When Avid released the Media Composer and Symphony v.11.8 [for Mac] and v.11.5 [for Windows] systems, we introduced a 23.976 project type. With this capability, editors are able to choose which frame rate to work in when starting new projects – a decision based on
acquisition and distribution requirements. Today, all versions of Media Composer Adrenaline and Avid Xpress Pro provide this capability. While the choice brings more flexibility and, ultimately, helps you work more efficiently, it’s not always clear at the outset which project type will work best, and why. Some guidelines follow, based on common workflows.

In the beginning…

The Avid Media Composer system was originally designed for use on television shows, editing at NTSC rates of 29.97 in order to create an online EDL and use matchback to create the negative cultists required. The Avid Film Composer system, introduced in 1992, grew out of this initial design – creating an NTSC-based editing system that could work at a true film rate of 24fps.

To support the double system workflow used in feature film, it was necessary to create a true 24fps environment. This allowed audio dailies from the set to be directly captured into the Film Composer and remain in sync with the picture. This capability became a requirement when audio recording moved to digital formats such as DAT. Productions wanting to maintain a pure digital pipeline for audio needed to capture as AES/EBU with no sample rate conversion in order to maintain the highest quality. Audio sample rate and digital audio workflow are the main decision drivers of working at 23.976 or 24 in the Avid.

The first question to ask …

When deciding which project type to create, first answer this question: “What is the picture frame rate that is in sync with 48kHz?” When you discover that, there will be no need to do a sample rate conversion or digitize via analog sources to change the sample rate of the incoming audio signal. Three commonly used workflows, as well as a fourth that is growing in popularity with the availability of hard disk recorders and the BWF file format, provide a good means for identifying all of the considerations.

1.		Feature film – double system at 24fps and 48kHz audio recording for 24fps postproduction.
2.		Film-based television providing sync dailies on DigiBeta (23.976 and 48kHz) for 23.976 postproduction.
3.		Film or HD Production at 23.976 with single or double system audio recording for 23.976 postproduction.
4.		Feature film and film-based television production at 24fps with hard disk recording at 48.048kHz for 23.976 postproduction.

 

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1. Feature Film Double System

Most, if not all, feature film production intended for theatrical shoots film at 24fps while recording audio digitally at 48kHz. This workflow has been supported by the Avid Film Composer since 1992. Because the audio elements tend to move to audio post via OMF, capturing the production audio digitally and at the highest quality and digitally is a requirement.

Picture: The camera negative is transferred to video directly or from a workprint, but the film is not running at 23.976fps during the telecine process in order to create a known 2:3 pulldown cadence to the 29.97fps video rate. Once digitized into the Avid in a 24p project, the frames are “stamped” as 24fps in order to play back in sync with audio captured directly via AES/EBU or Broadcast WAV files recorded at 48kHz.
Audio: Because the audio was captured digitally – either synced to work clock or imported as 48kHz – it expects to be in sync with the picture as it was originally captured – 24fps. The native sample rate of a 24p project is 48kHz and all other rates are resolved to that during capture. An example of this is capturing analog audio with the .99 setting active. This tells the Media Composer to “count” samples .1% slower and stamp the captured files as 48kHz.
When playing back at 48kHz, the audio plays back .1% faster creating a true 24fps playback from 23.976
sync sources. When capturing digitally at 48kHz, no samples are converted. It is a digital clone.

2. Film-Based Television with Sync Dailies

Due to the tight schedules in television programming, dailies are already synced when delivered to the editing room. The transfer facility has already resolved the original shooting rate of 24fps to 23.976 and has sample-rate-converted the digital audio sources to be in sync in the DigiBeta source tapes. Because DigiBeta expects only 48 kHz for 29.97 NTSC, the audio must be sample rate converted when going from 24fps to 23.976 on the video. The path looks like this:

Picture: 24 -> 23.976 to 29.97 video creating 2:3 pulldown
Audio: 48kHz -> 47.952 slow down (.1%) sample corrected -> 48kHz to 29.97 video

The edit room now gets digital audio from their DigiBeta for capture into the editing system. If the editors are cutting in a 30i project (29.97 NTSC video), the audio sample rate is unchanged when capturing – it is a digital clone.
If it’s decided that postproduction will work in a 24p project, the audio can no longer be captured digitally when directly connected to the Media Composer. So you’ll need to capture via analog sources where the Avid counts the
digitized samples slower to bring everything back to a true 24fps = 48kHz environment.
In this case, the postproduction should be done in a 23.976 project type, since it assumes that the 48kHz audio sample rate is in sync with picture playing back at 23.976fps from the DigiBeta captured sources. It has the same result than that of a film-to-tape transfer to tape. But since there is no need to speed up to true 24fps in this project, audio samples remain untouched at 48Khz throughout the
postproduction process, through the audio mix and back to the NTSC broadcast master. Using this project type for this workflow will only go through one sample rate conversion during the film to tape transfer.

