Why did you switch from MIDI files to MP3 playback?
What are the differences between MIDI files and MP3 files?

The short answer to both questions is "bandwidth". MIDI files consist of data that instructs a sound card what type of pre-stored or pre-loaded sound (like piano) to use, how loud and long to play each note, pedaling, and other special effects. Since the only data included is an instruction set and notes only as they are needed, and no sound is actually contained in the file, MIDI file sizes are relatively minute. MP3 or similar files such as WMA, AAC or OGG, consist of a compressed version of recorded sound, which even with compression makes them relatively large in comparison to MIDI files. MP3 files require substantially more server space and download time (both facets of bandwidth). The advantage of such sound files is that there is a consistent rendition of the recording, whereas MIDI files are at the mercy of the sounds stored sound card or the browser MIDI plug-in. Also, MIDI has not been properly support in browsers and sound plug-ins since 2012, and bandwidth is not the same issue it was in the first decade of the century.

My MP3 files are rendered in a medium definition mode, specifically with a 96k sampling rate and lower bit resolution as opposed to near CD or iTunes quality AAC files. By using these somewhat smaller files my server space needs are greatly reduced, your uploads are much quicker, and there is a smaller likelihood that my CDs will be pirated, an alarmingly common practice in the internet society that has financial impact on artists. That is also why I can provide you with hundreds of tunes without the need to shell out excessive personal resources on additional server space, and therefore can make them accessible to the public for personal enjoyment and educational purposes. That makes the trade-off worthwhile to all. The MP3 files and their MIDI counterparts are still protected due to the recording methodology I use, making it difficult to create accurate printed renditions or recordings that duplicate the quality that I have on CDs or iTunes. It allows the public maximum access along with incentive to help support the site through the preferred purchase of recorded materials.