A man playing an accordion-like instrument made from two Commodore 64s

The Commodordion Turns Two C64s Into A Single Instrument

October 22, 2022 by Robin Kearey 16 Comments

One of the main reasons the Commodore 64 became an icon of the 1980s was its MOS 6581 “SID” sound chip that gave it audio capabilities well beyond those of other microcomputers of the 8-bit era. The SID became something of a legend by itself among chiptune enthusiasts, and several electronic instruments have been designed that generate their sound through a SID chip. Not many of those look anything like traditional musical instruments however, so we’re delighted to see [Linus Åkesson]’s new project: two Commodore 64s joined back-to-back using a bellows to form a wonderful new instrument called the Commodordion. It can be played in a similar way one plays a traditional accordion: melodies are played with the right hand, chords with the left, and volume is adjusted by varying the pressure in the bellows.

The two computers are basically unmodified, and boot Commodore BASIC like they normally would. A custom circuit board emulates a cassette player and provides the software to be loaded into memory. Both computers run the same program and can be switched between the right-hand and left-hand role by pressing a specific key combination. The software in question is called Qwertuoso, and basically maps notes and various features of the SID chip to keys on the Commodore’s keyboard.

Of course, it’s the bellows that makes this instrument a true member of the accordion family. Made from 5.25″ floppy disks and sticky tape, it forms a more-or-less air-tight system linking the two computers. The airflow in the bellows is measured through a microphone placed next to the air intake: the amount of noise generated is roughly proportional to the amount of air being expelled or inhaled. This information is then used to modulate the volume generated by the two SID chips.

By [Linus]’s own admission it’s not the most ergonomic of instruments, so we’re doubly impressed by the amount of skill he demonstrates while playing it in the video embedded below. It’s not the first time either that he has turned a Commodore 64 into a musical instrument: he previously built a church organ and a theremin. While the Commodordion may look complicated, it’s actually much simpler in construction than a mechanical accordion.

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How Many Commodores Does It Take To Crack A Nut?

September 7, 2019 by Erin Pinheiro 19 Comments

It’s brilliant enough when composers make use of the “2SID” technique to double the channels in a Commodore 64 with two sound chips, but even then some people like to kick things up a notch. Say, five times more. [David Youd], [David Knapp] and [Joeri van Haren] worked together to bring us just that, ten Commodore computers synchronously playing a beautiful rendition of the Dance of the Sugar Plum Fairy at this year’s Commodore Retro eXpo.

The feat is composed of nine Commodore 64 computers and one Commodore 128, all fitted with the SID chip. It is a notorious synthesizer chip for utilizing both analog and digital circuitry, making each and every one of its revisions unique to a trained ear, not to mention impossible to faithfully reproduce in emulation. The SID was designed by Bob Yannes at MOS Technology, who later went on to co-found Ensoniq with his experience in making digital synthesizers.

How this orchestra of retro computers came to be, including details on how everything is pieced together can be found on this slideshow prepared by the authors of the exhibition. It’s interesting to note that because of timing differences in each computer’s crystal clock and how only the start of the song is synchronized between them, they can’t play long music tracks accurately yet, but a 90-second piece works just fine for this demonstration.

These synthesizer chips are slowly going extinct since they’re no longer being manufactured, so if you need a new replacement solution, FPGAs can fill that SID-shaped hole in your heart. If you need the whole computer though, the newer Teensy 3.6 will do just fine emulating it all. Check out this beast of a display in action after the break. While we’re at it, this isn’t the only time multiple 8-bit computers have been combined as an orchestra, though these Commodores sound a lot better than a table full of ZX Spectrums.

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Giving The World A Better SID

November 24, 2016 by Brian Benchoff 60 Comments

Here’s a business plan for you, should you ever run into an old silicon fab sitting in a dumpster: build Commodore SID chips. The MOS 6581 and 8580 are synthesizers on a chip, famously used in the demoscene, and even today command prices of up to $40 USD per chip. There’s a market for this, and with the right process, this could conceivably be a viable business plan.

Finding a silicon fab in a dumpster is a longshot, but here’s the next best thing: an FPGASID project. The FPGASID is a project to re-create the now-unobtanium MOS 6581 found in the Commodore 64.

The Commodore SID chip has been out of production for a while now, and nearly every available SID chip has already been snapped up by people building MIDIbox SIDs, or by Elektron for their SidStation, which has been out of production for nearly a decade. There is a demand for SID chips, one that has been filled by “clones” or recreations using ATmegas, Propellers, and nearly every other microcontroller architecture available. While these clones can get the four voices of the SID right, there’s one universal problem: the SID had analog filters, and no two SIDs ever sounded alike.

From the audio samples available on the project page for the FPGASID, the filters might be a solved problem. The output from the FPGASID sounds a lot like the output from a vintage SID. Whether or not this is what everyone agrees a SID should sound like is another matter entirely, but this is the best attempt so far to drag the synth on a chip found in the Commodore 64 into modern times.

The files, firmware, and FPGA special sauce aren’t available yet, but the FPGASID is in alpha testing, with a proper release tentatively scheduled for early 2017. Maybe now it’s time to dig out those plans for the Uber MIDIbox, with octophonic SID goodness.

Creating A MIDI Synth From A Commodore SID

October 18, 2012 by Brian Benchoff 24 Comments

The Commodore SID was the audio chip in the venerable Commodore 64 and in the 30 years since release has attained classic status and become one of the best ways to get your chiptune on. Designed by famous synthesizer designer [Bob Yannes], it was only a matter of time before we saw a real, homebrew MIDI synth based on the Commodore SID.

Because real SID chips are rare as hen’s teeth nowadays, [Jeff Ledger] built his SID synth around an emulated system running on a Pocket Mini Computer. This very cool microcontroller platform runs on the Parallax Propeller. An emulated SID runs in one of the Propeller’s 8 cores, with the remaining cores kept open for reading MIDI notes and displaying info on a display.

The hardware portion of this build is amazingly simple; just an optoisolater, a few resistors, and a diode connect a MIDI keyboard to the Pocket Mini Computer. The buttons and dials on [Jeff]’s MIDI keyboard control the waveforms, filters, and envelope controls. A very neat setup if we do say so ourselves, and just perfect if you’re needing more chiptunes in your life.

You can check out [Jeff]’s video after the break.

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