/// <summary>
/// Computes LPCC vector in one frame.
/// </summary>
/// <param name="block">Block of data</param>
/// <param name="features">Features (one LPCC feature vector) computed in the block</param>
public override void ProcessFrame(float[] block, float[] features)
{
// The code here essentially duplicates LPC extractor code
// (for efficient memory usage it doesn't just delegate its work to LpcExtractor)
// and then post-processes LPC vectors to obtain LPCC coefficients.
block.FastCopyTo(_reversed, FrameSize);
// 1) autocorrelation
_convolver.CrossCorrelate(block, _reversed, _cc);
// 2) Levinson-Durbin
for (int k = 0; k < _lpc.Length; _lpc[k] = 0, k++)
{
;
}
var err = Lpc.LevinsonDurbin(_cc, _lpc, _order, FrameSize - 1);
// 3) compute LPCC coefficients from LPC
Lpc.ToCepstrum(_lpc, err, features);
// 4) (optional) liftering
if (_lifterCoeffs != null)
{
features.ApplyWindow(_lifterCoeffs);
}
}
/// <summary>
/// Method for computing LPCC features.
/// It essentially duplicates LPC extractor code
/// (for efficient memory usage it doesn't just delegate its work to LpcExtractor)
/// and then post-processes LPC vectors to obtain LPCC coefficients.
/// </summary>
/// <param name="block">Samples for analysis</param>
/// <param name="features">LPCC vector</param>
public override void ProcessFrame(float[] block, float[] features)
{
block.FastCopyTo(_reversed, FrameSize);
// 1) autocorrelation
_convolver.CrossCorrelate(block, _reversed, _cc);
// 2) Levinson-Durbin
for (int k = 0; k < _lpc.Length; _lpc[k] = 0, k++)
{
;
}
var err = Lpc.LevinsonDurbin(_cc, _lpc, _order, FrameSize - 1);
// 3) compute LPCC coefficients from LPC
Lpc.ToCepstrum(_lpc, err, features);
// 4) (optional) liftering
if (_lifterCoeffs != null)
{
features.ApplyWindow(_lifterCoeffs);
}
}
/// <summary>
/// Method for computing LPCC features.
/// It essentially duplicates LPC extractor code
/// (for efficient memory usage it doesn't just delegate its work to LpcExtractor)
/// and then post-processes LPC vectors to obtain LPCC coefficients.
/// </summary>
/// <param name="block">Samples for analysis</param>
/// <returns>LPCC vector</returns>
public override float[] ProcessFrame(float[] block)
{
// 1) apply window (usually signal isn't windowed for LPC, so we check first)
if (_window != WindowTypes.Rectangular)
{
block.ApplyWindow(_windowSamples);
}
block.FastCopyTo(_reversed, FrameSize);
// 2) autocorrelation
_convolver.CrossCorrelate(block, _reversed, _cc);
// 3) Levinson-Durbin
for (int k = 0; k < _lpc.Length; _lpc[k] = 0, k++)
{
;
}
var err = Lpc.LevinsonDurbin(_cc, _lpc, _order, FrameSize - 1);
// 4) compute LPCC coefficients from LPC
var lpcc = new float[FeatureCount];
Lpc.ToCepstrum(_lpc, err, lpcc);
// 5) (optional) liftering
if (_lifterCoeffs != null)
{
lpcc.ApplyWindow(_lifterCoeffs);
}
return(lpcc);
}
/// <summary>
/// <para>Computes PLP-RASTA feature vector in one frame.</para>
/// <para>
/// General algorithm:
/// <list type="number">
/// <item>Apply window</item>
/// <item>Obtain power spectrum</item>
/// <item>Apply filterbank of bark bands (or mel bands)</item>
/// <item>[Optional] filter each component of the processed spectrum with a RASTA filter</item>
/// <item>Apply equal loudness curve</item>
/// <item>Apply nonlinearity (take cubic root)</item>
/// <item>Do LPC</item>
/// <item>Convert LPC to cepstrum</item>
/// <item>[Optional] lifter cepstrum</item>
/// </list>
/// </para>
/// </summary>
/// <param name="block">Block of data</param>
/// <param name="features">Features (one PLP feature vector) computed in the block</param>
public override void ProcessFrame(float[] block, float[] features)
{
// 0) base extractor applies window
// 1) calculate power spectrum (without normalization)
_fft.PowerSpectrum(block, _spectrum, false);
// 2) apply filterbank on the result (bark frequencies by default)
FilterBanks.Apply(FilterBank, _spectrum, _bandSpectrum);
// 3) RASTA filtering in log-domain [optional]
if (_rasta > 0)
{
for (var k = 0; k < _bandSpectrum.Length; k++)
{
var log = (float)Math.Log(_bandSpectrum[k] + float.Epsilon);
log = _rastaFilters[k].Process(log);
_bandSpectrum[k] = (float)Math.Exp(log);
}
}
// 4) and 5) apply equal loudness curve and take cubic root
for (var k = 0; k < _bandSpectrum.Length; k++)
{
_bandSpectrum[k] = (float)Math.Pow(Math.Max(_bandSpectrum[k], 1.0) * _equalLoudnessCurve[k], 0.33);
}
// 6) LPC from power spectrum:
var n = _idftTable[0].Length;
// get autocorrelation samples from post-processed power spectrum (via IDFT):
for (var k = 0; k < _idftTable.Length; k++)
{
var acc = _idftTable[k][0] * _bandSpectrum[0] +
_idftTable[k][n - 1] * _bandSpectrum[n - 3]; // add values at two duplicated edges right away
for (var j = 1; j < n - 1; j++)
{
acc += _idftTable[k][j] * _bandSpectrum[j - 1];
}
_cc[k] = acc / (2 * (n - 1));
}
// LPC:
for (var k = 0; k < _lpc.Length; _lpc[k] = 0, k++)
{
;
}
var err = Lpc.LevinsonDurbin(_cc, _lpc, _lpcOrder);
// 7) compute LPCC coefficients from LPC
Lpc.ToCepstrum(_lpc, err, features);
// 8) (optional) liftering
if (_lifterCoeffs != null)
{
features.ApplyWindow(_lifterCoeffs);
}
// 9) (optional) replace first coeff with log(energy)
if (_includeEnergy)
{
features[0] = (float)Math.Log(Math.Max(block.Sum(x => x * x), _logEnergyFloor));
}
}
/// <summary>
/// Standard method for computing PLP features.
/// In each frame do:
///
/// 1) Apply window
/// 2) Obtain power spectrum
/// 3) Apply filterbank of bark bands (or mel bands)
/// 4) [Optional] filter each component of the processed spectrum with a RASTA filter
/// 5) Apply equal loudness curve
/// 6) Take cubic root
/// 7) Do LPC
/// 8) Convert LPC to cepstrum
/// 9) [Optional] lifter cepstrum
///
/// </summary>
/// <param name="block">Samples for analysis</param>
/// <returns>PLP vector</returns>
public override float[] ProcessFrame(float[] block)
{
// fill zeros to fftSize if frameSize < fftSize (blockSize)
for (var k = FrameSize; k < block.Length; block[k++] = 0)
{
;
}
// 1) apply window
block.ApplyWindow(_windowSamples);
// 2) calculate power spectrum (without normalization)
_fft.PowerSpectrum(block, _spectrum, false);
// 3) apply filterbank on the result (bark frequencies by default)
FilterBanks.Apply(FilterBank, _spectrum, _bandSpectrum);
// 4) RASTA filtering in log-domain [optional]
if (_rasta > 0)
{
for (var k = 0; k < _bandSpectrum.Length; k++)
{
var log = (float)Math.Log(_bandSpectrum[k] + float.Epsilon);
log = _rastaFilters[k].Process(log);
_bandSpectrum[k] = (float)Math.Exp(log);
}
}
// 5) and 6) apply equal loudness curve and take cubic root
for (var k = 0; k < _bandSpectrum.Length; k++)
{
_bandSpectrum[k] = (float)Math.Pow(Math.Max(_bandSpectrum[k], 1.0) * _equalLoudnessCurve[k], 0.33);
}
// 7) LPC from power spectrum:
var n = _idftTable[0].Length;
// get autocorrelation samples from post-processed power spectrum (via IDFT):
for (var k = 0; k < _idftTable.Length; k++)
{
var acc = _idftTable[k][0] * _bandSpectrum[0] +
_idftTable[k][n - 1] * _bandSpectrum[n - 3]; // add values at two duplicated edges right away
for (var j = 1; j < n - 1; j++)
{
acc += _idftTable[k][j] * _bandSpectrum[j - 1];
}
_cc[k] = acc / (2 * (n - 1));
}
// LPC:
for (var k = 0; k < _lpc.Length; _lpc[k] = 0, k++)
{
;
}
var err = Lpc.LevinsonDurbin(_cc, _lpc, _lpcOrder);
// 8) compute LPCC coefficients from LPC
var lpcc = new float[FeatureCount];
Lpc.ToCepstrum(_lpc, err, lpcc);
// 9) (optional) liftering
if (_lifterCoeffs != null)
{
lpcc.ApplyWindow(_lifterCoeffs);
}
return(lpcc);
}