[sdiy] 2164 SVF sound/noise?

[Tom Wiltshire]

Dan,

Others can tell you what they think, but here's my view after I have played with these chips a fair bit.

> 1. Do they avoid the HISSY nature of OTA SVF filters? (the self noise of an 13700 filter can be quite noticeable with no signal)

The SSM2164 is not as noisy as the LM13700. This isn't a carefully-measured fact (for that we have datasheets - yeah, right!) but just my perception. I've built a filter module with three of these filters in parallel and even that isn't noisy.

> 2. do they SOUND different? or can you swear you are working with an OTA SVF?

The SSM2164 sounds round and fruity. So yes, I'd say it stacks up well against other OTAs. Way better than the CA3080, which is noisy as hell and distorts like mad.

> 3. how is the resonance

Depends on the configuration. In the SVF, there are the much-discussed problems of getting it even across the audio range. Aside from this, it *sounds* good, even when it isn't even!
I know some other people have built 4-pole LPFs with this chip, so maybe they can comment on those. I haven't tried that yet.

> maybe these questions are too general but it sure seems like these chips are all the rage

They're cheap, they're in current production, and they're widely available. What's not to like?!

One thing to note though; the CV response is exponential. This is an audio VCA, not an OTA. This is good for filter cutoff, and good for the resonance amp on an SVF, but not good for the resonance amp on a standard LPF, where a linear response (or even reverse-expo) would be more appropriate.

If you've got some in the drawer, get them out and play with 'em. They're great. I'll send you an SVF diagram when I'm done fiddling with it.

T.