synthesizer ⁽⁶⁾

Aka “ADDDA” or "AuDiDeDrAr" or "aww dee dee drawer" or "A3DA"

I've had this idea bouncing around in my head that you could use 1-bit wide DRAM as a delay line if you simply counted up through it's addresses, reading and writing as you go. 1-bit wide DRAM like the M3764 have separate pins for Data In and Data Out which makes the read-and-write method easier.

The light bulb moment was coming across an old post on diystompboxes.com where one commenter provides a short snippet of code to do a Delta-Sigma analog to digital converter using the Arduino's analog comparator pins. I had planned to do this purely in software by using the normal ADC pins and then calculating the Delta myself. But the built-in comparator makes this dead simple!

Conway’s Game of Life (CGoL)has always fascinated me. It is probably the most well known of all cellular automata and also probably the most intuitive. Yet even simple patterns can turn into complex sequences of shapes, patterns, and noise. Years ago, when learning about the…

I have a few prototype Eurorack modular synth modules in the works. I tend to get them working well enough to be musically interesting and then move to work on the next prototype. It’s not because I don’t plan on finishing them - it’s more…

I wrote earlier about a new eurorack synth module I'm working on. I left off having made a test bed that made some sort of sound but wasn't integrated with the synth. This weekend, I built out the test bed to a full prototype and really got to take it for a spin. Guess what? It's awesome.

Lets start by talking about what I finally decided to choose as an interface. This part is probably the most insightful design choice of the whole project. Earlier, I realized that I didn't need to worry about the envelope generators on the YM3812 and that I'd simply patch those in from traditional (and more versatile) eurorack modules. That leaves far less analog parameters:

• Operator 1 multiplier
• Operator 1 feedback
• Operator 1 amplitude
• Operator 1+2 pitch

The OPL2, aka the Yamaha YM3812, is a multi-voice FM synthesis sound chip. It was used in early PC sound cards such as the Adlib and a variety of other arcade machines and computers of the late 80s and early 90s. It operates completely digitally and produces sound via a specific DAC chip, the YM3014.

FM synthesis is an interesting way of producing sound and music but is particularly onerous to set up on a modular synth. These Yamaha chips (or clones thereof) are still easily and inexpensively available online. I decided a module showcasing the OPL2 would make a great addition to my modular.