AW: showing frequency and amplitude after doing fft on signal

[Schirmacher, Rolf]

> -----Ursprüngliche Nachricht-----
> Von: address@hidden [mailto:help-octave-
> address@hidden Im Auftrag von Rick T
> Gesendet: Dienstag, 27. November 2012 18:15
> An: address@hidden
> Betreff: showing frequency and amplitude after doing fft on signal
> 
> Greetings All I execute an fft on a wav file of a person saying "ahhh"
> which shows the frequency and amplitude of the audio file.  The problem I'm
> having is when I run it on a wav file it shows the frequency 0hz with having
> the highest amplitude.  I'm not sure where the problem is within my code
> and how I can fix it.
> 

This should not be a problem with your code, but probably with the wav file or 
the recording equipment...

> How does 0hz have the max amplitude?  The reason I'm trying to fix this is
> that I want to find the frequency with the highest amplitude in the wave file
> then run some calculation against it but running calculations against 0hz
> doesn't make any sense to me especially when I have to do multiplication
> with it.
> 

0 Hz is the DC component. So, if your signal has any kind of DC offset, it is 
natural to expect 0 Hz to be the largest component. You could probably check 
whether it is reasonable for your data to have a relevant DC offset or whether 
it is some kind of "noise".

Assuming it is a kind of recording, check your recording equipment including 
your AD converter (soundcard?) Typically, there should be some kind of high 
pass filter, but nevertheless, there might be some electrical offset later on 
in the signal chain (e.g. at the converter, some grounding issue, ...).

If you are sure that you do not need DC, then add a high pass filter to your 
processing. For acoustical measurements, traditionally 22 Hz filtering is 
common (but perhaps even more common on the analog side to get rid of high low 
freq components likely to overload the AD).

Sorry, I did not look into the details of your processing or your signal. Hope 
this helps anyway.

Regards,

Rolf