The term „Soundfont“ pictures very well what it’s all about: Same as choosing a font for a text in a word processor, a tone for the music can be selected in music software. And same as formatting headings, text and footnotes with different fonts, each soundtrack of a piece of music can be assigned its own Soundfont sound.
A Soundfont file can contain sounds for any number of instruments. There are countless Soundfonts available for free on the Internet. It is recommended to use a Soundfont covering the 128 General MIDI Standard instruments.
capella reader offers many free General MIDI capable Soundfonts for download. You can simply select the Soundfont whose sounds you like best. You can also mix sounds from different Soundfonts, combine them to your liking and thus individually assemble your own "orchestras".