You know in sci-fi how you’ll see robots and other machines that can transform, re-program themselves on the fly for a new task? (Okay, sometimes they’re evil robots.) Well, imagine a single-board – looking a bit like an ultra-compact computer – that does that for sound, and you have the basic notion of the RetroCade Synth. For lovers of classic computer audio chips, and chip music associated with gaming and the demo scene, it means a single device that can be all those vintage sounds from the moment you switch it on. You can even leave the computer at home.

The magic here is all via something called a “field-programmable gate array,” or FPGA. Normally, when you create a circuit, you can’t really change it after the fact – not without a soldering iron and a steady hand, anyway. The FPGA is different; it uses basic logical building blocks that can be reprogrammed at will after you’ve shipped it.The RetroCade Synth is open source hardware – perhaps the first high-visibility project to use an FPGA for sound. (See the awesome MilkyMist for an example of a FPGA-based, open source hardware for video; the MilkyMist uses these features to add more video-processing techniques as the project develops, and has inspired other projects well beyond video or music.)

Hackers will love this, of course. But even if you know nothing of how these boards work, the RetroCade Synth is looking like a useful musical tool. A Kickstarter project is being used to fund production. Note that this differs from projects that use Kickstarter to fund development; by funding production of a complete or nearly-complete design, Kickstarter can help designers jump over the hurdle of the initial capital needed to manufacture something their users want. The Kickstarter model is suited to this scenario, as it was designed as a kind of “preorder” system in some of its first applications.

What the RetroCade provides:

  • Emulation of Commodore 64 SID, Atari ST’s Yamaha YM-2149, Amiga MOD, and more. Use as an instrument or play MIDI or .mod files composed for these architectures.
  • Control from a custom VST front-end.
  • Specs: Papilio FPGA + Xilinx Spartan FPGA (Spartan 3E 500K or Spartan 6 LX9)
  • Audio and MIDI onboard, SD card for loading files.
  • Built-in MicroJoystick and LCD display.
  • Analog and digital inputs for adding physical controls (sliders, knobs, and the like).
  • Software for control built in SynthMaker so it can be easily modified.

(Those computer control features are just extras; you can use the hardware.)

RetroCade @ Kickstarter

The funding will complete documentation and the first prototype and production runs. Beyond that, extra funding will pay for time of the developers to do more. That could include other chips based on open source implementations. (See more details on the site of their grander schemes.)

Open source hardware also made the collaborations possible that would allow musicians to delve into such an ambitious project. “Standing on the shoulders of giants,” that includes building on implementations of specific chips for FPGA, as well as other important hardware developments. See the technical video for more of the technical goodness in there.

Modification isn’t for the feint of heart – if you don’t know what the acronym “VDHL” means, for instance, you’re probably not going to be that interested. But it’s nice to know that stuff is open, perhaps not so much for the music community per se as other engineers working with these sorts of platforms.

  • Peter Swimm

    Man this would be a great candidate for anyone wanting a nord micro modular 2 as well.

  • Random Chance

    I don’t quite get it. Why use an FPGA to do what can be done using a microcontroller? It’s fun (for some definition of “fun”, people who had to deal with FPGA development will know what I mean) but otherwise it is not the most efficient way to create digital simulations of mixed analog/digital audio chips. I might have missed something about the analog capabilities of this Papillon FPGA though.

    • Peter Kirn

      Generally, the short answer is, “because they’re comfortable working with an FPGA,” and “because there was some code to work with,” both of which are true here.

    • josh giesbrecht

       Wouldn’t an FPGA set to emulate one of these chips run faster than purely software emulation running on a microcontroller? Might be a performance thing. (I haven’t touched an FPGA since engineering classes 10+ years ago though so I’m no expert.)

    • skrasms

      The trick to fun FPGA design is to not use VHDL. SystemVerilog is where it’s at. 

      A chip like the Atari POKEY effectively had a 1.79 MHz sample rate. The pseudorandom number generators updated 1790000 times per second, while lower speed blocks would periodically grab the results  and combine them in different ways to create the output waves. The interaction between the different clocks was very important to the character of the sound. Accurately emulating a 1.79 MHz sample rate in a microcontroller is not simple. 

      On the other hand, running an FPGA at 1.79 MHz is trivial. That makes many of these old soundchips great candidates for recreating in an FPGA, as they had similar internal clocks in the low MHz range. 

      The downside to FPGAs is that they don’t have the analog components/flaws that were often part of the original sounds. The most common example is the analog SID filter. Another example is the nonlinear POKEY D/A converter, where the output channels modulate each other more as volume increases. On the upside for FPGAs, working at higher sample rates makes it easier to handle the non-linear aspects without adding aliasing.

      I’m not speaking on behalf of this product, but just as someone who writes soundchip emulations for fun. 

  • Peter Swimm

    I think he is just trying to leverage existing code bases. Think of it as a fpga midi shield.

  • retroz

    The big gotcha here is that the SID core doesn’t include the analog filter. 

  • mckenic

    I guess I need to re-read the Kickstarter page and leave a question or two… Is the control software coming to Mac? When it says Sid, YM, MOD etc – how many of these can it play at the same time with how many notes etc. Will there be an enclosure? I really liked the video and it sounds great IMHO but I’d need more dumb user kind of questions answered…

    Also – REALLY not trying to be a PITA Peter – and I LOVE CDM but “The Kickstarter system is suited to the system, as it was designed as a
    kind of “preorder” system in some of its first applications.” That is a heck of a lotta systems mate :)

  • Puneonnet


  • klubovi

    Nice info for me… i do songs for some time and this upgrade my knowledge m8 ;)