simple 3-band crossover

[Mike Burgundy]

Hope this might benifit someone:
I always felt multiband processing has a lot going for it, wether it's smoothing out intermodulation in distortion effects, or with compressors. Hey, maybe someone has a brilliant idea we've never heard of ;P
This is about the simplest way to get a 3-band crossover that should work well enough. with the math (in the schematic) it's easy enough to change it if need be. There's nothing new or hard here, but maybe it'll save somebody some work.
I haven't built it (yet), but the sim looks promising enough.



Lowpass is at 300Hz, Highpass at 2kHz, bandpass (U3 and 4) is a series connection of a 2kHz LP (letting through anything below 2k) and 300Hz HP (anything above 300 gets through) which neatly leaves a 300-2k bandpass. The bandpass inverter (U7) is (as per standard) necessary since this circuit has a 180 degree phase shift at the corner frequencies. Leave that out and you'll get two huge dips in the frequency response, even if the filters are individually right.
If you want to insert ciruitry into the three bands (compressors, maybe), do so between the filters and the 10k mixing resistors(R9,10,11). The 10k gain (R21) resistor on the output mix opamp may have to be tweaked, depending on the circuits used and your wishes.

Frequency plot:

Green=output response.  Red/Grey/Blue is LP/BP/HP.
Notice there are no level controls, it just splits up the input into 3 bands, and then mixes them back together. Result is linear to within half a dB.

If anyone tinkers around with this, let me know. Any lessons to be learned by me from this are also very welcome ;p
Happy tweaking.

(edit: added parts numbering for clarity)

[Keppy]

I recently did a similar thing to make a 2-band distortion pedal. I used 2-pole HP/LP filters very similar to these. I used a TS-style input buffer though. The circuit proved effective for my uses. Are you planning on building anything around this?

[Mike Burgundy]

I'd like to insert 3 engineers thumbs perhaps. attack and release switchable fast/slow and progressively speeding up from low to high.

[WGTP]

So you use a Rat for one band, a FF for another and a Tube Screamer for the third. 

[frank_p]

I'd like to insert 3 engineers thumbs perhaps. attack and release switchable fast/slow and progressively speeding up from low to high.

That would sound nice on my old drum machine. Did you try one on one band ?

[Mike Burgundy]

never got around to it. I will, in good time. Have to focus on landing a new job, while I also need some time off from that every now and then.
I really would like a multiband compressor ;P

[Mike Burgundy]

@WGTP: well, you could. But if you use the same "engine" 3 times, you might get rid of some of that ugly intermodulation when playing chords more complex than 1-5-8. Try playing a jazz chord through anything even moderately dirty. There are several things out there employing this trick and it works very well.