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Scan format: P vs PSF, what's the difference? And other monitorin questions

alexapsf scan monitoring output

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#1 davide sorasio

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Posted 27 April 2016 - 05:51 PM

Hi everybody, scrolling through the alexa menu I saw items that I'm not sure what the are.

 

- in the recording/rec out menu I see SCAN FORMAT, with the possibility of choosing between P or PSF. What is the difference between them?

 

- in the same menu I also see HD-SDI FORMAT with the possibility of choosing between 422 1.5 SL/DL, 422 3G SL, 444 1.5G DL and 444 3G DL/SL. While I know that 422/444 have to do with the color sampling I have no idea what 1.5G and 3G mean, and same with SL/DL

 

- in the MONITORING/MON OUT menu I see scan format and the options are P or PSF? Is this the exact thing I've ask in question number 1?And why in the frame rate option in this menu it doesn't let me choose 23.976 but only 24, 25 and 30 fps?

 

Thank you in advance for the help!


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#2 Tyler Purcell

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Posted 27 April 2016 - 07:10 PM

From my understanding, PSF is an interlaced signal which can be used to distribute progressive material. There is no motion between the two fields, so the equipment simply combines them.

PSF is most commonly seen/used on HDCAM or DV/HDV recordings which use broadcast standards to record.

P is simply progressive frame, which can't be carried on an interlaced signal.

P is most commonly seen/used with cameras/equipment that don't use broadcast standards.

So PSF would be used for standard monitors that only can accept normal broadcast video standards. P would be used for monitors that can accept a true progressive signal. Most HDSDI monitors CAN accept a true progressive signal.

23.98 is only a "for broadcast" frame rate, so for a monitor output of a camera, it's not really going to make any difference on a film set.
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#3 David Mullen ASC

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Posted 27 April 2016 - 07:14 PM

3G is double the data rate of 1.5G -- 4:4:4 recording I believe requires either dual-link (two cables) running 1.5G each, or a single cable running 3G if you have a recorder capable of receiving that.


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#4 Tyler Purcell

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Posted 27 April 2016 - 07:40 PM

Yep 3G is 10 bit 4:4:4, which most monitors won't accept.
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#5 David Mullen ASC

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Posted 27 April 2016 - 07:46 PM

You might want to read this discussion regarding P vs. PsF

https://www.reddit.c...erence_between/

 

PsF stores a progressive scan capture as two fields, recombined on playback as a full "P" frame.  It is basically used in HD tape formats.


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#6 davide sorasio

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Posted 02 May 2016 - 09:19 AM

thank you, those are great infos! My last question is about the frame rate in the Monitoring out of Alexa Cameras. I can see listed all teh different options but I can only choose 24,25 and 30 fps, but not 23.976. Can anybody tell me why?

 

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#7 davide sorasio

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Posted 02 May 2016 - 09:25 AM


23.98 is only a "for broadcast" frame rate, so for a monitor output of a camera, it's not really going to make any difference on a film set.

Can you tell me more about this? Why is not going to make any difference?


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#8 David Mullen ASC

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Posted 02 May 2016 - 09:39 AM

If 23.976 and 29.97 are listed but grayed out then the camera must be set-up somewhere else in the menu that caused them to be grayed out. Perhaps you've set the camera's frame rate to 24fps.
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#9 Landon D. Parks

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Posted 02 May 2016 - 11:50 AM

I can't speak for an Alexa, but on my GH4 if you go in and change the frequency settings, it will alter what rates are available in the menu. For example, one must set the camera from 60Hz to 24Hz in the frequency menu in order for true 24.00 to be available. Perhaps the Alexa has a similar setting, allowing it to switch between 24Hz, 50Hz, and 60Hz?


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#10 Tyler Purcell

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Posted 02 May 2016 - 12:19 PM

Can you tell me more about this? Why is not going to make any difference?


23.98 is not the same speed as 24fps.

So what you monitor in has to be directly connected with the format you're recording.

23.98 doesn't make a difference on a film set because you should be recording in 24FPS.
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#11 Brian Drysdale

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Posted 02 May 2016 - 12:47 PM

My understanding is for shooting digtial in the USA you shoot at 23.98 for audio post production reasons, in Europe you shoot at 24fps, where it's not an issue.


