I've been encoding music for leasten on my pc at very low bitrate (like 30-40kb/s) and mono. I don't get what I want, and that's not good sound, but something that doesn't make me to cut at 12khz and fills the music with horrible artifacts. I made a set of 4 cd's with all my music, but I discovered that realaudio makes a really good job at 24kb/s. Is there something to do with mp3, or even other format at such bitrates? I think it isn't, but if anyone...
Thanks and sorry about my english...

It's quite normal, different codecs are tuned for different bitrates. RealAudio has always been targeted towards streaming, therefore it has the best tuning for very low bitrates. MP3 is not the codec to use for anything less than 128kbps.

For other codecs which might work at that bitrate you want, try WMA or MP3Pro.

I might get some crap from others for recommending this, but if you want a decent 80kbps codec, look into VQF - Nero includes a decent encoder, but you'll have better luck if you feed it files that are highpassed at 15Hz and lowpassed at 16kHz.

I agree, VQF is very nice for low bitrates. I encoded a stereo 96 kbps piano piece and it sounded quite nice. Perhaps mono lets you half the bitrate.

-gft

If encoding in the 40kbps/channel mode, if your using a mono file, then yes, you can get equivilant results of an 80kbps VQF at 40kbps, and likewise for 48kbps/channel mode (if my memory serves me correctly).