matlabaudiosignal-processingsound-synthesis

How to synthesize a thunder sound with bandpass filter

I am working on synthesizing sound of thunder in MATLAB. I had generated pink noise and now I'm trying to add bandpass filter on 30Hz, but I am getting the error: 

The frequency specifications Fpass, Fstop must have increasing values.

Here's my code:

dur=[0:1/Fs:time-1/Fs];
sz=length(dur);
g=randn(1, sz); %
Y=fft(g);

NumUniquePts = sz/2 + 1;
n = 1:NumUniquePts;
n = sqrt(n);
Y(1:NumUniquePts) = Y(1:NumUniquePts)./n;

Y(NumUniquePts+1:sz) = real(Y(sz/2:-1:2)) -1i*imag(Y(sz/2:-1:2));

y = ifft(Y);

y = real(y(1, 1:sz));

y = y - mean(y);
yrms = sqrt(mean(y.^2));
y = y/yrms;

d = fdesign.lowpass('Fp,Fst,Ap,Ast',30,10,0.5,50,48e4);
Hd1 = design(d,'equiripple');
Hd2 = design(d,'butter');

out = filter(Hd1,y);

Maybe there an other way to synthesize it?

Solution

  • I am getting an error. "The frequency specifications Fpass, Fstop must have increasing values."

    This error means that Fstop should be greater than Fpass. You mentioned that you need Fpass=30Hz. So you would need Fstop > 30, but you specified a value of 10Hz. To fix this error you should increase the Fstop value (for example to 100Hz for starters then tweak until you get what you like).