[Mp4-tech] public AAC at 128kbps listening test open

[Ivan Dimkovic]

Hi Jenn,
Actually it was debated in earlier tests - I fully agree that comparing
so-called 'CBR' codec (although they are not really CBR in strict terms) and
'VBR' ones is comparing apples and oranges.  However, like in earlier test
("128 kb/s extension test") codecs were used with settings which equal to
128 kb/s >in average<
Although Nero codec in fact gives 141 kb/s on this sample set - it has been
found out  (
http://www.hydrogenaudio.org/index.php?showtopic=18474&view=findpost&p=18586
8 ) that it gives ~2% higher bit rate than 128 kb/s in average (more than
500 tracks encoded)  - which is OK for this test (last extension test had
even bigger deviations) - fact that it is 141 kb/s on this particular sample
test only tells that the sample set is hard to encode - when encoding to VBR
you want to end up with constant quality, not constant rate.
Problem with testing 'VBR' encoding modes is that you can't really tell
encoder that you want some bit rate, otherwise you end up with CBR codec...
but I agree that in that case you shouldn't really mix CBR and VBR operating
modes of encoders.
-- Ivan
----- Original Message -----
From: ejenn2000-mp4 yahoo.com
To: mp4-tech lists.mpegif.org
Sent: Friday, February 20, 2024 9:28 AM
Subject: Re: [Mp4-tech] public AAC at 128kbps listening test open
Glad to see this is happening. However, I am sorry (and hate) to say that
the result may not have any value because it is comparing apples with
oranges. The average bitrate for Ahead/Nero AACenc (a VBR codec) to encode
these test samples is as high as 141 kb/s!!!!! However, CBR codecs like
iTunes and Real are only at 128 kb/s for all these test samples. Any
experienced AAC developer will tell you that at this high bitrate 7-8 kb
more will significantly improve the resulting sound quality. It would really
be a surprise if iTunes or Real can beat Nero with such a lower bitrate.
This is just not a test at 128 kb/s as the title called. It is comparing
samples encoded at 141 kb/s and at 128 kb/s. I think the winner is obvious
without going thru the test...
Jenn
> From: bond <b-o-n-d gmx.net>
> Date: February 18, 2024 1:11:29 PM PST
> To: mp4-tech lists.mpegif.org
> Subject: [Mp4-tech] public AAC at 128kbps listening test open
>
> Hi!
>
> Since there has been a lot of development in the AAC codec market in
> the last months, Roberto Amorim kindly set up a listening test, open
> for everyone to join, aiming at finding out what encoder performs best
> AAC encoding at an average bitrate of 128kbps.
>
> The used method of comparing codec quality is by performing so-called
> "Double Blind Listening Te! sts". In this sort of test, the participant
> compares various encoded samples against each other and against an
> uncompressed reference sample. The blind part means that the
> participant doesn't know which sample was encoded by which encoder.
> That guarantees there'll be no psychological bias towards his/her
> favorite codec, or against the codec he/she dislikes.
>
>
>
> The AAC at 128kbps listening test is now open. Everyone is invited to
> participate!
>
> Instructions on how to participate are available at this page:
> http://www.rjamorim.com/test/aac128v2/presentation.html
>
> The test will run until February 28th, and may be extended if proven
> necessary.
>
>
> Results of already conducted listening ! tests can be found here:
> http://www.rjamorim.com/test/
>
> enjoy

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