how to calculate central frequency from fft of wave function
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hi all, is there any difference between central freq and maximum freq of a wave function. how i can calculate central frequency of this function using fft in matlab y=0.5(1-cos(2*pi*f*t)*sin(2*pi*f*t)
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Wayne King
il 24 Mag 2012
Are you trying to show us an AM signal? If so, are the two f's really the same frequency, or did you mean something like this:
t = 0:1e-4:1-1e-4;
f0 = 50;
fc = 1e3;
y=0.5*(1-cos(2*pi*f0*t)).*sin(2*pi*fc*t);
ydft = fft(y);
ydft = ydft(1:length(y)/2+1);
freq = 0:1e4/length(y):1e4/2;
plot(freq,abs(ydft))
Wayne King
il 24 Mag 2012
It appears to me that just rewriting that using trigonometric identities you see that it equals
1/2*sin(2*pi*f*t)-1/4*sin(2*pi*2*f*t)
So you get a line component at 20 kHz and one at 40 kHz with 1/2 the amplitude of the component at 20 kHz.
freq = 0:fs/length(y):fs/2;
ydft = fft(y);
ydft = ydft(1:ceil(length(y)/2));
plot(freq,abs(ydft))
So I'm guessing you call the center frequency 30 kHz.
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