[Top] [All Lists]

Re: Audacity Question

Subject: Re: Audacity Question
From: derek holzer <>
Date: Sun, 26 Feb 2006 21:26:12 -0700
Hi Natalie,

nbioacoustics wrote:

> Does anyone know how to cut off all data below a certain frequency
> threshold? I don't want to use the HighPass Filter, I just want to get
> rid of all the sound below 1kHz... 

Technically, these are one and the same. A highpass filter will 
attenuate frequencies below its cutoff point. The steeper the slope of 
the filter, the more the frequencies below the cutoff are reduced.

> Also, if I run the the highpass filter, it doesn't affect things above
> the threshold I give it at all, right?

Filters usually have a "bump" right at the cutoff frequency. Frequencies 
just above the cutoff frequency will be slightly amplified. The steeper 
the slope of the filter, and the higher the resonance, the more of a 
"bump" you get.

If you wanted an approach which isn't based on the traditional highpass 
filter model, you could investigate an FFT-based model. This is what 
gets used for most software noise-reduction filters (although I don't 
think Audacity has such a noise reduction utility). In this case, 
however, the sound gets reduced to a specific number of frequency 
channels in a process much like MP3 compression. Then you can simply 
"erase" the unwanted frequency channels and reconstruct the sound from 
what's left. I consider FFT-based filtering to be both destructive and 
lossy, especially when you are working with very frequency-sensitive 
material like binaural recordings and bioacoustics.

In short, both methods will change your sound in some way you probably 
don't intend, so you have to decide which method is least destructive 
for your purposes.


derek holzer :::
---Oblique Strategy # 196:
"What else is this like?"


<Prev in Thread] Current Thread [Next in Thread>

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the naturerecordists mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU