/* * 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 MELSPECTROGRAM_HPP #define MELSPECTROGRAM_HPP #include "PlatformMath.hpp" #include #include #include #include #include namespace arm { namespace app { namespace audio { /* Mel Spectrogram consolidated parameters */ class MelSpecParams { public: float m_samplingFreq; uint32_t m_numFbankBins; float m_melLoFreq; float m_melHiFreq; uint32_t m_frameLen; uint32_t m_frameLenPadded; bool m_useHtkMethod; /** @brief Constructor */ MelSpecParams(const float samplingFreq, const uint32_t numFbankBins, const float melLoFreq, const float melHiFreq, const uint32_t frameLen, const bool useHtkMethod); MelSpecParams() = delete; ~MelSpecParams() = default; /** @brief String representation of parameters */ std::string Str(); }; /** * @brief Class for Mel Spectrogram 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 MelSpectrogram { public: /** * @brief Extract Mel Spectrogram 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] trainingMean - Value to subtract from the the computed mel spectrogram, default 0. * @return Vector of extracted Mel Spectrogram features. **/ std::vector ComputeMelSpec(const std::vector& audioData, float trainingMean = 0); /** * @brief Constructor * @param[in] params - Mel Spectrogram parameters */ MelSpectrogram(const MelSpecParams& params); MelSpectrogram() = delete; ~MelSpectrogram() = default; /** @brief Initialise */ void Init(); /** * @brief Extract Mel Spectrogram 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 Mel Spectrogram features. **/ template std::vector MelSpecComputeQuant(const std::vector& audioData, const float quantScale, const int quantOffset, float trainingMean = 0) { this->ComputeMelSpec(audioData, trainingMean); float minVal = std::numeric_limits::min(); float maxVal = std::numeric_limits::max(); std::vector melSpecOut(this->_m_params.m_numFbankBins); const size_t numFbankBins = this->_m_params.m_numFbankBins; /* Quantize to T. */ for (size_t k = 0; k < numFbankBins; ++k) { auto quantizedEnergy = std::round(((this->_m_melEnergies[k]) / quantScale) + quantOffset); melSpecOut[k] = static_cast(std::min(std::max(quantizedEnergy, minVal), maxVal)); } return melSpecOut; } /* 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(const float freq, const 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(const float melFreq, const 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& fftVec, std::vector>& melFilterBank, std::vector& filterBankFilterFirst, std::vector& filterBankFilterLast, std::vector& melEnergies); /** * @brief Converts the Mel energies for logarithmic scale * @param[in/out] melEnergies - 1D vector of Mel energies **/ virtual void ConvertToLogarithmicScale(std::vector& melEnergies); /** * @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 Return float value to be applied * when populating the filter bank. */ virtual float GetMelFilterBankNormaliser( const float& leftMel, const float& rightMel, const bool useHTKMethod); private: MelSpecParams _m_params; std::vector _m_frame; std::vector _m_buffer; std::vector _m_melEnergies; std::vector _m_windowFunc; std::vector> _m_melFilterBank; std::vector _m_filterBankFilterFirst; std::vector _m_filterBankFilterLast; bool _m_filterBankInitialised; arm::app::math::FftInstance _m_fftInstance; /** * @brief Initialises the filter banks. **/ void _InitMelFilterBank(); /** * @brief Signals whether the instance of MelSpectrogram has had its * required buffers initialised * @return True if initialised, false otherwise **/ bool _IsMelFilterBankInited(); /** * @brief Create mel filter banks for Mel Spectrogram calculation. * @return 2D vector of floats **/ std::vector> _CreateMelFilterBank(); /** * @brief Computes the magnitude from an interleaved complex array **/ void _ConvertToPowerSpectrum(); }; } /* namespace audio */ } /* namespace app */ } /* namespace arm */ #endif /* MELSPECTROGRAM_HPP */