Re: fourier analysis/MP3 to WAV format conversion

"Take Vos" <Take.Vos@xxxxxxxxxxx> wrote in message
news:1176535717.790344.271430@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Hello ibrtchx,

I need to do fourier analysis on speech files.
~
is it possible to do it right from MP3 files?
~
if not, is it possible to do convert MP3 files to WAV ones?

I am not sure why you need the analysis, but I have to warn you about
how mp3 got compressed.
audio is first converted with DCT (which is similar to a fourier, but
without the complex numbers) into the frequency domain. Then they
remove all the frequencies that you are not supposed to hear, like a
frequency with a low amplitude right next to a frequency with a high
amplitude. As there are now a lot of zeros in the frequency domain
they use run-length-counting to compress and than encode the result
with something huffman.

The kicker for you is when they started removing the frequencies.
Which means you will not get an accurate fourier of the voice.

Cheers,
Take

Interesting info there, but I would be very surprised if your speech data
would suffer from first being mp3's. There are many factors involved and you
won't get results with empty bins next to peaks for instance. In the old
days they had 8KHz 8 bit files for speech analysis and it didn't do them any
harm..... possibly. : )

If you're doing the coding then definitely convert to wav first though, it
will just make it all simpler. Just search for "mp3 to wav converter" into
google and you'll pick a share/freeware package that does batch processing,
there's a lot out there...


Dave



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