*Now* I remember what this was about: "preset=12" is an edcast/Icecast setting in the .ini that is sent to the lame_enc.dll to invoke standard CBR encoding, as opposed to a VBR preset.
I was actually able to dig up an email from years ago regarding that, and here are all the Ed/Icecast presets and what they map to in the .dll:
LQP_NORMAL_QUALITY = 0,
LQP_LOW_QUALITY = 1,
LQP_HIGH_QUALITY = 2,
LQP_VOICE_QUALITY = 3,
LQP_R3MIX = 4,
LQP_VERYHIGH_QUALITY = 5,
LQP_STANDARD = 6,
LQP_FAST_STANDARD = 7,
LQP_EXTREME = 8,
LQP_FAST_EXTREME = 9,
LQP_INSANE = 10,
LQP_ABR = 11,
LQP_CBR = 12
I have no idea what the "normal/low/high/voice" of 0-3 map to, and that fact that good ol' "r3mix" is in there gives you an idea of how old those presets are, but preset 12 does/did give better results than preset 0 at the same bitrate.
Also, IIRC ( ) the "quality=" switch didn't map directly to LAME's -q switch, i.e. it invoked the -q switch, and lower numbers were higher quality, like LAME, but I don't think it was a 1:1 relationship - I never saw any actual documentation on that, though.
In any event, "preset=12" does give the best quality CBR encoding in Ed/Icecast, and the "quality=" parameter is something of a wildcard, although it should be at least set to 3 because I think the default was 5, and that did make at least a bit of an improvement with CBR.