samer@0: % amelspec - arrow from audio to log mel spectra
samer@0: %
samer@0: % amelspec :: 
samer@0: %    N:natural      ~'size of FFT used to compute spectra',
samer@0: %    M:natural      ~'number of mel bands to compute' 
samer@0: %    nonneg         ~'sampling frequency',
samer@0: %    options {
samer@0: %       windowfn :: N:natural->[[N]] / @hanning ~'window function';
samer@0: %       lowf     :: nonneg / 100                ~'filter bank low frequency in Hz'
samer@0: %    }
samer@0: % -> arrow( {[[dftbins(N)]]}, {[[L]]}, empty).
samer@0: %
samer@0: % Uses antialiased triangular filterbank from lowf to fs/2.
samer@0: 
samer@0: function o=amelspec(N,M,fs,varargin)
samer@37: 	opts=options('windowfn',@hanning,'lowf',100,'floor',5e-9,varargin{:});
samer@0: 	melW = lin2mel(N,fs,[opts.lowf,fs/2],M);
samer@0: 	noise_floor=opts.floor;
samer@0: 	o = apowspec(opts.windowfn(N))*arr(@cc);
samer@0: 	function y=cc(x), y=log(melW*x+noise_floor); end
samer@0: end