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.
best,
d.
--
derek holzer ::: http://www.umatic.nl
---Oblique Strategy # 196:
"What else is this like?"
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