mfcc

Functions

int main(int argc, char *argv[])

mfcc [ option ] [ infile ]

• -n int

  • number of channels \((1 \le C)\)

• -m int

  • order of coeffcients \((1 \le M)\)

• -l int

  • FFT length \((2 \le N)\)

• -c int

  • liftering parameter \((1 \le L)\)

• -s double

  • sampling rate in kHz \((0 < F_s)\)

• -L dobule

  • lowest frequency in Hz \((0.0 \le F_l < F_h)\)

• -H dobule

  • highest frequency in Hz \((F_l < F_h \le 500F_s)\)

• -q int

  • input format

    • 0 amplitude spectrum in dB

    • 1 log amplitude spectrum

    • 2 amplitude spectrum

    • 3 power spectrum

    • 4 windowed waveform

• -o int

  • output format

    • 0 MFCC

    • 1 MFCC and energy

    • 2 MFCC and C0

    • 3 MFCC, C0, and energy

• -e double

  • floor value of raw filter-bank output \((0 < \epsilon)\)

• infile str

  • double-type windowed sequence or spectrum

• stdout

  • double-type MFCCs

The below example extracts the 12-th order MFCCs from data.short. The analysis condition is that: frame length is 10 ms, frame shift is 25 ms, and sampling rate is 16 kHz. A pre-emphais filter and the hamming window are applied to the input signal.

x2x +sd data.short |
  frame -l 400 -p 160 -n |
  dfs -b 1 -0.97 |
  window -l 400 -L 512 -w 1 -n 0 |
  mfcc -l 512 -n 40 -c 22 -m 12 -L 64 -H 4000 -o 1 |
  delta -m 12 -d -0.5 0.0 0.5 -d 0.25 0.0 -0.5 0.0 0.25 > data.mfcc

The corresponding HTK config file is shown as below.

SOURCEFORMAT = NOHEAD
SOURCEKIND   = WAVEFORM
SOURCERATE   = 625.0
TARGETKIND   = MFCC_E_D_A
TARGETRATE   = 100000.0
WINDOWSIZE   = 250000.0
USEHAMMING   = T
RAWENERGY    = F
ENORMALIZE   = F
PREEMCOEF    = 0.97
NUMCHANS     = 40
CEPLIFTER    = 22
NUMCEPS      = 12
LOFREQ       = 64
HIFREQ       = 4000
DELTAWINDOW  = 1
ACCWINDOW    = 1

The correspondence between the HTK’s configuration and the SPTK’s command option for extracting MFCC is shown in the following table.

Parameter	HTK	SPTK
Frame length	WINDOWSIZE = _ (unit is 100 ns)	frame -l _ (unit is point)
Frame shift	TARGETRATE = _ (unit is 100 ns)	frame -p _ (unit is point)
Sampling rate	SOURCERATE = _ (unit is 100 ns)	mfcc -s _ (unit is kHz)
Subtract mean	ZMEANSOURCE = T	frame -z
Pre-emphasis coefficient	PREEMCOEF = _ (windowed waveform)	dfs -b 1 -_ (entire waveform)
Window	USEHAMMING = T	window -w 1 -n 0
FFT length	N/A (auto. calculated)	mfcc -l _ (same as input length)
Number of fbank channels	NUMCHANS = _	mfcc -n _
Lowest frequency	LOFREQ = _	mfcc -L _
Highest frequency	HIFREQ = _	mfcc -H _
Floor value of fbank	N/A (fixed value: 1.0)	mfcc -e _ (default value: 1.0)
Order of cepstrum	NUMCEPS = _	mfcc -m _
Liftering coefficient	CEPLIFTER = _	mfcc -c _
Output energy	TARGETKIND = MFCC_E	mfcc -o 1
Output 0th coefficient	TARGETKIND = MFCC_0	mfcc -o 2
Use raw energy	RAWENERGY = T	N/A (do not use raw)
Normalize log energy	ENORMALIZE = T	N/A (do not normalize)
Delta window size	DELTAWINDOW = _	delta -d _
Accel window size	ACCWINDOW = _	delta -d * -d _

Parameters

• argc – [in] Number of arguments.

• argv – [in] Argument vector.

Returns

0 on success, 1 on failure.

See also

fbank

class sptk::MelFrequencyCepstralCoefficientsAnalysis

Perform mel-frequency cepstral coefficients (MFCC) analysis.

The input is the half part of power spectrum:

\[ \begin{array}{cccc} |X(0)|^2, & |X(1)|^2, & \ldots, & |X(N/2)|^2, \end{array} \]

where \(N\) is the FFT length. The outputs are the \(M\)-th order MFCCs with the zeroth cepstral parameter:

\[ \begin{array}{ccccc} c(0), & \bar{c}(1), & \bar{c}(2), & \ldots, & \bar{c}(M) \end{array} \]

and the log-signal energy \(E\).

The MFCCs are calculated from mel-filter-bank outputs \(\{F(j)\}_{j=1}^C\) using the discrete cosine transform

\[ c(m) = \sqrt{\frac{2}{C}} \sum_{j=1}^C F(j) \cos \left( \frac{\pi m}{C} \left(j - \frac{1}{2}\right) \right), \]

and the liftering

\[ \bar{c}(m) = \left( 1 + \frac{L}{2} \sin \frac{\pi m}{L} \right) c(m), \]

where \(L\) is the liftering parameter.

[1] S. Young et al., “The HTK book,” Cambridge University Engineering Department, 2006.

Public Functions

MelFrequencyCepstralCoefficientsAnalysis(int fft_length, int num_channel, int num_order, int liftering_coefficient, double sampling_rate, double lowest_frequency, double highest_frequency, double floor)

Parameters

• fft_length – [in] Number of FFT bins, \(N\).

• num_channel – [in] Number of channels, \(C\).

• num_order – [in] Order of cepstral coefficients, \(M\).

• liftering_coefficient – [in] A parameter of liftering, \(L\).

• sampling_rate – [in] Sampling rate in Hz.

• lowest_frequency – [in] Lowest frequency in Hz.

• highest_frequency – [in] Highest frequency in Hz.

• floor – [in] Floor value of raw filter-bank output.

inline int GetFftLength() const

Returns

FFT size.

inline int GetNumChannel() const

Returns

Number of channels.

inline int GetNumOrder() const

Returns

Order of cepstral coefficients.

inline int GetLifteringCoefficient() const

Returns

Liftering coefficient.

inline bool IsValid() const

Returns

True if this object is valid.

bool Run(const std::vector<double> &power_spectrum, std::vector<double> *mfcc, double *energy, MelFrequencyCepstralCoefficientsAnalysis::Buffer *buffer) const

Parameters

• power_spectrum – [in] \((N/2+1)\)-length power spectrum.

• mfcc – [out] \(M\)-th order MFCCs.

• energy – [out] Signal energy \(E\) (optional).

• buffer – [out] Buffer.

Returns

True on success, false on failure.

class Buffer

Buffer for MelFrequencyCepstralCoefficientsAnalysis class.