// Beat detection, algorithm put together by Ben Fisher after reading some things
// numbers here are arbitrary, based on what seemed to work ok. I'm sure it could be better.
public static double GuessBpm(WaveAudio input)
{
const double minBpm = 60, maxBpm = 150;
WaveAudio w = Effects.Derivative(input); // take the derivative of samples.
// divide samples into chunks of size 1024.
int nBufsize = 1024;
double chunkframerate = input.getSampleRate() / nBufsize; // the chunks go by at this rate.
// do first FFT
double[][] frequencyData = SpectrumContentOverTime(w, 4, nBufsize);
// create a new signal in time, consisting of the energy at lowest 1/4 freqs of the chunks.
int slength = (int)Fourier.findNearestPowerOfTwo((uint)frequencyData.Length);
double[] lowerdata = new double[slength];
for (int i = 0; i < slength; i++)
{
lowerdata[i] = frequencyData[i][0]; // the bottom 1/4 freqs (index 0-255,0Hz to 5512.5Hz or something ?)
}
// now take a second FFT on this new signal. Frequency should be range 0.6 to 2.5 Hz (40 to 150 Bpm).
double[] reout, imgout;
RawSamplesToFrequency(lowerdata, out reout, out imgout);
// only keep track of output inside the range we are interested in
int minFreqindex = (int)(reout.Length * ((minBpm / 60) / chunkframerate));
int maxFreqindex = (int)(reout.Length * ((maxBpm / 60) / chunkframerate));
// find the best candidate
double highestEnergy = -1; int highestEnergyIndex = -1;
for (int b = minFreqindex; b < maxFreqindex; b++)
{
double magnitude = Math.Sqrt(reout[b] * reout[b] + imgout[b] + imgout[b]);
if (magnitude > highestEnergy)
{
highestEnergyIndex = b; highestEnergy = magnitude;
}
}
double freqHertz = chunkframerate * (highestEnergyIndex / (double)reout.Length);
double freqInBpm = freqHertz * 60;
return(freqInBpm);
}
public WaveAudio doModify(WaveAudio src, int bufsize)
{
WaveAudio wout = new WaveAudio(src.getSampleRate(), 1);
wout.LengthInSamples = src.LengthInSamples;
//reuse the buffers.
double[] ffreqmaghalfout = new double[bufsize / 2], ffreqanghalfout = new double[bufsize / 2];
double[] ffreqmaghalfin = new double[bufsize / 2], ffreqanghalfin = new double[bufsize / 2];
double[] fbuffertime = new double[bufsize];
for (int partnum = 0; partnum < src.LengthInSamples / bufsize; partnum++)
{
//copy into buffer.
Array.Copy(src.data[0], partnum * bufsize, fbuffertime, 0, bufsize);
double[] ffreqreal, ffreqimag;
Fourier.RawSamplesToFrequency(fbuffertime, out ffreqreal, out ffreqimag);
//we only care about the first half of these results.
for (int i = 0; i < bufsize / 2; i++)
{
ffreqmaghalfin[i] = Math.Sqrt(ffreqreal[i] * ffreqreal[i] + ffreqimag[i] * ffreqimag[i]);
ffreqanghalfin[i] = Math.Atan2(ffreqimag[i], ffreqreal[i]);
}
this.modifyAngular(ffreqmaghalfin, ffreqanghalfin, ffreqmaghalfout, ffreqanghalfout);
if (partnum == 0)
{
this.drawPlots(ffreqmaghalfin, ffreqanghalfin, ffreqmaghalfout, ffreqanghalfout);
}
for (int i = 0; i < ffreqreal.Length / 2; i++)
{
ffreqreal[i] = ffreqmaghalfout[i] * Math.Sin(ffreqanghalfout[i]);
ffreqimag[i] = ffreqmaghalfout[i] * Math.Cos(ffreqanghalfout[i]);
}
for (int i = ffreqreal.Length / 2; i < ffreqreal.Length; i++)
{
ffreqreal[i] = ffreqimag[i] = 0;
}
double[] fbufout;
Fourier.RawFrequencyToSamples(out fbufout, ffreqreal, ffreqimag);
Array.Copy(fbufout, 0, wout.data[0], partnum * bufsize, bufsize);
}
return(wout);
}
public WaveAudio doModify(WaveAudio src, int bufsize)
{
WaveAudio wout = new WaveAudio(src.getSampleRate(), 1);
wout.LengthInSamples = src.LengthInSamples;
//reuse the buffers.
double[] ffreqmaghalfout = new double[bufsize / 2], ffreqanghalfout = new double[bufsize / 2];
double[] ffreqmaghalfin = new double[bufsize / 2], ffreqanghalfin = new double[bufsize / 2];
double[] fbuffertime = new double[bufsize];
for (int index = 0; index < src.LengthInSamples - bufsize; index += bufsize / overlap)
{
//copy into buffer.
Array.Copy(src.data[0], index, fbuffertime, 0, bufsize);
double[] ffreqreal, ffreqimag;
Fourier.RawSamplesToFrequency(fbuffertime, out ffreqreal, out ffreqimag);
//we only care about the first half of these results.
for (int i = 0; i < bufsize / 2; i++)
{
ffreqmaghalfin[i] = Math.Sqrt(ffreqreal[i] * ffreqreal[i] + ffreqimag[i] * ffreqimag[i]);
ffreqanghalfin[i] = Math.Atan2(ffreqimag[i], ffreqreal[i]);
}
this.modifyAngular(ffreqmaghalfin, ffreqanghalfin, ffreqmaghalfout, ffreqanghalfout);
for (int i = 0; i < ffreqreal.Length / 2; i++)
{
ffreqreal[i] = ffreqmaghalfout[i] * Math.Sin(ffreqanghalfout[i]);
ffreqimag[i] = ffreqmaghalfout[i] * Math.Cos(ffreqanghalfout[i]);
}
for (int i = ffreqreal.Length / 2; i < ffreqreal.Length; i++)
{
ffreqreal[i] = ffreqimag[i] = 0;
}
double[] fbufout;
Fourier.RawFrequencyToSamples(out fbufout, ffreqreal, ffreqimag);
WaveAudio ww = new WaveAudio(44100, 1);
ww.data[0] = fbufout;
//Array.Copy(fbufout, 0, wout.data[0], partnum*bufsize, bufsize);
ConstructionUtil.placeAudioRamp(wout, ww, index, (bufsize / overlapRamp));
}
return(wout);
}
