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[bushwick]

Has anyone still using mix tried out the big ben with their AD8000's? Any comments here?

Thanks,
joshua kessler

[Roland Storch]

Uuuuuuuh, not again Big Ben.
Apogee seems to make a real good marketing strategy on BB.

Also the AD8000 should work better clocked internally. Safe the money.

[snakecained]

Agree that Apogee have pushed this quite hard. However I have tried this and there was some improvement in the sound although not hugely.

I always think Ben is most useful when you have a lot of digital devices and not so important if you have just one or two.

Try before you buy??

[bushwick]

Generally, yes, try before you buy. If my question received 20 replies with laughter, I would be less inclined to give it a whirl. As it stands, I am somewhat inclined. Should I do it, I'll give a report. Today, however we are beta testing some new input amps and transformers for my console. That should prove interesting.....probably post that in Klett.

Thanks,
joshua kessler

[danlavry]

bushwick wrote on Thu, 02 June 2005 14:54

Generally, yes, try before you buy. If my question received 20 replies with laughter, I would be less inclined to give it a whirl. As it stands, I am somewhat inclined. Should I do it, I'll give a report. Today, however we are beta testing some new input amps and transformers for my console. That should prove interesting.....probably post that in Klett. Thanks, joshua kessler

Whenever possible, use internal clock for AD's. You may have to use external, when synchronizing more AD's that can be contained within one chassis, but "all things equal", you end up with more jitter when using external clocks.

Placing a good low jitter clock inside the AD chassis, next to the AD converters, is the best you can do. If you place the same circuit in another chassis, you will end up with a lot more jitter, because the clock path to AD connection contains a driver, cable, receiver and a PLL circuit, all adding jitter.

Whenever you use clock switching and distribution, you are getting away from internal clocks into the cables and PLL world. A good PLL circuit can help a lot but as a rule, will be a step down from internal clocking, thus a compromise of jitter for more channels.

Also, an external clock can not fix or improve your AD jitter problems because it does not know what is needed inside the AD box. My doctor can not help me if he lives in a different state and I do not talk to him ever. The same thing for external clocks and AD's: The AD does not send the clock box ANY INFORMATION about what it needs to be improved. The cable between clock and AD is for sending a clock FROM the clock TO the AD. No information goes from AD to the clock.

In fact, when operating with external clock, the jitter added due to the extra hardware (drivers, cable pickup of unwanted noise, receiver, PLL circuit) is so much higher than an average crystal clock circuit, that the difference between one external clock and another becomes difficult to impossible to tell.

In other words:

A 1psec clock source accumulating additional 50psec (driver, cable, receiver, termination issues, pll circuit) amounts to 50.01psec at the AD input.

A 10psec clock source, accumulating additional 50psec random jitter (driver, cable, receiver, termination issues, pll circuit) amounts to 50.99psec at the input of the AD.

But internal 10psec clock (no driver, no cable, no receiver, no termination issues, no pll circuit) will yield a 10psec performance.

So save your money...

But if you still need clock distribution and switching, there are many comments in my bag. But it will be a very long writeup, so I will stop for now.

Regards
Dan Lavry
www.lavryengineering.com

[bushwick]

Very kind of you Mr. Lavry. Very kind. Well that is on par with what I have read in your column yet the question still remained that I am clocking three AD8000's off of one master (4 converters) and would the overall benefit remain, assuming that perhaps the big ben is a better clock for external driving than the one in the AD8000. Clearly if I had one converter only, this would not be in question, but where do the tradeoffs begin if you catch my meaning?

If you can answer feel free to be concise. I feel badly taking up your time.

Thanks,
joshua kessler
bushwick studio
brooklyn, ny
www.bushwickstudio.com

[danlavry]

bushwick wrote on Thu, 02 June 2005 21:16

Very kind of you Mr. Lavry. Very kind. Well that is on par with what I have read in your column yet the question still remained that I am clocking three AD8000's off of one master (4 converters) and would the overall benefit remain, assuming that perhaps the big ben is a better clock for external driving than the one in the AD8000. Clearly if I had one converter only, this would not be in question, but where do the tradeoffs begin if you catch my meaning? If you can answer feel free to be concise. I feel badly taking up your time. Thanks, joshua kessler bushwick studio brooklyn, ny www.bushwickstudio.com

The issue boils down to details including specifications and numbers. A funny thing, if there is one single specification number I would want to see, it would be the jitter number. It is the MAIN ISSUE. After all, what do you expect from a clock? The signal goes up and down and up and down and…. It is a simple square wave, not a complex thing… You just want to know how repetitive that “up down” is, not much to ask for. But don’t hold your breath. Some clock makers say next to nothing, others tell you about cures for the jitters, testimonials, features, subjective claims about sonic improvements…

So I will do my best to answer “without the numbers”. In my opinion and experience, there is no way on earth that you can have a high speed cable driver, 6 foot non rigid coax cable of the highest quality, termination (for the cable) and a clock receiver IC and not pick up some jitter. Let us be optimistic and agree that you pick up only 50psec jitter (that would be great). Let’s call it the “link jitter”.

