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function mapsound (w,dt,fmin,fmax,simpl,rate)
// Plots a sound map for a sound.
// It does FFT at time increments dt.
// rate is the sampling rate.
// simpl points are collected for speed reasons.
// Copyright INRIA
[lhs,rhs]=argn(0);
if ( rhs <= 5 ) then rate=0;end
if ( rhs <= 4 ) then simpl=1; end ;
if ( rhs <= 3 ) then fmax=1500; end ;
if ( rhs <= 2 ) then fmin=100; end ;
if ( rhs <= 1 ) then dt=0.1; end ;
n=prod(size(w));
defaultrate=22050;
if rate==0; rate=defaultrate; end;
dp=dt*rate;
points=2^floor(log(dp)/log(2));
ind=fmin/rate*points/simpl:fmax/rate*points/simpl;
f=abs(fft(w(1:points),1));
f=sum(matrix(f,points/simpl,simpl),'c')';
M=f(ind);
i=1;
i=i+dp;
while i+points <= n;
f=abs(fft(w(i:i+points-1),1));
f=sum(matrix(f,points/simpl,simpl),'c')';
M=[M;f(ind)];
i=i+dp;
end;
[nl,nc]=size(M);
if nl==1 ; return;end
x_abs= (0:(nl-1))*(n/rate)/(nl-1);
y_abs= (0:(nc-1))/(nc-1);
y_abs= fmin*(y_abs-1) + fmax*(y_abs)
grayplot(x_abs,y_abs,-M)
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