Temperature-compensated resonance ( was Re: [sdiy] RE: [AH] Parametric EQ)

[Dave Leith]

The old ARP 2500 - 1047 multi-mode filter had a tempco in the voltage
controlled resonance circuit. I built the circuit and performance
seems quite usable in a synth way without the tempco (I purchased but
still need to install:-)

http://www.guitarfool.com/ARP2500/1047.html

and the VCA blocks with the tempco
http://www.guitarfool.com/ARP2500/encapsulation.html


On 2/22/10, Tom Wiltshire <tom at electricdruid.net> wrote:
>
>  On 22 Feb 2010, at 14:54, cheater cheater wrote:
>
>
> > Tom,
> >
> > > Aww, c'mon! Who ever bothered having a temperature-compensated resonance
> > > control anyway? Certainly no synth I own has one. You're lucky if you
> get a
> > > tempco in the filter *cutoff*, let alone the resonance.
> > >
> >
> > This only shows the sad state synth designs are in. Most high quality
> > equalizers have tempco Q.
> >
>
>  Can you back that up with examples? I'm curious to see some.
>  A quick search turned up this extremely expensive EQ
> (http://www.yoursoundsource.com/mw-avalon-ad2077.html) but
> it doesn't mention tempco Q.
>
>
> >
> > > One thing I'm really learning about synth building is that you can often
> get
> > > away with a lot less than you think you need. It's amazing, but the
> human
> > > ear really isn't "hi-fi" at all. I thought I needed 16-bit parameter
> values
> > > for everything, but 12 will do, and often 8 is enough.
> > >
> >
> > The way I think of this is that I can't figure out all ways that
> > people will be using my synth/eq/computer program/other invention,
> > therefore I shouldn't compromise where *I* think that *I* don't need
> > the accuracy. I usually go and ask experts, I'm definitely not the
> > best expert in the use of anything I created.
> >
>
>  I'm not talking so much about 'possible use' as the limits of human
> perception. Digital 'stepping' is the big evil that everyone is trying to
> avoid, and the question is "how many steps do you need before they become
> imperceptible?". This does depend on the situation (a slow sweep of a highly
> resonant filter is about the worst case scenario) but is a practical
> question that can be answered by experiment. Whilst some people's ears might
> be more sensitive than others, it's not a subjective point.
>  A similar example is the question of how small a pitch difference is
> audible ("about 6 cents" is the accepted answer, with caveats). Obviously
> some people have a much better ear for pitch than others, but if your
> oscillator is producing discrete pitches every 0.01 cents, you don't need to
> waste time and effort trying to  "improve" it to 0.001 cents accuracy. For
> synth use "better than human hearing" is a useful day-to-day definition of
> "good enough".
>
>
>  Regards,
>  Tom
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