Basically SoundFonts are files that contain recorded audio samples of various musical instruments. A "pure" synthesizer would not use any recorded sound. It would create sound electronically, using different parameters to imitate instruments.
Such an imitation, however, is far from natural sound.
Sampling synthesizers are different. They take a recorded sample and reuse it at different pitches and dynamic levels. Quality of sound depends here mainly on how many samples per instrument were recorded.
MIDI to MP3 Converter is able to play role of a sampling synthesizer. It takes a MIDI file and converts it to WAV (or some other format) using SoundFonts. Different SoundFonts allow you to produce different sound out of the same piece, and that's can be fascinating by itself. Professional musicians can use specialized SoundFonts - for piano, trumpet, guitar etc. Also complete GM (General MIDI) sets of sounds exist, you need them to play all instruments in a complex MIDI file.
There is a great number of SoundFonts on the internet. Some of them are free, some are not. For free SoundFonts we recommend to explore the following websites:
I also use the MIDI converter software to create audio CDs for choir members to learn their parts. Some of them don't have computers and e-mail to use MIDI files, so with the converter I can give them a CD to play on standard audio equipment.Earl Hughes