[sdiy] RE: [AH] Parametric EQ

[cheater cheater]

That's a great way to use EQs for synths, but bear in mind that it
could require about 6 bands to really emulate something intriguing,
see the body frequency response of a violin under those two links:

http://www.soundonsound.com/sos/May03/articles/synthsecrets49.asp
http://www.soundonsound.com/sos/Jun03/articles/synthsecrets50.asp

One cool thing about having CV is that you can morph from a violin to
a viola to an upright bass. Which is real cool.

Another thing that a CV EQ is good for is to animate pads and strings:
serves the same function as a phaser or flanger, except you control
when, how and where the peaks and throughs happen, and they're
generally much more pleasant in quality. You can for example make a
very pleasant barber pole effect without making the sound stand out
too much.

Six bands are also cool because then you can use two 'mixer'
SSM2164's: they have 8 vcas, one for each band, one for input
(pre-distortion), and one for output. So the signal chain could look
like this:

input jack -> input vca -> distortion 1 -> 6x(input distortion 2 ->
filter -> distortion 3 -> vca) -> unity-gain mix with output of
distortion 1 -> distortion 4 -> output make-up vca

Distortion 1 would happen with much higher levels than distortion 2.
For example 1 could be a FET style or transistor style while 2 could
be a germanium diode style, I think those clip faster, correct me if
I'm wrong.

I don't think you'll need *that* much precision for the input and
output VCAs? Again.. correct me if I'm wrong..

Tom,
> Anyway, if there was a DAC controlling it, I'd still save the hardware and
> use a lookup table to linearize the resonance response. But that's just me.

But a LUT is not temperature dependant, and will probably not work
that well with resonance settings which can be really delicate around
the generative point.

Cheers
D.

On Sun, Feb 21, 2010 at 20:21, Tom Wiltshire <tom at electricdruid.net> wrote:
>
> On 21 Feb 2010, at 17:58, David G. Dixon wrote:
>
>>> What did you do about the resonance response of the SSM2164? I found
>>> that getting a reasonably constant resonance out of it w.r.t cutoff
>>> was quite difficult. Did you bother with any compensation? In the
>>> end, I think I decided I didn't care that much (it sounded so *fat*
>>> and *good* anyway...yuummmm!) and I've just got a couple of back-to-
>>> back 4V7 zeners on the LPF output amp. This isn't shown on this
>>> earlier circuit diagram, but they're on IC2.2, in parallel with C4.
>>>
>>> http://www.electricdruid.com/VCResonator.jpg
>>
>> One thing that strikes me about this schematic is that the Res CV will
>> have
>> an exponential effect on the degree of resonance feedback.  Of course, an
>> exponential response is desired on the variable resistors and the output
>> level.  However, I would have thought that a linear response would be more
>> appropriate on the Res CV.  Of course, that would require two 2164 VCAs (a
>> la Mike Irwin), thus raising the total number to five, which is pretty
>> darned inconvenient unless the output one is sacrificed, or moved to a
>> dedicated four-input mixer.  Also, that might not improve the problem of
>> not
>> achieving constant Q with constant Res CV, but then again it might, and it
>> would definitely make it easier to "dial in" a certain Q with a pot.
>
>
> If I was to try and linearize the resonance response, I'd probably do it
> using a lookup table in the software ahead of the CV DAC, much like I
> recently did with the pan law for my stereo VCA (also SSM2164).
> I intended the circuit to be used as a "body-modelling filter"; e.g. for
> modelling formants and resonances in instrument bodies, rather than for
> going "BEEEOOOWWW!" every note. If you're not moving the cutoff, the
> variable-Q-with-frequency isn't much of a problem, and neither is the
> exponential Q response. In practice, the frequency-dependent element of the
> Q is the worst of the two. I don't find it hard to get the setting I want
> once cutoff is set.
>
> T.
>
>
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