External clock source

I was using my Vamp-Pro as an external clock source for my FW-1884. I did this because I was using the digital out of the VAmp. But, I was having some problems with intermittent pops and clicks the audio stream. For the most part the noise was pretty rare, but when I started using P52 as a rewire instrument it really became a problem. So, I decided to simplify my setup in order to get to the root of the issue. Since I did not have to use digital out on the VAmp I removed the digital out and the clock source to the FW-1884 and set the FW-1884 to use its internal clock.

All the pops, clicks and wierd distortion went away. P52 worked flawlessly as a Rewire client. In fact my setup has never ran smoother!
Is it possible that the VAmp was just a bad clock source? Are there inherent risks in using an external clock source? Should one only use an external clock source from one of those expensive dedicated clock units?

ORIGINAL: jyoung

I was using my Vamp-Pro as an external clock source for my FW-1884. I did this because I was using the digital out of the VAmp. But, I was having some problems with intermittent pops and clicks the audio stream. For the most part the noise was pretty rare, but when I started using P52 as a rewire instrument it really became a problem. So, I decided to simplify my setup in order to get to the root of the issue. Since I did not have to use digital out on the VAmp I removed the digital out and the clock source to the FW-1884 and set the FW-1884 to use its internal clock.

All the pops, clicks and wierd distortion went away. P52 worked flawlessly as a Rewire client. In fact my setup has never ran smoother!
Is it possible that the VAmp was just a bad clock source? Are there inherent risks in using an external clock source? Should one only use an external clock source from one of those expensive dedicated clock units?

Yes, I'm sure the Vamp clock is lesser quality then the FW-1884. Digital interfaces like SPDIF, ADAT, AES, etc are a pain in the @. And in almost all cases your sound card should be the master clock. The only problem is digital audio interfaces are single direction only so the only way you can clock from the FW-1884 is if you have another cable connected the other direction like SPDIF or word clock. Even then you are limited to the highest sample rate the Vamp can do. In fact all devices and your project have to be set for the same sample rate. So I would just use the analog outs of the Vamp unless it has a word clock in and the FW-1884 has a word clock out.

You are only dealing with two devices trying to interface digital, when you get to three it's even harder.

Ok, I just checked and it looks like the Vamp does have word clock in. So you need to get a word clock cable (62ohm coax with BNC connectors) and connect from the FW1884 word clock out to the word clock in on the Vamp. Then set the Vamp to get clock from the word clock input and you should be good to go. Oh, and you still need the SPDIF hooked up out of the Vamp in to the FW1884.

Thanks for all your advice. I've decided to simplify things and going with just using the audio out of the Vamp into the FW-1884 and using the FW-1884 internal clock.

Jeff:
Thanks - I would like to get the DM24 back to all digital - so I'll look through the manual to explore slave and master settings. Any opinions on the 2408 as a master clock?

-D

The single most important step I took within my Studio setup was to incorporate an Aardvark Master Clock Generator & the matching Distribution unit.

Yes, I looked at that option but I my budget would not justify it for such a small home studio as mine.

Hi Frank,

You seem pretty experienced with the digital sync stuff and I have a question I always wanted to ask...how does SPDIF decide what is "master" or "slave" if neither device has a selection for it? It has always intrigued me as every part of my system clocking makes sense except the connection between my J-Station and one of my Yamaha DSP Factory cards.
J-Station has an SP/DIF out, i plug that into the DSPF SP/DIF in. THe DSPF is definitily NOT syncing to it(it is configured to internal sync) so the only explanation I have is that SP/DIF outs always sync to SP/DIF in's. I guess I should do something like go read the spec I guess... Anyway, figured you might have some insight. I actually have my little home studio working great without wordclock but if I could afford it, I would use it. I have only two other devices(a second DSPF and an AI3) and both of them sync to the master DSPF flawlessly. The only quandry for me has been "WHY does the J-Station digital out work?".

Howdy....

Actually, neither T/DIF or ADAT lines pass word clock. Word clock is very different than using your digital connection for a timing source. You can certainly send or receive timing info through an ADAT or T/DIF connection, but that is not word clock. For example, on a DM24 you have the digital optioins page, where you can set your timing reference to: Internal, External Word, ADAT, or T/DIF. Another example is the Echo Console for my Layla24: timing can be set to Internal, ADAT, S/PDIF, Word, or MMC.

Timing reference is much more accurate using word than a digital input signal. If you have more than one piece of gear communicating digitally, an single external source distributing word clock is really the best (only) way to ensure you're not getting jitter and lost data (the pops and clicks are obvious examples of jitter). The downside is that a really good external clock like the Apogee Big Ben is generally pretty expensive, although I got my Lucid Gen/X on Ebay for around $350/US.

And for the record, I guarantee the clock source in the Behringer is lousy. Digital timing is one area that you really do have to spend the money to get it right - BNC cables should always be the best you can afford, the clock should use the highest quality crystal elements, blah blah blah....

Conrad St. Clair
www.kicksville.com

ORIGINAL: kicksville

Howdy....

Actually, neither T/DIF or ADAT lines pass word clock.

Whilst you may be technically correct in that statement as regards ADAT, it's not strictly true with reference to TDIF.
The sync reference through TDIF is actually called LRCK and is passed through separate pins of the TDIF cable (5 for LRCK out and 9 for LRCK in). It is therefore not extracted from the digital audio stream such as with SPDIF or ADAT but passed down separate cables much as Word Clock is.

Word Clock and LRCK are just about interchangeable in every respect other than, in some circumstances, phase which may be 90 degrees out. As such the Mixtreme allows phase to be selected from a menu.

Manufacturers, such as Tascam themselves, often refer to LRCK as Word Clock in their literature so who am I to argue with them?