| /* |
| * 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 <vector> |
| #include <cstdint> |
| #include <cmath> |
| #include <limits> |
| #include <string> |
| |
| 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() const; |
| }; |
| |
| /** |
| * @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<float> ComputeMelSpec(const std::vector<int16_t>& audioData, float trainingMean = 0); |
| |
| /** |
| * @brief Constructor |
| * @param[in] params Mel Spectrogram parameters |
| */ |
| explicit 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. |
| * @param[in] trainingMean training mean. |
| * @return Vector of extracted quantised Mel Spectrogram features. |
| **/ |
| template<typename T> |
| std::vector<T> MelSpecComputeQuant(const std::vector<int16_t>& audioData, |
| const float quantScale, |
| const int quantOffset, |
| float trainingMean = 0) |
| { |
| this->ComputeMelSpec(audioData, trainingMean); |
| float minVal = std::numeric_limits<T>::min(); |
| float maxVal = std::numeric_limits<T>::max(); |
| |
| std::vector<T> 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<T>(std::min<float>(std::max<float>(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] melFreq 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<float>& fftVec, |
| std::vector<std::vector<float>>& melFilterBank, |
| std::vector<uint32_t>& filterBankFilterFirst, |
| std::vector<uint32_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 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<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<uint32_t> m_filterBankFilterFirst; |
| std::vector<uint32_t> 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() const; |
| |
| /** |
| * @brief Create mel filter banks for Mel Spectrogram calculation. |
| * @return 2D vector of floats |
| **/ |
| std::vector<std::vector<float>> CreateMelFilterBank(); |
| |
| /** |
| * @brief Computes the magnitude from an interleaved complex array |
| **/ |
| void ConvertToPowerSpectrum(); |
| |
| }; |
| |
| } /* namespace audio */ |
| } /* namespace app */ |
| } /* namespace arm */ |
| |
| |
| #endif /* MELSPECTROGRAM_HPP */ |