Now we need to combine the jitter coming out of the “Clock box” of your choice to the link jitter. But I said “combine” instead of add because when dealing with random phenomena, you do not go for a direct addition.  Adding 2 equal sine waves doubles the signal, but adding 2 equal amplitude (on average) random signals increases the magnitude by only 40%. Sometimes the random signals enforce each others, other times they oppose each other….  When you take a random source A with amplitude 1, and B with amplitude 2, the combined outcome is 2.236

For A=1 and B=1  the outcome is 1.414  
For A=1 and B=2  the outcome is 2.236  
For A=1 and B=3  the outcome is 3.162
For A=1 and B=5  the outcome is 5.099
For A=1 and B=10 the outcome is 10.05

You can see that when one random source (B) is only twice as big as the other (A), the outcome is already almost completely up to the noisy one (B). By the time B is 3 times noiser than A, the contribution of A is "near negligible" ….

So having stated the above, lets get back to jitter. The big jitter is the “link jitter” (this is our B) and we "agree" it is 50psec (on a good day). So how much jitter can you afford to have from our clock source (this is out A)?

A clock source with 1psec jitter and a 50psec jitter link combine to 50.01psec

A clock source with 10psec jitter and a 50psec jitter link combine to 51.0psec

A clock source with 20psec jitter and a 50psec jitter link combine to 53.9psec

A clock source with 30psec jitter and a 50psec jitter link combine to 58.3psec

In other words, the difference between a 1psec clock and a 10psec is a change of 1psec. I would not pay for a 1psec clock source.

The difference between a 1psec and a 30psec clock is 8.3psec. Is that worth spending money for?

Keep in mind that most crystal oscillators, including the lowest cost clocks on the market will yield better than 30psec.  

I would simply buy a low cost clock source, and put the attention into a WELL SPECIFIED cable and a good termination.

Regards
Dan Lavry
www.lavryengineering.com

[bushwick]

Thank you for the very meaningful reply Mr. Lavry.

Very Best,
joshua

[Yannick Willox]

May I add that - in my case - using 3 units of Soundscape IO896 (8 ch AD/DA - co designed by Apogee) and using ONE of them as the reference clock gives me the great advantage that I can have my main mic/solo mic/main support mic on the 8 channels with the internal clock.

For me that is a big argument against using an external clocking device.

[AB7]

With all respect Mr. Lavry, because you know one hundred times more than I do, I have a Lynx Aurora.  I recorded with it as a master and with the Lavry Blue as a master clock to it.  The recording definitely sounds better clocked to the Lavry Blue.  Yet the Aurora is suppose to have a good clock.  I have to assume that the ears mean more than the theory?   There are several other people who heard the same comparisons and draw the same conclusion that the Lavry clock improved the AD of the other unit.

[michal @ mytek]

AB7 wrote on Thu, 09 June 2005 18:21

With all respect Mr. Lavry, because you know one hundred times more than I do, I have a Lynx Aurora.  I recorded with it as a master and with the Lavry Blue as a master clock to it.  The recording definitely sounds better clocked to the Lavry Blue.  Yet the Aurora is suppose to have a good clock.  I have to assume that the ears mean more than the theory?   There are several other people who heard the same comparisons and draw the same conclusion that the Lavry clock improved the AD of the other unit.

It could be a possibility- it really depends how clocking of actual AD and DA chips implemented. It might be better it might be worse it really depends on the design of particular AD/DA box.

Another issue here could be- are you indeed sure it's better?

The best test to answer which is really better (or rather "transparent") in this particular case of jitter would be to do a THD test with Audio Precision. You'd  see jitter effect in such test.

If you use your ear - it's good to gain some experience what jitter does- the effect depends a bit on the converter used but generally upper midrange gets emphasize with small amount of jitter and some people think it is good, because some things will jump forward, but this is just an euphonic distortion. Then as you increase jitter the top loses clarity, bass gets less tight and eventually the stereo image collapses inward.

The "better" you pick , might not be the more transparent one. It depends. The issue has few factors one has to be aware of to draw the right conclusion about clock.

Our Stereo96DAC has two modes of clocking. Flipping a switch btw incoming clock and internal is almost equivalent to listening to signal with some jitter vs no jitter.  It's an interesting exercise to try that on different playback material. Not always is the one "without" jitter "better".

Regards, Michal www.mytekdigital.com

[zmix]

hmmm..... music so boring that the jitter is the only thing keeping the brain engaged...