The 35 Year Music Synthesizer That Spawned Chiptune

If you are a certain age, MOS6581 either means nothing to you, or it is a track from Carbon Based Lifeforms. However, if you were a Commodore computer fan 35 years ago, it was a MOS Technologies SID (Sound Interface Device). Think of it as a sound “card” for the computers of the day. Some would say that the chip — the power behind the Commodore 64’s sound system — was the sound card of its day. Compared to its contemporaries it had more in common with high-end electronic keyboards.

The Conversation has a great write up about how the chip was different, how it came to be, the bug in the silicon that allowed it to generate an extra voice, and how it spawned the chiptune genre of music. The post might not be as technical as we’d do here at Hackaday, but it does have oscilloscope videos (see below) and a good discussion of what it took to create music on the device.

The article talks a lot about the music side of things but in a technical way. Besides — as the author points out — in those days the musicians had to be programmers, too. Luckily, there are a lot of musical programmers — or perhaps programming musicians, we aren’t quite sure.

If you want your own SID to play with, there’s always the FPGA version. Or get a real chip and control it with a Raspberry Pi.

36 thoughts on “The 35 Year Music Synthesizer That Spawned Chiptune

  1. Ah, the SID chip. The reason why Commodore 64s are the world’s best selling computer and yet are still difficult to find today.

    I seriously don’t understand why people take perfectly fixable C64s and throw the whole thing out for a low-end synthesizer chip. Your phone is capable of much nicer, warmer sounds than a SID can.

      1. C64 consoles still crop up from time to time but 9 out of 10 times the rather unique and (IIRC) hard to replace PSU is missing. Without a proper PSU the C64 is useless and suddenly pulling the SID makes a lot of sense.

        1. IT’s not unique, has a 9VAC-50/60 Hz and a 5V 1500 mA output, easily obtainable from off-the shelf parts. The problem of a number of original power supplies is that they could fail catastrophically to regulate the 5V rail, so actually building a power supply from scracth using modern switching circuitry colud be better than using an original PSU.

        2. There’s nothing unique there. Find the connector and replicate the power supply. Find out what voltages are needed, and find a linear or analog supply that supplies them. You may have to add a regulator or even supply, depending on what’s needed. And yes, the supply needs some AC or rectified but not filtered AC, I can’t remember which, but then find a mall transformer of the right voltage, old transistor radios might offer something.

          If the connector is odd, then make one. When I had an Atari ST, I made a connector for something that wasn’t common, maybe cutting down a “DB-25” connector or using a piece of circuit board with some pin, I forget.

          A power supply is hardly something difficult to replicate for the audience here.


          1. I think the connector was a round DIN connector, nothing special. If I want to recreate the PSU today, I would use a switch-mode PSU for the 5V and some small transformer for the 9VAC, it did not need much power on this.

          1. I jumped the gun with that response. After may years of live HV work (>25kV) I don’t get too bother with mains voltages.

            I had a look at the C64 schematic and it’s quite complex how it uses the 9 Volts AC so you may be better off using two separate supplies like wall warts. There is no common ground between the two supplies.

          2. AC of that 9V is only used for time of day clock, and nothing EVER used that feature, well nothing other than 30 second ‘click to something happening’ demo of a GUI os called GEOS.
            other than that its
            -boosted to 12V DC for SID
            -rectified to 6V DC for tape drive
            -google says some versions used same tape drive unregulated 9V DC for RF modulator, but its not like you will use that.
            -routed to the user port edge connector for no idea what, no clue if any cartridges used it.

            this means you can power whole C64 with one 5V supply and one $1 5V to 12V boost converter, optionally another $1 5V to 6V converter if you are planning on using real tape drive. or a PC AT/ATX supply, or 5V/12V supply for external USB drives. Obviously C64 will need a small mod (one jumper wire).

        3. They weren’t THAT hard to replace. My family had three C64s up and running when I was growing up – all getting their power from hacked Colleco Adam PSUs since the Commodore bricks had died. IIRC, you had to change a couple resistors in there to make them put out a different voltage and splice on the Commodore’s plug. There’s probably some other readily obtainable PSUs out now that could be adapted for the purpose.

        4. Not really just get a +5V DC PSU of 2 amps or so , a 9V AC transformer and a 7 pin DIN connector and make your own.
          I got a C=64 I found at a thrift store running that way.
          Half the people who post here probably have most of those parts on hand.

    1. And yet if you put an entire C64 on eBay, it doesn’t sell nearly as well as the SID itself. And sometimes you can get more money for the SID than the whole C64.

    2. “Your phone is capable of much nicer, warmer sounds than a SID can.”
      That’s the reason why 303s go for 2500 bucks these days, because you could just take your phone.

    3. Well you can get c64 for 10 to 50 dollars here in poland. We have plenty of them. Few years ago noone would ask more than 25 $ for it.
      Just remember that for this price you can get perfectly flexible board with more powerfull 8/16/32bit cpu. It will take less space, power, time etc.
      Nowdays c64 and others are usefull for old automation system, hobby recycling and museums. Maybe also for some education.

  2. SID was also responsible for random number generation in the C64, and prone to static damage. Many games became unplayable on my C64, whilst others became trivially predictable. Elite became interesting – it seemed I gained a 100% chance of encountering Vipers upon a jump, so it was impossible to clear my legal status…

    1. The third voice could be muted and set to white noise briefly to generate random numbers in hardware instead of using a pseudo-random number generator. The SID also had a sound input and two ADC channels which were used by some game controllers, such as paddles.
      Interestingly, most sound chips designed after the SID have a sound input too. Old Nintendo game systems have one broken out in the cartridge slot, and some games had bank-switching chips with built-in sound generators (e.g. Nintendo MMC5 and Konami VRC6) connected to that pin.

      1. SID didnt have ADC channels, it had a very basic timer circuit, reading paddles worked almost exactly like reading joystick on PC. Original IBM PC gameport was build using dual/quad NE555 (556/558) and few address decoder chips, reading pots was accomplished by measuring how long it takes to charge capacitor in series with the pot. Main difference was on PC you had to do whole thing manually = you were stuck in a loop repeatedly checking port 201 for up to ?100 μs every time you wanted position, on C64 SID ran the loop internally and buffered readings. Commodore had the luxury of in house semiconductor fab, IBM build gameport using 5 off the shelf chips.
        This also means using gameport should lower your framerate, but I cant find any evidence/complaints about that in ze google.

        I learned this while reading about proportional C64 mouse, they used analog paddle input for the mouse crazy bastards, even patented emulating paddle with a mouse!
        To know more that anyone would ever want about C64 mouse and SID “analog” input:

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