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samer@32
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1 function edges=as_cqedges(fs,range,res,F0)
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2
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3 % as_cqedges - Audio Spectrum linear to log frequency map (no checking)
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4 %
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5 % Converts a constant-Q filterbank specification into a list of band
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6 % edges, and optionally the sparse mapping matrix
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7 % which can be multiplied by a STFT power spectrogram to get a
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8 % constant-Q spectrogram.
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9 %
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10 % as_cqmap0 ::
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11 % real ~ 'sampling rate',
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12 % [[2]] ~ 'requested lower and upper cut-off frequencies',
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13 % real ~ 'resolution in octaves',
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14 % real ~ 'origin of frequency grid in Hz (defaut=1kHz)'
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15 % ->
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16 % [[L-1]] ~ 'frequency bin edges',
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17 % [[L,M]] ~ 'L by M sparse array'.
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18
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19 % origin of frequnecy grid defaults to 1kHz
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20 if nargin<4, F0=1000; end
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21
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22 % quantise requested edges and represent them in
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23 % in units of res on a log frequency scale.
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24 limits = round(log2(range/F0)/res);
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25
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26 % convert to normalised frequencies (fs=1)
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27 edges = (F0/fs)*2.^(res*(limits(1):limits(2)));
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28
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29 % remove any edges above Nyquist rate
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30 if edges(end)>=0.5, edges = edges(edges<0.5); end
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