[flac-dev] Retuning compression levels

[Martijn van Beurden]

Hi all,

With the patch I mailed earlier today, I found out a few 
adjustments could be made to the compression level settings.This 
retuning speeds up the encoding and improves compression, while 
not changing anything decoding-wise.

Currently, compression settings are as follows

-5, -l 8 -b 4096 -m -r 5 -A tukey(0.5)
-6, -l 8 -b 4096 -m -r 6-A tukey(0.5)
-7, -l 8 -b 4096 -m -e -r 6-A tukey(0.5)
-8, -l 12 -b 4096 -m -e -r 6-A tukey(0.5)

I suggest the following, in case my previous patch is accepted

-5, -l 8 -b 4096 -m -r 5 -A tukey(0.5)
-6, -l 8 -b 4096 -m -r 6-A tukey(0.5);partial_tukey(2)
-7, -l 8 -b 4096 -m -r 6-A 
tukey(0.5);partial_tukey(2);punchout_tukey(3)
-8, -l 12 -b 4096 -m -r 6-A 
tukey(0.5);partial_tukey(2);punchout_tukey(3)

See this graph for comparison:

http://www.audiograaf.nl/misc_stuff/setting-visualisation.pdf

This data was acquired with a reasonably large dataset (one 
track from each album with which the comparison on 
http://xiph.org/flac/comparison.html was made, so 43 tracks from 
43 different CDs), which I think is quite nicely balanced.

It looks like -6 will be almost as good as -8 is now, but much 
faster. -7 will be a bit slower and -8 will be a bit faster, but 
both will compress beter than -8 does now. I dropped -e because 
it's compression improvement isn't worth the slowdown, but it is 
easy for the user to add this anyway.

Would this be a good idea? Any comments?