I compared 3.90.2 and 3.94.a12 --standard profile on a contempory piano track. Nice and clear recording. I'm impressed by the overall quality of the new compile. On the sharpest attacks, 3.90.2 is easy to ABX (pre-echo, smeared attacks). 3.94a12 is much harder : crisp sound.
EDIT both are 137 kbps (30 seconds). I can't put encspot graphs, but they are interesting. 3.94 is generous in 256 & 320 frames in the pre-echo area. Bitrate is the same, because of 37% of 96 & 122 kbps frames. 3.90.2 is giving 80% of 128 kbps frames.
Bitrates:
----------------------------------------------------
32 1.8%
128 |||||||||||||||||||||||||||||||||||||||| 78.7%
160 ||||| 11.4%
192 || 4.4%
224 1.6%
256 0.9%
320 1.0%
----------------------------------------------------
Type : mpeg 1 layer III
Bitrate : 137
Mode : joint stereo
Frequency : 44100 Hz
Frames : 1480
ID3v2 Size : 0
First Frame Pos : 0
Length : 00:00:38
Max. Reservoir : 511
Av. Reservoir : 305
Emphasis : none
Scalefac : 2.1%
Bad Last Frame : no
Encoder : Lame 3.90
Bitrates:
----------------------------------------------------
32 || 1.8%
96 |||||||||||||||||||| 13.4%
112 ||||||||||||||||||||||||||||||||||||||| 25.0%
128 |||||||||||||||||||||||||||||||||||||||| 25.5%
160 |||||||||||||||||||||||||||| 18.2%
192 |||||||||||||| 9.1%
224 ||||| 3.6%
256 ||| 2.1%
320 || 1.3%
----------------------------------------------------
Type : mpeg 1 layer III
Bitrate : 138
Mode : joint stereo
Frequency : 44100 Hz
Frames : 1480
ID3v2 Size : 0
First Frame Pos : 0
Length : 00:00:38
Max. Reservoir : 511
Av. Reservoir : 83
Emphasis : none
Scalefac : 4.2%
Bad Last Frame : no
Encoder : Lame 3.94 (alpha)