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Full Version: lame 3.96.1 - new ATH type

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Zenzile

Feb 8 2005, 21:42

hi,

first sorry for bad english...

I noticed that the 3.96.1 version of lame uses ATH type 4 by default, the olders versions used ATH type 2 by default.

i understand that ATH means 'Absolute threshold of hearing' and it means that whats encoded will only be frequencies that humans can hear.

but why they have decided to use 4 as the default if 2 is supposed to be optimal in olders versions ?

and what's the difference between all types ? (1 to 5)

thank's for all answer

Zenzile

Feb 8 2005, 21:57

i just find this in the "Full command line switch reference" :

QUOTE

* --athtype 0/1/2 select ATH type
The Absolute Threshold of Hearing is the minimum threshold under which humans are unable to hear any sound. In the past, LAME was using ATH shape 0 which is the Painter & Spanias formula. Tests have shown that this formula is innacurate for the 13-22 kHz area, leading to audible artifacts in some cases. Shape 1 was thus implemented, which is over sensitive, leading to very high bitrates. Shape 2 formula was accurately modelized from real data in order to real optimal quality while not wasting bitrate. In CBR and ABR modes, LAME uses ATH shape 2 by default.
In VBR mode, LAME is adapting its shape according to the -V value, going gradually from the 0 shape at -V9 up to shape 2 at -V0.

a mp3 encode with this command line :

--abr 128 -m j -q2

EncSpot says that the ATH type is 4, is this a lame bug ? encspot bug ? Zenzile bug ? other ?

music_man_mpc

Feb 8 2005, 21:58

The encoder has changed in a wide variety of ways since the older versions asking why one or two different variables have changed since 3.90.3 is meaningless. The default settings for the --alt-presets in 3.90.3 would produced very different results in 3.96.1 due to developments in the code, not to mention sub-optimal results.

music_man_mpc

Feb 8 2005, 22:07

QUOTE (Zenzile @ Feb 8 2005, 12:57 PM)

a mp3 encode with this command line :

--abr 128 -m j -q2

EncSpot says that the ATH type is 4, is this a lame bug ? encspot bug ? Zenzile bug ? other ?

#1. I believe that --abr 128 should produce the same files as --preset 128, but if not --preset 128 will be a better choice. If they are the same then -m j is default and you need not add it to your command line.

#2. If -q2 is not the default for --preset 128 it is probably sub-optimal so just use --preset 128.

#3. Encspot isn't perfect, but be it right or wrong the default ATH is almost certainly perferrable, just leave the presets alone.

#4. If you don't mind using VBR -V5 --athaa-sensitivity 1 will produce better quality at ~128kbit/s. --athaa-sensitivity 1 is used because of a bug in LAME 3.96.1 by the next version adding this switch will probably reduce quality, but for now it is better.

Zenzile

Feb 8 2005, 22:30

ok thank's for your answer

don't you think it could be an error made by the developpers ? I think that it would be better to ask us...

finally, what the switch "--athaa-sensitivity 1" do ?

Gabriel

Feb 8 2005, 23:00

Ath4 has a parameter to adjust its slopness, so it can take the shape of ath 0-3 from previous versions.
In current versions every ath curve is internally ran through the ath4 model, with different parameters.
So this is just a simplification in the code.

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