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Topic: How much better is aac than ac3 ? (Read 9737 times) previous topic - next topic
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How much better is aac than ac3 ?

i got a clear understanding from this forum that AAC woulde provide better audio quality then AC3 (alias Dolby Digital)

But how big is the difference..roughly ???

1: If i had acces to the uncompressed 5.1 sound for a movie
at what bitrate would psytell aac give a quality equal to 384kbits AC3 ?

2: If i was to compress a 384kbits ac3 stream. How low could i get bitrates befores big loss of audio quality* and/or loss of channels ?

*compared to running stereo at 128 mp3-abr



What i was hoping for was to get 5.1 audio below 256kbits but it almost sound like to few bits..


[edit]
Spelling errors corrected
Sven Bent - Denmark

How much better is aac than ac3 ?

Reply #1 –
Quote
Originally posted by sven_Bent
i got a clear understanding from this forum that AAC woulde provide better audio quality then AC3 (alias Dolby Digital)

But how big is the difference..roughly ???

1: If i had acces to the uncompressed 5.1 sound for a movie
at what bitrate would psytell aac give a quality equal to 384kbits AC3 ?

2: If i was to compress a 384kbits ac3 stream. How low could i get bitrates befores big loss of audio quality* and/or loss of channels ?

*compared to running stereo at 128 mp3-abr

What i was hoping for was to get 5.1 audio below 256kbits but it almost sound like to few bits..

[edit]
Spelling errors corrected


I would compare 448 kbps AC3 with 256 kbps MPEG-4 AAC for normal music. With transient signals
AC3 has much bigger problems than MP3, some examples also sounds at 640 kbps worse.

See compare of time resolution at my webpage.
--  Frank Klemm

How much better is aac than ac3 ?

Reply #2 –
Take a look at:

http://mpeg.telecomitalialab.com/quality_tests.htm

Document of interest:

http://mpeg.telecomitalialab.com/public/NBC_results.zip

(NBC encoder used was older version of MPEG AAC - current encoders are probably much better)

Codec and bitrate (kbit/s)   Encoding/decoding verification by:   Bitrate verification by:   Verified bitrate (kbit/s)
MPEG-2 NBC (320)   DMV, University of   Five Bats   320
MPEG-2 NBC (256)   Hanover and Five Bats      256
MPEG-2 NBC (224)         224
MPEG-2 NBC - low complexity (320)         320
Dolby AC-3 (640)   DMV, Five Bats, BBC   Not evaluated   Not evaluated
Dolby AC-3 (512)   Verification not possible (see section 2.3)   Not evaluated   Not evaluated
MPEG-2 Layer II (640)   Deutsche Telekom and   Deutsche Telekom   640
MPEG-2 Layer II (512)   Deutsche Thomson Brandt      512

How much better is aac than ac3 ?

Reply #3 –
I will use some 2 channels considerations (all assuming good implementations):

Ac3 192 is slighlty better than mp2 192. Aac 96 main profile should be equivalent to mp2 192.

I don't know if multichannel is better used by aac or ac3, but for 2 channels only, I think that you could consider that for the same quality aac should be 60% of an ac3 size

How much better is aac than ac3 ?

Reply #4 –
thanx for the info
Sven Bent - Denmark