Dolby AC-3

This format has different names:

• Dolby Digital
• DD (an abbreviation for Dolby Digital, often combined with channel count; for instance, DD 2.0, DD 5.1)
• AC-3 (Audio Codec 3, Advanced Codec 3, Acoustic Coder 3. [These are backronyms. Adaptive Transform Acoustic Coding 3 is a separate format developed by Sony.])[12]
• ATSC A/52 (name of the standard)[13]

http://en.wikipedia.org/wiki/Dolby_Digital

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http://emptyeyed.tistory.com/450