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Re: Secondary Harmonics

Subject: Re: Secondary Harmonics
From: Walter Knapp <>
Date: Tue, 03 Jun 2003 15:03:01 -0400
> Dear Experts,
> I seem to remember form my class at Cornell many years ago that secondary 
> harmonics as shown on a spectrogram are really a result of the recording 
> equipment and filtering these out of a cut will not degrade the final audio 
> product. 
> Actually, what I am trying to determine is if I filter a cut to reduce insect 
> noise and this noise is also in the band where the secondary harmonic is, 
> will 
> I be significantly degrading the final audio product?

The harmonics can also not exist at all, but be a result of the math 
that created the sonogram. In which case filtering will make no 
difference at all. Not everything on a sonogram is really there. Not 
only are there false "harmonics", but a lot of the spatter around a loud 
call is not there either. Same with some "echoes".

The best way to find out what will happen is to do the filtering and 
listen. If your software will not allow previews, then do it on a copy 
of your sound file. Do a new sonogram too.

This is why I like filtering with Spark XL, I have the real-time 
sonogram, and can immediately see what a filter change will do before 
applying the entire filter set.

As far as the question if it's all real, that's really a judgment call. 
Will removing the insects help more than removing the harmonic hinders. 
In most cases where I need to do that here, removing the insects is 
almost always the better way as they are so loud here. Judge it by 

Note on listening, use as many different ways to listen as you can. Some 
filtering is just fine in headphones and awful in speakers, or the 
reverse is true.



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