External Clocking - is it all that?

madtheory · 27-01-2010 12:45pm

studiorat- FYI I learned dem big words before I studied electronics... from Monty Python sketches

I wasn't aware that the Black Lion mods were popular. They seem like snake oil to me. The guy was asked to back up his claims on SOS forum and never responded. It's the kind of thing that hi fi buffs love, but it's not any kind of engineering.

PSUs cause jitter in the clock oscillator circuit so when a jitter measurement is stated (which is rare) the PSU flaws are auomatically included, because the jitter is measured at the o/p.

studiorat · 27-01-2010 4:12pm

On the black lion mod for the 002 the PSU is the first thing that gets changed. Much like the HiFi mods of yore I suppose.

It's given usually as error rate (BER) rather than actual jitter measurements because it adds both types of jitter in to the figure.

Anyway, all this talk of jitter seems a bit out of context I've been scanning over the thread and find no mention of what kind of jitter we are talking about. Apateur, Clock, whatever... Not to mention that jitter can come from cables connectors, ground bounce, EMI, all sorts of sh1t. So a machine with a seemingly good clock may have introduced errors in it's design. I digress...

Anyway, here's a bit of a rant. Power supply related jitter will be periodic so it's easier to figure out where it comes from. Does it concern us more than Gaussian varations, I couldn't say... The effects and measurments of the two types are different. Sinusoidal will create sidebands.

Now my point is, in theory where human hearing is concerned these frequencies are usually masked off. However since we can sometimes hear tones as much as -25dB into white noise it is necessary to try and keep the sidebands below that level. In the case of 16 bit that tone is in the region of -120dbfs and still audible to some...

So it's certainly a case of some hearing it and others not. I have heard differences in different clocks for instance the difference between Windmills HD rig connected and not connected to a RADAR clock and there really is a difference. For the most in the literature people will tell you there is a difference, usually in the stereo field, a by product of better high frequency information and HRTF's IMO but it's just a hunch.

Anyway, adding an external clock is not a minimum jitter solution. Apogee's clocks add shaped jitter to their outputs to help the sound. I've read recently where adding high levels of 600hz jitter into a clock actually helped make a cd player sound better. So it's more of a case of the type of jitter that exists in a circuit than how much or how little there is.

madtheory · 27-01-2010 4:26pm

Interesting stuff! IMO if a cable is causing jitter, then the converter is defective (or ancient) and should be replaced (to paraphrase Watkinson). IMO HD boxes are not defective. I'm dubious about hearing stuff at -120dB, so IMO "jitter type" is a red herring, but I'm open to the possibilty if there's a proper test. Was that in a blind A/B test? Was jitter the only variable? Room modes are often forgotten in these tests. Was your Windmill test done in a treated room, and was it blind A/B? IMO, Apogee are also purveyors of snake oil. They established their name with Lavry designs and he's long gone from them as we know. Surely you mean shaped dither, not shaped jitter? Your stuff about noise floor sounds like dither also...

Seziertisch · 27-01-2010 4:36pm

God be with the days of pluggin' in a 57, pointin' it at the source and then hittin' record says I to Old Mr. Brennan ...

Ha, says he, you won't find any jitter in my bread ...

madtheory · 27-01-2010 4:38pm

Jeepers, sorry studiorat, Apogee do have "shaped jitter". Sounds like marketing voodoo to me...

You won't find any jitter in my conrflakes either

studiorat · 27-01-2010 10:04pm

The test was as A/B as you can get bearing in mind we stopped the machines to swop over, I would be up for attending a proper one again. But all the critical ears in the room noticed a difference although slight. It was through the main system in the control room.

Because we're dealing with tiny differences I think the cable thing is particularly important to note since we are also working with super high frequencies (44.1kHz etc.) and impedance is a factor. But don't get fooled by the marketing on low jitter cable either. The digital formats are robust enough, I remember reading about sending an AES signal along a piece of wet string. Blah blah! But we need to remember that cables and electronics effect the shape of a pulse wave used for sampling, try putting a square wave through a transformer to see that!

On a more philosophical note meself, considering how an audio signal is completely savaged by the digital process, and that we are all discussing audible differences at the very edge of our perception on how they are cut up and put back together. We're doing pretty well.

