While an increasing number of studios are gearing up for surround production, listening to the six discrete 5.1 tracks is definitely not the same as hearing the product as it sounds after passing through the encode/decode chain. Up until now, many producers skipped this vital step, due to the cost of hardware. And although the price of a Dolby Digital reference encoder has dropped from $50,000 to $30,000 to $19,600 over the years, it was still on the pricey side for studios that needed an encoder only occasionally. Now, with its DP569, Dolby has brought the cost of a professional reference encoder down to an affordable $5,000, while offering more features than did the product's predecessor and fitting the unit into a single-rackspace chassis. The DP562, a companion reference decoder, is $3,600.
Since its debut in 1992 with the film Batman Returns, Dolby Digital (AC-3) has been used on hundreds of films. AC-3 provides six channels of surround sound information in the 5.1 format, using the psychoacoustic phenomenon known as auditory masking and both inter- and intra-channel redundancy for the efficient storage and transmission of digital audio.
But beyond its application in feature film presentation, Dolby Digital has been used on laserdiscs, and it is the audio format for DVD-Video, SCTE digital cable TV and the audio standard for ATSC digital broadcast TV. Dolby Digital also allows tailoring the number of channels and bit rates for various applications, such as 5.1 (at 384 to 448 kbps) for consumer surround or two channels (at 192 kbps) for stereo programming. More than 7 million consumer products equipped to decode programs with Dolby Digital audio are already in use, from DVD players to set-top boxes.
The DP569 supports encoded bit rates from 56 to 640 kbps and channel configurations from mono to 5.1-channel surround sound. LTC and VITC timecode inputs allow automatic configuration changes in a broadcasting environment. Disc authoring facilities can also use timecode to encode separate program segments accurately and create single encoded soundtrack files; serial control via an RS-232 port is also available for customized automation applications.
Designed to complement the DP569, the Dolby DP562 decoder provides state-of-the-art AC-3 decoding for reference monitoring of 5.1 Dolby Digital tracks as well as 4-channel Dolby Pro Logic decoding. The DP562 also has a mode for monitoring "downmixed" signals, where a 5.1 Dolby Digital input is automatically mixed down to a 2-channel (Lt-Rt) Dolby Surround signal and then is processed through the unit's built-in Pro Logic decoder. This allows engineers to hear what end-users would experience if they listened to a 5.1 transmission or source received through a 2-channel decoder and a Pro Logic decoder-equipped playback system. Other DP562 modes offer the ability to listen to multichannel material in multichannel, stereo or mono systems, LCR systems without surrounds, or surround systems that lack a center channel.
The DP569 has a single AES digital output, three pairs of AES digital inputs (for channels 1/2, 3/4 and 5/6) and another AES input for use as a clock reference or for multiplexed AES bitstreams containing multiple Dolby Digital signals. Previously encoded Dolby Digital audio bitstreams pass through unchanged-and automatically, if the DP569's bitstream detection feature is activated. Matrix encoding on Dolby Surround input signals is also unaffected. The DP562 decoder has one AES digital input that accepts either PCM or AES audio in IEC 1937 format; outputs are three male XLRs carrying the 5.1 signals as three stereo pairs. A headphone output and balanced analog outputs (routed through onboard 20-bit DACs) on XLRs are also standard on the DP562.
The front panels on both units have channel activity LEDs and alphanumeric LCDs showing status parameters. Front and rear panel serial interfaces, along with application software, make it possible to configure and control the DP569 from Windows 95/NT-equipped PCs or other remote devices. The DP569 includes a record utility that acts as a data packer, stripping out any redundant extra zeros from the AES3 output, and putting the data into the ".AC3" format for multimedia applications.
For more information, contact Dolby or check out the company's Web site, which has extensive information about Dolby Digital, AC-3 coding and other aspects of surround sound.
Dolby Laboratories, 100 Potrero Ave., San Francisco, CA 94103; 415/558-0200; fax 415/863-1373. Web site: www.dolby. com.