3. Film or HD Production at 23.976

Film cameras have been able to shoot at 23.976fps for many years, but it was not until HD acquisition became popular that people started using the frame rate regularly in
production. Although HD cameras can shoot at true 24fps, the preferred shooting rate is 23.976fps because of the audio consideration when down converting to NTSC. No one wanted to deal with a sample rate conversion in the audio when working in a fully digital environment. In a double system environment, the DAT or hard disc recorder records at 48kHz. So shooting at 23.976fps eliminates the need to do a sample rate conversion or an analog audio capture with the .99 setting.
The resulting NTSC down convert is now the same as in the previous example where 23.976 video with 2:3 pulldown is in a DigiBeta tape with sync 48kHz audio. Keep in mind that when capturing directly from the Sony HDW-F500, the down conversion and 2:3 insertion processes cause the picture to lag 2 frames behind the audio. To address this condition, Avid Media Composer Adrenaline and Avid Xpress Pro systems include an audio delay feature in the Capture Window to delay audio by 1-5 frames as needed to resync picture and sound during the digitizing process.
If working double system, the DAT or BWF files from the hard disk recorder, the 48kHz recording will come straight in with no sample rate conversion or speed change to sync with the 23.976 picture.

4. Feature Film with 48.048kHz Audio Recording

Even though film cameras can run at 23.976, using them in that way never caught on for a variety of reasons. However, the audio workflow can change to allow a 23.976
postproduction workflow despite the film running at 24fps. This workflow is only for picture capture frame rate of true 24fps and a NTSC postproduction workflow. DAT, and more common to this workflow, hard disk recorders, can record at 48.048 kHz – which is really just 48kHz with a .1% speed up as part of the capture.
- .1% Normal + .1%
47.953 kHz 48 kHz 48.048 kHz

Most recent versions of the Avid Meridien-based editing
systems with 23.976 project types, as well as Media Composer Adrenaline and Avid Xpress Pro systems,
support a 48.048kHz BWF import workflow. If a BWF file is detected as having been recorded as 48.048, you will be presented with a dialog box asking whether the import should perform a sample rate conversion or import as 48 kHz. If no sample rate conversion is chosen, the imported files are stamped as 48kHz, thus slowing them down by .1%; the same amount that the film is slowed down during the film to tape transfer. This way no sample rate conversion is performed, and a digital audio pipeline is maintained for the postproduction process.

The same can be done during the film-to-tape process from DAT or BWF recorded at 48.048kHz to create sync digital dailies directly to disc via a MediaStation or directly to a DigiBeta tape.

Capture, Edit, Digital Cut

The Avid Media Composer, Symphony and upcoming release of Media Composer Adrenaline systems, address 23.976 in three areas; during capture, during editing and playback from the timeline, and during the digital cut process back to tape.

Capture: The project type determines the native capture rate of the project, either 23.976 or 24p. It also determines the
native audio sample rate of that project that will not have a
sample rate conversion or analog process involved when
capturing, playing, or digital cut.

Edit: In the Film/24p settings you will see the “Edit Play Rate” as either 23.976 or 24. This control sets the play rate of the timeline. It does not affect any of the digital cut
output settings. This control lets you set a default state of frame rate for outputs that are made directly to tape, such as a crash record.

Digital Cut: Here you can output the timeline as 23.976, 24, or 29.97. The important thing to remember is that this is the playback speed of the Avid timeline, not the source tape destination. The NTSC frame rate of 29.97 cannot be changed. What is changing is the frame rate of the picture within the NTSC signal.

1. 23.976. This creates a continuous 2:3 cadence from
beginning to end of a sequence and is the expected frame rate of a broadcast NTSC master from 24 frame sources.

2. 24: This is used for feature film production to create a true “film projected” speed from an Avid timeline on NTSC video. It is also the output type to use when using picture reference in a Digidesign Pro Tools system using OMF media from a 24p project type. Note that this is not a continuous 2:3 cadence. Adjustments are made over 1000 frames with the pulldown cadence. No frames are dropped, just the field ordering with the 2:3 cadence.

