SIDish

SID chip type synthesizer for Arduino

Goal

The goal for this project is to make a synthesizer that can run on an Arduino Uno with capabilities similar to that of the Commodore 64's famous SID chip. It is not meant to be a perfect reproduction, especially as I currently assume the Atmega 328 in the Uno isn't powerful enough to do real-time filtering and possibly not ring modulation. But I plan to find how close I can get. As a minimum, I hope to get:

• 4 voices (up from the 3 of a SID since mixing 4 voices may be less processor intensive than 3)
• 4 available waveforms: sawtooth, triangle, pulse, and noise
• ASDR envelope

Stretch goals:

• Ring modulation
• Oscillator sync
• Support for filtering
• Extra channels that can sync external hardware effects with music
• Work on desktop systems for faster debugging

History

Since I grew up with the Commodore 64, I've always loved the kind of music it generated and have been fascinated with synthesizers in general. In the last few years, I've been playing with the Arduino and related processors and recently came across the Miduino. I like the idea of the producing music with an Arduino, but don't like the limitations of that project, specifically that:

• Only pulse waves are supported
• No percussion sounds are available
• Only 3 voices are supported
• All 3 timers of the 328 are used, which no possibility of using them for anything else I don't think there's anything wrong with the Miduino at all, I just wanted to see if I could do any better.

Status

The current status is that basic support for playing goattracker files works. Not everything is implemented or works correctly, but songs are okay to recognizable. It can be compiled both to write out .wav files on the host system or play in realtime on an ATmega. ATmega output works for both PWM output on a single pin or to the Adafruit Wave Shield. It happens to have a 10 bit DAC and a headphone jack which is exactly what I needed to experiment on the couch without bothering anyone else, so that's what I've been using.

Feature status:

Group	Feature	Status
Synthesizer Features
	Sawtooth Wave	Works
	Triangle Waveform	Works
	Pulse Waveform	Mostly works though there are still some bugs with pulse width and very big and small pulse widths
	Variable pulse width	Works
	Synchronize	Not implemented
	Ring modulation	Not implemented
	Multiple simultaneous waveforms per channel	Not implemented and not likely to get implemented
Pattern commands
	Portamento	Not implemented
	Toneportamento	Not implemented
	Vibrato	Not implemented
	Alter ADSR from pattern data	Not implemented
	Filter	Not implemented
	Set master volumne	Not implemented
	Funktempo	Not implemented
	Set global tempo	Works
	Set channel tempo	Works
	Non audio effects	Not implemented
Wavetable commands
	Delay	Works
	Waveform values	Works
	Execute command	Not implemented
	Relative notes	Works
	Negative relative notes	Maybe - needs testing
	Unchanged notes	Works
	Absolute notes	Works
	Non audio effects	Not implemented
Pulsetable commands
	Modulation steps (positive)	Works
	Modulation steps (negative)	Maybe - needs to be tested
	Jump	Works
Instrument features
	ASDR	Works
	Wavetable support	Partial
	Pulsetable support	Works
	Filtertable support	Not implemented possibly never to be
	Vibrato	Not implemented
	Gateoff timer	Not implemented
	Hard reset	Not implemented
Orderlist
	Pattern number	Works
	Repeat pattern	Works
	Transpose pattern	Works
	End/jump	Partial
Song features
	Subtunes	Just barely (only enough to not break when encountered)

To Do

• Split out the synthesizer from the player. I'm not sure why I combined them so much other than the comment in the code about allowing better optimization. Seems like a weak argument to me now.
• Fix Windows support to cleanly exit
• Fix Windows support for printing numbers in hexadecimal