Dolby E o Aaton Time Code
JOINT MEETING BETWEEN THE TORONTO SECTIONS OF AES AND SMPTE -March 1999
1) DOLBY E AND MULTI-CHANNEL DISCRETE SOUND
Presented by Tim Carroll of Dolby Laboratories Inc. (AES)It was standing room only at Ryerson's Eaton Lecture Theatre for our joint AES/SMPTE meeting on March 9th. We were very fortunate have to Tim Carroll from Dolby Labs in San Francisco to give us the much anticipated, pre-NAB look at Dolby E--Dolby's new audio coding technology.
With the creation of ATSC, the new HDTV audio standard for North America, Dolby E becomes even more important in the industry's attempt to offer: i) a new level of quality in audio; ii) flexibility to the producer and end user and iii) more choices for the consumer.
THE DOLBY E ENCODER AND DECODER
Tim explained that the DP571 Dolby E Encoder and DP572 Dolby E Decoder incorporate Dolby E and are designed to ease the digital TV broadcaster's transition from two-channel to multi-channel audio.
Dolby E allows programs to be decoded, processed, and re-encoded many times without audible degradation as they make their way through the distribution chain. The DP571 encoder provides inputs for up to eight audio channels, plus SMPTE timecode, which can help establish solid audio/video synchronization. A standard video "color black" reference input signal maintains the equal audio and video frame rates necessary for smooth editing. The synchronized audio and video frame rates enables precise video picture cuts to the video frame without mutes, glitches or restrictions.
Remote-control connectors, an alphanumeric display, channel activity LEDs, and menu navigation buttons facilitate access to various operational modes. A multiplexer combines Metadata with the encoded audio signals, and a one-frame utility PCM audio delay circuit keeps linear PCM audio in sync with encoded audio. The DP572 decoder recovers the associated Metadata and decodes the Dolby E audio data to four PCM audio output pairs locked to the local sampling rate by a video color black reference signal.
SO WHAT IS METADATA?
Dolby Digital, an accepted standard for DTV audio transmission, carries supplementary information about the program audio known as Metadata. Added during the production or post- production stage, Metadata instructs Dolby Digital decoders in home receivers to tailor the audio presentation to individual listeners' needs. Metadata identifies each program's original production format: mono, stereo, matrixed, or discrete surround to ensure the proper playback mode. It maintains a subjectively constant, dialogue keyed loudness level as the listener switches between programs, and allows the listener to apply a pre-determined amount of dynamic range compression when listening conditions warrant. The DP571 and DP572 provide a signal path for Dolby Digital Metadata by multiplexing it into the Dolby E-encoded audio stream. Each group of audio channels, defined as a single program, has its own set of associated Metadata to control program loudness and the program dynamic range by establishing better peak level to average level ratios. The aim is to offer the end user the widest possible dynamic range while maintaining an appropriate average listening level.
2) TIMECODE ON FILM - AATON TIME CODE
Presented by Tony Meerakker, Magnetic North (SMPTE)Next to present was Tony Meerakker representing SMPTE to speak about timecode on film. The production community has traditionally relied on some form of reference code on film, such as Keycode, which is pre-printed on the edge of the film by the manufacturer. More recently the industry has come to rely on two new types of timecodes that are actually printed on the film during the shoot: Aaton and Arri timecode. With Aaton timecode, the camera is equipped to record timecode using a light emitting diode which prints the code during the shoot. The sound recording device, with its own timecode system, is jammed via Aaton's Origin C timecode generator, which is used to jam all the recording devices to ensure precise video and audio sync throughout the post- production process.
Benefits include: smart slate is not required during the shoot, which means you end up shooting less film, which means less film to be processed, which results in major savings. Also synching audio during telecine can be automated using new Indaw technology, which eliminates the need for post sync, which results in a further savings. The Indaw System is an audio recording device (a "glorified workstation") which burns a CD of the audio with a timecode reference. Tony sited examples of projects that have came through Magnetic North using Aaton timecode such as "My Private Oshawa" for . In another example was Cronenberg's most recent film "eXistenZ" in which the location audio was recorded to Nagra D (4 channels). The audio and video was then digitized into the Avid Media Station at Magnetic North. The audio was then transferred to Jaz for export into ProTools. Other examples of television shows currently using Aaton timecode are: Seinfeld, DS9, Voyager, and Baywatch.
Tony warned that there are certain pitfalls to watch for when using Aaton timecode. The cameras and recording devices must be re-jammed periodically during the production day to avoid drift in sync, accurate record keeping during all stages from production to post production is a must, the wrong ASA exposure setting for timecode system can degrade the timecode signal, Aaton timecode is only good for 24, 25 or 30 frame rates, it can not handle variables or varispeed, and Arri and Aaton timecode systems are currently not compatible.
Finally Tony played a video of a live demonstration of Aaton timecode in which Magnetic North participated called "Codeworks". "Codeworks" involved a three camera shoot of a band in front of a live audience, the film was then processed at the Lab immediately and digitized into Media Station at Magnetic North. Finally the picture was edited into a music video, all in about 3 hours and 15 minutes.
A special thank you to Tony Meerakker and our friends at SMPTE, Tim Carroll of Dolby Laboratories Inc., Sean Cowan for organizing the evening and our hosts, Ryerson
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