I dunno suppose we'd have to examine the way in which clock pulse onset effects the sampling process to have a definitive answer, and then there'd be another dragon to fear...

PaulBrewer · 27-01-2010 10:17pm

studiorat wrote: »

Anyway, all this talk of jitter seems a bit out of context I've been scanning over the thread and find no mention of what kind of jitter we are talking about.

Why, bad jitter of course !

madtheory · 27-01-2010 10:18pm

Apogee do a lot of "fooling" about cables...

studiorat · 28-01-2010 7:17pm

madtheory wrote: »

Apogee do a lot of "fooling" about cables...

anyone read the discussion about it with Dan Lavery on pro-sound web? About word clock "jitter free" cables? priceless...

woodsdenis · 28-01-2010 7:33pm

studiorat wrote: »

anyone read the discussion about it with Dan Lavery on pro-sound web? About word clock "jitter free" cables? priceless...

The Max Gutnik from Apogee who annoyed Dan Lavry so much in the thread is
one of the head honchos at Digidesign now.:eek:

studiorat · 28-01-2010 7:43pm

woodsdenis wrote: »

The Max Gutnik from Apogee who annoyed Dan Lavry so much in the thread is
one of the head honchos at Digidesign now.:eek:

Shakespearian isn't it?

madtheory · 30-01-2010 12:58pm

Clearly he's a good salesman...

madtheory · 28-02-2010 5:36pm

Bob Katz is endorsing the Grimm audio CC1 clock box, says it makes a 192 sound better. The Tape Op review linked to there makes interesting reading. I'm pretty certain he's tested the Big Ben in the past. Good to see scientific backup for external clock improving some converters.

studiorat · 01-03-2010 12:19pm

I was in a mates studio recently. Where we had an RME box, an SSL convertor and an Apogee Rosetta.

Connecting them all together using word clock in different combinations, apogee first, SSL and RME as slave. Then changing them all around.

Each time a square wave was recorded into all three machines. Thing was, on every recording in each configuration the Apogee was 30 samples ahead of the other two.

It was also pretty interesting to note the shape if the edges of the wave. But the real conundrum was that every time the Apogee was ahead by 30 samples.

madtheory · 01-03-2010 12:32pm

So the Apogee had the shortest delay? I hope so! Otherwise there was time travel going on!

Or maybe the Apogee was actually behind by several whole cycles plus 30 samples?

30 samples sounds like a lot for a digital routing? It would be about 30 to 40 with ADA. Idon't know, but there's some info here:
http://www.soundonsound.com/forum/showflat.php?Cat=&Number=811748&page=3&view=collapsed&sb=5&o=&fpart=1#811748

PaulBrewer · 01-03-2010 4:31pm

madtheory wrote: »

Bob Katz is endorsing the Grimm audio CC1 clock box, says it makes a 192 sound better. The Tape Op review linked to there makes interesting reading. I'm pretty certain he's tested the Big Ben in the past. Good to see scientific backup for external clock improving some converters.

Good to see too 'Science' is catching up with what some of us already knew

In fairness though, it was mostly 192s we heard and one instance of the SSL.
Interesting too, was the point they were making about different converters reacting differently.

madtheory · 01-03-2010 6:20pm

Seems to me that the Grimm is far superior to the Big Ben, which is why we heard no difference... I don't know the price of the Grimm, but it's probably still better value to change the 192 for a Mytek or a Prism.

PaulBrewer · 01-03-2010 7:18pm

madtheory wrote: »

so an external clock makes no difference whatsoever.

Have you changed your stance ?

madtheory · 01-03-2010 10:07pm

Almost! I want to hear a Grimm clock in action. I'm certain the Big Ben doesn't make a difference, it appears that the Grimm is just better than it. Maybe the Radar is too. I don't trust Apogee anyway

But I trust Bob Katz, he's changed his stance about external clocking in general- basically he's saying "it depends". That tape op article mentions noisy clock circuits as an explanation, very interesting.

PaulBrewer · 01-03-2010 10:12pm

madtheory wrote: »

Almost! .

GOTCHA!

madtheory · 02-03-2010 9:51am

RIght that's it. I'm never giving you my football again. And your mam is a hamster.

jtsuited · 02-03-2010 10:08am

this thread has delivered big time.

