Digital interfacing FX.....problems

[Jay]

I have started interfacing my external FX units with PT via AES but have discovered this is causing audible clicks.
Should I be using an external clock referance.Not all of my FX units have word clock inputs (namely the DSP4000), I know AES is supposed to carry word clock info but I'm still hearing clicks and pops which I know to be a sync problem.What does one do if there is no word clock input.
Which master clock generators are good (has to be able to generate video B&B)
btw. Where does pro tools take its own referance from, the mac or the 888.

[DigiTechSupt]

The Pro Tools clock is in the audio interface, 888 in your example.

You are correct that the AES digital signal can carry clock. An important thing to point out is that the 888 will only recognize that AES clock on input 1 so, your digital device needs to be connected to AES input 1 (&2).

Also, depending on how you've got things configured, Pro Tools and the 888 should be set to "digital" sync mode. As you mentioned, with word clock, black burst, etc. there are potentially other ways to deal with this but this should help, if not let me know.

Jon Connolly
Digidesign Product Specialist

[Jules]

So what about the other 3 stereo AES inputs then?
Jules

[DigiTechSupt]

The other three AES ins and outs (channels 3 thru 8) are usable for any digital device they just can't be used to "clock" the Pro Tools system.

Again, there are several ways to use these ins and outs but the first that comes to mind is using them with any digital device that can be resolved to word clock, Black burst, etc. Make sure that Pro Tools is either the master or that it is getting it's clock from the same source.

Bottom line in connecting two or more digital devices digitally is that there must only be one clock. Depending on what gear you have, the choice of which device is the master and which are the slaves is yours. That decision, however, is often made for you by the capabilities (or limitations) of the digital devices you are using.

Most multitrack digital devices that I know of only use channel 1 in and out for AES "clocking" info, all other ins and outs are for digital data (your music).

Jon

[Robert U]

I have a Finalizer and a PCM91 and a coupe of 888/24. If I want to connect the units with AES/EBU... Should I only use input 1&2 on the interfaces?


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Robert

[Nick Batzdorf]

I'm a little confused by Jon's advice. If the fx unit is simply clocking to its input, why should PT be set to sync to the fx output?

It seems to me that the 888 should always be the master - unless you have distributed WC, in which case you also don't want to put the 888 in Digital Sync mode either.

(And I can in fact hook up NuVerbs, which have no WC input and don't generate digital clock, to 888 I/Os 3-8 without a problem.)

[Peter Duemmler]

The same here. No problems with a PCM90 on 3/4, a PCM80 on 5/6 and a NuVerb on 7/8.

Peter

[Ang1970]

Jay,

I suspect the problem is with configuration of your fx.

On the dsp4k, press setup, then the 4th softmenu key for audio options. Make sure the unit is properly receiving and sending aes format at the right sample rate. The 888 should be set to internal sync, and digital input. If the eventide is sending at the same rate it receives, there should be no pops. If that doesn't work, check your cables. Plain ol' mic cables don't always work - proper impedance is important, so make sure you get cables marked specifically for use with AES digital. Same goes for any s/pdif connections.

Check your manuals of the other fx and make sure they are also set up to slave to incoming sync and outputting at the same rate.

If you've already done that and it still doesn't work, run through all your sync and interface cables with a fine tooth comb... etc... you know, troubleshooting 101.

Posting more information about your setup could help too.

Good Luck.


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Angelo Quaglia
AQ Productions