August 21, 2006
A Fresh Slate

Most cost overruns occur in the telecine suite because of incorrect numbers on the time-code slate – in other words, the numbers that are photographed on the slate do not match the expected audio. The iXML MetaSlate will eliminate this problem from ever happening again by automating the placement of a sync point wirelessly into the metadata of each take. The technology is already supported by Final Cut Pro. In future articles, we'll detail how to build your own or contact Gotham for a quote on a custom built iXML METASlate.


THEORY
Traditional “film” syncing (where rushes are synced on film) works because both the picture and sound are “marked” with a common, synchronous event – the sound records the slap of the sticks when they snap shut and the camera photographs the sticks closing. The separate media (audio mag stock and film work print) are then lined up so that the two events are synchronized.

As electronic editing evolved, the introduction of the so-called “smart slate” allowed the audio time code to be displayed at the beginning of each shot. The telecine operator types the time-code numbers that they read off the photographed time code slate, and locks the audio recorder to that specific frame of picture.

When everything works together, this method is extremely efficient – unfortunately, because the slate must be precisely jam synced to the audio recorder, it has several potential pitfalls:

  1. The slate’s time code can drift from the audio time code, due to either faulty time-base crystals or user error.
  2. The slate can be inadvertently reset, and consequently will have a constant offset from the audio recorder’s time-code.
  3. The numbers on the slate can be blurry, overexposed or otherwise unreadable.

When problems occur, additional expenses incurred in the telecine room grow exponentially – and quickly become an untenable situation for all parties involved, including the post facility.

The solution proposed here eliminates the ambiguity of the time-code displayed on the smart slate by ignoring it. Instead, we store the time that the sticks were closed within the metadata of each take. The time information is stored as a relative value – it is the number of samples from the beginning of the file. Thus, all ambiguity about frame rates, sample rates and time-code drifts and offsets are eliminated.


MECHANICS

Taking advantage of the new slating method requires a minimal investment on behalf of the end user, and the process of slating remains almost identical.

The sound mixer’s current slates are retrofitted with a “flash” type radio transmitter that transmits a single “pulse” when the sticks are closed. The receiver triggers the audio recorder when activated by the transmitter.

The recorder stores the sync-point information within the iXML <SYNC POINT LIST> object. This information is them parsed by the downstream playback devices – be they Fostex 824 recorders, Aaton InDaw workstations, Avid or Final Cut NLEs or Pro-Tools DAWs.

The system is modular and scalable –multiple slates can be identified separately if needed (e.g. for “A” camera, “B” camera, etc.), and any slate or recorder can be retrofitted with nominal difficulty. The actual processing of the trigger will be slightly different for each recorder – in general those recorders that have a keyboard interface or GPI I/O will be able to be retrofitted quite easily.


THE FUTURE

Currently, Gallery Software’s MetaCorder is the only audio recorder that is embedding iXML sync points. Obviously, for this to be successful, we need other field recorders to support embedding, and we also need Fostex and Aaton to parse (and allow quick access to) the embedded data.

Looking farther into the future, we envision a kind of “set area network” where the camera, slate, script supervisor’s notes and the audio recorder are all linked wirelessly so that metadata is entered (and corrected) only once.


REFERENCES
www.ixml.info
http://www.aaton.com/products/post/indaw/index.php
http://www.fostexdvd.net/fxdvd_route/docs/product/dv824/dv824_overview.htm
http://www.metacorder.info/


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