Dialog still rolling

[Paul Schreiber]

Hey, this is the most fun on here in weeks!!

> First, no VCO has a "sound", sterile or otherwise. They may have THD,
>but a pulse is a square is a saw. But what they DO have is drift and have
>linearity errors. 

Q)But THD and drift are such an important part of a VCO's "sound" - how can 
you just disregard them to justify a VCO's lack of "sound"?  Sometimes 
you want a clean, clinical VCO like a 3340, sometimes you want something 
whacky like a 303 VCO.  It's easier to build a VCO you like the 
sound of than to take a 3340 and selectively mess it up to sound the way 
you want in different circumstances.

A) I'll restate this. One VCO sitting there doesn't have ANY sound quality. Neither does my HP function generator. What does have "sound quality" is multiple VCOs happily drifting against each other. Now what's interesting is the following: when do we want 'wacky' (JD's word) versus 'clean'?? I suppose it depends entirely on what sound(s) you are trying to make. If you're Wendy Carlos, trying to lay down 8 parts in 16 hocketed timbres, the whole mess microtuned to 18 notes/octave, then by God, you want stability. However, if you are trying to do the Pink Floyd "Meddle" VCS-3 stuff, the driftier the better. What is interesting about a DCO is you can algorithmically "screw up" the tracking in infinite ways: apply Gaussian noise, triangular PDFs, Rayleigh channel fades (sorry, I'm getting carried away). In other words, with a little experimentation emulate ANY VCO response you want: from "3340" to "PAiA" <grin>. And the digital circuitry is easily expanded to 32 to 64 independent outputs simultaneously.

Q)Have you ever listened to the sawtooth duty cycle modulation in a 
Chroma? 

No, but older readers of Electronotes will recall Bernie's "Sawtooth Animation" module which the Chroma kind of swiped.

Q)How many oscillators can do thru-zero PWM?  Thru-zero FM?  Not every VCO 
design lends itself to these capabilities, does it?

No, but I don't know of any commercial synth that has thru-zero FM. The 3340 can do linear FM, which is required for DX-7/Synergy type sounds.

Q)Would you consider sync to be a part of the VCO design?  Roland decided 
the sync in the 3340 wasn't "Roland" enough, so they bypassed the sync 
on the chip & put in their own sync circuit - sure enough, it sounds very 
"Rolandish" compared to other 3340 designs.

Well, lets talk about sync. They are referred to as "hard" and "soft". Hard means when VCO #1 discharges it's sawtooth, then so does all the others down the line. What this sounds like is lack of any beat frequencies. You hear a bunch of distinct tones (1 per VCO) but no beating. Note the "out of tune" VCOs are in fact AMPLITUDE MODULATED.

Soft sync (invented by Dave Rossum of Emu) means that any slave VCO that is within 5% of the discharge voltage of the master will discharge. This is done, BTW, with a comparator to (.95)(10) = 9.5 volts for example. This means VCOs tuned closely will not beat, but others may. It does sound different. But there is no standard centered around 5% (although most synth copy it, as does the 3340). Roland uses 15% I think. Hey, toss in a pot and we have VARIABLE Soft Sync Threshold (VSST). This variance trades off "in-tune-ness" for "beat-ness".

Q)Then there's some of the VC waveshapin from Buchla & Serge...

Well, this is not the VCO per se. Look at the CEM3396 data sheet. It has VC waveshapers: you can get about 27 distinct shapes out of it. Still used in Waldorf stuff.


Q)But they distort in a really cool way...besides, why do you need better 
than AM quality when amplifying a CV?

Because most VCAs are in the audio path.

> I like quiet VCAs with NO feedthrough.

I like having a choice between clean & nasty.  Again, it's easier to make 
a 3080 soound like a 3080 than it is to make a CEM VCA sound like a 3080.

Can't argue on that!

> 
> The 3310 EG > ========= > > All agree, this is the chip. So concern over
the availability. Gene, I GOT 1200!! Now, this is certainly enough for
now. So don't be shy using it. I will design an equivalent from discrete
later this year.

Woo! must save for a few dozen - VC EGs are cool!


Or argue here, either.
 

> > Power Supplies > =========== > > It's hard to beat a
723/D40xxxx pass transistor. This is a case where 'vintage' is better. I
will ask Walt Jung for permission to publish his "super high tech" power
regulators. They have 1/1000th of the residual noise of a LM7812.
Amazing!! Can be built for about $8/side. 

Q)Did Walt ever publish this?

A) Yes, in the Audio Amateur magazine. Everyone should subscribe. Best source of audio design out there. Back issues available. AND...they sell KITS!!!!