evertveldhuis wrote:
>
> What are the differences between a sonogram and a spectrum analyse?
>
> If for instance I would like to know if there are inaudible
> frequencies in my soundfile, like below 20 Hz and above 15 kHz.
> I would use a spectrumanalyser so that I can see the frequency and
> the amplitude of the whole signal.
>
> I haven't used a sonogram yet, but from what I have read I had the
> feeling it is some kind of fingerprint from a soundfile, but what
> does it show, energy, amplitude? And how does it relate to a spectrum
> analysis, what are the pros and cons?
People sometimes use the terms interchangeably. But, I consider a
spectrum to be just a snapshot of frequency distribution at a particular
moment. It's two dimensional, frequency vs sound intensity. A sonogram
adds a third dimension, time. Take a spectrum and sweep it along the
time scale and you have a sonogram. Generally the x axis is time, the y
axis is frequency and the intensity is given by some form of contour
plotting. Either ranging along gray tones, or different colors for
different intensities. A lot of data is packed into a sonogram.
If you check my website:
http://wwknapp.home.mindspring.com/GAFrog.Toad.html
Each species has a sonogram linked to it's page. That will give you some
idea what sort of info you can gather.
To my mind a sonogram is far more useful than the spectrum, in fact I
don't bother with a spectrum display as I have software that will
generate sonograms while the sound plays. Though you should note that
the math to produce such a display from a set of digital samples is not
trivial. And it cannot do the display sample by sample, it actually
works off groups of samples, and depending on just how that's done
various resolutions and so on will be found. The math can also produce
anomalies in the display, these are really there in a spectrum, but you
find it much harder to pick them out.
The sonograms on my site use a linear frequency scale, while our ear's
response is more log scale. This overemphasizes the higher frequencies
compared to what we hear. There are more and more sonogram routines that
give the choice of a log scale. In my next revision of my website's
sound stuff I plan to switch to log scale sonograms.
BTW, I did my first sonograms on a machine that scratched them out on a
sheet of smoked paper on a rotating drum. We have it good now.
Walt
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>From Tue Mar 8 18:22:40 2005
Message: 2
Date: Mon, 26 Aug 2002 22:06:22 -0000
From: "evertveldhuis" <>
Subject: Re: Cutting frequencies in Cooledit
Luis,
If you filter low freqs (or high freqs) out of a wav file, the size
of the file in MB will be the same. Only shortening the duration
(time) will shorten the file (I noticed you were going to stay in the
16 bit 44k1Hz format).
So it only changes the way it sounds, nothing more.
Regards, Evert
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