[cerol]

A couple of years ago, I took a "Music and Computers" course at my undergraduate computer science program. I had known the professor for a while, and he had some incredible projects under his belt. He had built a full fledged Hammond-like MIDI synth using an Arduino Due, all the way from writing the code, and building the stainless steel casing. I took that as an inspiration for my final project, and tried to build a FM synth using ESP32.

I based my project on the Yamaha DX7, which is an amazing feat of musical engineering. I had to write the code, wire together a MIDI Input, and an audio output (using a DAC). It was one of the coolest projects I've ever made, although I did not get too far.

At the core, all you're doing is generating sine waves. Digital Synths in the 80s would not have the computation power to actually compute sine waves, so what you have to do is precompute the values of a sine wave, and store it in memory [0]. Also, you don't get floats, so it's all fixed point arithmetic [1]. FM Synthesis is essentially a carrier wave and a modulator wave [2]. The DX7 goes beyond that with the concept of Operators, which can be mixed and matched in an Algorithm [3].

I managed to make it produce notes, which were in tune. I started making the envelope (attack, decay, sustain and release), but that's where I got stuck and eventually abandoned it.

[0] https://github.com/fercgomes/churrosfm/blob/master/src/Table...

[1] https://github.com/fercgomes/churrosfm/blob/master/src/Oscil...

[2] https://github.com/fercgomes/churrosfm/blob/master/include/A...

[3] https://djjondent.blogspot.com/2019/10/yamaha-dx7-algorithms...

[khedoros1]

I've written a software emulation of a Yamaha YM2413 (OPLL) for use in a Sega Master System emulator, although that was a couple of years ago. What I remember is a table for the sine wave (1/4 of the full cycle, since the rest can be done by mirroring and inversion), but stored in some logarithmic format so that multiplications can be done through addition, and then a lookup table to convert the output value to an actual integer.

It was cool because there were set values that you could subtract to cut the volume in half, for example. It makes the envelopes into just adding and subtracting values, and getting a cool volume curve out of it.

I remember that I got it reliably producing recognizable output for most register settings, but there are some parameters that I must've gotten wrong, because some settings sound way off from how they do on real hardware.