Open Source Commercial Synthesisers You Will Love

April 23, 2025 by Jenny List 16 Comments

Drumboy and Synthgirl from Randomwaves are a a pair of compact electronic instruments, a drum machine and a synthesiser. They are commercial products which were launched on Kickstarter, and if you’re in the market for such a thing you can buy one for yourself. What’s made them of interest to us here at Hackaday though is not their musical capabilities though, instead it’s that they’ve honoured their commitment to release them as open source in the entirety.

So for your download, you get everything you need to build a pair of rather good 24-bit synthesisers based upon the STM32 family of microcontrollers. We’re guessing that few of you will build your own when it’s an easier job to just buy one from Randomwaves, and we’re guessing that this open-sourcing will lead to interesting new features and extensions from the community of owners.

It will be interesting to watch how this progresses, because of course with the files out there, now anyone can produce and market a clone. Will AliExpress now be full of knock-off Drumboys and Synthgirls? It’s a problem we’ve looked at in the past with respect to closed-source projects, and doubtless there will be enterprising electronics shops eyeing this one up. By our observation though it seems to be those projects with cheaper bills of materials which suffer the most from clones, so perhaps that higher-end choice of parts will work in their favour.

Either way we look forward to more open-source from Randomwaves in the future, and if you’d like to buy either instrument you can go to their website.

Thanks [Eilís] for the tip.

Rockbox 4.0 Released

April 19, 2025 by John Elliot V 22 Comments

It’s traditional to launch new software on April Fool’s Day, which is when we heard that Rockbox 4.0 has been released. But, in this case, the venerable MP3 firmware actually did update after a long absence. It’s great to see that good old Rockbox is still kicking along. We first mentioned Rockbox here at Hackaday approaching 20 years ago. How time flies. There used to be a whole ‘scene’ around hacking Personal Media Players (PMPs), also known as “MP3 Players”.

We tracked down Rockbox contributor [Solomon Peachy] to ask for some simple advice: If someone wants to install Rockbox on a personal media player today, what hardware should they buy? [Solomon] referred us to the AIGO EROS Q / EROS K, which is the only compatible hardware still being manufactured and sold. Beyond that, if you want to buy compatible hardware, you’ll need to find some secondhand somewhere, such as eBay. See the Rockbox Wiki for supported hardware.

Smartphones and streaming services have subsumed the single-purpose personal media player. Will you put the new Rockbox on something? Let us know in the comments.

Designing An FM Drum Synth From Scratch

April 17, 2025 by Dan Maloney 11 Comments

How it started: a simple repair job on a Roland drum machine. How it ended: a scratch-built FM drum synth module that’s completely analog, and completely cool.

[Moritz Klein]’s journey down the analog drum machine rabbit hole started with a Roland TR-909, a hybrid drum machine from the mid-80s that combined sampled sounds with analog synthesis. The unit [Moritz] picked up was having trouble with the decay on the kick drum, so he spread out the gloriously detailed schematic and got to work. He breadboarded a few sections of the kick drum circuit to aid troubleshooting, but one thing led to another and he was soon in new territory.

The video below is on the longish side, with the first third or so dedicated to recreating the circuits used to create the 909’s iconic sound, slightly modifying some of them to simplify construction. Like the schematic that started the whole thing, this section of the video is jam-packed with goodness, too much to detail here. But a few of the gems that caught our eye were the voltage-controlled amplifier (VCA) circuit that seems to make appearances in multiple places in the circuit, and the dead-simple wave-shaper circuit, which takes some of the harmonics out of the triangle wave oscillator’s output with just a couple of diodes and some resistors.

Once the 909’s kick and toms section had been breadboarded, [Moritz] turned his attention to adding something Roland hadn’t included: frequency modulation. He did this by adding a second, lower-frequency voltage-controlled oscillator (VCO) and using that to modulate the drum section. That resulted in a weird, metallic sound that can be tuned to imitate anything from a steel drum to a bell. He also added a hi-hat and cymbal section by mixing the square wave outputs on the VCOs through a funky XOR gate made from discrete components and a high-pass filter.

