SV: [sdiy] Mopho modulation DAC configuration, update rate, etc

[Jerry Gray-Eskue]

I agree. But is the change of a magnitude that changes the harmonics or
timbre in a noticeable way?

-----Original Message-----
From: cheater cheater [mailto:cheater00 at gmail.com]
Sent: Saturday, February 06, 2010 11:05 AM
To: Jerry Gray-Eskue
Cc: Synth-diy at dropmix.xs4all.nl
Subject: Re: SV: [sdiy] Mopho modulation DAC configuration, update rate,
etc


Jerry,
between two triggers of the integrator core of the carrier, the
variation of the fm modulator, if that modulator stays above zero,
shows itself in the changed convexity of the signal on that cycle.

D.

On Sat, Feb 6, 2010 at 16:32, Jerry Gray-Eskue <jerryge at cableone.net> wrote:
>
> Not to step on any toes here, but I wonder if pure analog VCO's can really
> be said be to "accurately" handle audio rate FM.
> I may be making some invalid assumptions, but here we go:
>
> Here is my point, the base frequency is determined by a charge rate into
an
> integrator, this may have some minor fluctuations in the slope when the
> added variable charge rate of the FM is added but there is only one
primary
> result of the analog calculations, the integrator hits the threshold level
> and resets or reverses direction.
> There will be some variation in the harmonics due to irregular charge
rates,
> but I suspect these frequency components are not audible. The audible
result
> will be the variation of the frequency of reaching the threshold and the
> harmonic content of the non FM wave form. It seems to me that with audio
> frequency FM a lot of the higher frequency will be "filtered out" by the
> integration. At most you only get one result for half cycle of the VCO,
the
> variation in frequency due to the RMS value of the FM signal during each
> period.
>
> - Jerry
>
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Tom Wiltshire
> Sent: Saturday, February 06, 2010 6:24 AM
> To: karl dalen
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: SV: [sdiy] Mopho modulation DAC configuration, update rate,
> etc
>
>
>
> On 6 Feb 2010, at 08:38, karl dalen wrote:
>>
>> Offcourse but there are basically no *modulation* frequency
>> limit within the PA397, it can go into audio frequency range
>> if one designs it in.
>
> If the Mopho uses the same DCOs as the Prophet08, then I disagree,
> Karl. I might be wrong (happened lots before) but I don't see how you
> can do audio rate FM on a DCO.
> Some people have argued that you can update the charging rate in the
> middle of a cycle without causing a glitch, by doing some
> recalculation of when the reset point would be, but I'm rather
> sceptical that it can be done accurately. And FM is the absolute
> worst-case, where you're changing the charging rate many thousands of
> times during a single cycle (48KHz sample rate would be a minimum for
> half decent FM). If you don't have some errors built up by the end of
> that, I'd be amazed.
> Delighted, but also amazed.
>
> Aside from the DCO, he's got an analog filter and VCA in there, so he
> can do audio FM on those, no problem.
>
> T.
>
>
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