[sdiy] Moogey jitter

[elmacaco]

Hi Ian,

> Well, I would say that this is the crux of the matter.  I believe that if
> there is a strong and obvious amount of jitter in a signal then a digital
> recording will capture it adequately.  After all, isn't Kevin's video
> digitized?  If there is such a large variation in the signal as the video
> shows then it seems to me that it would have to show up in a wav
> file.  (And Kenneth's is a wav file, not an mp3, as you state.)  Analysis
> of Kenneth's file does show that there is some jitter, just not as much as
> suggested in the video.

Right, I reread the whole mess yesterday, he counted the jitter in the wave
files for 40 cycles and found that there was jitter in the moog and
technosourus files, but considerably more in the technosuarus files.  The
Mp3 was with the whole mimmick a moog challenge which Eldhardt did just fine
and was the departure point for the whole confusion.

I would like to see more measurements done to find how much jitter is really
there, and if jitter in an oscillator actually has a pleasing psychoacoustic
quality, or if it is indeed inaudible and not what we are chasing.

I imagine whatever it is that makes the sound it will be a combination,
perhaps noise in the power supply, the power supply voltages, the headroom
of the circuitry, etc.  I think detailed analysis of this combined with the
talents of the people on this list can be a very useful thing.

>
> I agree, of course, that digital recording has imperfections and
> limitations.  But measuring the zero crossings of a strong steady signal
is
> a perfectly valid method of looking for timing variations on the order of
> milliseconds, which is what Kevin claims to see.  Note that in the SMPTE
> collection of suggested measurement techniques for jitter there are
methods
> involving digital scopes, but there is nothing similar to Kevin's
measurement.
>
<http://www.smpte.org/smpte_store/standards/pdf/rp192.pdf#search='jitter%20m
easurement'>

Right, this is great stuff to guide us in further inquiry.  Right now we
have established that there is Jitter in the moog oscillators, and we have a
questionable scope measurement and someone counting 40 cycles of a wav file.
I think we can do better than that.  What we are left with is the question
of is the jitter significant to the sound?


>
>
> >Someone please lend Eldhart a moog and some oscilloscopes so we can do
this
> >without fighting.
>
> I'm sorry, I must have misunderstood.  I thought Kenneth's file came from
a
> Moog.  The early part of tha AH thread is apparently lost, so I didn't get
> to read it.

Yes, he verified the jitter for 40 cycles from recordings of a moog
oscillator in software, tedious work I'm sure, but we know he's got the
patience for that kind of work.

The whole mess because of a misunderstanding IMO.  It was between Eldhardt
and Mike Peake where Eldhardt matched MP's moog sample with detuned
oscillators and a bit of pitch modulation, and MP tried to get elusive when
Eldhardt said it is relatively simple compared to the string work he did.
Seems fine and logical to me, as the conversation was based on drift of the
moog sound and not the totality of the sound, and Eldhardt made that clear
to all.
Then the antagonism carried over when Kevin brought up the jitter being a
contributer to the moog sound, more so than drift, then the battle ensued,
with a lot of misunderstandings as to what was being discussed and what was
being claimed.
My interest in this is because I've heard moog oscillators that are stable
have something extra about them, even the ua726 ones that Kevin is
specifically excluding from his discussion.  I want to know if jitter is a
factor of this sound, because I don't believe it is a matter of instability
alone, I believe stable oscillators can have this too, it just may be that
the best examples we have of this sound happen to be unstable oscillators,
and perhaps jittery ones too.  If it isn't jitter then it might be something
else.  Still, I think the whole Power supply voltages question that Kevin
brings up is interesting enough to warrent further investigation.

>If I had a moog 901-B I'd give you 192kHz 24bit
> >files, and information would still be lost, but wouldn't you rather have
it
> >there to hook up to your scope?
>
> No, I would not.  :-)
>
> My scope cannot measure jitter.  It can tell if there is some present, but
> it cannot do an acceptable measurement.  Much better to analyze the
> digitized data.

I see your point, but how much jitter is audible?  It seems that any
measurement would provide fairly irrelevant numbers until we know how we
perceive it.  if the number is small we can think it is undetactable but we
have not proven that yet.  One might notice it but not be able to say it is
instability, but if it is removed we might immediately hear the difference.
We all have our suspicions, but more data would certainly help.

Kevin brought up a CEM Osc that has no jitter as a comparison, but I think
we'd need to go a little further to really have any sort of controlled
experiment.

I would like to watch it as well and see if it correlates to the sound.
Perhaps finding a way to eliminate the jitter temporarily and see if it
changes the character or not.

> Sure.  But remember that Kevin tested his modules using a stable lab
> supply, not a Moog supply.

Right, which he stipulated in his manifesto and Bob Moog commented on it.
The 901-b's were also totally rebuilt to spec, but practically new and
calibrated.  All in all a very interesting experiment that perhaps would
have been better received had he filmed the pulse wave.

Eldhardt also admitted later that he EQed the sample and filtered his
computer generated waveform, presumably in his Software program, which takes
is further from an ideal measurement.  And software EQ's and filters have a
lot of math to do, it leaves the realm of pure physics there, but is still a
useful tool.  He did verify that jitter is there, the rest really remains to
be tested.


>
>
> >How much and if it is
> >audible needs to be determined further since it is so controvercial now,
but
> >I don;t think moog warmth is magical, it sounds good, and no one can
explain
> >it satisfactorily.
>
> OK, it sounds good to you.  Does it sound good on CDs or just live?  :-)

Good on both counts, but live it certainly sounds different, as there is
more perceived, and more to perceive.  I have yet to hear a perfect
recording of anything, all I ask is that the recording sound good and that
it minimally change the sound unless I want it to change, but for
measurement I still think having the unit is essential, then you can use all
the tools at your disposal, software and hardware, to find the effect of
these circuit behaviors.

I think with everyone's help we can really plot a good course for chasing
this white rabbit ; )

Ed