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#12 Satsuki Murashige

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Posted 02 May 2016 - 01:31 PM

My last question is about the frame rate in the Monitoring out of Alexa Cameras. I can see listed all teh different options but I can only choose 24,25 and 30 fps, but not 23.976. Can anybody tell me why?
 


As Landon says, the camera may set up for 50Hz, or PAL. It's telling that the two 60Hz NTSC video frame rates (23.976 and 29.97) are both greyed out. Most likely that setting will be under 'System.'
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#13 Landon D. Parks

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Posted 02 May 2016 - 02:04 PM

My understanding is for shooting digtial in the USA you shoot at 23.98 for audio post production reasons, in Europe you shoot at 24fps, where it's not an issue.

 

Perhaps that was an issue in the past, as I think David mentioned above (or on another recent similar thread). The audio issue is not present when recording directly to the camera, nor should it be present when recording external sound to a digital device.

As David also said, you can shoot either frame rate, and there should not be a large difference. Either way, you're going to have to do a transfer to either 24 or 23.976 for your output if you plan to do Cinema and anything else. Frankly, I stick with 24.00 FPS because just because it sounds good, and seems like the logical way a 'film' camera would capture images. 


Edited by Landon D. Parks, 02 May 2016 - 02:05 PM.

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#14 Tyler Purcell

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Posted 02 May 2016 - 10:24 PM

My understanding is for shooting digtial in the USA you shoot at 23.98 for audio post production reasons, in Europe you shoot at 24fps, where it's not an issue.


It's all about 3:2 pulldown and drop frame in the US.

For broadcast, most people shoot 23.98 because it natively converts perfectly to 29.97, which is the US broadcast standard instated decades ago. Very few people shoot 29.97 outside of news/live broadcasts.

In PAL countries, they don't have "drop frame", so 23.98 doesn't mean anything. Most shows in PAL countries shoot everything 25 and slow it down by one frame per second in post production if they need a 24 frame output for whatever reason.

For theatrical, most people shoot 24 frames per second without the slight slow down. This is only due to the theatrical workflow, which is based on 24fps world wide.

With professional audio recording equipment, frame rate is super important. On most modern set's, there will be a master clock that the camera and audio recorder will sync to. If the audio recorder is set to 23.98 and the camera is set to 24, they will drift out of sync. This way the lab can automatically sync the audio and picture in the dailies prep phase. The same technique is used on film dailies. A timecode slate is used which is synched to the audio recorder. When the slate is clapped, the timecode number of the audio where the marker is, is visible in screen. There is auto detect software which can read that timecode number and with all the audio loaded, they will automatically sync for dailies.

So you can see how if you mess this up, it will really screw up your post production workflow. Not a big problem on set, but a HUGE problem in post. The key is to understand who you are delivering to; Broadcast or theatrical, then make sure you use the appropriate capturing frame rate.
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#15 Landon D. Parks

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Posted 03 May 2016 - 01:22 AM

So you can see how if you mess this up, it will really screw up your post production workflow. Not a big problem on set, but a HUGE problem in post. The key is to understand who you are delivering to; Broadcast or theatrical, then make sure you use the appropriate capturing frame rate.

 

As much as I agree with what you say, this last part is sorta iffy to me. If you're making a feature film that you plan to show in theaters to some degree, then you'd probably want to stick with 24.00 recording. But, the kicker is that all theatrically-destined films will also end up on television, DVD, etc. So simply shooting for your intended display format will only work if that format is not planned for cinema. Once you throw Cinema into the blend, you'll always have to convert to something at some point.

As such, my opinion is that as long as everyone is on the same page on set and in post, there is little reason one frame-rate should be more or less available. You mention the timecode sync on set - you'd of course want to make sure that sync was set to 24 if you're shooting that, and you'll have no problems. I shoot 24 because it feels more natural to me. I also ensure all my post work is done at 24, though. Audio is no problem, because I record a primary track into my camera with a pre-amp, and then the audio and video are sent in perfect sync over HDMI to the Shogun, where recording happens. No matter what format I shoot in on the camera, the audio will also be in sync because I'm essentially recording audio and video together. 

