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Old September 13th, 2006, 11:54 AM   #1
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Another AC3 Question

Does anyone know exactly how the DolbyDigital AC3 compression works, the technical specs? I know the converter needs a certain bitrate and sampling rate input (I am using apples A.Pack), but what is the output that comes out of the DVD decoder?

I am mostly concerned with the sampling rate . For my purposes the accuracy of the timing of the sound impulses is absolutely crucial to me since they need to be synchronized with other 48kHz equipment.

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Old September 14th, 2006, 08:09 AM   #2
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Dolby Digital supports sampling rates of 32khz, 44.1khz and 48khz, though the DVD spec only allows the last. HD allows higher sampling rates, of course, all the way up to 96khz and even 192khz. Whitepapers can be found here.
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Old September 17th, 2006, 09:26 PM   #3
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The decoder in the DVD player will output straight PCM.

AC3 is a great format because it doesn't compress too much, and has extensive metadata for dialogue normalization and dynamic range compression. Usually 2 channel AC3 is CBR 192kbit. 5.1 is typically 384 or 448 kbit, depending on how much space is available on the DVD.

Some people say DTS is worth the extra bitrate (near 1500kbit for 5.1 IIRC), but I have never been able to hear a difference. Maybe on really killer equipment.

AC3 is definately the way to go for DVD though, because its way smaller than PCM, and is much higher quality than MP2 (and smaller to boot). The metadata is an added bonus!

-Derek Prestegard
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