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//
// Copyright © 2020 Arm Ltd and Contributors. All rights reserved.
// SPDX-License-Identifier: MIT
//
#pragma once
#include "MFCC.hpp"
/* Class to provide Wav2Letter specific MFCC calculation requirements. */
class Wav2LetterMFCC : public MFCC
{
public:
explicit Wav2LetterMFCC(const MfccParams& params)
: MFCC(params)
{}
Wav2LetterMFCC() = delete;
~Wav2LetterMFCC() = default;
protected:
/**
* @brief Overrides base class implementation of this 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
*/
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) override;
/**
* @brief Override for the base class implementation convert mel
* energies to logarithmic scale. The difference from
* default behaviour is that the power is converted to dB
* and subsequently clamped.
* @param[in,out] melEnergies 1D vector of Mel energies
**/
void ConvertToLogarithmicScale(std::vector<float>& melEnergies) override;
/**
* @brief Create a matrix used to calculate Discrete Cosine
* Transform. Override for the base class' default
* implementation as the first and last elements
* use a different normaliser.
* @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.
*/
std::vector<float> CreateDCTMatrix(int32_t inputLength,
int32_t coefficientCount) override;
/**
* @brief Given the low and high Mel values, get the normaliser
* for weights to be applied when populating the filter
* bank. Override for the base class implementation.
* @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 normalising.
*/
float GetMelFilterBankNormaliser(const float& leftMel,
const float& rightMel,
bool useHTKMethod) override;
};
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