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[Greg Foad]

I've been testing Alexa Time Code.

It looks to me like there are two clocks.  The project speed code that you can set and/or jam, and a second off speed code that acts like a free run off speed code.  This off speed code keeps counting up like a free run code starting at zero the first time you go off project speed.

Can any one shed any light on this if what I'm saying makes sense?

[Michael Borenstein]

Greg,

This is correct.  During normal at speed (project=sensor FPS) shooting, the TC works in the way you described.  When the sensor and the Project FPS's do not match, the camera forces the TC to "Internal Rec Run Regenerate."

Hope that helps.

[Guenter N.]

Greg,

Project speed is basically "playback" speed and it is defined by the way TC is counted. TC can only count to max 29 then jumps to zero. If you have a project of 24fps TC only counts to 23 then jumps to 0 again and so on. You will get original play back speed if sensor speed and project speed match. If they do not match you will have either slow motion or fast motion.
You can only jam TC if the frame rate of your external TC matches the project speed of the camera. If it does not match - jamming is not possible and camera uses the internal TC.
If TC is set to "Free Run" it will constantly run and count like a clock. (time of day)
If it is set to "Rec Run" - it will only run during recording based on any value that you entered.

Hope this makes things clear.

Best,
Guenter

[Greg Foad]

Thanks.  All of that is pretty clear.

A little more under the hood though.

I'll use an example for what I mean.  I jam to 10 hours at 23.98.  I can go off speed and come back to 23.98 and TC (from what I can tell) has continued to count up accurately from 10 hours over a period of time of even an hour.

Meanwhile the off speed TC started at 00:00 and if I switch back and forth from 23.98 to any off speed the TC will accurately (seemingly...) continue the count up from 00:00 over the same one hour time period.

To boil it down.... does one TC clock remember two codes then.  The Jam code (or free run) and an internal code.

Also, going into high speed mode doesn't seem to affect the project TC when I go back to project speed.  Does that mean the high speed mode leaves the TC counting, and only boots the sensor and required bits into that mode?

And, is all of this frame accurate?  My guess is no its not, and that a frame is lost here and there as changes are made. 

My hope is, it is frame accurate.   

Thanks guys.

[Michael Borenstein]

Greg,

I think the quick answer is yes, the TC clock accurately increments two clocks simultaneously. 

I think the only true way to test if both clocks would be frame accurate through the switch however, would be to record two slates or clocks with each TC running and then switch between the two frame rates and record.  Then see if the TC recorded in the Metadata matches the TC on the clock.  I will see if we can try this in the lab next week.

I have also asked the question of the developers in order to get a more concrete answer to this.  FYI.

Regards
Mike

[Greg Foad]

Thanks Michael.

I know most people don't care as they either jam after each camera change, or run a lockit box of some kind.  Regardless its still good to know for those weird circumstances that always arise.

Somebody really thought this out well.

[Michael Borenstein]

Greg,

So here's the way it works.  There are 2 independent TC tracks that can be maintained in the camera, Rec Run and Free Run.  When the sensor and project speeds are the same, this allows you to select free run and jam sync, as you know and use when you jam sync at 23.98.  When you switch to 120fps (sensor and project speed differ but project speed still set to 23.98) the TC track switches to rec run and begins to increment.  You can now switch back and forth between off speed and normal speed with frame accurate TC for both as long as the project speeds are the same. 

The only time you will loose frame accuracy is when you switch the project speed from an integer based to a non-integer based TC, or vice versa, when going back and forth from normal to off speed.

Hopefully this clarifies the issue.

Regards
Mike

[Greg Foad]

Yes it does and that makes total sense.

Now I have something else to test from what you said lol.

Thanks!!

Greg

[Michael Borenstein]

No problem. 

Happy testing.
Regards
Mike