Reply by locchamp December 4, 20052005-12-04
Hi guys I really need help designing FM system using PLL as a
demodulation. I have matlab code below and it is not working at the
filtering end am I doing everything right? I basically how do I set
the filter up to work? The way I set this up would be a PLL as a
demodulation right? THanks guys

[Y,Fs,NBITS,OPTS] = mp3read('jem.mp3');
t = 0:1/Fs:(length(snd)-1)/Fs;

fc 000;
kf = (fc/Fs)*(2*pi)/(max(max(abs(snd))));

outfm = Ac * cos(wc.*t + 2 * pi * kf * cumsum(snd));
Mp = max(snd); % Calculating the frequency deviation constant of the modulation.
deviation = kf*Mp;

% Demodulating the signal.
Defreq= ademod(outfm,fc,Fs,'fm',deviation);

Wn = .95;
% Designing butterworth band pass filter.If Wn is a two-element
vector with
% w1 < w2, butter(n,Wn,'s') returns an order 2*n bandpass analog
% with passband w1 < < w2.
% [b,a] = butter(n,Wn,'ftype','s') designs a highpass or bandstop
[num,den] = butter(2,Wn,'high');
output = filter(num,den,Defreq);