 

Bottom line: when dealing with frame rates, the important thing is making sure everything is on the same program. If you plan to shot 24.00 on set, you need to make sure your timecode is set for 24.00 so it doesn't throw your audio out of sync (if you're shooting dual system sound). You then need to make sure your post production is done on a 24.00 timeline, with your VFX artist also working in 24.00. The same exact thing could be said for 23.976.

 

While post audio can be an issue with different frame rates, a big issues will be mixing 24.00 and 23.976 footage on a timeline. Since they are not truly the same speed, you'll need to convert some of the footage.


Edited by Landon D. Parks, 03 May 2016 - 01:26 AM.

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#16 David Mullen ASC

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Posted 03 May 2016 - 01:32 AM

But Landon, the majority of features shot in the U.S. digitally use 23.976 fps, so clearly it is not a problem.  Someone even pointed out to Roger Deakins that the monitors on a behind-the-scenes shot from "Unbroken" (I believe, maybe it was "Sicario") show that the frame rate was 23.976 fps.

 

There is no difference in terms of how the image looks, 24 vs. 23.976.

 

I don't have a vested interest one way or the other.


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#17 Brian Drysdale

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Posted 03 May 2016 - 02:06 AM

I understand it''s because so much of audio post production in the US is centred about broadcast standards that shooting with double system sound at 24 fps causes issues.

 

Visually you can't tell the difference and when I've shot 25fps and it's been projected at 24fps, the images don't look any different, in that case it was audio and the longer running time could be sensed. I suspect most 35mm projectors don't run exactly at 24fps, ( I gather 23fp to 26fps is allowed http://www.iceco.com...DA20 Specs.pdf)so 23.976 fps would be an excellent speed for a projector.


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#18 Tyler Purcell

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Posted 03 May 2016 - 02:12 AM

I always shoot 23.98 because mostly everyone works in that frame rate here in Hollywood and it's an easy to put 2:3 into the file for 29.97 conversions, which is a constant requirement for deliverables. I can do those conversions locally without any extra hardware. Converting 24p to 29.97 is a whole heap of problems. You first have to convert the 24p to 23.98, which alters the pitch. Then you have to correct the pitch during the conversion to 29.97. Premiere can automatically correct for the pitch change, but it has issues with putting 2:3 into the file unless it's already been exported as one clip. So the first step is to export the entire show with final audio, then put it back into Premiere as a 23.98 clip in a 29.97 sequence. That in of itself is very time consuming. Where on Avid (premiere as well), in my 23.98 sequence, I just hit the export button when I'm done and a 29.97 clip is sitting on my desktop ready for delivery.
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#19 Tyler Purcell

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Posted 03 May 2016 - 02:15 AM

I suspect most 35mm projectors don't run exactly at 24fps, ( I gather 23fp to 26fps is allowed http://www.iceco.com.../DA20 Specs.pdfso 23.976 fps would be an excellent speed for a projector.


Ohh for sure, they don't have crystal lock or anything of that nature. They rely on the frequency of the electricity to hold them in sync. You'd need a pretty decent sized power conditioner to stabilize the electricity in order to get the projector anywhere near the proper speed.
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#20 Robin R Probyn

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Posted 03 May 2016 - 04:11 AM

Hi everybody, scrolling through the alexa menu I saw items that I'm not sure what the are.

 

- in the recording/rec out menu I see SCAN FORMAT, with the possibility of choosing between P or PSF. What is the difference between them?

 

- in the same menu I also see HD-SDI FORMAT with the possibility of choosing between 422 1.5 SL/DL, 422 3G SL, 444 1.5G DL and 444 3G DL/SL. While I know that 422/444 have to do with the color sampling I have no idea what 1.5G and 3G mean, and same with SL/DL

 

- in the MONITORING/MON OUT menu I see scan format and the options are P or PSF? Is this the exact thing I've ask in question number 1?And why in the frame rate option in this menu it doesn't let me choose 23.976 but only 24, 25 and 30 fps?

 

Thank you in advance for the help!

 

 

I think PSF ,s most useful role is being able to see a Progressive recorded  image on a monitor that will not take P input..  thats why its often a choice for monitor out..


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