MelScale.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "DSP/FloatArrayMath.h"
#include "HAL/Platform.h"
#include "Templates/UniquePtr.h"
 
namespace Audio
{
    SIGNALPROCESSING_API float MelToHz(float InMel);
 
    SIGNALPROCESSING_API float HzToMel(float InHz);
 
    enum class EMelNormalization : uint8
    {
        EqualAmplitude,     //< Useful when working on magnitude spectrum
        EqualEuclideanNorm, //< Scale energy by euclidean norm. Good when using magnitude spectrum.
        EqualEnergy         //< Useful when working on power spectrum
    };
 
    struct FMelSpectrumKernelSettings
    {
        int32 NumBands;                     //< Number of bands in Mel spectrum
        float KernelMinCenterFreq;          //< Minimum frequency of lowest mel band.
        float KernelMaxCenterFreq;          //< Maximum frequency of highest mel band.
        EMelNormalization Normalization;    //< Mel band scaling. EqualAmplitude is better for the magnitude spectrum, while EqualEnergy is better for the power spectrum.
        float BandWidthStretch;             //< Controls the wideness of each band.
 
        FMelSpectrumKernelSettings()
        :   NumBands(26)
        ,   KernelMinCenterFreq(100.f)
        ,   KernelMaxCenterFreq(10000.f)
        ,   Normalization(EMelNormalization::EqualEnergy)
        ,   BandWidthStretch(1.f)
        {}
    };
 
    SIGNALPROCESSING_API TUniquePtr<FContiguousSparse2DKernelTransform> NewMelSpectrumKernelTransform(const FMelSpectrumKernelSettings& InSettings, const int32 InFFTSize, const float InSampleRate);
}