[sdiy] Filter frequency cutoff with linear response?

Justin Owen juzowen at gmail.com
Mon Feb 20 18:29:17 CET 2012

On 20 Feb 2012, at 13:19, Florian Anwander wrote:

> Am 19.02.2012 21:32, schrieb Olivier Gillet:
>>> But is there any
>>> of these synths that does this VCF modulation linearly?

>> The Doepfer Dark Energy does it.
>> ???
>> The DE is based on a CEM 3394, so most of the 3394 based synths should do that: AX60, SixTrak, MAX, M1000...

> I was just having a look at the CEM3394 datasheet, and they did it that way for exactly the reason predicted - linear FM of the filter. The cutoff CV is exponential (3/8V per octave) but the chip also includes a filter modulation VCA from the VCO triangle output, and that input is linear.

So assuming that CV control of Frequency Cutoff on the 3394 (I haven't looked at the data sheet) is handled via a VCA - it appears they've made a decision to use a Linear response for the other cutoff modulation source...

...is that a correct assumption? 

Curiouser and curiouser.

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