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Old 19th August 2009, 12:49   #9204  |  Link
Fiffy
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Join Date: Jun 2009
Posts: 21
Quote:
Originally Posted by jruggle View Post
Both AC3 and E-AC3 use random noise as part of the decoding process. From the tests I have done so far, the difference between the output of libavcodec and Nero is approx. the same as the difference between using 2 different types of random number generators in the libavcodec decoder. The type of RNG used is not defined in the specification. It even says that the level of the noise, which should be 0.707, can be approximated to 0.5 and still be compliant.
Maybe I'm missing something (haven't looked into the spec in a long time), but as far as I know, an AC3 decoder only uses random noise if dithflag is set in the stream. Apart from that the decoder is deterministic (of course an implementation may still use dithering to reduce the word length for output). I'm sure Dolby takes this into account in the certification process.
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