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nickreich

Genlocking Alexa Mini from a Tentacle

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As Alexas, Alexa Minis and Amiras can Genlock or sync from the incoming timecode stream, they can be genlocked to a Tentacle Sync box just as they would any other brand. I'm wondering if anyone has experience doing this successfully as I have a gimbal cam operator who'd prefer one, but a client who's a little unsure of the tiny Tentacles, and I have no direct experience with syncing from it. We can't get the cameras in advance for a meaningful test. These are long-take concert recordings where sync is required to reduce TC drift.

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Do you mean real genlock or just jamming the internal TC generator, or running in ext TC mode?  Arris don't look at ext genlock, so we don't hook up that side of real Lockits to them, just the TC.  Their clocks are generally stable enough that sync with pro audio recorders works fine.  So the TC output of a Tentacle would serve just as well as any other TC box available.  For Alexa Minis working on gimbles, Easy Rigs, handheld, Steadicam or crane arms the nearly zero weight and size of the Tentacle is pretty cool, and I've had Steadi-folks request them by name.

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WE've been having the best luck with the Mini just jamming about every three hours - for us that is start of day, morning subs, after lunch, and afternoon subs, and at the 12 hour mark if necessary. In our case, nothing with a TC box constantly on the camera works as well for sync as our new method (which many crews have been using for a good while now).  Post is happy with the results, even though the original workflow requested a box on all cameras all the time, which is the way we have always worked until now. You may have to find a small offset to program in. BTW, this also works well for the SXTs we are using. YMMV. 

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Yes, have used Tentacles on the Alexa, Mini and Amira, they work as advertised........... lightweight and accurate to within 1 frame per day.

Camera Dept love them too.

 

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The Alexa mini can generate Genlock from the incoming timecode signal or from a Genlock signal. To connect a Genlock signal one of the sdi outs can be modified to a Genlock in. This however has to be done inside the camera and is a job for service.

I had a project last year where we couldn't get the camera to sync properly with a tentacle or a tiny lockit. There always were one or two frames offset in an inconsistent way. Finally we had the camera modified to accept a Genlock signal and used a lockit box with Genlock out. This solved the problem.
I still don't know what went wrong this time. I had other Alexa mini projects where there were no problems at all.

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I'm talking about Tri-Level Sync, actually clocking the camera as opposed to just jamming TC. On many cameras, this requires a separate Sync or Genlock feed in from a suitably equipped Lockit box. On Arri cameras, they can be set to Sync (as well as accept external TC in Regen mode) from the one incoming LTC feed. This is done in the Sensor menu from memory, separate to setting the TC to Jam or Regen. On the Amira you can source the Sync signal from either a dedicated BNC or from the TC in BNC. This is how I work with Ambient Lockits on Arris, the purpose of sync is to keep the camera in time with the audio recorder over long takes, not just when the TC was stamped. I'm wanting to know if anyones doing that with a Tentacle. As it takes over as the camera's 'clock' it's a bit more unforgiving than just reading external TC.

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As far as I was aware Tri-Level Sync was normally only required for 'Live' switched situations or 3D acquisition ......... I could be wrong but in my experience (Mainly TVC) having Camera TC Sync matching Audio File TC has been more than sufficient for Post. The Alexa is solid as long as they don't go off-speed, not so much the Mini or the Amira, hence the need for an accurate external feed like the Tentacle.

 

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I'm wanting to know if anyones doing that with a Tentacle. As it takes over as the camera's 'clock' it's a bit more unforgiving than just reading external TC.

I have not tried this myself, but I remember the Tentacle guys telling me that their boxes are precise enough for this. You could ask them, I think they are upfront enough about things to tell you honestly. And they may know someone who would have done this or maybe they can set up a test.

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18 hours ago, Steve Foy said:

As far as I was aware Tri-Level Sync was normally only required for 'Live' switched situations or 3D acquisition ......... I could be wrong but in my experience (Mainly TVC) having Camera TC Sync matching Audio File TC has been more than sufficient for Post. The Alexa is solid as long as they don't go off-speed, not so much the Mini or the Amira, hence the need for an accurate external feed like the Tentacle.

