Dolby Digital Maximum Data Rate
Dear Gary: In your response to Mr. Ware on page 34 of Issue 31, you made a few errors about Dolby Digital. “Already Dolby is pushing for DVDs to be encoded at the higher limit of the AC-3 coding, 448 kb/s, rather than 384 kb/s, that is supported by the IC silicon decoders now in use. AC-3 is supposed to support a data rate of 640 kb/s as its maximum capability, but there are no chip sets that actually support that data rate.” 384 kb/s is not the limit for any AC-3 IC decoders. If you have a Sony 7000 DVD player and a Delos DVD Spectacular with the “hidden” 640 kb/s track (29), you can easily confirm every decoder will play the 640 kb/s stream, let alone 448 which is even easier to confirm from any number of standard DVDs. So there are indeed many chip sets that can handle 640 kb/s.
Roger Dressler, Technical Director, Dolby Laboratories, San Francisco, California
Editor Gary Reber Comments:
I stand corrected. Some Dolby Digital chips sets can decode 640 kb/s, but I am not convinced that “all” Dolby Digital chip sets can do so. The phrase I should have written is “...but not all chip sets can actually support that data rate.” It is true that a number of motion picture titles on DVD have 448 kb/s data rate soundracks. Our “Find It DVDs” section of our Website, www.Widescreen Review.com, has extensive criteria search fields including ones on Dolby Digital and DTS Digital Surround data rates.
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