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Author Topic: Syncing AD via SPDIF  (Read 2551 times)

prairiedog

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Syncing AD via SPDIF
« on: October 09, 2004, 10:52:07 am »

When, on accasion, I'm working on a DAW with no word clock in/out and syncing the DAW to external SPDIF (or ADAT lightpipe), what exactly are the sonic penalties?

This seems to work fine in practice, but will I spend eternity in a lake of fire?

Lovin' the Lavry Blues!
Jason Keillor
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bobkatz

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Re: Syncing AD via SPDIF
« Reply #1 on: October 09, 2004, 03:03:18 pm »

prairiedog wrote on Sat, 09 October 2004 10:52

When, on accasion, I'm working on a DAW with no word clock in/out and syncing the DAW to external SPDIF (or ADAT lightpipe), what exactly are the sonic penalties?

This seems to work fine in practice, but will I spend eternity in a lake of fire?

Lovin' the Lavry Blues!
Jason Keillor



Jason, I can't tell you where you are spending eternity, but rest assured, AES or SPDIF sync are perfectly legitimate.

As long as you are not processing analog. In other words, as long as you are mixing in the box, there should be no audible consequence whatsover.

But you may, depending on the susceptibility of your listening DAC, find apparent audible differences that are really not there at all. What I call "ephemeral jitter". Get a jitter-resistant DAC, mix in the box, and don't care what sync you are using!

The real trouble in audibiity problems with different sync methods starts to happen when using external analog processors, or mixing outside the box.
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J Schroder

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Re: Syncing AD via SPDIF
« Reply #2 on: October 09, 2004, 08:51:43 pm »

The real trouble in audibiity problems with different sync methods starts to happen when using external analog processors, or mixing outside the box.

Bob-

I have been using a Mytek Stereo96 DAC for monitoring, using the DAC's clock as the master.  The only outboard processor I have is a Z-Qualizer.  I have just acquired another Mytek DAC which will come after the Z-Q and before an analog processor, an Avalon 747.  A Mytek Stereo96 ADC will come after the 747 and input into the DAW.

I haven't set any of this up yet, so my question may be premature.  My question is, what should my clock setttings be on the three converters?  The outputs and the inputs of the DAW are RME cards, which so far with just the Z-Q have been set to AutoSync.  Now, putting the 747 in the chain, after the Z-Q and input DAC, I assumed that the input DAC would be set to master, the output ADC would be set to internal, and the RME cards would remain at AutoSync.  The monitoring DAC would remain at master.  Does this seem correct?

John
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bobkatz

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Re: Syncing AD via SPDIF
« Reply #3 on: October 09, 2004, 11:26:57 pm »

J Schroder wrote on Sat, 09 October 2004 20:51

The real trouble in audibiity problems with different sync methods starts to happen when using external analog processors, or mixing outside the box.

Bob-

I have been using a Mytek Stereo96 DAC for monitoring, using the DAC's clock as the master.  





Good questions. Michal designed the interconnections between the DAC and ADC so that the DAC could contain the master clock and reportedly this really helps on the jitter situation (as the DAC no longer has to deal with the PLL as its clockbase). But I only know this to be the case with their 8 channel unit, so I cannot speak how this relates to their particular 2 channel unit.

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The only outboard processor I have is a Z-Qualizer.  I have just acquired another Mytek DAC which will come after the Z-Q and before an analog processor, an Avalon 747.  A Mytek Stereo96 ADC will come after the 747 and input into the DAW.

I haven't set any of this up yet, so my question may be premature.  My question is, what should my clock setttings be on the three converters?  The outputs and the inputs of the DAW are RME cards, which so far with just the Z-Q have been set to AutoSync.  Now, putting the 747 in the chain, after the Z-Q and input DAC, I assumed that the input DAC would be set to master, the output ADC would be set to internal, and the RME cards would remain at AutoSync.  The monitoring DAC would remain at master.  Does this seem correct?

John


Won't work, John. In your above scenario you've proposed two masters.

Unless either the processing DAC or the processing ADC are set to external, then your above scenario will break down. (What you call the "input DAC" I'm calling the processing DAC.

BL
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prairiedog

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Re: Syncing AD via SPDIF
« Reply #4 on: October 10, 2004, 11:15:17 am »

Thanks Bob -- You should have a forum here, you've clearly answered more tiresome questions than a high school sex-ed teacher...

JK
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bobkatz

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Re: Syncing AD via SPDIF
« Reply #5 on: October 10, 2004, 11:55:17 am »

Thanks for your wonderful comments! I try to explain things simply because otherwise they're too hard for me to understand either!

Let me give you as an example, my own processing and clocking route as a kind of "template" that might help you. There are many variations on this, of course.

Assuming we're starting with a 44.1 kHz EDL in SADiE:

SADiE is on External Sync (you'll see where this is coming from in a moment)

SADiE's output 3/4 feeds an independent "jitter immune" DAC

This DAC feeds external analog processors

Analog processors return via Cranesong HEDD A/D on Internal Sync (Cranesong performs best on internal sync) running at 96 kHz. This effectively upsamples the rest of the chain to 96K and also allows the HEDD's digital processing to run at 96K, which reduces alias distortion (basically the HEDD sounds better this way).

Digital output of Cranesong feeds a chain of digital Processors

End of line of Digital processors at 96K is downsampled back to 44.1K in the Weiss SRC

This 44.1K signal returns into SADiE, which is effectively slaved to the downsampled clock from the HEDD, which also functions as the master clock for SADiE in this situation. And I can can cut a CDR master or reference LIVE this way. One hour after hitting play, the client gets a master! If I'm running my automation. But if the analog processors need to be adjusted on each song, or for some reason some function cannot be automated, then it becomes a song-by-song capture first, followed by cutting to a CDR master.

There are many variations on this scheme, depending on the sample rate in the EDL. If the EDL is NOT at 44.1K, then I capture the 44.1K output in Wavelab, acting like an independent "tape recorder", and I also make a simultaneous 24 bit, higher sample rate capture in SADiE for future DVD release, etc.

Of course I do not use analog processing all the time, nor do I use digital processing all the time.
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