|The presets (R3mix, Standard, Xtreme etc.)are all VBR/ Joint Stereo and are fairly well refined. They sound good and are wholly adequate for computer use
Actually the dm-preset standard, xtreme, insane presets use a
more conservative joint-stereo mode called nssafejoint. Joint stereo allows the encoder to decide whether to use simple stereo
(L/R) or mid-side stereo (m/s), The dm-presets use much fewer
m/s frames because of the nssafejoint mode than settings using normal joint stereo. I think it only uses m/s frames when the signal is perceptually mono.
This means there is much less chance of having joint stereo screw up. Generally, its a good idea to use joint stereo at 192 Kbs
and less the extra bits it gives the encoder usually does a lot more good at these mid to lower bitrates than the small chance of having joint stereo "mess up". nssafejoint tries to make a tradeoff between the two cases.
btw I highly recommend using the --dm-preset presets. If you want great (you probably can't do much better for mp3) quality at an avg. bitrate of 230-256 Kbps
try using --dm-preset xtreme and the latest 3.90 alpha. (the insane mode is still being tweaked and makes bigger but not nessecarily better files than xtreme)