Splice Now

It seems like a lot of people are confused about the new “23.976p” Avid project type. This is an alternative to the traditional Avid film project (“24p”) and you can only work with such a project on a modern machine (Meridien 10.8 or later). People have been using it for roughly a year now and over time, it’s probably going to be widely adopted.

The difference between the two types is pretty subtle. In both, the machine digitizes from video running at 29.97 fps and removes pulldown (aka “reverse telecine”). You end up with the original 24 film frames. What makes the project types different is the audio sample rate that’s synchronized with picture.

In a traditional 24 fps project, pulled down audio is synched with pulled down video. That is, video running at 23.976 fps (or 29.97 fps) is synched with audio running at 47952. All the speeds are a tenth of a percent slower than their “normal” rates.

That has worked very well for the film industry for a decade and a half. But when this scheme was originally developed there was no such thing as digital videotape — and therein lies the rub. Digital videotape works differently, synchronizing pulled down video to full rate audio. Video running at 29.97 (or 23.976) syncs with audio running at 48K, not 47952.

A 23.976 project works like digital videotape, synchronizing pulled down video with full rate audio. That makes it appropriate for video-originated material shot at 23.976. It can be useful for film originated material, as well, because it can give you better sound in the Avid.

If your film was telecined to digital video, with dailies synchronized in telecine, and you’re loading from tape, then you want to load digitally, if possible. You won’t have to set audio or video levels and everything will be pristine. The problem is that in a traditional 24p film project your Avid expects to see video at 29.97 and audio at 47952. Unfortunately, your tape has audio running at 48K. In Meridien, this was handled with “poor man’s sample rate conversion” — the system simply dropped audio samples to convert 48K to 47952. That worked okay for dialog but it’s not ideal.

In Adrenaline that trick won’t work — sync will drift. So you’ll have to load your audio analog. (Your audio will also have to be analog when you play out to digital videotape.) The alternative is to use the 23.976p project type. That will allow you to load everything digitally.

There are a couple of issues that you should be aware of. First, your sound editors will have to work differently, and set their Pro Tools systems to work 48K “not pulled down” — the way they would for a 29.97 project or a show that shoots on video. That shouldn’t be a problem, but it will be a surprise, and they should be warned — before you make a final decision about your project type.

The second issue has to do with production audio and how it’s recorded. On a film shoot, audio is normally recorded at 48K with 30 fps timecode. When that audio lands in telecine it gets pulled down for transfer — to 47952. But the tape wants to see 48K, so, even though the 23.976 project has allowed you to create a digital audio path in your cutting room, you’re facing at a sample rate conversion in telecine. The answer is for production to shoot audio at 48048. When that audio is pulled down in telecine it’ll end up at 48K and will go to your digital videotape without conversion. If your final delivery format is HD video, then shooting at 48048 means that dialog can run through your whole workflow without sample rate conversion.

Here are a few rules of thumb:

1. If you are shooting on film and transferring to tape and your workflow is well established, there’s no need to change it. You still want to use a traditional 24p project type.

2. If you are shooting on HD video at 23.976, then you want the 23.976 project type.

3. If you are shooting on film and telecineing to digital video and you want the purest audio you can get in the Avid, you may want to consider a 23.976 project. For even better audio in the Avid, production should shoot at 48048. (This is especially true if you’re making a TV show where your final delivery will be on HD tape.) But before you try this, check with your post supervisor, production mixer and sound effects supervisor. Make sure everybody is on board.

For those of you who are interested, here’s a table that lays out the rates:

Final Cut, for what it’s worth, only works one way — like digital videotape. That’s simpler, but less flexible. It works in a video-dominated world, but can present problems in certain circumstances with film production.

Technorati Tags: avid, edit, film, final cut pro, video

This entry was posted on April 24, 2007 at 7:38 am and is filed under Avid, Avid Technical Tips, Avid vs. Final Cut, Final Cut, Workflow. You can subscribe via RSS 2.0 feed to this post's comments. You can comment below, or link to this permanent URL from your own site.