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Dustin Moore

LTC out with Tascam DR-701D through Rube-Goldberg magic

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Here's what I have:  Ambient Lockit 202CT and a Tascam DR-701D recorder.

 

Here's what I want: I want a LTC audio signal that is drift free (relative to the wordclock) of the BWF in the DR-701D.

 

Why I want this: I need to make an 8 hour continuous audio recording that can be easily(ish) synced in post to 5+ cameras that are all turning on and off at random. Each camera will record the LTC to an audio track. The duration of each video track will be so short that the difference between each cameras clock and the wordclock/LTC is sub frame.

 

Plan A: If I took the tri-level sync and wordclock from the Lockit and had a magic box that could make SDI+audio, I could turn that into HDMI+audio and then feed that HDMI into the Tascam and the Tascam would sync its wordclock to the hdmi. I can take the LTC from the lockit and feed it to the Tascam as well and then I would have BWF's that were wordclock-locked to the Lockit and had the appropriate timecode in the bwf from the LTC. I don't know where to find this magic box cheap.

 

Plan B: If I had a device that could take HDMI with embedded timecode from the Tascam and then burp out LTC, I could just let the Tascam be the master source of LTC + wordclock for itself. I don't know how to find this magic box either.

 

I wish the Tascam just had an LTC out. Any ideas/hope? 

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I would not over complicate things.

Why not distribute the LTC to the Tascam as well, sacrificing a channel.  Set it up to split fairly often, and have post using a couple of files.
Perhaps at the breakpoint the TC will shift a frame, but the edit will still be seamless of course.
 

Should be the easiest way, and still frame accurate.

Plan B is to rent another recorder for the day.

You still need either a lot of cabling or 5 transmitters and a distribution amp.
(And a laptop with software to test each cam / recorder.)

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Thanks for the comment!

 

Yeah, I guess I could split the audio file on a regular basis, let the editing software align using LTC, and then just fill any gaps with room tone.

 

I should just get a Sound Devices ****T for the week. If they come out with a MixPre 3T, I would be all over that. I used to have a 702 without the timecode board. I was so close.  

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I don't think the Tascam will synch word clock from HDMI embedded timecode.  I'm pretty sure it is just a timestamp like most other devices that read LTC without having Genlock capabilities.  Also do cameras have genlock, or using cameras that have the unique ability to regen synch from the timecode source?  (Arri for example). If not, then you basically have all devices free-running / drifting during takes and only the beginning of takes guaranteed to be timestamped accurately.

 

I'm pretty sure that there is some combination of boxes that would work to get LTC from embedded HDMI.  Probably looking at something that converts to HDMI to SDI and then some sort of LTC de-embedder from there.  Wouldn't be cheap though, would be cheaper to buy or rent a different recorder quite frankly.

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On 7/10/2019 at 4:31 AM, Dustin Moore said:

and then just fill any gaps with room tone.

 

There won't be any gaps in the sound!
But, if the Tascam files are importing NOT as being spanned, the TC on the butt-edits might skip or double a frame.
This will NOT have any impact on the actual sound, and syncing will be painless.
If the cams don't shoot very long takes there will be no noticable drift, since all TC's come from the same clock. (No matter how inaccurate / unlocked that clock may be.)

Downside, you'll loose one track on the Tascam.
Next, I would NEVER use HDMI on a pro shoot where my recording signal depends on such crappy connectors.

 

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Update: I put together an experiment where I fed the composite black into a $12 composite to HDMI converter. I am certain that the HDMI converter was creating a signal before I plugged the composite black in so, consequently, it is extremely unlikely that the HDMI was in sync with composite black and the clockit.

 

I think I am just going to send Zoom or sound devices some money for a recorder that can output LTC itself.

 

Thanks all, 

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