, according to the filter bank's first and last + * indices (pre-computed for each filter bank element + * by _CreateMelFilterBank function). + * @param[in] fftVec Vector populated with FFT magnitudes. + * @param[in] melFilterBank 2D Vector with filter bank weights. + * @param[in] filterBankFilterFirst Vector containing the first indices of filter bank + * to be used for each bin. + * @param[in] filterBankFilterLast Vector containing the last indices of filter bank + * to be used for each bin. + * @param[out] melEnergies Pre-allocated vector of MEL energies to be + * populated. + * @return true if successful, false otherwise. + */ + virtual bool 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); + + /** + * @brief Converts the Mel energies for logarithmic scale. + * @param[in,out] melEnergies 1D vector of Mel energies. + **/ + virtual void ConvertToLogarithmicScale(std::vector<float>& melEnergies); + + /** + * @brief Create a matrix used to calculate Discrete Cosine + * Transform. + * @param[in] inputLength Input length of the buffer on which + * DCT will be performed. + * @param[in] coefficientCount Total coefficients per input length. + * @return 1D vector with inputLength x coefficientCount elements + * populated with DCT coefficients. + */ + virtual std::vector<float> CreateDCTMatrix( + int32_t inputLength, + int32_t coefficientCount); + + /** + * @brief Given the low and high Mel values, get the normaliser + * for weights to be applied when populating the filter + * bank. + * @param[in] leftMel Low Mel frequency value. + * @param[in] rightMel High Mel frequency value. + * @param[in] useHTKMethod bool to signal if HTK method is to be + * used for calculation. + * @return Value to use for normalizing. + */ + virtual float GetMelFilterBankNormaliser( + const float& leftMel, + const float& rightMel, + bool useHTKMethod); + + private: + MfccParams _m_params; + std::vector<float> _m_frame; + std::vector<float> _m_buffer; + std::vector<float> _m_melEnergies; + std::vector<float> _m_windowFunc; + std::vector<std::vector<float>> _m_melFilterBank; + std::vector<float> _m_dctMatrix; + std::vector<int32_t> _m_filterBankFilterFirst; + std::vector<int32_t> _m_filterBankFilterLast; + bool _m_filterBankInitialised; + arm::app::math::FftInstance _m_fftInstance; + + /** + * @brief Initialises the filter banks and the DCT matrix. **/ + void _InitMelFilterBank(); + + /** + * @brief Signals whether the instance of MFCC has had its + * required buffers initialised. + * @return true if initialised, false otherwise. + **/ + bool _IsMelFilterBankInited(); + + /** + * @brief Create mel filter banks for MFCC calculation. + * @return 2D vector of floats. + **/ + std::vector<std::vector<float>> _CreateMelFilterBank(); + + /** + * @brief Computes and populates internal memeber buffers used + * in MFCC feature calculation + * @param[in] audioData 1D vector of 16-bit audio data. + */ + void _MfccComputePreFeature(const std::vector<int16_t>& audioData); + + /** @brief Computes the magnitude from an interleaved complex array. */ + void _ConvertToPowerSpectrum(); + + }; + +} /* namespace audio */ +} /* namespace app */ +} /* namespace arm */ + +#endif /* MFCC_HPP */
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