The write speed index (1x, 2x, 4x, 6x, 8x) is a number that expresses the speed at which the CD is written as a multiple of the play speed of a normal audio CD player. At "single speed" (1x) the recorder will take just as long to write the tracks as a CD player would take to play it -- for example, 60 minutes for 60 minutes of music. At quadruple-speed (4x) the recorder will only takes 15 minutes to write the same data to a CD. However, at higher speeds the bit error rate also increases, resulting in a certain deterioration of audio quality.
Since the arrival of CD recorders a great deal has been written about the advantages and disadvantages of reading and writing audio CDs at speeds higher than the normal playback speed. Purists insist that you must always only use normal playback speed (1x) both for reading (ripping) tracks from audio CDs and for writing (recording) audio CDs.
It's true that increases in speed generally produce a measurable decrease in audio quality, and that single-speed recording does provide the best absolute quality. However "measurable" doesn't necessarily mean that you can actually hear the difference on your audio system. The quality degradation also depends to a great extent on the performance of your CD recorder and the drive you are using to rip the audio tracks. Some drives will produce a very audible difference when recording and ripping at higher speeds, others deliver much better performance. To a certain extent this can also depend on the performance of your computer system.
Because of all these variables and imponderables, many of which are subjective, it's not possible to provide any hard and fast rules on recording speeds. All you can really do is experiment carefully with your system before sitting down to record a whole stack of CDs. Try recording the same tracks at different speeds and compare the results carefully on the best audio system that you plan to use for listening to the CDs later on -- then choose the speed that delivers the best trade-off between speed and quality for your needs and wishes.
The same applies to read speeds for extracting (ripping) audio tracks from music CDs. Some CD-ROM drives, particularly older models, are not designed for high-speed ripping and although they may extract the tracks without producing error messages the resulting music can sound pretty terrible. If this happens you must set the Single Speed read option to force AudioCD MP3 Studio 2000 to read the tracks at single (i.e. playback) speed. You can set this permanently in Options - Settings - Source Drive and for individual read sessions in the Read CD dialog. Again, purists prefer to rip all tracks at single speed only for maximum audio quality. Try it for yourself; you may find that it is worth it, you may find that you can't hear any difference.
Some CD-ROM drives (for example some Teac models) have an internal setting that prevents them from ripping audio tracks at the maximum possible speed. This feature was introduced because the engineers felt that ripping at higher speeds produced an unacceptable degradation in quality. If your drive is ripping more slowly than you might expect this may be the reason. Teac has a software utility that allows you to change this setting. It's available from the Teac website at http://www.xxxxxxxxxxxxxxxx.