Programmer Guide/Command Reference/EVAL/dct

Compute the forward or inverce discrete cosine transform (dct) of the input vector x. This function was implemented for the computation of the MFCC (mel-cepstrum coefficients).

Usage

dct(x {, n {, dir)

x

the data or coefficient vector

n

the number of dct coefficients to compute or to use (default=nrow(x)); the meaning of this argument depends on the value of dir

dir

the direction of the dct (default=0)

dir=0	-> forward dct
otherwise	-> inverse (or backward) dct

Result

A vector y containing the result of the transformation. In the following table NX is equal to nrow(x).

dir	x	n	dct- length	y	nrow(y)	description
0	data samples	0<n<=NX	NX	dct coefficients	n	forward dct; if n<NX only the first n coefficients are computed
1	dct coefficients	0<n<=NX	NX	data samples	NX	inverse dct; if n<NX only the first n coefficients of x are used, all other are set to 0 (smoothing or liftering)
1	dct coefficients	n>NX	n	data samples	n	inverse dct; the vector x is expanded with zeros to length n and the inverse transform is applied to the expanded vector (smoothing or liftering)

See also

fft, ifft, dft, cepstrum, lpc, complex arithmetic

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