Build a SoundFont MIDI Synthesizer (Part 1)

摘要

Back in Circuit Cellar issue 328 (November 2017), I described a Hammond tonewheel organ emulator using a Teensy 3.6 module. The Hammond organs used mechanical tonewheels to generate 91 sine waves at the required "musical" frequencies, and the organ mixed these to produce a wealth of different "voices." It was based on the mathematical principle that you can generate virtually any desired waveform by combining sine waves consisting of the fundamental tone and various proportions of higher harmonic frequencies. Although these organs produced a rich variety of voices, many sonic subtleties are present in conventional musical instruments that were not present in the Hammond organ's sound-or any electronic organ, for that matter. The most notable difference is that when you play a conventional musical instrument, each note has an amplitude envelope. That is, its amplitude rises quickly from silence, stays at some relatively constant value while the note is being held and then decays (usually exponentially) back to silence after the musician stops playing that note.