I made a little test. I encoded two files with LAME 3.97 @ -V2 --vbr-new
Encoded with fb2k's Track Gain, Preamp +5 dB, Clipping prevention, 24-bit output to the encoder
(this is practically the same as the source file would have been wave gained to max peak):
CODE
File Name : Julia max.mp3
File Path : D:\Rip\gaintest\Julia max.mp3
Subsong Index : 0
File Size : 3 811 541 bytes
Last Modified : 2006-10-08 00:07:52
Duration : 2:54.200 (7682220 samples)
Sample Rate : 44100 Hz
Channels : 2
Bitrate : 175 kbps
Codec : MP3
Codec Profile : MP3 VBR V2
Encoding : lossy
Tool : LAME3.97
Tag Type : id3v2|id3v1
Track Gain : -1.57 dB
Track Peak : 1.002913
<ENC_DELAY> : 576
<ENC_PADDING> : 2196
<MP3_ACCURATE_LENGTH> : yes
<MP3_STEREO_MODE> : joint stereo
Encoded without replay gain:
CODE
File Name : Julia.mp3
File Path : D:\Rip\gaintest\Julia.mp3
Subsong Index : 0
File Size : 3 807 037 bytes
Last Modified : 2006-10-08 00:07:52
Duration : 2:54.200 (7682220 samples)
Sample Rate : 44100 Hz
Channels : 2
Bitrate : 175 kbps
Codec : MP3
Codec Profile : MP3 VBR V2
Encoding : lossy
Tool : LAME3.97
Tag Type : id3v2|id3v1
Track Gain : +7.20 dB
Track Peak : 0.362403
<ENC_DELAY> : 576
<ENC_PADDING> : 2196
<MP3_ACCURATE_LENGTH> : yes
<MP3_STEREO_MODE> : joint stereo
Suprisingly both files have the same bitrate. I tried to ABX the files with foobar, but couldn't make any differance.
Based on this I would assume that a 8.77 dB volume level drop in otherwise practically identical source files is not enough to make LAME degrade the perceived quality when the MP3 files are levelled back to the same volume during playback. (Naturally I used replay gain when I tried to ABX the files.)
EDIT
However, the files are not identical. EncSpot Pro found slight differences:
Julia max.mp3CODE
Bitrates:
----------------------------------------------------
32 0.5%
128 0.6%
160 |||||||||||||||||||||||||||||||||||||||| 51.9%
192 |||||||||||||||||||||||||||||||||| 44.5%
224 | 2.2%
256 0.1%
320 0.0%
----------------------------------------------------
Type : mpeg 1 layer III
Bitrate : 174
Mode : joint stereo
Frequency : 44100 Hz
Frames : 6672
ID3v2 Size : 2534
First Frame Pos : 2534
Length : 00:02:54
Max. Reservoir : 511
Av. Reservoir : 61
Emphasis : none
Scalefac : 0.1%
Bad Last Frame : no
Encoder : Lame 3.97
Lame Header:
Quality : 77
Version String : Lame 3.97
Tag Revision : 0
VBR Method : vbr-mtrh
Lowpass Filter : 18600
Psycho-acoustic Model : nspsytune
Safe Joint Stereo : yes
nogap (continued) : no
nogap (continuation) : no
ATH Type : 4
ABR Bitrate : 32
Noise Shaping : 1
Stereo Mode : Joint Stereo
Unwise Settings Used : no
Input Frequency : 44.1kHz
Julia.mp3CODE
Bitrates:
----------------------------------------------------
32 0.5%
56 0.0%
64 0.0%
80 0.1%
96 0.0%
112 0.1%
128 0.6%
160 |||||||||||||||||||||||||||||||||||||||| 52.1%
192 ||||||||||||||||||||||||||||||||| 44.0%
224 | 2.4%
256 0.2%
320 0.0%
----------------------------------------------------
Type : mpeg 1 layer III
Bitrate : 174
Mode : joint stereo
Frequency : 44100 Hz
Frames : 6672
ID3v2 Size : 2534
First Frame Pos : 2534
Length : 00:02:54
Max. Reservoir : 511
Av. Reservoir : 62
Emphasis : none
Scalefac : 0.1%
Bad Last Frame : no
Encoder : Lame 3.97
Lame Header:
Quality : 77
Version String : Lame 3.97
Tag Revision : 0
VBR Method : vbr-mtrh
Lowpass Filter : 18600
Psycho-acoustic Model : nspsytune
Safe Joint Stereo : yes
nogap (continued) : no
nogap (continuation) : no
ATH Type : 4
ABR Bitrate : 32
Noise Shaping : 1
Stereo Mode : Joint Stereo
Unwise Settings Used : no
Input Frequency : 44.1kHz