diff dsp/cqedges.m @ 32:c3b0cd708782

Imported core dsp tools.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dsp/cqedges.m	Sun Jan 20 13:48:47 2013 +0000
@@ -0,0 +1,30 @@
+function edges=as_cqedges(fs,range,res,F0)
+
+% as_cqedges - Audio Spectrum linear to log frequency map (no checking)
+% 
+% Converts a constant-Q filterbank specification into a list of band
+% edges, and optionally the sparse mapping matrix
+% which can be multiplied by a STFT power spectrogram to get a 
+% constant-Q spectrogram. 
+%
+% as_cqmap0 ::
+%    real     ~ 'sampling rate',
+%    [[2]]    ~ 'requested lower and upper cut-off frequencies',
+%    real     ~ 'resolution in octaves',
+%    real     ~ 'origin of frequency grid in Hz (defaut=1kHz)'
+% ->
+%    [[L-1]]  ~ 'frequency bin edges',
+%    [[L,M]]  ~ 'L by M sparse array'.
+
+% origin of frequnecy grid defaults to 1kHz
+if nargin<4, F0=1000; end
+
+% quantise requested edges and represent them in
+% in units of res on a log frequency scale.
+limits = round(log2(range/F0)/res);
+
+% convert to normalised frequencies (fs=1)
+edges = (F0/fs)*2.^(res*(limits(1):limits(2)));
+
+% remove any edges above Nyquist rate
+if edges(end)>=0.5, edges = edges(edges<0.5); end