/// <summary>
/// Method for computing a spectrogram.
/// The spectrogram is essentially a list of power spectra in time.
/// </summary>
/// <param name="samples">The samples of signal</param>
/// <returns>Spectrogram of the signal</returns>
public List <float[]> Spectrogram(float[] samples)
{
var block = new float[_fftSize];
var zeroblock = new float[_fftSize];
var spectrogram = new List <float[]>();
for (var pos = 0; pos + _windowSize < samples.Length; pos += _hopSize)
{
zeroblock.FastCopyTo(block, _fftSize);
samples.FastCopyTo(block, _windowSize, pos);
if (_window != WindowTypes.Rectangular)
{
block.ApplyWindow(_windowSamples);
}
var spectrum = new float[_fftSize / 2 + 1];
_fft.PowerSpectrum(block, spectrum);
spectrogram.Add(spectrum);
}
return(spectrogram);
}
/// <summary>
/// Method for computing real cepstrum from array of samples
/// </summary>
/// <param name="samples"></param>
/// <param name="cepstrum"></param>
/// <param name="power"></param>
/// <returns></returns>
public void Direct(float[] samples, float[] cepstrum, bool power = false)
{
// complex fft
_fft.PowerSpectrum(samples, _realSpectrum, false);
// logarithm of power spectrum
for (var i = 0; i < _realSpectrum.Length; i++)
{
_realSpectrum[i] = (float)Math.Log10(_realSpectrum[i] + float.Epsilon);
_imagSpectrum[i] = 0.0f;
}
// complex
_fft.Inverse(_realSpectrum, _imagSpectrum);
// take truncated part
if (power)
{
for (var i = 0; i < _cepstrumSize; i++)
{
cepstrum[i] = (_realSpectrum[i] * _realSpectrum[i] +
_imagSpectrum[i] * _imagSpectrum[i]) / _realSpectrum.Length;
}
}
else
{
_realSpectrum.FastCopyTo(cepstrum, _cepstrumSize);
}
}