 

No, Tri-Level is needed if you really want/need frame accurate sync between cameras.  This has been particularly true with RED cameras when we use them in long-run interview situations where lip sync is important and the takes might run longer than an hour at a go.  The way post is done anymore, for situations where the takes are shorter or the the cameras are not shooting exactly the same talent all the time, genlock isn't needed so much.  I have not found that there's been any issue with any Arri as long as we leave a TC box hooked up and work in Ext TC, and none of the cams was modified to convert TC to genlock.   My tests w/ my Tentacles vs. Lockit vs. Mozegear vs. Denecke have had them all about the same over 8+ hrs, ie plenty close enough.

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9 minutes ago, Philip Perkins said:

No, Tri-Level is needed if you really want/need frame accurate sync between cameras.  This has been particularly true with RED cameras when we use them in long-run interview situations where lip sync is important and the takes might run longer than an hour at a go.

Good to know, thanks Philip.

Sounds like you would agree though that for most situations, a Tentacle feeding TC to a almost any Camera capable of 'EXT TC' is sufficient for Post.

 

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I agree if your takes are in the "normal" movie range, like 15 min max, and the cameras involved aren't Reds.  Even then, the way we do post now I find the strict genlock thing is really most important for situations where multiple cameras are shooting the same person/action etc, for a long period of time, and it's really just a "help" for post in getting them started: I've also done very long-take jobs (like concerts) with a total mishmash of cameras run by operators who don't really have a firm understanding of how to set up their gear and we made it all work in post somehow anyhow.

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22 hours ago, Philip Perkins said:

I agree if your takes are in the "normal" movie range, like 15 min max, and the cameras involved aren't Reds.  Even then, the way we do post now I find the strict genlock thing is really most important for situations where multiple cameras are shooting the same person/action etc, for a long period of time, and it's really just a "help" for post in getting them started: I've also done very long-take jobs (like concerts) with a total mishmash of cameras run by operators who don't really have a firm understanding of how to set up their gear and we made it all work in post somehow anyhow.

Yes, that all makes perfect sense.......... much appreciated.

 

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Hi Csaba, do you have the camera set to Sync to the TC connector (in the Sensor menu) as well as reading external Timecode in Regen mode?

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I dont undersand. Do you ask for cable? Or what?


Sent from my iPhone using Tapatalk

We use regen mode. The tentacle is the main timecode generator for every camera and the sound equipment. The alexa mini always gets timecode from tentacle.


Sent from my iPhone using Tapatalk

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It's not a direct answer to Tri-Level, but I just finished 3+ weeks of shooting with 4 cameras running 20-30(or more) minute takes.
Tentacle attached to each camera and everything jammed once in the am, again at lunch.
Post checked in with me at least twice per day and they advised sub frame accuracy across 2 recorders, 3 slates, and 4 cameras for the entire duration of the gig.
Post is well pleased.

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I work with 3 Alexa Minis for 5 weeks using 3 Tentacles, at the beginning post had problems.

I found this in the Tentacle Forum and it Work.

Arri Alexa Mini & Amira

 

The first is when doing multi camera shoots without genlock  timecode can be off by one frame, because the timecode and the video signal of the camera are not synchronized. you will usually not be able mention this if you do only sync audio to video. Even when the audio is a bit off (<1 frame) it will still be assigned to the correct video frame. But when syncing video to video things are a bit different. When not using Genlock the camera has to decide to wich frame the actual timecode will be assigned to.

The other thing we have found out and tested by our self is that especially the Amira (and the Alexa Mini wich shares the same design) having issues (SUP 4.xx) with timecode. Here tc will always be something about 1 frame behind. As I said we have tested this (also with a competitors product 

 

I would recommend to use the following settings inside the Amira or Mini

  • Goto System/Sensor Menu and set Genlock-Sync to TC-In
  • Goto TC/Options Menu and set TC-Offset to +1

 

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