*goes hunting for more contentious issues for you lads to get stuck into* (although nothing more contentious than jitter/clocking stuff from what i've seen)

madtheory · 04-03-2010 11:52pm

I'm still at "almost". I have yet to hear it. I will try to get a Grimm clock. THe Big Ben definitely does not have an audible effect IME. More here:
http://www.jstage.jst.go.jp/article/ast/26/1/50/_pdf

madtheory · 07-03-2010 2:22pm

Just to clarify my postion- I have yet to hear a difference between internal and external clock. I am open to persuasion, via a blind A/B test. Don't take anyone at their word!

Bob Katz's latest test with the Grimm shows that there might be difference. The research pdf I linked to above is from 2005, and brings the audibility of jitter into question:
In order to determine the maximum acceptable size of
jitter on music signals, detection thresholds for artificial
random jitter were measured in a 2 alternative forced
choice procedure. Audio professionals and semi-professio-
nals participated in the experiments. They were allowed to
use their own listening environments and their favorite
sound materials. The results indicate that the threshold for
random jitter on program materials is several hundreds ns
for well-trained listeners under their preferable listening
conditions. The threshold values seem to be sufficiently
larger than the jitter actually observed in various consumer
products.

However they only sampled 24 people.

madtheory · 18-03-2010 2:04pm

Bruno Putzeys's, ace electronics designer:

http://recforums.prosoundweb.com/index.php/mv/msg/14361/246388/2432/

madtheory · 24-05-2010 9:31am

Hugh Robjohns, SOS this month (requires esub):

http://www.soundonsound.com/sos/jun10/articles/masterclocks.htm

Echoplex · 28-05-2010 9:00pm

BK:We conducted a blind test at Phat Planet with 8 listeners,
10 trials each — a total of 80 trials. Chief engineer Aaron
Gandia and I carefully chose the source material, trained the
listeners, and presented the comparisons in a way that made
it as easy as possible to detect the differences. Nevertheless,
a rigorous blind test is extremely hard to make, especially with
such subtle sonic differences; while I took the test I found
that if I lost concentration for even a moment, I could easily
make a mistake.

So slightly over half a panel of 80 listeners, were 'trained' in a process. Trained not to make a 'mistake' perhaps.
How can you make a mistake on a blind test?

The details of this blind test are also omitted. Slightly over half it seems could reliably identify the Grimm. As better or worse, or just identify? There are a handful of praise comments, not 60%

Here's a reasoned comment from Hugh

http://www.gearslutz.com/board/high-end/495010-new-clock-7.html

DD

MilanPan!c · 28-05-2010 10:34pm

This:

"To be fair -- and as my tests have shown -- the measureable artefacts produced when operating an A-D on an external clock are small, but I would suggest that their anharmonic nature makes them far more audible than the raw figures would suggest. But even so, the sonic differences are nothing like as chalk and cheese as they once were. Give it another five-ten years and I expect this issue will have been cracked too... There are enough products out there already now to prove that external clocking can be done without unwanted side effects if it's done right. It just needs more people to learn how to do it right.

Regarding the rest of this long and often combative thread, it is very clear from my own qualitive and subjective tests, as well as general user feedback, that external clocking can and often does result in an audible change. It's usually a subtle change, but many people can hear it and it seems that some people actually like the change.

I have no problem with that. Some people like heavily distorted guitars and pop music with no dynamics whatsoever. Each to their own....

But the tests we've published in Sound On Sound (and which several high end manufacturers and well established 'experts' agree with and support) also demonstrate very clearly that external clocking doesn't improve the performance of A-Ds in any technical, measureable sense. Quite the reverse, in fact. Noise and distortion increased in almost every case.

And that's the long and short of it. If someone prefers the sound of their system when running on an external clock, that's fine. SOme people like the higher noise and distortion levels of certain equipment purely becaues of the character it brings to the party. That's fair enough. I'm not going to argue with their perception. If they claim that they think it sounds subjectively better that way, then that's fine too -- it's their personal perception, after all, and music is all about perception and mood and art. which is an inherently personal thing."

External Clocking - is it all that?

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