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Mix Magazine

This installment of The Bitstream column appeared in the October 2002 issue of Mix Magazine.

The Bitstream

This column discusses the AES31 standard…

The Sheep are Still Asleep

The late great sci-fi writer, Douglas Adams, envisioned a portable, piscine solution to the problem of incomprehension. His babelfish was simple to use and was available via vending machine. Pity that session interchange isn’t as straightforward in the real world.

Although there have been weak efforts in the past and a good deal of lip service addressing file and session interchange, little actual help for the average practitioner is afforded by old school methods unless you are a one vendor house. What began a decade ago as a proprietary solution, the OMF standard and its spawn AAF are, in large part, controlled by Avid and have made life not much easier for end users and pure hell for other audio manufacturers. Back in 1998, the Audio Engineering Society, identifying a need in the industry for an open approach to session interchange, tendered a first attempt to bring some order to the chaos. So began the AES31 standard: open, international and designed to simply address interchange of audio content and metadata. Mel Lambert covered AES31 in detail in the October, 2001 issue of Mix, so I won’t dig into the gory details. The ongoing standards effort has ratified two parts, AES31-1-2001 or Part 1, describing “a common platform so that files may be interchanged among hardware of different manufacturers of audio and video equipment” and AES31-3-1999, Part 3 of the spec, which provides “simple but extensible system for passing audio material between systems.”

The essence of Part 1 is straightforward and succinct. In a word, FAT. Whether it be 12 bit for floppies or 16 or 32 bit for rigid media, Microsoft’s antique de facto disk file system standard, is the foundation for AES31FT, the standard’s file allocation table disk format. Since this is a lowest common denominator standard, the more widespread FAT won out over the much improved NTFS since universality is paramount. NTFS, the file system developed for Microsoft’s professional NT operating system, is a more robust approach than FAT32, a 32 bit version of the File Allocation Table first developed for their original operating system, MS-DOS. NTFS has better user access control and handling of modern volume sizes and file counts along with improved reliability. We all like reliability.

On we go to Part 3, which outlines a “…convention for expressing edit data in text form in a manner that enables simple and accurate computer parsing while retaining human readability.” In other words, sample accurate session data expressed as ASCII text. ASCII text is the simplest data format for “human readability,” consisting of the upper and lower case alphabet plus common metacharacters like # and $ along with the numbers 0 through 9. So, like the CMX EDL or edit decision list format for video tape editing that started it all, AES31 Audio Decision Lists (ADL) can be read by any engineer who’s learned to parse or understand their grammar. As an example, the following fictitious entry would identify a source file used in a project.

(F) “URL:file:08/26/01/localhost/Kingston03/AUD001.WAV”
09:11:03.03/1101 00:00:07.00/1101
“NAME: MOS RoomTone2”

The first line identifies a (F)ile entry, then states the location of that file, as expressed in a URL or Universal Resource Locator like you’d see on the Web. That’s followed on the second line by the Unique Identifier, a pseudorandom string unique to that file. The third line (starting with 09:…) provides the starting time code address from the source reel, then comes the file’s starting time code address. The fourth line gives the source reel name and the fifth line completes or closes the entry. Not too scary, huh? AES31 ADL files can be identified by their, you guessed it, “.ADL” extension.

Part 3 also describes the Edit Decision Markup Language (EDML), a very simple “language designed to accommodate the requirements of edit data exchange. A primary design objective is to maximize platform and transmission compatibility and to provide simple and explicit parsing.” Notice how many times the word “simple” is used in the descriptions. Simplicity is a key feature of AES31, as most creatures—including software engineers and their project managers—are pain–adverse. In the world of computer–based products, one basic equation rules: complexity equals pain. Remember though that “simple” is a relative term and, though AES31 is simplified relative to prior exchange methods in many regards, it’s no walk in the park. Since there are so many proprietary session formats from products old and new, any solution can’t help but be fairly complex.

By this time, you may wonder what happened to Part 2. This portion of the spec identifies a preferred audio file format; the EBU’s Broadcast Wave Format (BWF) has been fingered as “suitable for this purpose.” BWAV files, a professional version of the ubiquitous WAV sound file format used on Win systems, contains additional time stamp and sync info. Multichannel audio is represented as monaural rather than interleaved files. So, a 6 channel mix would be stored as six monaural files. At the time of writing, the AES hadn’t posted this part of the spec so I assume there are some last-minute details to work out.

