Is it possible to modify OS X default MIDI sounds?
Louis Boux wants to substitute the default DLS soundfont of General MIDI sounds used by QuickTime to another DLS soundfont. Such soundfonts are files that end in .sf2 format.

It was possible to do this in earlier versions of QuickTime, such as QuickTime 5 or QuickTime 6, back around the year 2002 and earlier. In fact, I did this myself on older systems. However, QuickTime X cannot read an .sf2 file directly. It must be converted into .dls format.

By way of background, when you click on a standard MIDI file linked to a Web page, for instance, QuickTime plays it back inside your Web browser using QuickTime's built-in MIDI sound library, which is of poor quality. This sound library was licensed from the Roland company some 15 years ago and has never been improved upon.

The soundfont that I was able to use as a substitute in older systems is a GeneralMIDI soundfont which is provided with MakeMusic Finale Reader, which is free.