Wired for multi-channel sound: at NAB 2001, Doug Ford from the engineering department of...

The issue in question was how to make it easier for film directors to remotely approve multi-channel mixes. At the time, this was an every-day problem for the film industry. As post production deadlines get tighter time is increasingly a part of the issue. The existing solutions were costly,

both in terms of time and money. Any mix approval required the sound track to be recorded onto a storage medium such as MO or a DA88.The tape containing the mix then had to be couriered to the director for approval--a process that, at best, was done overnight or the next day. With foreign language overdubs and simultaneous worldwide releases to contend with, the pressure on schedules was immense. Bad weather and a courier company missing a flight could immeasurably impact the project, leaving studios empty, resulting in expensive downtime. Another alternative was flying the director to the foreign studio for a prolonged period, adding a great deal of unnecessary inconvenience and expense to the project.

In the early 1990s, ISDN provided a solution for Stereo approval. However, multi-channel surround sound offered a challenge in terms of magnitude of data and how to move that data from Point A to Point B--a 20 minute linear PCM 5.1 Mix using 24 bit resolution creates a 900MB file. With the acceptance of network based and computer-aided technology in the film industry, the use of "store and forward" and "streaming" partially answered some of these problems. What would further ease the process was the use of a non-destructive industry accepted digital audio data compression algorithm.

APT's roots are in both multi-channel audio for cinemas and ISDN movement of audio. It has long been accepted in the film, music and broadcast industries that APT's suite of apt-X algorithms are the "Rolls Royce" of compression technology. Non-destructive in nature and with an exceptionally low encode/decode latency (sub 2 milliseconds at 48kHz Sampling Frequency), the apt-X algorithm is the fundamental core technology for DTS cinema products and also for the APT manufactured WorldNet range of ISDN audio codecs. The WorldNet codecs have been installed in 80 per cent of high-end post production facilities worldwide for stereo mix approval with SMPTE Timecode. With this pedigree, experience, and industry acceptance, it made sense for APT and Skywalker Sound to jointly develop a solution for 5.1 remote approval mixes.

SkyLink is born

APT invested heavily in the development of a solution, which included several intensive on site brain storming sessions at Skywalker Ranch and in APT's corporate headquarters in Belfast, Northern Ireland. Although the technology existed in principle, the challenge was to encapsulate the various components into a reliable, user-friendly product.

In early 2003, APT launched the WorldNet SkyLink, which implemented the. Enhanced apt-X suite of algorithms and offered 16, 20 and 24 bit word resolution. Windows XP Embedded was chosen as the operating system. APT used its experience to develop hardware technology that would compress/decompress and multiplex/de-multiplex up to eight discreet audio channels and SMPTE Timecode. The operator could use any one of four separate options--for example record to the internal 60GB hard drive, record to a removable ORB drive, record to an FTP server via the TCP/IP interface for "store and forward" or stream in real time (data rates dependent).

If the operator decided to use "store and forward" and had access to a 1 Mbit/s ADSL circuit, a ten minute 5.1 16 bit digital audio word resolution mix (with SMPTE Timecode) would take 11 minutes to deliver. Fast streaming (or real-time with a low latency) would require 70 per cent of a T1 (1.1 Mbit/s) to transport a 5.1, 16-bit mix. One key concern for Skywalker, and the film industry in general, was security. As such, the WorldNet SkyLink was designed to offer four levels of security including Seed Encryption, Bit Swapping on the apt-X algorithms, Reel Shelf Life, and locking playout access to specific decoders or users.

Standing trial

Extensive tests were undertaken by Skywalker to ensure that the WorldNet SkyLink was a viable product and met with its high degree of expectation. This procedure was part of the jointly agreed route map and project plan to take the product to the market place. However, to conclusively prove the technology, other post facilities had to trial the hardware. Several studios requiring different applications were approached, among them ARRI in Munich and Lakeshore Entertainment, which was using the Laser Pacific Media Corporation facility in Los Angeles. Between these two facilities the aim was to evaluate the WorldNet SkyLink and use the codec to send a 5.1 mix in non-real-time (store and forward mode) from Germany to the US.

In March 2003, Tom Scott, engineering VP of EDnet, APT's North American distributor, brought an interesting project to the attention of Noel McKenna, APT's CEO/managing director. An EDnet client, Lakeshore Entertainment, would be mixing one of its films, Underworld, in Munich in May. Might there be a chance to use the new WorldNet SkyLink so that editors and producers in Hollywood could approve the mix without having to travel to Europe? Noel quickly assented to a trial, and moved to deploy units immediately following its NAB 2003 debut.

ARRI Sound, in Germany, in conjunction with Claude Letessier in Paris, were handling the sound design and were mixing the film for James McQuaide, the Underworld producer, and Len Wisemen the director. Hans Hohenwarter was the ARRI technical sound supervisor on the project, while Dave Register was the engineer at Laser Pacific Media. ARRI received the music files from Los Angeles and VFX shots from London after special effects processing. Audio post production was undertaken at ARRI Sound's "Dubbing Stage One" by Michael Hinreiner and Tschangis Chahrockh.

The audio mix was on six 20-minute reels. The 6-channel audio was fed from a Tascam HD-Recorder in AES/EBU 24 bit format. The 5.1 audio reels, together with embedded SMPTE Timecode, were encoded by the WorldNet Skylink in Enhanced 24 bit apt-X mode and transmitted from Munich. Access to Laser Pacific LA was via a 2MBit/s Internet access. The 5.1 mix was received in LA and ready to play out within two hours.

Having used the WorldNet SkyLink to download and decode the audio files, Laser Pacific arranged an approval session with several Lakeshore executives. The Beta tapes (PAL format @ 25fps) were played out with the video locked to timecode generated by the WorldNet SkyLink. The session was a success and achieved the objective of allowing the Lakeshore team to remotely approve the 5.1 Mix within hours of the mix being completed in Germany.

Simon Factor, APT's US sales manager, co-ordinated the project in Los Angeles. In Munich, Hartmut Forster of Pro Audio Systems (APT's distributor in Germany) was on-site to provide support for ARRI. The event was managed by APT's distributor in the US, EDnet, under the guidance of Tom Scott, who was present during the replay in Laser Pacific's 5.1 channel review room.

Speaking after the trial, Scott said: "I was thrilled by the precision and quality of the Underworld mix. A great sound system and a stunning mix make for an unmatched theatre experience."

He adds that EDnet is very excited by the possibilities for the WorldNet Skylink. "We've been supporting long distance audio supervision and collaboration for almost 12 years and the use of the Internet for this sort of session is finally coming of age. The audio quality of apt-X, the engineering skills of APT and the application expertise of EDnet should combine to make this the next big thing".

Conclusion

The WorldNet SkyLink has been designed specifically to address a problem in the post production industry. Existing solutions for remote approvals of Surround Sound Multi-Channel audio files introduces unnecessary cost, risk and time pressures. The WorldNet SkyLink can achieve in minutes or hours what previously took days, not only saving time but ensuring optimum quality, security and ease of use. The prolonged tests by Skywalker Sound and the ARRI project indicate that the market is ready for the WorldNet SkyLink.