OVER = number of scalefactor bands with distortion that exceeds the allowed distortion given by the masking thresholds. OVER is computed by outer_loop, and the masking thresholds are computed by the psycho-acoustic model.
VBR_q = the minimum value of OVER which is to be allowd. Default = 4. Can be set from 0..9 with -V. Setting VBR_q = 0 is the highest quality, but will produce larger files. VBR_q = 9 will produce small files and poor results.
VBR_min = the minimum allowed bitrate. Default = ? Can be set with -b.
VBR_max = the maximum allowed bitrate. Default=256kbs, unless the minimum bitrate is 256kbs or higher, in which case VBR_max=320kbs. (the highest allowed by MP3)
The LAME VBR algorithm is at present very simple:
LAME will find the smallest allowed bitrate such that OVER <= VBR_q.
If the frame contains short blocks, then the minimum bitrate is made much larger since the OVER will not measure distortion casued by pre-echo. We use bitrates of at least 160kbs for short blocks to make sure they sound good.
Usage notes:
If you want to use VBR to improve the quality of 128kbs encodings while only making the file slightly larger, use:
% lame -v -b 112 input.wav output.mp3
If you want to ge t the maximum compression, try:
% lame -v -b 32 input.wav output.mp3
If the encoded file is much too big, add the option -V n, and try values
of n>4. To improve the quality (and make the file bigger) try
-V n with n<4.