We found an interesting video on YouTube demonstrating additive synthesis on an FPGA – in this case an Altera DE2 board. These guys have set up a MIDI controller keyboard to send note-on, note-off, and velocity for each note played to the DE2. The DE2 has been programmed with VHDL to decode the MIDI messages, and generate a sine, square, triangle, or sawtooth waveform. This data is then run through their TEK TDS-210 oscilloscope for visual feedback, and of course to the speakers so we can hear the results.
Additive synthesis is based upon the “addition” of simple waveforms to create complex harmonics (overtones), which to the human ear result in a more interesting timbre, or tonal quality. Additive synthesis is one of the four basic types of sound synthesis, the others being subtractive synthesis, nonlinear synthesis, and physical modelling synthesis. An FPGA board (including the RetroCade!) can be programmed to achieve each of these types as well. There are many other types of synthesis also (granular, wavetable, etc.) but some of these would inherently be much harder to program. Not saying it can’t be done though!
These guys in the video wind up creating some great MiniMoog type sounds, and even manage to pick out that awful techno song that they play at hockey games… ha ha. A very cool project overall, and definitely something that can be done on our own RetroCade Synth.
To all you RetroCade users out there, we would love to see what you’re working on. I’m sure there are a lot of cool synth projects underway, so keep us posted on what you’re up to!