[sparqee]

A sound card is an audio interface but when people use the term "audio interface" they are usually referring to a card or external device which is a bit more "high end" than the standard computer sound card. A typical sound card will offer stereo output and perhaps a stereo input though it may only have a mono mic input where as most audio interfaces give you multiple high qualith inputs and outputs. The latency of most sound cards is an issue for music recording (i.e. latency is high which creates a time lag between what the computer is playing back and what you actually hear coming out of the sound card) this can make it tough to overdub in sync to previously recorded tracks. A good audio interface will have low latency and therefore not introduce any noticeable lag time to your audio. I highly recommend getting an audio interface intended for use with music recording. You can get them for as little as $100 or so. Many have an integrated midi interface as well.

In order to turn your midi tracks into a wave file you need to record the audio output of your keyboard into your computer and onto an audio track in Cubase. Once you have your synth recorded as an audio track(s) you can then "export to audio mix down" to create your wav file. I don't believe Cubase LE supports exporting to an MP3 format.