This subject came up recently on HelpScreen.com.au, and is an FAQ topic on most MP3 and audio sites. Although many audio programs, such as Windows Media Player and Winamp, will play MIDI files along with MP3s and other digital audio files, MIDI files are fundamentally different from the others. Unlike MP3 and WAV files, they contain no sound data at all, just score notation for the music to be played. This information needs to be interpreted by a piece of musical software or hardware, just as a written piece of music needs to be interpreted by a musician with an instrument. In a sense, you could think of MIDI being like HTML, and the music like a Web page.
When you play a MIDI file with a media player, the music is played through the built-in synthesiser chip in your sound card. More often than not, this will result in a very cheesy and artificial sounding piece of music -- regardless of how good the piece of music may actually be! This is because most sound cards are designed with very low quality on-board MIDI instruments, even if the output is technically CD quality audio. If you are fortunate enough to have a professional sound card with high-quality MIDI implementation, then this may not be an issue and you can simply play the file in Winamp while recording the sound card's output in sound recorder, Cool Edit or any other audio program.
With a SoundBlaster Live! card, you select "What U Hear" as the audio record device. Other sound cards use "Playback", "Sound card Output" or other similar terms for the same thing. If your sound card doesn't have this feature, you can simply plug the speaker output of your sound card into the line-in and record it, although this is not ideal. If, however, your sound card makes everything MIDI sound terrible, regardless of how you record it, then you may want to try one of the following alternatives.
WAVmaker (http://www.polyhedric.com/software/wavmaker/)WAVmaker is a program dedicated to the task of rendering MIDI files into WAV files (which you can then convert to MP3 using your favourite MP3 encoder). The benefit of using WAVmaker over the methods described above is that you can individually select each instrument to be used in the composition. It also comes with a CD full of quality MIDI instruments that can be used in the program -- giving you a lot more flexibility than simply using your sound card's built-in sounds. It is extremely easy to use and even supports batch conversion. Just open the MIDI file, preview with the default instruments, select any new instruments whose sounds you prefer, and click render (Figure 1).
Audio Compositor (http://home.att.net/~audiocompositor/)Audio Compositor is aimed at the professional musician and is a more sophisticated and versatile MIDI to WAV rendering application (Figure 2). The benefit of Audio Compositor over most other MIDI converters is that it supports standard file formats such as SoundFonts (SF2), Kurzweil instruments (KRZ), and Downloadable Sounds (DLS). These files can be downloaded from the Internet, purchased on CD, or hand crafted with the built-in patch editor -- giving almost infinite flexibility for your MIDI sounds. Audio Compositor can also be used in real time with a sequencer as a virtual MIDI instrument. Plus, because it comes with a patch editor, wave editor, and sample librarian, it could be the all-in-one solution you need if you don't already own any other audio software.
Edirol Virtual Sound Canvas (http://www.edirol.com/products/info/vscmp1.html)At the top end of the spectrum is the Edirol range of MIDI instrument software, of which Virtual Sound Canvas (VSC) is the most comprehensive (Figure 3). VSC is designed to be used within music composing software such as Cubase, Logic Audio, Sonar, Cakewalk or FruityLoops, as a virtual instrument' (using both VSTi and DXi standards). It also has a built-in MIDI to WAV conversion function, so you can use it as a stand-alone application (Figure 4). Either way, it is intended to be a software replacement for expensive hardware sound modules such as the Roland JV1080 (Figure 5) and Yamaha MU15 (Figure 6).
Got a digital audio question? Ask HelpScreen.