SV: Re: Re: Re: Re: [sdiy] Boogey jitter

[Magnus Danielson]

From: karl dalen <dalenkarl at yahoo.se>
Subject: SV: Re: Re: Re: Re: [sdiy] Boogey jitter
Date: Sun, 23 Apr 2006 03:27:19 +0200 (CEST)
Message-ID: <20060423012719.87290.qmail at web25512.mail.ukl.yahoo.com>

> I was just suppriced that whole ""HiFi"" story ended up beeing discussed here!

Someone had a need to vent his views on this.

> > Personally I'm convinced that
> > a) Different VCOs have different amount and type of built-in modulation.
> 
> What?? So you are a Kevin follower? Im suppriced JH! ;-)
> Seriously, we all know that VCO exhibit amounts of phasing
> due to leakage  and that they behave (frequency whise) as the 
> supplies behave.

Actually, as I pointed out earlier, there is a cancelation effect between the
reference-voltage for the expo-transistor (collector-current of the "incomming"
transistor) is usually from the V+ to ground voltage difference via a resistor
and then the comparator reference is usually derived from the V+ to ground
using a resistor divider. The dependence on V+ cancels. Almost.

Since we integrate the current comming out of the expo-pair, the charge and
thus voltage of the cap is an average of V+ since last reset, and if V+ is
modulated (by any signal, white noise included) the reset-point will be "off"
in time and we have modulation. For the wrong voltage or veeerrrryyyy
ssslllooowwww modulation the main effect will be amplitude modulations rather
than noticeable phase modulations, since cancelation works better, but the
amplitude is still affected.

Naturally, there are loads of errors in this model, which causes the modulation
not to be quite as good, such as the reference-current resistor is not
actually terminated at ground, infact that voltage change with pitch from the
summer etc.

> > b) If analysed properly, this could be emulated perfectly with a "perfect"
> >     VCO, and external modulation sources.
> 
> Theres no need for a perfect VCO, all you need is a VCO
> who's caracter is caracterised and well documented.

Indeed.

> > c) For my needs, expressive means of manually controlled modulation
> >     are more important than the build-in modulations.
> 
> Such as linear detune for instance.
> As Harry toughtfully said earlier: if a VCO is faulty i try to fix it!

Indeed.

> > I tried to explain the importance [to me] of (c) with my aftertouch example.
> > I'm _slightly_ interested in research on (a), leading to (b), but my life
> > doesn't depend on it. It would be fairly interesting, yes.
> 
> I prefer beeing in the garden and pooking around rather having
> a swelling itching brain even looking for something defined as
> warmth/magic/fattness of one VCO singing its sorry tune of jitterbug!

Mmm... I'm heading for the garden now... ;O)

> The whole idea is filled with pain!!

At least how it has been discussed.

Cheers,
Magnus