holger@0: function X = idceps(c, w)
holger@0: % X = idceps(c, w)
holger@0: %
holger@0: % computes the inverse discrete cepstrum, i.e. given a number of discrete 
holger@0: % cepstral coefficients, it returns the spectrum.
holger@0: %
holger@0: % c contains the discrete cepstral coefficients
holger@0: % w contains the frequency at which the spectrum is evaluated.
holger@0: % c and w must be column vectors.
holger@0: %
holger@0: % Further details can be found in:
holger@0: % [1] Diemo Schwarz. Spectral envelopes in sound analysis and synthesis.
holger@0: % Master's thesis, Universitaet Stuttgart, 1998, pp. 36-38.
holger@0: % [2] T. Galas and X. Rodet. An improved cepstral method for deconvolution
holger@0: % of source filter systems with discrete spectra: Application to musical
holger@0: % sound signals. In International Computer Music Conference, 1990.
holger@0: 
holger@0: pmax = length(c)-1;
holger@0: numW = length(w);
holger@0: 
holger@0: exponent = sum(  repmat(c', numW, 1) .* cos(w*(0:pmax)), 2  );
holger@0: X = exp(exponent);