Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[dyno]

I've noticed that some of the high end A/D boxes don't have lightpipe output (HEDD/192 for example). Is that because AES is more stable than optical? If so, is the difference even audible?

Thanks,

dyno
Fertile Ground Studios

http://www.dougploss.com

[Nika Aldrich]

The difference is only audible under two conditions:

1.  You have gross error, meaning that the wrong bits get recognized at the wrong times because you are running too long of a cable length and getting too much degradation.  Note: rare - almost always a broken box or too long a cable.

2.  You are using the signal heading down the cable to clock a crucial component with (A/D, D/A or aSRC converters).  Optical induces a lot of jitter.  We try to avoid that if the clock signal heading down the cable will be used for critical purposes.

Nika

[jfrigo]

dyno wrote on Mon, 06 December 2004 19:23

I've noticed that some of the high end A/D boxes don't have lightpipe output (HEDD/192 for example). Is that because AES is more stable than optical? If so, is the difference even audible?

A quick clarification apart from Nika's answer. Optical does not necessarily mean lightpipe. Lightpipe is an Alesis format that sends 8 channels of digital audio using the optical connector. Other equipment sends stereo (2 channel) AES or SPDIF from an optical connector, and that is not lightpipe. Generically it's called toslink.

[Nika Aldrich]

A clarification on Jay's clarification.

Optical devices in our industry use two types of connectors.  One is called Toslink and it is a squarish connector, about 1/4" by 1/4."  The other type is about the size of a 1/8" minijack connector.  The toslink connector is used for SPDIF and ADAT lightpipe signals, carrying 2 and 8 channel information respectively.  The other connector is used for SPDIF on occasions - mostly on consumer equipment.  

Either way, the optical format itself causes enough degradation that cable lengths have to be watched and wordclock running down the cable (embedded in the signal) will generally suffer.

Cheers!
Nika

[jfrigo]

Nika Aldrich wrote on Mon, 06 December 2004 22:31

A clarification on Jay's clarification. Optical devices in our industry use two types of connectors.  One is called Toslink and it is a squarish connector, about 1/4" by 1/4."  The other type is about the size of a 1/8" minijack connector.  The toslink connector is used for SPDIF and ADAT lightpipe signals, carrying 2 and 8 channel information respectively.

I guess we could keep clarifying 'til the cows come home, so what the heck? Why not one more?

There's nothing to prevent you from sending AES data through toslink. It's not like non-SPDIF data gets lost in the ether, though one does usually expect to see an XLR connector for AES. As Dan was mentioning in another recent thread, you can often use an XLR to RCA adapter with no transformer and make AES more or less into workable SPDIF.

This sure leaves open room for clarification... or I guess at this point we should probably call it elaboration!  (for those who feel compelled, please mentally insert smiley emoticon here)

[Nika Aldrich]

I believe that AES, by definition (or spec, rather) is a balanced signal?  SPDIF can go down balanced cables, and we've seen many devices like this, but I believe that it isn't really AES if it's heading down an unbalanced cable.  I think it inherently becomes SPDIF.  SPDIF inherently carries more data - it is AES with extra info.

Nika

[Bob Olhsson]

First off, there is an unbalanced AES specification that uses BNC connectors. It's called AES-3 if I remember correctly. There is also AES-EBU which requires transformer isolation on both ends.

SPDIF differs from AES in voltage level, the bit-depth supported and all of the flags indicating a number of properties.

Compatibility between the two is entirely up to the transceiver chip manufacturer and ultimately the equipment manufacturer. Most contemporary gear can handle either one interchangeably although SPDIF needs to be cheated a bit in order to accommodate 24 bits.

[danlavry]

Bob Olhsson wrote on Tue, 07 December 2004 15:54

First off, there is an unbalanced AES specification that uses BNC connectors. It's called AES-3 if I remember correctly. There is also AES-EBU which requires transformer isolation on both ends. SPDIF differs from AES in voltage level, the bit-depth supported and all of the flags indicating a number of properties. Compatibility between the two is entirely up to the transceiver chip manufacturer and ultimately the equipment manufacturer. Most contemporary gear can handle either one interchangeably although SPDIF needs to be cheated a bit in order to accommodate 24 bits.

Yes, but it is not difficult to shove 24 bits on SPDIF. But one needs to “get the various flags and status bits in order at some point later (part of the mastering, I believe).
And I have not seen any digital audio transmitters or receivers lately that could not handle both AES and SPDIF
   
Regards

Dan Lavry

[dyno]

Ok guys...

Practical question here...

For right now I need to stay with ADAT lightpipe. I'd have to spend about 3K in new cards and cables without really knowing if there will be an audible difference. I'd rather be blowing that money on a couple more 1176's!

I would probably be better off at this point to  pick up some high quality glass cables, keep my run as short as possible, and put them where I need it most.

And where is the most critical place? Tracking, playback or both?

A/D >>>>>>>> HDR >>>>>>> Digital console

Thanks,
dyno

Fertile Ground Studios
http://www.dougploss.com

[danlavry]

dyno wrote on Wed, 08 December 2004 01:38

Ok guys... Practical question here... For right now I need to stay with ADAT lightpipe. I'd have to spend about 3K in new cards and cables without really knowing if there will be an audible difference. I'd rather be blowing that money on a couple more 1176's! I would probably be better off at this point to  pick up some high quality glass cables, keep my run as short as possible, and put them where I need it most. And where is the most critical place? Tracking, playback or both? A/D >>>>>>>> HDR >>>>>>> Digital console Thanks, dyno Fertile Ground Studios http://www.dougploss.com

Glass is better than plastic, Single mode fiber is better than multi mode, short cable is better than long, and if you can run the AD on internal clock, the most critical connection is the playback one leading to the DAC. Otherwise, if you run the AD sync clock on a fiber, it becomes the most critical connection, than the DAC connection becomes second most importent. The data transfer from AD to computer is not critical at all.

BR
Dan Lavry

[dyno]

Dan, thank you for your reply, but I need some clarification for my rig:

I am running A/D directly to Mackie HDR. You say the quality of that cable is not critical.

I have 3 ADAT cables output HDR to input Mackie D8B. What about those? No D/A going on there...

I have no lightpipe D/A going on at all...I run out of mackie AES > HEDD D/A > analog gear > HEDD A/D spdif out to Wavelab.

I believe you are also correct about using the A/D converter's clock as master for best results.

Thanks,
dyno
Fertile Ground Studios
http://www.dougploss.com