3. 29.97: Timeline will play back 25% faster to create a 1:1 film frame to video frame relationship. This can be considered a 2:2:2:2 pulldown cadence. This
output is useful for animation workflow or low cost kinescope transfers where a 2:3 pulldown cannot be properly handled.

The above workflows are intended to maintain a digital audio pipeline from capture through post and into the final mix. It is possible to cross frame rates with sample rates using analog capture instead of digital or using a digital audio sample rate converter at time of capture.

Michael Phillips is the principal product designer at Avid Technology, Inc. He can be reached by E-mail at Michael_Phillips@avid.com

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But now, a new generation of digital audio recorders is coming onto the market. These machines record six, eight or even ten tracks onto a non-linear recording medium — either a magnetic or optical disk. They promise to streamline our audio workflow, simplify audio post production and finally bring easy-to-use digital audio into the picture editing room.

We recently completed a feature using one of these machines, the Fostex PD-6, along with its companion studio model, the DV40. They record six tracks of audio onto DVD-RAM disks. In this article we’ll discuss our experiences, pro and con, and talk about the specific procedures we employed. (For a production-oriented look at this technology see Chris Munro’s article in the last issue.)

Figure 1. A standard 12-cm DVD-RAM disk alongside its diminutive 8-cm cousin. Production records on the small disks; the large disks are used to play back synchronized dailies in the screening room or in telecine.

Overview

We used the Fostex machines primarily because they were available and seemed to fit our purposes. We found them to be capable, reliable and simple to operate in a cutting room environment — but we did not directly compare them to machines from other manufacturers, namely Zaxcom/Deva, HHB and Aaton.

The PD-6 records directly onto small, 8-cm, DVD-RAM disks that reside in a protective cartridge (Figure 1). The disk works in the Fostex machines and in computer DVD-RAM drives (we used a FireWire version from LaCie). It can also be read (but not recorded) with a conventional DVD-ROM drive. The PD-6 records six tracks simultaneously as a pair of Broadcast Wave files. (These are “BWF” files, labeled with the filename suffix “wav.” The system can record in other formats, as well.) At the same time, it can create an ALE file that serves as a machine-readable sound report. It records in either of two configurations: “4+2,” where one file contains four tracks and the other two, or “5+1,” where one file contains five tracks and the other is monophonic. (Multi-track files are known as “polyphonic,” which means that a single file contains many tracks.) The idea is that the mixer records four or five tracks that represent separate microphones, and one or two tracks as a mix appropriate for the picture editing department and the screening of dailies. We used the 4+2 format because Media Composers prior to Adrenaline can’t handle more than four tracks per clip, so audio containing five tracks would have been broken into two clips.

This logical separation of material is a powerful reason to use this system. The production mixer can give the picture department an appropriate mix that will work for editing and screening. And the sound department can still have access to all the separated tracks and use them in the final. But it means that sound editors will inevitably do more work, if only because they have much more raw material to deal with.

Audio files are imported into the Avid via a few simple commands. This is another advantage in using these machines — no digitizing required, D-to-D quality and much faster than real-time import. The picture assistant then synchs dailies in the Avid. If he or she uses Avid’s Slip by Perfs function, then sync is as good as or better than traditional mag synching.
Screening and sync checking are done with Fostex DV40s — one connected to a projector, the other to a KEM. This means that everyone hears excellent quality audio in dailies screenings. The Fostex does not lock to bi-phase (the sync pulse generated by a KEM or projector) so a biphase-to-timecode converter must be installed. We used a device made by Rosendahl Studiotechnik, called the “BIF.”

Figure 2. The 8-cm DVD disk can be removed from its protective cartridge by breaking two plastic tangs on the inner shell. The disk can then be loaded into a DVD-ROM or DVD-RAM drive. It should be reinserted into the housing for storage.

Turnover is done via OMF and/or EDL. With modern Avid and Pro Tools systems, OMF turnover finally makes it possible for all the audio work that the picture editor does, including volume graphing and equalization, to find its way to the sound department.

We found this process to be effective, powerful and easy to use, once we’d learned the necessary procedures.

