If you want to convert MIDI file to WAV file online, you can use some of the following free converters:
Hamienet – upload your MIDI file, select desired sample width, sound system (mono/stereo) and instrument set (the best feature). You can also change the volume, transpose the song and select bit rate. Then click the “Convert” button and you are done.
Media.io – upload MIDI file, select output format (WAV, MP3, OGG or WMA), select bitrate quality and press the “Convert” button.
Free MIDI converter – upload MIDI file, enter the title, select genre and press the “Submit” button.
For Winamp users, there’s a great tutorial in MIDI to WAV conversion using Winamp.
If you want to use free MIDI to WAV converter, you can download this free converter.