MIDI Converter Studio supports 4 popular audio formats that can be used for output files: WAV, MP3, WMA, and OGG Vorbis.
Select the desired format from the drop-down menu:
For advanced options click "Setup..." button. "Options" window will appear.
Here you can set parameters that determine quality of the resulted files: frequency, mode (Stereo or Mono), and bitrate. The lower are frequency and bitrate, the smaller will be output files, but the worse will be quality. You can also make files smaller by switching to mono.