samer@33: function [edges,map]=cqmap(parms,range,res)
samer@33: % cqmap - Audio Spectrum linear to log frequency map
samer@32: % 
samer@32: % Converts a constant-Q filterbank specification into a sparse matrix
samer@32: % which can be multiplied by a STFT power spectrogram to get a 
samer@32: % constant-Q spectrogram. Note that though the logarithmic frequency 
samer@32: % sampling grid has an adjustable spacing (the resolution parameter),
samer@32: % its origin is FIXED at 1kHz. 
samer@32: %
samer@33: % cqmap ::
samer@32: %    struct {
samer@32: %       fs:real          ~ 'sampling rate',
samer@32: %       FFTsize:natural  ~ 'FFT frame size to be used to get STFT'
samer@32: %    }        ~'framing parameter structure (see h_fparms)',
samer@32: %    [[2]]    ~ 'requested lower and upper cut-off frequencies',
samer@32: %    real|nan ~ 'resolution in octaves, or return one band if nan'
samer@32: % ->
samer@32: %    [[L-1]]  ~ 'frequency bin edges, excluding 0 and fs/2',
samer@32: %    [[L,M]]  ~ 'L by M sparse array'.
samer@32: 
samer@32: % If resolution is nan, we just use the two edges unmodified
samer@32: % as per MPEG-7 spec (except we're using nan instead of the 
samer@32: % magic '8'). Obviously, we can't even quantise the band edges 
samer@32: % without a valid resolution.
samer@32: if isnan(res),
samer@32: 	edges=min(range/parms.fs,0.5);
samer@32: else
samer@32: 	F0=1000; % MAGIC number - origin of frequnecy grid is 1kHz
samer@33: 	edges=cqedges(parms.fs,range,res,F0);
samer@32: 
samer@32: 	% remove edges from bottom end until each band can be resolved
samer@32: 	e = 0.5+edges*parms.FFTsize;   % band edges relative to FT bin edges
samer@32: 	k = find(diff(e)<1);           % find bands narrower than one bin
samer@32: 	k = k(ceil(e(k))==1+floor(e(k+1))); % filter out bands spanning >1 bin
samer@32: 	% if any bands remaining, then remove these from main edges list
samer@32: 	if ~isempty(k), edges=edges(1+max(k):end); end
samer@32: end
samer@32: 
samer@32: % build sparse matrix of standard size if requested
samer@32: if nargout>1,
samer@32: 	map = specbasis(parms.FFTsize*edges,dftbins(parms.FFTsize));
samer@32: end