/*

 Copyright (C) 2016 Apple Inc. All Rights Reserved.

 See LICENSE.txt for this sample’s licensing information

 Abstract:

 This class demonstrates how to use the Accelerate framework to take Fast Fourier Transforms (FFT) of the audio data. FFTs are used to perform analysis on the captured audio data

 */

#include "FFTHelper.h"

// Utility includes

#include "CABitOperations.h"

const Float32 kAdjust0DB = 1.5849e-13;

FFTHelper::FFTHelper ( UInt32 inMaxFramesPerSlice )

: mSpectrumAnalysis(NULL),

mFFTNormFactor(1.0/(2*inMaxFramesPerSlice)),

mFFTLength(inMaxFramesPerSlice/2),

mLog2N(Log2Ceil(inMaxFramesPerSlice))

{

    mDspSplitComplex.realp = (Float32*) calloc(mFFTLength,sizeof(Float32));

    mDspSplitComplex.imagp = (Float32*) calloc(mFFTLength, sizeof(Float32));

    mSpectrumAnalysis = vDSP_create_fftsetup(mLog2N, kFFTRadix2);

}

FFTHelper::~FFTHelper()

{

    vDSP_destroy_fftsetup(mSpectrumAnalysis);

    free (mDspSplitComplex.realp);

    free (mDspSplitComplex.imagp);

}

void FFTHelper::ComputeFFT(Float32* inAudioData, Float32* outFFTData)

{

    if (inAudioData == NULL || outFFTData == NULL) return;

    //Generate a split complex vector from the real data

    vDSP_ctoz((COMPLEX *)inAudioData, 2, &mDspSplitComplex, 1, mFFTLength);

    //Take the fft and scale appropriately

    vDSP_fft_zrip(mSpectrumAnalysis, &mDspSplitComplex, 1, mLog2N, kFFTDirection_Forward);

    vDSP_vsmul(mDspSplitComplex.realp, 1, &mFFTNormFactor, mDspSplitComplex.realp, 1, mFFTLength);

    vDSP_vsmul(mDspSplitComplex.imagp, 1, &mFFTNormFactor, mDspSplitComplex.imagp, 1, mFFTLength);

    //Zero out the nyquist value

    mDspSplitComplex.imagp[0] = 0.0;

    //Convert the fft data to dB

    vDSP_zvmags(&mDspSplitComplex, 1, outFFTData, 1, mFFTLength);

    //In order to avoid taking log10 of zero, an adjusting factor is added in to make the minimum value equal -128dB

    vDSP_vsadd(outFFTData, 1, &kAdjust0DB, outFFTData, 1, mFFTLength);

    Float32 one = 1;

    vDSP_vdbcon(outFFTData, 1, &one, outFFTData, 1, mFFTLength, 0);

}