The Process

1.		Production audio is recorded on 8-cm DVD-RAM disks. On our show, audio was recorded in 16-bit at 48K to avoid potential compatibility problems with the Meridien Avids we were using. But 24-bit audio is available as well. The production recordist also creates an ALE file in the PD-6 that describes all the material recorded and backs up the day ’s work on a Mac or PC.
2.		The DVD-RAM disks are delivered to the cutting room, and the assistant editor immediately copies them to a backup drive via a normal drag-and-drop file copy. To read the 8-cm disks in our FireWire DVD-RAM drive we had to remove them from their protective cartridges (Figure 2). The two files created for every recording are copied separately — the four-track files are stored in one group of folders (organized by scene) and the two-track files in another. The ALE files are also backed up and organized by date. Then the assistant creates an Avid bin and imports all the day’s files. Again, the two-track files are kept separate from the four-track files. The Avid converts the polyphonic files into multiple monophonic files and saves them as Avid media. We digitized all the audio media to a separate partition so it could easily be handed over later to sound. Meridian Media Composers can work with Broadcast Wave files as the standard audio format, so no file conversion except the automatic separation of the tracks is necessary.
3.		When they are initially loaded, the Avid audio clips do not appear to contain audio timecode information. Instead, the timecode is initially present in the “Start” column. This entire column must be copied to the “Audio TC” column to create audio timecodes. At the same time, audio timecodes should be carefully checked against the ALE file created by the production recordist. Finally, the assistant finds the audio slate closures and marks them with a locator.
4.		Meanwhile, the film assistants are building silent picture rolls in whatever order is desired. As they build these rolls, they mark the slates and splice points between takes and record that information on paper.
5.		When a reel is completed, these notes are handed to the Avid assistant, who builds an audio sequence from the dailies that matches the picture notes. This sequence is then exported as a single .wav file, and that file is recorded onto a 5 1/4” DVD-RAM disk. One file is created for each daily roll and labeled with the daily roll number.
6.		The film is loaded on the KEM, and the audio disk is inserted into the connected Fostex DV40 playback machine and sync is checked for each take (Figure 3). The Fostex locks up in a second or two, making it easy to check a whole roll quickly.
7.		If there is a sync error, the person on the KEM immediately reviews the notes and rechecks the work on the Avid to determine the source of the problem. When the needed adjustment is worked out, a new audio file is created in the Avid and rechecked on the KEM.
8.		Dailies are screened using another DV40 connected to a projector. We found the DV40 to be a reliable machine in the projection room, and relatively simple to operate. Once they went through a brief training period, projectionists liked the machine — largely because when using it they don’t have to thread or rewind mag rolls. We used only one machine in the screening room, and as a result, there was a brief pause between reels while the projectionist selected a new file on the DV40 and flipped a switch to connect it to the correct projector. To do changeover screenings, one would install two DV40s, one for each projector.
9.		Dailies are telecined. Another DV40 is used in telecine for audio reproduction, and tapes with sound are dubbed and distributed normally. Other systems can be used for playback as well, as long as they are compatible with the files you create in the Avid. We used .wav files, and our telecine played them back with a Tascam MMR-8.
10.		Though the telecine tape has audio, only the video is digitized into the Media Composer. The digitized video is then combined with the audio sequences created in step 5 to create a video and audio sequence representing each reel. Each shot is then subclipped and autosynched to merge the audio and video into single clips.
11.		The subclips are individually loaded into the source monitor and, using a custom timeline view, the individual frames near the slate are displayed along with an audio waveform. Avid’s Slip By Perfs function is used to touch up the sync to the subframe level.
12.		The clips are then organized into a bin and made ready for the editor to begin work.
13.		The four-track files are saved in bins organized by scene. They are available to the picture editor if he or she ever needs audio that can ’t be heard in the mix.
14.		Turnover occurs as it would on any other OMF-based show. All of the original audio media files are delivered to the sound department. (We used a FireWire drive for this purpose.) As reels are locked, an OMF without embedded media is turned over to sound. The sound editors then link the OMF to the master media. Any audio files added since the end of production, such as sound effects and render files, must also be turned over.
15.		The sound department builds the dialogue tracks with either Titan or a new product called MetaFlow [see Metadata and MetaFlow, in the May/June 2003 issue]. Either way, they are able to listen to the mixed and unmixed tracks created in production and use whichever sounds best.

