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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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On 7/11/2019 at 9:53 PM, Bouke said:

Downside, you'll loose one track on the Tascam.

The Tascam DR701D has a timecode BNC input, so he doesn't have to lose a mic input. 

 

On 7/8/2019 at 9:55 AM, Dustin Moore said:

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? 


Buy a handful of timecode boxes (such as Tentacle Sync E, or Timecode Systems Ltd Ultrasync ONE), make one of them as your "Master". Sync all your other timecode boxes plus your DR701D to your "Master" TC box. 

Done. Easy as!

No need whatsoever to fluff around with crazy contraptions (that don't even exist yet, you'd need to invent it yourself!) trying to extract timecode from an HDMI input. 

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Have a look at my Zoom F8n sync experiments in another post here. 

 

I had a DR-701D for awhile, and an experiment I was never able to try was syncing a pair of them via HDMI.  Documentation is scant, but it suggests you might get a word clock regen via that method, but maybe not to any outside world.  

 

Note I'm more of a recording studio guy who has occasionally uses LTC, rather than someone who lives in that world daily.  

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New experiment with the F8N in internal free run mode. This is a test to see if the wordclock running the A to D's and the LTC generator are locked to the same clock.

 

I took the LTC out port and wired it to the mic input and let it record it's own timecode for an hour. I used libltc's dumpltc.exe program to extract the locations of the frames in the sound file and then I plotted the rate of change of LTC relative to the samples using some Python that I came up with. Drop frame timecode arithmetic sucks.

 

Anyhow, the slope of that line was indistinguishable from 1 out to the number of decimal places that the experiment would allow. It is better than one part per 10^8. I believe the F8N has an LTC out that is hard-locked to the wordclock it is using.

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On 7/23/2019 at 5:11 PM, EmRR said:

Have a look at my Zoom F8n sync experiments in another post here. 

 

I had a DR-701D for awhile, and an experiment I was never able to try was syncing a pair of them via HDMI.  Documentation is scant, but it suggests you might get a word clock regen via that method, but maybe not to any outside world.  

 

Note I'm more of a recording studio guy who has occasionally uses LTC, rather than someone who lives in that world daily.  

I sold my dr-701d as well and bought a mixpre. Syncing The tascam via hdmi worked if you use record trigger for the audio. But record trigger only works in 99 percent and sometime you didn’t record audio at all. If you hit record manually not the tascam, Audio was drifting so there was definitely no wordclock.. 

‘but that’s only the hdmi in. All in all I found the tascam was very unreliable. So for a five cam shoot maybe a mixpre is the better option and cheaper if you sell the tascam.

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