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Re: address@hidden
From: |
Quentin Spencer |
Subject: |
Re: address@hidden |
Date: |
Mon, 13 Sep 2004 08:16:12 -0500 |
User-agent: |
Mozilla Thunderbird 0.7.2 (Windows/20040707) |
Neil Bryan B. Cazar wrote:
hello guys! i'm a newbie when it comes to octave. i would like to ask
for some help if some of you can give me a source code in octave that
does the following tasks.
1.) first the program would load a wav file.
I think there may be functions for this kind of a thing in the
octave-forge package (octave.sf.net), but I don't know what they are, so
perhaps someone else on the list can respond.
2.) if i'm not mistaken, the wav file is in time-domain format. it
needs FFT (fast fourier transform) for it to be in the frequency domain.
In theory, yes, an FFT converts from time to frequency domain, but it
depends on what you want to do in the frequency domain. Filtering is
usually done in the time domain, but if you want to look at the spectral
content of the signal, what you really want is a function such as
"pwelch" in octave-forge that estimates power spectral density.
3.) it then passes through a notch filter which filters out the
noise. the noise is the hissing sound you hear when you play cassette
tapes
or old records. the output is then converted back to a wav file.
The problem here is that the noise on most old recordings is what is
referred to as "white noise", meaning that it contains equal energy at
all frequencies (the same way white light contains energy at all
frequencies). As a result, you can't really just filter it out.
Recordings made on very old equipment had limited ability to reproduce
high frequencies, so sometimes old recordings are "cleaned" by
filtering out the very high frequencies, but otherwise there's not much
you can do (and some audiophiles would prefer to leave the noise there
so you don't mess with the music). White noise exists in all recording
media, really. It's just that modern equipment has been able to push the
level of the noise down to a level that it's barely audible, if at all.
Anyway, if you really want to try filtering recordings, I would suggest
a low-pass filter, rather than a notch filter.
I hope this helps.
regards,
Quentin Spencer
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-------------------------------------------------------------
- address@hidden, Neil Bryan B. Cazar, 2004/09/12
- Re: address@hidden, Joerg Kampmann, 2004/09/13
- Re: address@hidden,
Quentin Spencer <=
- Re: address@hidden, Miquel Cabanas, 2004/09/13
- Complex Conjugate, robert Macy, 2004/09/15
- Re: Complex Conjugate, Geraint Paul Bevan, 2004/09/15
- Re: Complex Conjugate, NZG, 2004/09/15
- Re: Complex Conjugate, Mike Miller, 2004/09/15
- Re: Complex Conjugate, Henry F. Mollet, 2004/09/15
- Complex Conjugate, John W. Eaton, 2004/09/15
- Re: address@hidden, robert Macy, 2004/09/13
- RE: address@hidden, grumpy steve, 2004/09/13