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Re: question on fft example
Posted:
Nov 17, 2012 5:49 AM


"Nasser M. Abbasi" <nma@12000.org> wrote in message <k829kk$hv6$1@speranza.aioe.org>... > On 11/15/2012 2:33 AM, oversky wrote: > > The mathwork fft example in the following link, > > http://bit.ly/SO9TuV > > why do we double abs(Y(1:NFFT/2+1) when plotting the amplitude? > > > > plot(f,2*abs(Y(1:NFFT/2+1))) > > > > This was talked about before. can google it. Here is my take on it: > > "Why does it multiply by 2?" > > http://12000.org/my_notes/on_scaling_factor_for_ftt_in_matlab/index.htm
To represent the same average power as the doublesided frequency representation.
the DC and Nyquist components should NOT be doubled.
plot((0:Fs/2), [abs(Y(1)), 2*abs(Y(2:NFFT/2)), abs(Y(NFFT/2+1)) ] )
Hope this helps.
Greg



