[sdiy] SAW core VCO flyback time

[Ian Fritz]

I agree with everything you say.  Just remember that 1 Hz beats will be 
produced by 1 kHz signals with just a 0.1% error.

Also remember that accurate tracking matters when doing deep audio 
frequency FM if you want constant waveforms over a wide frequency range, 
especially if you are using not-too-simple frequency ratios.

Oh, and also if you want to run at a high frequency and use a multistep 
waveshaper, you need accurate tracking to much higher frequencies. 
(This was my original motivation for working on accurate HF tracking.)

Running the core at a lower voltage and using a carefully shaped reset 
pulse helps alleviate the issues you bring up.

Thanks for your suggestion about "thinking harder", but I have worked on 
this problem since 1974.  All the issues you mention have been brought 
up many times before.

Ian



On 8/30/2016 11:40 AM, mskala at ansuz.sooke.bc.ca wrote:
> On Tue, 30 Aug 2016, Richie Burnett wrote:
>> BTW, I think it's fascinating how the analogue designers strive to achieve
>> perfection in the form of "instantaneous" sawtooth resets, low-distortion
>> sinewaves, and symmetrical triangle waveforms without the little nipple at the
>
> I was holding off on saying it, but if you're serious about analog design,
> do you even *want* a super-fast reset?  It seems to me prioritizing that
> is going to force you to use wider-bandwidth op amps everywhere the signal
> is going; think harder about stability; think harder about EMI (both
> radiated and conducted into the power supply); and it's all going to be
> wasted anyway once someone runs it through the average audio patch cable
> that attenuates such frequencies.  I think if you're generating an audio
> sawtooth wave with significant energy above 100kHz (and probably lower)
> then your design may not be the best possible for its purpose.
>
> If reset time has an impact on tracking then maybe you want it to be
> shorter internally than what you will present at the final output; but
> there *is* still a tradeoff.  Overall I think it usually isn't difficult
> to make the reset time shorter than optimal, and then a contest of "who
> has the shortest reset time?" is a bit silly.
>


-- 
ijfritz.byethost4.com