[sdiy] Fixed filter bank questions

Tom Wiltshire tom at electricdruid.net
Thu May 9 17:09:29 CEST 2019


Fair enough. In your situation it probably doesn’t make much odds. It’s certainly very different to what I was doing.

I was recently playing with a distortion effect and added a mid cut/boost control to it. The first one I built I used a 800Hz centre frequency, and with the second one I built I tried 640Hz. In that case, there's a clear difference. The 640Hz one has a more “honky” trumpet-like sound. It’s also more noticeable on the peak rather than the cut, I thought.

> On 9 May 2019, at 00:16, David G Dixon <dixon at mail.ubc.ca> wrote:
> 
> Concerning changing the centre frequency from 1000 Hz to 640 Hz...
> 
> I've done a bit of analysis, and my assessment is that it really doesn't
> matter.  
> 
> If you use 1000 Hz as the centre, then you have 6 BP filters below that
> going down to 125 Hz, with the LP at 88 Hz, and 5 BP filter above that going
> up to 5657 Hz, with the HP at 8000 Hz.
> 
> If you use 640 Hz as the centre, then you have 5 BP filters below that going
> down to 113 Hz, with the LP at 80 Hz, and 6 BP filters above that going to
> 5120 Hz, with the HP at 7241 Hz.
> 
> The result is that all of the BP filters have shifted a little less than two
> semitones downward.  Nobody is going to notice this difference.  I'm going
> to stick with the more Moogy frequencies out of a sense of tradition.  Plus,
> I like putting the rounder numbers on the front panel.
> 




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