By the way, interleaved files are a hold over from the days when all audio on computers derived from studies in “computer music.” Those were the days when computers were BIG, the size of a ’fridge or two and disk drive were slow and stupid. Anyway, interleaved files take all the channels and time domain multiplexes them into one chubby file by slicing each channel up into discreet chunks of time then assembling the pieces, each in turn, into a serial string. Interleaved files, universally frowned upon these days, make disk transfer easier but processing individual channels a pain in the butt.

Much more complicated is Part 4, the effort to “…identify a system, capable of working cross-platform, using object-oriented computer techniques because they offer much greater flexibility than is possible in a simple list.” Ouch! Though this process began in 1997, it isn’t scheduled for completion until 2005 and my guess is even that date is optimistic. A liaison with the rich media–oriented AAF Association was started a while back to promote audio interchange within the AAF framework in order to provide some cross–compatibility with AES31. Not surprisingly, recent activity in this area has languished since vested interests are usually stronger than any desire for improved interoperability.

Let’s talk about vendor support. Since I last visited this topic, the list has grown considerably. The pioneers at SADiE have long been the champions of AES31 and now the list of participants includes Euphonix, Fairlight, WaveFrame, iZ, Nuendo, Zaxcom, Genex and Akai. AES31 implementation is in process at DAR, Merging Technologies, Studer, Mackie, Tascam and SEK'D.

Paul de Benedictis is the Director of Marketing Communications at Euphonix and he offered this vendor perspective: “The industry has embraced digital recording and computers. Now we need a way to archive these projects and files that is not platform–dependent. Fifteen years from now, who knows what systems will be available? The AES31 format is a solid solution that includes more than just linear audio.” See the sidebar below for more on this issue…

In all this, one cannot help but wonder how our little world of pro audio will fit into the much larger context of digital teleproduction and rich media production as a whole. The AES is working with the SMPTE to make AES31 part of a larger production infrastructure and I applaud both the AES and SMPTE for taking the initiative to make all our lives easier. Maybe someday, the AES, EBU, ITU, NAB and SMPTE will become one unified body creating harmonious pan–industry standards, but I’m not holding my breath. Until then, go with what works and AES31 works.

This discussion of AES31 and other tools is all well and good, but the one important onlooker that’s invisible—but essential—to these proceedings is Avid and its Digidesign division. As the market makers, their lack of leadership has induced the strong sense of apathy that pervades the industry whenever this subject comes up. Personally, I think AES31 is strong medicine for the session interchange malaise and, with vocal support from users like you, it can become a everyday success. I’ve said it once and I’ll say it again: Demand support for AES31 in the products you purchase and use. You may not need it today, but you most likely will tomorrow. AES31 has reached a surprising state of maturity. So, don’t stay asleep, wake up and participate!


OMas provides professional services to content creators and manufacturers large and small. This column was written while under the influence of Edith Frost’s Wonder Wonder and Brian Eno’s classic work, Apollo. For links to my previous installment of the AES31 soap opera and other useful arcana relating to this column, visit


Babelfish Unite!

A Call to Incorporate More Metadata in AES31

AES31 includes the ability to reference a single video file, but it doesn’t go far enough for the likes of Bill Johnston, VP of engineering for Liberty Livewire’s Audio Division: “Whatever the ADL format is for sharing, the sound files and their edit metadata are only a small part of the equation. AES31 doesn’t directly address the flow of other important metadata throughout the post process… It is frightening how hard it is right now and AES31 will not solve this dilemma.

“As an adjunct to AES31, a standardized file format (BWF-P) must be used. The metadata in the header of the sound files must be further defined and used by multiple manufactures to ensure a flow of data such as:

• Original Timestamp
• Current Timestamp
• Roll Name
• Scene
• Take
• Production
• Original Date Stamp
• Original Name
• Channel Number
• Number of Channels

“The list, of course, is defined differently by everyone and can get unwieldy. But, without a common format and predictable data, no manufacturer can implement anything logical! Right now, to get a Deva recording into an Avid and Pro Tools, and have the OMF and EDL’s reference the original multichannel sound files is about as easy as finding Deschutes Brewery Porter on tap in Southern California. It takes too much time and planning…”

To help bridge the many gaps, a few hearty software vendors provide conversion applications for proprietary formats. Two Win utilities, Cui Bono Soft’s EDL Convert line and Fairlight’s recently acquired AV Transfer, provide comprehensive coverage. For Mac OS folk, Dark Matter Digital’s Media Magic, covers most bases. There are also file–only conversion utilities (no session/EDL support) such as Gallery Software’s TurboMorph and AudioEase’s BarbaBatch.