Audio Drop Outs when PT is chasing LTC

[LukeFromBerlin]

When my PT 8.01 is slave-synced to timecode (LTC received through SYNC i/o interface) I have small dropouts in the digitally recorded audio tracks (usually STEMS, sometimes up to 10 minutes long, no big start/stop or punch in/out action). This occurs whether I am recording via AES/EBU as well as using ADAT Lightpipes. I usually record around 30-40 tracks simultaneausly.

These dropouts are usually around 10-200 Samples long, enough for a dirty POP
When I closely examine the waveform I see it continues exactly after the dropout. So it is not like a part of the waveform is missing but there is just no data during the drop out in the timeline - and after that the waves continues normally. So no data is gone - but it is in a wrong position in the timeline (on sample level) after the drop out. This can happen once or 20 times during the recording of a stem audio track.

I don't know whether the problem is connected to Timcode (LTC) issues or a WordClock problem. PT is the WordClock Master (Sync i/o), the interfaces are synced via Loopsync.

Generally asking: when recording long stems digitally while PT is slave synced to LTC: does PT CHASE the LTC ? Meaning does it update the positional reference all the time, only sometimes or just the moment the recording STARTS and from there on ALL OTHER syncing to the incoming digital signals is only done via WordClock ? How do WordClock and LTC interact during digital recording ?

I appreciate your expertise, thanks !

[the dude]

First most assurably have a timecode framerate mismatch
On the sync io on the slave when chasing is the lock/resolve LED blinking
If yes
Fast = incoming code is faster than session
Slow = incoming code is slower than session

Quick fix is to set position and ref both to LTC while chasing ( slave )

If this resolves it find your TC mismatch
Are you using video in the session ?

[LukeFromBerlin]

Originally Posted by the dude

First most assurably have a timecode framerate mismatch ?

No (I guess not ;-) ALL set to 25 FPS (Europe standard)

Originally Posted by the dude

On the sync io on the slave when chasing is the lock/resolve LED blinking
If yes
Fast = incoming code is faster than session
Slow = incoming code is slower than session

I cant find that LED
I don't have a Sync HD, only Sync i/o, but also the HD seems to only have a "locked" LED, nothing like "resolve"...
But this LED does not seem to blink (I'll keep an eye on it)

Originally Posted by the dude

Quick fix is to set position and ref both to LTC while chasing ( slave )

Tried this in the past, this doesn't work at all. also the master TC has no sub-frames so the resolution is a problem too. So far it has only worked (but at least for months) with PT being the WORDCLOCK master but LTC slave

Originally Posted by the dude

Are you using video in the session ?

No, the LTC master is a second, MAC-based workstation with sequencer software (Logic pro)


Appreciate your help & tips, we seem to narrow it down.

Still the biggest for me is whether PT, when being WordClock master and LTC slave CHASES the LTC or not during the digital audio recording process.... Does it only set a "start" marker and then wordclock (internal) sync only or does it "update" the TC position during rec (like every frame or 10 frames or whatever...). I have been wondering about this since a long time, if anybody knows what is REALLY happening during audio rec with ext LTC sync... give me enlightment

[Frank Kruse]

When you say "PT is WC master", did you actually slave the Logic system to the PT WC? If not it´s not really surprising that you are encountering drop-outs due to clocking errors.

Either clock PT to the incoming AES signal or make sure you are clocking the TC master to the same WC.

I don´t know your application but why not simply export the file from Logic instead re-recording it in real time in PT? Just wondering...

regarding your other question: LTC just give positional trigger sync. After that a DAW runs on the given clock to main to speed. It does not slowly re-chase like an analog tape machine.

Which is why studios have a common house sync for all units to avoid digital glitches or sync issues.

[LukeFromBerlin]

Dear Frank

thanks for the answers !

Unfortunately Logic needs to be TC master, 'caus slaving Logic is a nightmare and never really worked ...at least in the digital domain. In Midi and tape-days it actually did work OK, but that was on frame-level, not KHZ / WC / Sample related digital timing- and clocking stuff...)

I'll try Wordclocking ProTools to AES. I just thought as I have a couple of PT-interfaces hooked (96 i/o, 192 i/o, Sync i/o) I'd better make sure they are running on their own clock (in this case the sync i/o being the loop-sync master) rather than from a PCI-card stuck in the other (logic-)mac and it's WC out....

Why I don't transmit the files (good point ) is because Logic doesn't have a command to bounce each track one by one automatically. In my songs I sometimes have like 50 tracks. Offline bouncing sounds worse (YES, even if little people believe it ) than online boncing in logic. So to have 50 tracks discretely bounced online one by one and then "pulled over" by hand, plus alligning them in PT - it would take like 5+1 minutes x 50 tracks = 5 hours.

With my current setup I press Play on Logic an REC in ProTools and after 5 min I have 50 tracks as 50 audiostemfiles ready to mix in PT.

BUT... it works only 6 out of 7 days... and that's why I post here and hope to gather additional info how to possibly turn this into 7/7 days...

Thanks for the info reg continous sync ...Good to know that even when PT is a LTC slave it only positions itself ONCE at the start and then calculates the positions internally (probably by calculcating some algorhythm with SampleRate and Tempo of the session...sounds reaonable )

Thankx for your advice and any additional thoughts from anybody...

[Frank Kruse]

You missunderstood. You can go either way regarding TC chase. The important point I was asking was wether you're sending the PT WC to your logic converter?

both rigs need to run to the same WC to avoid glitches. either that or you need to run PT as a WC slave from one of the digital ins.

My suggestion would be that you WC slave PT to your logic rig when Logic is the TC master. This can either be done via WC or you sync PT to one of it´s digital inputs (ADAT, AES or whatever).
Don't run them on independent clocks otherwise digital glitches are almost guaranteed and they might even drift apart over a longer time.

PT "calculates sync internally" (you said). Sync is maintained via the converter clock which is why the most important thing is to put everything on the same clock. TC will only tell PT where to start playing/recording.

frank.