Jitter, Revisited

Taking a break from the jiggy series to tell a "jittery" story...

A couple years before I met Kevin, Hans Zimmer hired him to build him a very large Moog modular.
(HZ just wrote Kevin to say it's still fine 16 years later, too!)
According to Kevin, they both discussed synths right and left then and what made them sound good.

Hans said that he preferred the sound of the Moog 901 oscillators.
At the time, Kevin didn't understand what he meant--An oscillator to him had pitch, waveform shape, volume and that was about it.
But Hans was certain this wasn't the case.

Two years later, right as Kevin was putting the finishing touches on Hans' big Moog, he found himself with many extra parts left over.
One part was a blank Moog 921B panel.
Kevin decided to use it to build a CEM3340-based oscillator, which is used in Jupiter 6's, Memorymoogs and many other synths we all know and love. (And Kevin's portable VCO!)

You'd think that using a VCO on a chip wouldn't be any different than what Moog used in a 921B... they're both oscillators, right?
Wrong.
When Kevin installed and made a patch with this new "CEM" 921B, he suddenly realized Hans was right.
There was some sort of sound the Moog's had that this new oscillator didn't.
In Kevin's words, the CEM3340-based oscillator "sounded razor sharp and sterile."

This keen observation wasn't thought of much for several years.
Then, a couple years ago, while restoring a Moog modular, Kevin made a video showing a Moog 901 oscillator plugged directly into an oscilloscope.
Here it is: http://www.minimoog.net/moogjitter.mp4
This video showed some sort of "jitter" in the waveform that wasn't present in the CEM3340 chip.

In an interesting and semi-amusing round of "shoot the messenger," Kevin was slammed when he showed this video to others.
They insisted that the video showed nothing that could actually be heard, and anyone who thought otherwise was probably hearing things.

Ken Elhardt took this position after looking for this jitter with his DAW (Digital Audio Workstation).
However, he didn't use an actual 901 oscillator. He used an mp3 of one. (That always struck me as odd, trying to analyze a digital sample of an analog waveform. But hey, I only change caps and rebush keyboards!)
Mr. Elhardt and others added that they prefer a very accurate and stable VCO and if they wanted any "jitter", they'd add it in with noise or whatever. (Personally, I'm not much for ultra-accurate, sterile-sounding oscillators.)

One person even said that Kevin had documented how Moog power supplies were actually responsible for this jitter.
This made me laugh, as the video clearly shows that he used a precision laboratory power supply, not a Moog power supply.
(More on that supply in future posts, as it's the heart of many things that will be featured in the "jiggy series".)

Finally, several people didn't understand what Kevin was showing at all and said whatever great Moog sound there might be is due to drift. (I hope these folks weren't the same ones who like their oscillators sterile!)

But one very well respected tech, Juergen Haible, also countered that Kevin was wrong.
This hurt Kevin's feelings because Kevin used to be friends with him.
He used to share parts, photos and music with him and hosted his site for free.

With all that in mind, I submit for your perusal:
http://www.jhaible.de/living_vcos/jh_living_vcos.html
It's a vco design made by Mr. Haible that he calls "living VCOs."

In reading his description, Mr. Haible describes things this way:
"...A good part of that special sound of early Moog and EMS oscillators is not because of any "randomness", "unstability", "instability" or "noisyness", as so often is said. A good deal of their behavior is because of that, but it is not the whole story. There are also some very deterministic factors in these old circuits which have been unpleasant side effects for the designers back then, but which are worth a closer analysis when we're designing a musical VCO today. "

Kevin found this amusing. (Once he reminded me of this whole jittery debacle, so did I.)
He pointed out that while Mr. Haible says what his VCO's aren't, he doesn't say what they are. No schematic or analysis was provided (at least yet.)
No mention of the word jitter either. ;-)


But Mr. Haible's board layout suggests a design very close to the Minimoog and Moog 921B oscillators. Many of the same exact parts are used as in Moog oscillators.
Mr. Haible's comments suggest that he learned something new here.
He designed his oscillators not to be super accurate, but to be musical instead.
He just built his "living VCOs" upon Moog's basic design.
He intentionally sacrificed perfection for musicality.
Isn't that what Hans originally observed and Kevin documented?

I think Mr. Haible changed his mind, and is skittish about using the word, "jitter."
No harm in a man having to change his position after being so insistent on it previously! (Though I suppose admitting that might be difficult.)

By the way, Kevin said he's has no hard feelings and would love one of his boards.
If we can find the extra cash, I wonder if Mr. Haible will sell us one? :)