Pix 240i Alexa Timecode Question

Ronnee Swenton · October 1, 2014

I'd like to record prores4444 from the alexa with the pix240i, while also having the alexa slaved to the pix for timecode.

Is this possible while still allowing the pix to follow the Alexa's record/stop record sdi commands?

I don't trust any digital camera to keep accurate timecode, which is why I'm trying to get the Alexa to be synced as a slave to the Pix240. This way the sound will sync up perfectly with both the pix 4444 footage as well as the alexa proxy files.

Thanks for any help/suggestions.

Satsuki Murashige · October 1, 2014

I've heard that the time code clock in the Alexa is same as the one in the Ambient lockit box. Haven't heard any sound guys complain about timecode drift on the Alexa, it's solid.

Why not record Prores 4444 in camera to SxS and record LT proxies on the Pix? Use the camera TC as the master, slave the Pix via SDI, pass audio via SDI, retain the ability to sync file names, and slave start/stop recording with one cable. Pretty simple workflow.

Ronnee Swenton · October 1, 2014

Thanks Satsuki.

If that is indeed true about the Alexa's TC reliability, then I'm going to follow your advice. The main reason for recording to the pix for the 4444 files was to be able to record highspeed footage in 4444, instead of 422 as the limit is set for the Alexa. I guess that's another question in itself...if the pix can handle the highspeed footage via rec out (if the alexa transfers via the project framerate I imagine it could, but I'm not sure if that's how the process even works)

Worst case scenario would be I'm forced to have 422 highspeed shots.

Dan Finlayson · October 1, 2014

I've actually heard of/seen ACs struggle to get the Alexa to take timecode from external sources. I was talking to a buddy about it today and he suggested that the Alexa is designed to run as the master clock and wasn't really intended to slave to other TC devices... I haven't really done any testing besides anecdotal evidence of this, but I would trust the camera to run TC more than take TC.

Mark Kenfield · October 1, 2014

The PIX can only support up to 30fps in 1080p, so the only way you're getting high-speed into it is to record the slow-motion playback from the Alexa. But if you're only getting 4:2:2 high speed material in-camera, then you'll only get 4:2:2 on to the PIX (whether it's in a 4:4:4 wrapper or not).

Another point to remember, the Alexa only outputs 10-bit 4:4:4 from the SDIs, whereas it can record 12-bit 4:4:4 internally. So the internal 4:4:4 has a definite advantage in bit-depth.

Satsuki Murashige · October 1, 2014

You might need to get an Alexa XT with Codex mags to record 1080p Prores 444 at more than 30fps. Never used one so I have no idea what the max fps is on those. I'm assuming up to 60fps?

Ronnee Swenton · October 2, 2014

Thanks for all the help guys.

I got some good news today that our producer might be getting us the XT M. So the workflow will have to be slightly reconfigured once it's confirmed. Regardless, I'm not too upset about being limited to 422 for highspeed footage considering how different it typically looked in some of my favorite movies shot on film. The under exposure, grain, and jarring shutter/flicker that filmmakers had to deal with with film. A bit of color information lost isn't the end of the world.

Dan Finlayson · October 2, 2014

XT M is the way to go for sure. It can do Arriraw at up to 120fps in 16:9 mode. 1080p Prores4444 up to 120fps, 2k Prores4444 up to 60fps.

http://www.arri.com/camera/alexa/cameras/camera_details/alexa-xt-m/subsection/technical_data/

Kar Wai Ng · October 3, 2014

I've actually heard of/seen ACs struggle to get the Alexa to take timecode from external sources. I was talking to a buddy about it today and he suggested that the Alexa is designed to run as the master clock and wasn't really intended to slave to other TC devices... I haven't really done any testing besides anecdotal evidence of this, but I would trust the camera to run TC more than take TC.

The Alexa has no problem taking a jam sync from an external source. Any problems might be due to cross-jamming from a different timebase, or using the 5-pin lemo cable backwards (yes there is an 'in' and an 'out' side of the cable). TC has to be set to Ext LTC. It's the simplest thing ever.