Hi everyone.

I am faced with a connectivity dilemma that I'm hoping I can get some advice on. My week of scouring the net for info has enlightened me somewhat, but still hasn't made me certain about the route to take. Your suggestions will help influence my purchasing decision. (Thanks in advance)

I currently own a Focusrite Liquid Channel and am about to purchase a new soundcard. I have decided to go for a MOTU - Either an Ultralite Mk 3 Hybrid (USB & Firewire) or an 828 Mk 3. They are at different price points and offer a differing feature set.

I would like to allow my Liquid Channel to do the A/D conversion and then stay in the digital domain by connecting the Liquid Channel's AES/EBU I/O to the MOTU's S/PDIF I/O. I own a converter box which handles the voltage change (the actual formats are practically the same), but am wondering about how to sync these 2 devices. I could use the AES/EBU - S/PDIF inbuilt clock, but have come across plenty of suggestions on the net that it's flawed - The audio and word clock data is piggy backed in the same signal. Jitter is an issue.

The Liquid Channel offers Word Clock out which I thought would be better to use as a sync source. Does it offer any benefits over S/PDIF in this simple device - device application? If I use wordclock, does that mean that the AES/EBU - S/PDIF connection no longer sends clock information and is strictly a digital audio stream? My goal is to keep the signal path as pristine as possible.

The 828 is the more comprehensive soundcard (and, as such more expensive) offering word clock sync, whereas the Ultralite only has S/PDIF to sync to. The only reason I would consider the 828 is for the wordclock, but if wordclock offers no advantage in this application, the Ultralite is perfectly fine.

I hope I've explained what I mean well. Please ask if you need further info.

I'd be grateful for any clarification that can be made on clocking in this respect.

Thanks.

Rich

I also have a couple of Liquid Channels and I link them digitally to an RME Fireface 800.

I like to use wordclock (from the FF as master) where possible, since the clock signal is not having to share its connection with audio data. This said I have to share the FF's digital connection with several bits of gear, so I've become a bit lazy of late and just let everything clock from the AES connection - and I've noticed no audible difference.

Not a definitive answer by any means, but as one who had similar concerns I now rest easier on the subject.

Enjoy the LC. It's a great pre - and fantastic to put in an external effects loop using the digital I/O.

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An Eagle for an Emperor, A Kestrel for a Knave.

Quote blastmasterd:

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... but have come across plenty of suggestions on the net that it's flawed - The audio and word clock data is piggy backed in the same signal. Jitter is an issue.

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Those suggestions are wrong, or you've misunderstood them.

Yes, the clock is embedded along with the audio data in the AES-3 and S/PDIF interface formats. And yes, this arrangement can lead to measureable interface jitter.

However, in your situation, with the Liquid Channel running as the clock master that (very small amount of) interface jitter it will have no effect on the sound quality whatsoever because that embedded clock is being used purely for passing the data from one digital device to another, and not directly for any analogue conversion which is the only place jitter is relevant (assuming it is not astronomically bad...). Added to which any decent interface should be capable of removing interface jitter with out too much problem these days.

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The Liquid Channel offers Word Clock out which I thought would be better to use as a sync source. Does it offer any benefits over S/PDIF in this simple device - device application?

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No. You could use it as an alternative to the embedded clock if you really wanted to, but it would offer no advantage.

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If I use wordclock, does that mean that the AES/EBU - S/PDIF connection no longer sends clock information and is strictly a digital audio stream?

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No, the embedded clock is an integral part of the data stream and it is always there... wherther you'r receiving device is making use of those clocks or not.

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The only reason I would consider the 828 is for the wordclock, but if wordclock offers no advantage in this application, the Ultralite is perfectly fine.

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Then go for the Ultralite.

Hugh

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Technical Editor, Sound On Sound

Good afternoon Gentlemen.

I'd like to say thank you for clearing up this confusion for me. It's been a bit of a minefield to navigate.

What a great place this is to come to get practical expert advice on such matters. You've made my decision so much easier to make.

Cheers.

Have a good weekend.

Rich

As a general rule, it is usually better to have your main convertor as the clock master as most convertors have less jitter when working from their internal clock.

Cheers

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net