Band-pass filters question

Counterparts · Post by **Counterparts** » Thu Aug 19, 2004 5:30 am

Is there a general rule which describes what the 'width' of a band-pass filter is at a given frequency?

It's just that I haven't come across one which allows you to vary this width (i.e. the frequency range between the high-pass and low-pass ends of the filter). Does such a thing exist?

Royston

at0m · Post by **at0m** » Thu Aug 19, 2004 6:04 am

Variable Q BP filters are very difficult to make. These are mainly found as peak filters in EQ, but without resonance of course... More common is an 1-, 2-, 3-, or 4-pole BPF, some with selectable pole. Also special is Flexor's BP-4 MultiStage, a variable pole BPF with resonance always from the 4th stage.

Counterparts · Post by **Counterparts** » Thu Aug 19, 2004 6:15 am

Hi at0m|c

Would varying the number of poles in use merely change the steepness of the slope of either side of the BPF or would it change the 'width' too?

I've been musing on what modulating the width of a BPF would sound like...might be quite interesting!

Royston

wayne · Post by **wayne** » Thu Aug 19, 2004 7:21 am

Looks like a job for Modular Man

Plato · Post by **Plato** » Thu Aug 19, 2004 7:27 am

I have a VST plugin called GRM tools whose BPF does just this....you have a handle for each end of the band and can slide them around to your hearts content.....You can get some pretty radical results - transform a mighty fat loop to a tiny little hi-hat etc, but I don't think the sound quality is quite as good as a lot of the Scope filters.
Fun though !

Counterparts · Post by **Counterparts** » Thu Aug 19, 2004 7:33 am

=KAZZZAM!=

It's...Modular Man!!

(Actually, I'm Secret Squirrel[1], not MM)

You have to set-up two things using a hi-pass & lo-pass filter I reckon:

a) have a control for the "BPF"'s c/o frequency (which would control both the HPF and LPF's c/o point together, increasing or decreasing both in unison).

b) have a control for the width of the "BPF" (which would either move the LFP & HPF's cutoffs towards or away from each other)

edit: thinking about it, the controls could be independant, the "linking" (as such) could be acheived just by using suitable MIDI control

Might have a tinker this evening.

Royston

[1] dammit! my secret identity revealed...

<font size=-1>[ This Message was edited by: Counterparts on 2004-08-19 08:37 ]</font>

scary808 · Post by **scary808** » Thu Aug 19, 2004 3:05 pm

you could link the two by using a constant val connected to the mod inputs of the filters & then adjust the mod input levels & cutoff accordingly.

Post by **hubird** » Thu Aug 19, 2004 9:05 pm

you bloody freaks