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Re: Secondary Harmonics

Subject: Re: Secondary Harmonics
From: "Raimund Specht" <>
Date: Wed, 04 Jun 2003 18:27:13 -0000
>  wrote:

> > Dear Experts,
> > 
> > Does anyone know if CoolEdit Pro's spectrogram would add 
spurious harmonics?

Hi John,

I still have not seen any spurious harmonics in CoolEdit. In fact, I 
can not remember of any other major program having such problems. 
However, theoretically it would be possible.

A simple test would be to generate a synthetic sine signal, that 
does not have any harmonics. When your spectrogram software does not 
show harmonics on that signal, your software would be ok.

Filtering would not be a reliable test for that. The reason is, that 
there is no ideal low-pass filter, that would remove the signals 
from the stop-band (the frequency range above the cutoff frequency) 
completely to 100 percent. The stop-band attenuation of common 
filters is limited to something like 60 or 90 dB (or even higher), 
depending on the type of filter. So, larger signals may remain in 
the filtered file (at much lower amplitudes of course). These 
remaining signals (or harmonics) visible on a spectrogram were not 
produced by the specrogram algorithm. They are really present in the 
sound file.




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