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Topic: FFT function isn't working on signals greater than a second
Replies: 2   Last Post: Mar 23, 2013 5:32 AM

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 Nasser Abbasi Posts: 6,677 Registered: 2/7/05
Re: FFT function isn't working on signals greater than a second
Posted: Mar 23, 2013 3:32 AM

On 3/22/2013 11:58 PM, sal22 wrote:
> Greetings All
>
> I have an fft function in matlab/octave that works great on an imported mono
> wav/audio signal that is 1 second long, but when the signal imported is more than 1
>second the frequency values become incorrect.

But I just wanted to say, that fft does not know any thing about
seconds, frequency, hz, time, units, clock or any of this.

All what fft does is take a sequence of numbers, and returns back
a sequence of numbers. that is all. It is a very dumb back box
function (but very fast). Notice the input to fft?

Y = fft(x)

So when you say fft does not work when 'signal is more than 1 second'
then this makes no sense. It must be a user error on how you are
preparing the data to feed to fft or how you are using the
result of fft.

If the signal is longer, this just means the sequence of numbers
wil be longer. that is all. (assuming you sample at same rate).

>>Can anyone help me get this function to work with signals greater than just 1 second

fft does not care how long the sequence of numbers are.

--Nasser

Date Subject Author
3/23/13 Nasser Abbasi
3/23/13 Greg Heath