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Lossy Audio Compression => AAC => AAC - Tech => Topic started by: hyaudio on 2018-05-13 12:28:17

Title: USAC (xHE-AAC) sample rate and bit rate
Post by: hyaudio on 2018-05-13 12:28:17
I'd like to know Sample rate and bit rate range supported by USAC.
Title: Re: USAC (xHE-AAC) sample rate and bit rate
Post by: saratoga on 2018-05-13 14:48:52
Lossy formats don't support a specific range of sample bits. Individual encoders might only accept certain sample sizes, but the format has no limit.

Sample rates should be the same as AAC as far as I know. It's backwards compatible.
Title: Re: USAC (xHE-AAC) sample rate and bit rate
Post by: naturfreak on 2018-05-13 15:13:40
Quote from: saratoga on
It's backwards compatible.
No, it's not. The bitstream format ist different from previous versions of AAC. xHE-AAC use a more efficient type of entropy coding.
Title: Re: USAC (xHE-AAC) sample rate and bit rate
Post by: saratoga on 2018-05-13 17:05:37
Quote from: naturfreak on
Quote from: saratoga on
It's backwards compatible.
No, it's not.

Pretty sure it is:  https://hydrogenaud.io/index.php/topic,109486.msg956185.html#msg956185

IIRC, an existing decoder can still decode the underlying HE stream, but not the xHE extension. 
Title: Re: USAC (xHE-AAC) sample rate and bit rate
Post by: naturfreak on 2018-05-13 18:48:06
Well, yes and no.
The answer is: There are two different profiles of xHE-ACC
One that uses the old bitstream format (Huffman-coding)
and the other one that uses the new, non-backwarts compatible bitstream coding (CBAC).
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