You can use Audacity sound editor to convert it to a wave or MP3 file. If you don't have audacity you should. It's free and you can download it here
http://audacity.sourceforge.net/.
Open Audacity and click on project on the top tool bar. Click on import MIDI and select your file hollow.mid. Then click file on the top tool bar and you have the option to export the file as a wave or an MP3. Very simple process