Sync question

[Cryos]

I have two protools rigs, one HD NATIVE + omni and 2 x 192 digital I/O's with a sync HD and a second protools 9 + cptk system with a presonus lightpipe interface.

I use the PT 9 as a dubber, here's my question: why when I slave the pt9 second system which is locked to "word clock" and Midi Time code the re-recorded stems are early by 1/2 or a 1/4 frame exactly depending on whether I've disabled delay comp on the dub system? All audio is transferred via Lightpipe via the 192's into the presonus interface.

As for sample accuracy of punches... all punches match up to the sample, no anomalies there. Any ideas folks. How can digital audio come in early?!

[Frank Kruse]

Are you sure that PT resolves midi-TC correctly to the clock?

AFAIK, it can only do this properly with LTC.

I'm not 100% sure but I don't think you can maintain TC edge sync with midi-TC.

Maybe that's the cause. It's probably not the audio that's coming in early, it's the TC that's not resolved to the clock.

[Cryos]

You may have a point it's the MTC that's not resolved to the clock.

Any one else care to chime in. I'm wondering if it also has anything to do with ADAT digital protocol.

[Brandonx1]

I would guess it's the compensate for delay on record issue. Pro tools thinks the interface is inducing a greater delay then it is so it's moving audio to early after each record pass. Can you adjust the delay settings in the I/o set up?

[capt kirk]

god only knows if its edge locked .....could lock in anywhere inside a frame...

[Chief Technician]

Originally Posted by Brandonx1

I would guess it's the compensate for delay on record issue. Pro tools thinks the interface is inducing a greater delay then it is so it's moving audio to early after each record pass. Can you adjust the delay settings in the I/o set up?

Agreed. MTC is only accurate to +/- .25 frames, so that is also a source of slop. If you need it spot-on without having to slide regions afterwards, then you will need to use LTC.

[philper]

How are you seeing/hearing the offset? By playing both systems back at the same time and listening? Or by comparing the address of transients or etc?

philp

[Fokke van Saane]

Originally Posted by Cryos

I have two protools rigs, one HD NATIVE + omni and 2 x 192 digital I/O's with a sync HD and a second protools 9 + cptk system with a presonus lightpipe interface.

I use the PT 9 as a dubber, here's my question: why when I slave the pt9 second system which is locked to "word clock" and Midi Time code the re-recorded stems are early by 1/2 or a 1/4 frame exactly depending on whether I've disabled delay comp on the dub system? All audio is transferred via Lightpipe via the 192's into the presonus interface.

As for sample accuracy of punches... all punches match up to the sample, no anomalies there. Any ideas folks. How can digital audio come in early?!

It might have nothing to do with your problem, but it could be.

The Presonus lightpipe won't lock to external clocks other then 44.1 and 88.2 KHz. Only if you use the internal clock it works. And this a kind of unit that i rather clock externally.

I found this video's:
Part 1: http://www.youtube.com/watch?v=OFb-h1k5um0
part 2: http://www.youtube.com/watch?v=TuYN7IqniRQ
Part 3: http://www.youtube.com/watch?v=6BVZ2wN2YJs

and then i found the note on the Presonus website:
http://support.presonus.com/entries/...ock-externally

[Cryos]

I'll try to answer a few of the responses:

1- it makes no difference whether I use delay comp or not there is always an 1/4 frame or 1/2 frame offset, I have not tried using Hardware insert offset, I'll take a look into that.

2- indeed I've discovered that the unit only acts as master at 48k,(weird) this isn't an issue as far as i'm concerned since I'm locking the HD Native to Word Clock or ADAT clock Sync.

3- like I said, regardless of the fact that there is a global offset to the re-recorded stems I've sat there zooming in on all the punch points and as far as I can tell everything appears and sounds 100% sample accurate, there's not even a click or tick sound at the punch points and the timing of each punch point is always the same it never varies. If I do the same thing and don't lock to any form of clock every time you hit play or record the timing fluctuates.

4- Overall I'm pretty confident with this setup, indeed the offset is a slight pain but that's what the 2 beeps are for right. Still doesn't really answer how a digital signal can be ahead of time though


Thanks for all your responses folks!!

[EarHole]

If it were a problem with the midi time ode, wouldn't it be drifting around the +/- .25 frame boundaries? I would think that it would be a little different each time.