[ecasound] Filters

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Subject: [ecasound] Filters
From: Nolan Darilek (nolan_d_AT_bigfoot.com)
Date: Wed Jan 23 2002 - 22:58:10 EET

I'm experimenting with various filters and effects, and had a few
questions. Since I'm extremely new to audio processing (I'm finally up
to mixing a few basic tracks) these will probably seem extremely
newbieish. :)

Out of curiosity, what exactly do the various filters (lowpass,
highpass, bandpass, etc.) do? I thought that they'd remove all
portions of an audio file which fall above/below/within the specified
frequencies, but when I'd run them over various songs to test this,
they didn't seem to work. For example, for the hell of it I wanted to
see if I could use a bandpass filter to extract the vocals from
Learning to Fly by Pink Floyd. (Ok, I don't expect perfection here,
this is just an experiment. :) So I used a bandpass filter centered on
191 Hz with a width of about 100 Hz (The song appears to be in G, and
if I'm correct then the frequency of that G is something around 191
Hz.) This doesn't seem to work however. Rather than bringing out the
vocals, or some portion of the audio, the entire song seems to be
quieter and muffled.

Looking at the effect presets file, it would appear that I can add
various effects to the areas of the frequency selected by the various
filters. I can't seem to figure this out, however.

ecasound -i *8* -efb:191,56 -ea:500 -efh:400 -ea:0

I was hoping that might work, thinking that maybe the filters used the
effect which followed them to determine how the region of audio is
processed, but this is obviously wrong, since the final -ea:0 doesn't
kill everything over the cutoff, but instead kills everything. :)

Am I at all on the right track with this?

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