sorry, I should probably explain a few things first about audio cds - since I live and breathe anything audio related, I keep forgetting lots of people are not like me, so sorry for that.
When you look at an audio CD in windows explorer, you will see the files on it have file extension .cda. These .cda files do not contain any audio itself though, they are just links to the real audio music. Internally, audio cd music is actually 44.1khz 16bit stereo PCM wave files, which are totally UNCOMPRESSED. It is not possible to compress audio CD music as you are asking, because audio CD music cannot be stored in any other format.
So with that in mind, how much audio can you have on a CD? If you are using a 650mb CD, you can put 74 minutes of music on there. A 700mb CD will hold up to 80 minutes of music.
As a side note, if you do not care about playing your CD in a standard CD or car player, you are free to burn music in "Data" mode, whereby you can put mp3 files on the CD - this will allow you to put much more music onto the disc than an audio CD will allow.