Sending timecode to audio track

[Marco Leavitt]

Anybody doing this? What's involved, and are post houses open to it? I was thinking about getting a Denecke GR-2 timecode box. Could that be used to send a signal to an audio track on a multitrack recorder?

denecke gr-2 | B&H Photo Video

[Richard Crowley]

Are you shooting video with a camera that has timecode AND a way to jam-sync the camera with the Denecke. What is the motivation for wanting to record timecode? We used to do that back in the bad old analog days when we had to "resolve" the playback speed of the reel-to-reel tape to match the film.

But this is the 21st century. What problem are you trying to solve here? What does your entire production work-flow look like if you do this?

[Marco Leavitt]

For a while the DSLR revolution allowed me to postpone offering timecode, but I'm getting asked about it more. Some clients just want to sync the camera on every setup even though their cameras don't have onboard crystal time clocks and others want to use a lockit box. I was talking with a DP the other week who owns his own Alexa and he said that he had seen guys recording timecode on one of the tracks of all these cheap multitrack recorders that are popping up these days. I had heard of doing this before, but had never talked to anybody with experience doing it on a professional shoot so the idea is intriguing. I figured if I got a GR-2 I could at least start offering timecode with my current gear and then save up my pennies for an SD552. At some point when I get a genuine timecode capable multitrack recorder I could still use the GR-2 as a lockit box of sorts. That was my thinking anyway. I'm just not sure how a client would react to having timecode on the audio track of the recorder and perhaps even on the camera if it was a DSLR.

[Marco Leavitt]

Oh I'm just handing the card off at the end of the day. I'm not part of the post production workflow.

[Rick Reineke]

I've recorded LTC on a audio track for transcriptions. Even with LTC, theres no guarantee sound and picture will stay locked. NLEs that 'can' read LTC on an audio trk. just converts it to TC stamp and places it on the TL accordingly. I've rented multible lock boxes for multi-camera shoots in large venues which at least kept the TC within a frame, it only really eliminated the need to hard wire TC to the cams. Most of the takes where less than 10 min,s though, so drift wasn't a big issue.
BTW, the 552 does not generate time code. It merely stamps the file with what's received from the TC input.

[Brian P. Reynolds]

Back in the 'bad old days' of analogue multitracks timecode was recorded on the last track of the tape (8,16 or 24) then the 'tack' less was left silent as a guard track as T/C is a VERY harsh signal and even then we recorded T/C -10db down to stop clipping and to stop saturation.
So an 8 track machine ended up as a 6 track, 16 became a 14, a 24 ended up as a 22 useable track machine.

These days people are going down the T/C direction for no other reason than to be trendy rather than valid workflow reasons.

[Marco Leavitt]

That's interesting. The fellow I mentioned had said that there was a problem with the TC signal corrupting an adjacent track. Some kind of crosstalk maybe? I would have thought that wouldn't be a problem in the digital world.

[Richard Crowley]

Unless you deliberately low-pass filter it, timecode is a very "spiky" square wave with endless harmonics. And there are still plenty of parts of the signal chain that are analog and subject to crosstalk. It typically is not noticed because audio does not have endless harmonics, and the left and right channels are typically "correlated". But dialog (or music) vs. a square-wave is pretty much the worst-case scenario for cross-talk.

[Steve House]

Unless the camera in use supports TC I/O so it can be jammed with the TC generator, recording LTC with the audio is pointless. Unless the camera supports GENLOCK, Lockits are pointless. Simply recording LTC alongside the audio doesn't do anything unless matching code is recorded with the video.

[Gary Nattrass]

Timecode is pretty much irrelevant as a synchronisation source these days and back in the days of analogue tape it was only useful if the speed of the tape transport was synchronised with the timecode frame rate in post.

Even for video the timecode became an integral part of the video sync framing system and was know as VITC (vertical interval timecode) but LTC (longditudinal time code) that was recorded as an audio signal could be used to allow a synchoniser system to vari the speed of the tape transport on 24 track and other audio tape systems so that the whole system was in sync with video frame rate.

Even for digital systems the clocking of the system is the critical part that keeps everything in sync and the frame rate needs to be synchronous over a period of time, if it isn't then the sync will drift but pro systems tend to have very accurate clocking systems that are resolved to the chosen frame rate.

Timecode does have a use as a positional reference during post and will also allow systems to sync together several sources but if the clocking system is not synchronous across the whole production chain then there can be problems, this is why gen lock tends to be used to sync numerous sources but certain situations can re-clock everything if for example a vision mixer or digital audio mixer is being used.

So just recording a timecode to an audio track can have a use as a positional reference to where you are in the project but if it is not synchronous to the clocking system of the recorder the two will not be in sync unless they are resolved to a common point in post.

In the old days of film we never even had timecode as such but the same principles applied where the camera motor was running to a crystal that was accurate to 50 or 60 hz so the gate was always running at 24/25 or 30 fps, the sprocket holes then made sure that the correct number of frames were going thru the gate.

The audio was generally recorded on a nagra 1/4 inch tape machine but that also had a 50 or 60hz crystal to make sure that a sync pule was accurately generated, this was then recorded onto the audio tape in a phase cancelling relationship so that it cancelled out and could not be heard on the audio tracks. This 50/60 hz pulse was then used ala the camera to drive a 16 or 35mm magnetic tape recorder and varied the speed of playback to ensure that it was always at 24/25 or 30 fps so that once the audio was on the perforated audio tape the sprocket holes once again made sure that the correct frame rate went through the gate.

After all of that the only form of timecode like numbering that was used was done by a rubber numbering machine that would imprint onto the film and the audio magnetic tape.

These days as others have said the pictures and audio need to have a common sync source and genlock can assist but as most pro clock systems tend to be very accurate they can be jam synced and run to true speed for several hours, it is only when semi pro kit is used that problems occur but just throwing a timecode recording into the equation will not magically help if the two sources are running wild and non synchronous to each other!