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

[Tom Wiltshire]

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