There’s a lot of information packed into this video, and by breaking everything down into small, simple blocks, [Moritz] makes it easy to understand analog synths and the circuits behind them.

Continue reading “Designing An FM Drum Synth From Scratch” →

A 17th Century Music Computer

April 12, 2025 by Al Williams 10 Comments

We don’t think of computers as something you’d find in the 17th century. But [Levi McClain] found plans for one in a book — books, actually — by [Athanasius Kirker] about music. The arca musarithmica, a machine to allow people with no experience to compose church music, might not fit our usual definition of a computer, but as [Levi] points out in the video below, there are a number of similarities to mechanical computers like slide rules.

Apparently, there are a few of these left in the world, but as you’d expect, they are quite rare. So [Levi] decided to take the plans from the book along with some information available publicly and build his own.

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Audio Effects Applied To Text

April 11, 2025 by Al Williams 3 Comments

If you are a visual thinker, you might enjoy [AIHVHIA’s] recent video, which shows the effect of applying audio processing to text displayed on an oscilloscope. The video is below.

Of course, this presupposes you have some way to display text on an oscilloscope. Audio driving the X and Y channels of the scope does all the work. We aren’t sure exactly how he’s doing that, but we suspect it is something like Osci-Render.

Does this have any value other than art? It’s hard to say. Perhaps the effect of panning audio on text might give you some insight into your next audio project. Incidentally, panning certainly did what you would expect it to do, as did the pass filters. But some of the effects were a bit surprising. We still want to figure out just what’s happening with the wave folder.

If text isn’t enough for you, try video. Filtering that would probably be pretty entertaining, too. If you want to try your own experiments, we bet you could do it all — wave generation and filtering — in GNU Radio.

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A Tiny Tape Synth

April 7, 2025 by Jenny List 12 Comments

Afficionados of vintage electric organs will know about the Melotron, an instrument from the 1960s that had pre-recorded sounds on a bank of tape loops. A real Melotron in working order will set you back a bit, but it’s possible to play with the idea using much more attainable hardware. [Decurus] has made a simple tape based synth using a cassette deck.

It uses a loop of cassette tape, and varies the pitch by changing the speed of the cassette motor. There’s an RP2040 and a motor controller, which can take a MIDI signal and use it to drive the motor. We’re sorry to see that there’s no recording of the result, but it’s described as a drone.

Part of this project is a 3D printed tape loop holder to fit a cassette mechanism. We won’t go as far as to call it a cassette in itself, instead it’s a sort of tape loop frame. We can see that it might be an interesting component for other tape loop experimenters, now that cassettes themselves are no longer ubiquitous. This certainly isn’t the first tape pitch synth we’ve seen.

3D Print (and Play!) The Super Mario Tune As A Fidget Toy

April 4, 2025 by Donald Papp 36 Comments

[kida] has a highly innovative set of 3D-printable, musical fidget toys that play classic video game tunes. Of course there’s the classic Super Mario ditty, but there’s loads more. How they work is pretty nifty, and makes great use of a 3D printer’s strengths.

To play the device one uses a finger to drag a tab (or striker) across the top, and as it does so it twangs vertical tines one-by-one. Each tine emits a particular note — defined by how tall the thicker part is — and plays a short tune as a result. Each one plays a preprogrammed melody, with the tempo and timing up to the user. Listen to them in action in the videos embedded just under the page break!

There are some really clever bits to the design. One is that the gadget is made in two halves, which effectively doubles the notes one can fit into the space. Another is that it’s designed so that holding it against something like a tabletop makes it louder because the surface acts like a sounding board. Finally, the design is easily modified so making new tunes is easy. [kida]’s original design has loads of non-videogame tunes (like the Jeopardy! waiting theme) as well as full instructions on making your very own versions.

Fidget toys are a niche all their own when it comes to 3D printed devices. The fidget knife has a satisfying snap action to it, and this printable linear toggle design is practically a fidget toy all on its own.

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