Very Important DAT Sound qeustion

[dori_bashan]

Hi

starting to shoot 4k 2:1 24fps on sunday.
sound recorded on DAT tapes. the soundman tells me that he wants to record sound at 25fps and not on 24fps. few people i ask here tells me that is the way to go. does it make any sense?? i will sync clips using clapper, cause there is no TC cable between the RED and the DAT.

need help as soon as yoc can cause time is an issue.

Dori

 

[Paul Hazlett]

I would get a real good reason from him because resyncing is not fun.
what kind of DAT machine? unless the dat machine is in sync it will drift AFAIK.

 

[ken rice]

put a lockit box on the camera jammed from the dat machine,if the dat machine can generate 24 frame tc

 

[dori_bashan]

what is "drift AFAIK?"
whats is a "lockit box"?
i will deal with the "sync by clapper" and not "sync by tc" problem. but, the soudman said, that this is the common workflow for film: shoot video at 24fps and record audio on 25fps, is it right?

is there any diffrence between syncing video thats was shoot 24fps and audio that was recorded at 24fps between syncing video 24fps and audio 25fps? if i'm goona use clapper insted of tc anyway(cause there will be no tc cable), what is the diffrence?

I dont know what kind of dat machine unfortunatly.

 

[Yannick Sadler]

I personally don't see any reason to do so (film 24fps and sound 25fps). To the contrary, I see a lot of problems in post as you will most likely get off-sync 1 second more for every 25 second of recording. Of course this can be fixed and some NLE maybe able to do it on the fly, but hey, you asking for trouble.

 

[Paul Hazlett]

AFAIK-as far as I know for lazy typers like me.

even with the clapper longer takes can drift or fall out of sync if there is no reference.

 

[Dan Hudgins]

Drift, smaples, and frame rate...

Drift, smaples, and frame rate...

AFAIK-as far as I know for lazy typers like me.

even with the clapper longer takes can drift or fall out of sync if there is no reference.

My tests show that if you input audio into a computer through the soundboard the sound will drift about one frame in four minutes. It could be as bad as one frame in one minute if the recording device is not holding the sample rate on playback. From mic to digital recorder probably also drifts from one frame per minute to one frame in a few minutes if you do not use pilot tone or SMPTE LTC or other digital sync. That is good enough if you are using a clap board for each take, that is how I shoot also. If you try to do one clap and make 15 minutes of takes you may be out on the last take enough to notice.

For my mixing is use 48000 samples per second 16bit, that gets chopped up into 2000 samples per frame, for absolute 24fps sync with no drift at all in the editing and mixing.

If you have an odd number of samples per frame you can get drift from some shots ending with rounding errors on the number of samples.

Just using a HI-VHS vcr to record sound on works, the color cristal holds sync better than one frame per minute, you need a stable video source though as a time bace. In this case the frame rate of the recorder does not matter since the sound goes into the computer analog and the computer's sound board's crystal sets the sample rate.

Most of the drift comes from getting to a WAV file after that the software, should, hold sync (maybe).

25fps does not divide into 60Hz, and some labs probably still use 60Hz sync motors on their optical sound recorder, so when 24fps sound is used you get a ratio 2.5:1 that can be used to sync the optical sound recorder without time code through 60Hz pilot tone track (or wire sync to the mag-film player's sync/syncro motors), from 25fps sound you might have issues making a 24fps mag-film master to make the optical sound, unless you resample and or find a way to sync. In the mix the frame rate may get lost and you just have samples in the end, so the sample rate may matter more than the frame rate in recording. You should talk to the lab that will make the optical sound negative and ask them what they need as far as sample rate and frame rate.

48000/24=2000 samples per frame.
48000/25=1920 samples per frame

You end up with odd parts of a sound frame on the edit, but still even samples, so that part works.

44100/24=1837.5 samples per frame.
44100/25=1764 samples per frame.

Notice at 44100 you get half a sample per frame at 24fps but not at 25fps, that may be why the sound guy wants to use 25fps, to have 44100 samples per second as an option, or at some point in the past that was an issue?

With 23.976 you may get more issues with fractions of a sample per frame or shot, that is why I recomend 48000 samples per second with 24fps exact for film work with my system. You can use 96000 at 24fps but I doubt you would hear much better in a theatre to get 4000 samples per frame.

What sample rate is your DAT running at?

What sample rate will you mix at?

Are you shooting images at 24fps or 23.976?

 

[Noah Kadner]

What is the guy thinking you're in the UK or something? Shoot 24fps picture & shoot 24 fps sound= really that simple. If he doesn't get "it" you fire him and hire someone who does...

Noah

 

[M Most]

Hi

starting to shoot 4k 2:1 24fps on sunday.
sound recorded on DAT tapes. the soundman tells me that he wants to record sound at 25fps and not on 24fps. few people i ask here tells me that is the way to go. does it make any sense?? i will sync clips using clapper, cause there is no TC cable between the RED and the DAT.

The most common way of doing double system recording in the US is to either shoot 24fps picture and record sound with 30fps NDF TC, or shoot 23.98fps picture and record sound with 29.97 NDF TC. The use of 24fps time code on sound is not common in most high end productions.

 

[dori_bashan]

shooting images at 24fps, DAT will run at 48000, mix probebly ay 48000 as well. what should i do? i'm just getting confused..

Dori

 

[Dan Hudgins]

Software requirements, DVD, and frame rate issues.

Software requirements, DVD, and frame rate issues.

shooting images at 24fps, DAT will run at 48000, mix probebly ay 48000 as well. what should i do? i'm just getting confused..

Dori

With my stystem true 24fps and 48000 samples would be just fine for making a movie that will end up on film, but if you are going out to the "Video world" you would need to resample the sound to have it sync at 23.976+.

Remember that to go to NTSC rates the frame frequency is,

1000/1001*even_frame_rate=video_frame_rate

so

1000/1001*24=23.97602398+

1000/1001*30=29.97002997+

If you do not use the right numbers your sound can drift, or you need to resample the image frame rate to match the sound. If you resample the image frames some frames are lost, duplicated, or merged. If you resample the sound the pitch can get shifted.

You should test your DVD workflow on two hours of junk frames and sound files with 24fps 48000 source files before you commit to that and talk to people who have been there and done that before you make up your mind.

For myself, I shoot at 24fps with a sync motor on the movie camera to get filcker/pulsation reduction when using 60Hz florescents with 144 degree shutter. If you use 23.976fps you can get a slow roll in the brightness of the image under 60Hz discharge lighting. With the camera phase locked to the line voltage the exposure is more even.

I wrote my "freeish" post system to eliminate any sound drift, I chop the 48000 sound into 2000 sample frames that are put into 256 tracks per 10000 shots, and into 256 tracks for the length of the project also. That gives me positive sync just like using the holes in Mag film, zero drift (in the processing). It also blops the sound cuts to eliminate any pops, and noise gates, takes out slug sound frames to free disk space, and has compressors for each of the 16 output channels.

Drift would come into play with the software you are using and how it relates the sound sample rate to the image frame rate, and how it deals with odd fractions of a sample on shot edits. See my post above about sample fractions.

With the new portable WAV recorders why would you need DAT if you are going to sync to slate with a clap board rather than SMPTE TC?

A WAV recorder should work well since you can download the WAV files without anything analog...