Problems

The process described above worked very well for us, providing perfect audio quality with few headaches. But we did encounter some glitches. We found that it’s essential that the production recordist be completely familiar with the PD-6. In particular, he or she should know how to rename files, how to delete files (and recover deleted files when necessary), how to create an ALE, how to format a disk and how to back it up. A standard backup routine should be worked out and reviewed with post production. These are all operations that would never occur when working with a typical DAT machine, but they are essential parts of the day-to-day use of any digital disk recorder.

photo by Steve Cohen

Figure 3. Checking synch using the DV40, shown here on top of the picture head on a KEM Junior. The machines are interlocked with a Rosendahl BIF bi-phase-to-timecode converter, visible above the DV40.

Second, it’s important to use the right kind of DVD-RAM disks and to format them properly. We successfully used disks from Maxell, HHB and Optodisk. Disks from Memorex consistently failed for us. The disks must be formatted in the “Universal Disk Format.” This can be done under Mac OS 9 or OS X or with the PD-6 itself. Disks formatted with the normal Macintosh Hierarchical File System won’t be readable on the DV40. It’s also important to note that DVD-RAM disks are available with or without the protective cartridges that the PD-6 and DV40 expect. At the time of this writing DVD-RAM disks aren’t in wide distribution and can be difficult to find, especially on distant locations. Consider purchasing them before you leave the U.S. We were only able to read 17 file names (i.e. 17 reels) on one side of a disk with the DV40. Fostex tells us that if we formatted our disks on the DV40 and put our files into a folder called “BWF” we would not have encountered this limitation.

We also found that some long-standing Avid bugs caused problems with this process. In particular, when we turned over to sound some of the timecodes in the audio timecode column had disappeared, making it impossible for us to create accurate EDLs. These timecodes had to be found and filled in by hand. We’ve seen this bug before — as long ago as the early nineties. Our workaround was to use the start timecode instead of the audio timecode to make audio EDLs.

In addition to disappearing timecodes, some clips acquired erroneous timecodes. The production recordist typically uses hour 1 for the first side of a disk and hour 2 for the second side. When we turned over, we found some clips labeled with hour 0. Again, we fixed these clips by hand using the production ALE files. For this reason, it’s essential that all imported audio clips be checked against the ALE files after loading to make sure that they have accurate timecode information.

We found that the process of synching by numbers to be relatively straightforward. But it became awkward when we found sync errors on the KEM. The assistant has to figure out the problem, go back to the Avid and create a new file on the DVD-RAM disk. This takes too much time. It also means that the new file will appear out of screening order on the disk, so the projectionist could have trouble finding it.

Turnover

We encountered some confusion during turnover, primarily because every audio file used in editing has an associated multi-track file, and it was essential for the sound editors to find and listen to them so that the best options could be presented in the mix. Our sound editors evaluated two systems for doing this. They rebuilt our dialogue using EDLs with SynchroArts’ Titan software, creating sequences with four new tracks for every cut we had created in the Avid. They also tried MetaFlow, a new tool from Gallery that uses OMF to precisely link the original editor’s tracks to the associated unmixed tracks, without any of the inaccuracies normally associated with EDLs. Titan won out on our show, but we know of other productions that have successfully worked with MetaFlow. Either way, the sound editors referred to a complete OMF copy of our tracks with all the audio work that we created: volume graphing, audio effects, etc.

Conclusion

From the editor’s perspective, this technology offers many advantages, including perfect digital audio in the Avid and in the screening room, excellent sync with accuracy equal to or better than mag and digital turnover with all work intact. The editor cuts with a simple, mixed track, but when there are problems with the mix, he or she can dip into the separated tracks, which reside in their own bin, and use them as needed. The sound editors work with the separated production tracks and aren’t limited to tracks that were designed to sound good in dailies screenings. No mag film is generated, no money is wasted on it, and it doesn’t end up in a landfill somewhere.

However, there is one issue we found that is part and parcel of this and other digital workflows: it means extra work for the Avid assistant. In a mag-based feature editing room, all the synching would be accomplished by the film assistants. But with a workflow like this one, much of that effort gets transferred to the person working on the Avid.

Two improvements might help. First, if a lower cost, laptop-based Avid system could be used for synching, then that work could be tackled by the film assistants and kept out of the Avid assistant’s domain. We did not try to use Avid Xpress Pro for this purpose, but it would be something we’d look into in the future. Second, it would be much easier to check sync and fix sync problems if an Avid could chase picture playing on a KEM. This is not currently possible, but Avid might incorporate this functionality in a future release.

In general, we found this system to be extremely usable in an editing environment, and its many advantages far outweigh the glitches that we encountered. Neither of us would ever want to work with mag film again. Digital disk recording has arrived and, in our view, there is no going back.