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From: David Cubero on 18 Jun 2010 14:31
In file exchange there is an example of Fmdemodulation but i do not know what beta is; nayone knows something?
thank you very much

function y = FM(x,beta)

[r, c] = size(x);
if r*c == 0
y = [];
return;
end;
if (r == 1)
x = x(:);
len = c;
else
len = r;
end;

Df = 2*pi*beta*100;

x = interp(x,20);
x = x*Df;

Fs = 20*8000;
Fc = 40000;
t = (0:1/Fs:((size(x,1)-1)/Fs))';
t = t(:, ones(1, size(x, 2)));

x = 2 / Fs * pi * x;
x = [zeros(1, size(x, 2)); cumsum(x(1:size(x,1)-1, :))];
y = cos(2 * pi * Fc * t + x );
plot(y)
From: Walter Roberson on 18 Jun 2010 14:45
David Cubero wrote:
> In file exchange there is an example of Fmdemodulation but i do not know
> what beta is; nayone knows something?
> thank you very much
>
> function y = FM(x,beta)

The most concise statement that I have found so far is,
"Note that beta is a parameter for designing a Kaiser window"

Not that that leaves me much much wiser...
From: Wayne King on 18 Jun 2010 15:06
"David Cubero" <sirdivi(a)hotmail.com> wrote in message <hvgdev$t01$1(a)fred.mathworks.com>...
> In file exchange there is an example of Fmdemodulation but i do not know what beta is; nayone knows something?
> thank you very much
>
> function y = FM(x,beta)
>
> [r, c] = size(x);
> if r*c == 0
> y = [];
> return;
> end;
> if (r == 1)
> x = x(:);
> len = c;
> else
> len = r;
> end;
>
> Df = 2*pi*beta*100;
>
> x = interp(x,20);
> x = x*Df;
>
> Fs = 20*8000;
> Fc = 40000;
> t = (0:1/Fs:((size(x,1)-1)/Fs))';
> t = t(:, ones(1, size(x, 2)));
>
> x = 2 / Fs * pi * x;
> x = [zeros(1, size(x, 2)); cumsum(x(1:size(x,1)-1, :))];
> y = cos(2 * pi * Fc * t + x );
> plot(y)

Just looking at this quickly, I think that beta is the frequency modulation index (peak frequency deviation divided by the bandwidth of the modulatiing signal).

The formula for the frequency modulation index is:

beta_f = DeltaF/B

where Deltaf is the peak frequency deviation and B is the bandwidth of the modulating signal.

I haven't run the code to see if that agrees with the final result. So you should verify that this makes sense.

Wayne
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