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Topic: question on fft example
Replies: 5   Last Post: Nov 17, 2012 11:02 PM

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Nasser Abbasi

Posts: 6,677
Registered: 2/7/05
Re: question on fft example
Posted: Nov 17, 2012 6:10 AM
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On 11/17/2012 4:49 AM, Greg Heath wrote:
> "Nasser M. Abbasi" <> wrote in message <k829kk$hv6$>...
>> On 11/15/2012 2:33 AM, oversky wrote:
>>> The mathwork fft example in the following link,
>>> 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?"


> 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

hi Greg;

Its been a while since I looked at this myself, so I am rusty now
to remember all the details (that is why I write down everything
before I forget it) but there were different views on these scaling
factors. Here is the same question, asked in 2009 here FYI


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