The Polyphonic Analog/Digital Synth Project

[Matt Bradshaw]’s entry in the Hackaday Prize is Polymod, a modular digital synthesizer which combines the modularity of an analog synth with the power of a digital synth. Each module (LFO, Envelope Generator, Amplifier, etc.) are connected with audio cables to others and the result is processed digitally to create music.

The synth is built with a toy keyboard with each key having a tactile switch underneath it, contained inside a wooden case upcycled from a bookshelf found on the street. Each module is a series of potentiometers and I/O jacks with a wooden faceplate. The modules are connected to sockets on the main board and are held in place with thumbscrews so that the modules can be easily switched out. Each module can be connected to others using audio cables, the same way modular analog synths are connected.

The main board contains a Teensy 3.6 and a Teensy Audio Adapter creates the audio for the synth. Software that [Matt] wrote runs on the Teensy and allows the digital synthesizer to run in either monophonic or polyphonic modes. In polyphonic mode, the software creates digital copies of each module to allow the playing of chords. The Teensy scans up to eight module sockets and for each module that it finds, it reads the potentiometer value as well as the status of the I/O jacks. The keyboard buttons are converted to a control voltage which can be sent to any of the modules to create a melody.

[Matt] has created a great synth that combines benefits of both analog and digital synths together and the result is an inexpensive modular synth that can create some really cool sounds. Check out the videos after the break. In the meantime, take a look at this mess of wires and this article on a slew of open-source synthesizers.

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Audio Hacking With The ESP8266

If you study the specifications of the ESP8266 WiFi-enabled microcontroller, you will notice that it features an I2S audio interface. This is a high-speed serial port designed to deliver 16-bit audio data in a standard format, and has its origins in consumer audio products such as CD players. It would be usual to attach a dedicated DAC to an I2S interface to produce audio, but [Jan Ostman]’s synthesiser projects eschew that approach, and instead do the job in software. His I2S interface pushes out a pulse density modulated data stream in the same manner as a 1-bit DAC, meaning that the only external components required to produce audio are a simple low-pass filter. He’s posted a video of the synth in action, which we’ve placed below the break.

The example he gives us is a basic clone of a Roland 909 drum machine, and he takes us through the code with extensive examples including MIDI. He’s using the Wemos D1 Mini board, but the same could be replicated with many other ESP8266 platforms.

We’ve featured [Jan]’s work many times before, from his minimalist Atmel-based devices through to small but perfectly-formed complete instruments.

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A Robotic 808 Drum Machine

If you spent the 1980s hanging out at your local record store, and you don’t have a hankering for spandex and bouffant rock-god hairstyles, the chances are you’ll have more than a few pieces of electronic music from the period in your collection. The proliferation of electronica during that era came through the arrival of relatively inexpensive mass-market digital polyphonic instruments, edging out the sounds of monophonic analog synthesisers for a subsequent generation to rediscover in a later decade. Individual instrument models became icons and entered the musical vernacular of the day, the Ensoniq Mirage sampling synthesiser, the Yamaha DX7 FM synthesiser, or the Roland TR-808 drum machine.

It is the Roland TR-808 that inspired today’s subject, the MR-808 robotic drum machine, from [Moritz Simon Geist]. A percussion sequencer featuring real instruments all built into a cabinet styled to resemble a huge Roland 808. Originally built as a performance instrument, but since reinvented as a piece of installation artwork that visitors can program for themselves.

Block diagram of the MR-808
Block diagram of the MR-808

There is a comprehensive description of the machine’s design and build on the creator’s website, as well as a more high-level introduction. A significant amount of effort was put in to creating mechanical instruments as close as possible to the Roland sounds, with each instrument being operated by solenoids driven by a MIDI-controlled Arduino Mega. A second Arduino, this time an Uno, controls lighting that follows the instruments.

The interactive part of the installation comes from a sequencer front-end running in a web browser on a Nexus 7 tablet, this appears to be served from a Raspberry Pi which supplies MIDI to the MR-808.

The results can be seen in the video below the break, and judging by the reaction of the audience the machine is rather popular.

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Digital Synth For The Non-chiptune Inclined

Chiptunes are great, and we can’t imagine a world without the Mega Man 2 soundtrack, but sometimes we all like a more 70’s style synth. This is where the Roninsynth steps in. It’s an Arduino shield that puts the basic components of a wall of synth into your pocket.

Unlike the analog oscillators of yore, the Roninsynth is based on a single dsPIC33F chip. It has all the waveforms we would expect from its big brother – sine, saw, triangle, square, and noise – and a couple modulation options.  What’s really interesting is the GUI the Roninsynth team put together. Instead of going with the knobs and buttons approach of the MIDIbox SID, the Roninsynth does everything with software. Think of it as a hardware-based softsynth.

Of course, there isn’t support for looping and phrases like what we saw yesterday, but there’s a ton of neat sounds that can be made and the capability for analog input. If you’ve ever wanted to sound like Radiohead, we can’t think of an easier way to build an Ondes Martenot.