Submodular Synthesizer

Introduction

The ISHIZENO 8 (aka i8) is a submodular synthesizer. It decouples faceplate from electronics in order to provide fine-grain modularity. It is built around a Raspberry Pi used as web server, patching controller, and digital signal processing unit. It provides 8 polyphonic channels, each of them being made of 6 analog ports and being supported by a dedicated Arduino Uno and an optional Arduino shield. Dynamic patching between the 48 analog ports is supported by a matrix of analog crosspoint switches configured through any web browser connected to the Raspberry Pi through a built-in WiFi hotspot or a local WiFi network.

Raison d'être

• Providing a mixed interface (analog × digital) for processing mixed signals (analog × digital)
• Making it easier to develop custom modules as Arduino shields while using a generic faceplate
• Enhancing the haptic interface of a modular analog synthesizer with end-to-end signal visualization
• Simplifying the development of rich user interfaces running on any PC or mobile device
• Experimenting with Low-Frequency Patching (think LFO, but for patching)
• Using dynamic patching and digital potentiometers to set and record patches and knob settings

8 Polyphonic Channels

Each of the 8 polyphonic channels provides:

• 6 analog ports (A0, A1, A2, A3, A4, A5)
• 4 knobs
• 4 digital potentiometers
• 1 Arduino Uno
• 1 Arduino shield (optional)

Dynamic Patching

Patching across channels can be done in a traditional way through the faceplate's 3.5mm jack chassis sockets, through the analog crosspoint switches, or through multi-channel shields. Using dynamic patching, any pair of ports of any pair of channels can be patched together, including two ports of the same channel. Furthermore, dynamic patching allows any analog port to be patched to any potentiometer. When the module is equipped with 8 switches, up to 16 concurrent patches can be established at a time. With 16 switches, this limit is increased to 32.

Dynamic patching is enabled by a matrix of 8 or 16 AD75019 analog crosspoint switches. These switches have no gain and a low 150 Ω on resistance. No more than two switches are ever used on the analog signal path, thereby limiting the overhead resistance to 300 Ω. Dynamic patching can be done through the web user interface, or by using a dedicated controller like the monome grid connected to the Pi through the faceplate's USB 3.1 Type C connector.

Submodular Architecture

Out of the box, the module does not provide any synthesis capabilities. Instead, these are added through optional Arduino shields, with up to 8 shields (one per channel). Programming of the module can be done through the Arduino of any channel, or through the Linux operating system of the module's Raspberry Pi. For example, the Pi could be used as software sequencer. The analog crosspoint switches can also be reconfigured dynamically in order to support low-frequency patching.

Arduino Shields

Every channel can be supported by an optional Arduino shield that is plugged onto the module's backplane. Because shields do not include any faceplate, controls, mounting hardware, or power connector, they should be much more cost effective than full-fledged Eurorack modules. As such, they are referred to as submodules, and the synthesizer is described as being submodular.

Examples of shields could include any of the following:

• Analog Filter
• Controller
• Digital Signal Processor
• Envelope Generator
• Low Frequency Oscillator
• Mixer
• Oscillator
• Phase Shifter
• Sampler
• Sequencer
• Waveshaper
• Etc.

While we hope that designers will create their own submodules, we will try to bootstrap the ecosystem by cloning a first set of popular open hardware modules, starting from the fantastic modules developed by Mutable Instruments. Please contact us at ishizeno at gmail dot com if you would like to develop a submodule for the platform ahead of its public release.

Multi-Channel Shields

By default, a shield is attached to a single channel, through a single Arduino. That being said, some applications might require more than 6 analog ports, more than 4 potentiometers, or more PCB space. For such applications, a multi-channel shield can be used, spanning any number of channels.

Arduino

Every polyphonic channel is controlled by a dedicated Arduino. The channel's analog ports are statically patched to the Arduino's analog inputs (A0, A1, A2, A3, A4, A5). Furthermore, all standard Arduino pins are exposed to any Arduino shield used to support its related polyphonic channel. As a result, any standard Arduino shield can be stacked on top of any channel shield, or can be used as channel shield. The Arduinos are directly built into the module's backplane using the Atmel ATMEGA328P microcontroller and the FTDI FT232RL USB interface.

Raspberry Pi

The module includes a user-upgradeable Raspberry Pi Model B+, which includes:
- 40 GPIOs
- 4 USB 2.0 ports
- 1 micro SD reader

48-channel Oscilloscope

The 6 analog ports of every polyphonic channel are connected to the six analog inputs of the channel's Arduino, which provides 10-bit analog-to-digital converters. This allows the web user interface to be used as a low-resolution 48-channel oscilloscope for signal visualization purposes.

Digital Potentiometers

4 physical knobs are assigned to every polyphonic channel. These knobs use rotary encoders with 24 detents and 24 PPR resolution. They also provide SPST momentary switching and RGB led illumination. Knob settings are passed to a channel through its I²C bus. Settings can be used from a channel's shield using a digital potentiometer like the AD5254. Alternatively, all 32 knob settings are converted into analog voltage levels through 8 built-in AD5254 quad digital potentiometers (1 per channel). From there, the voltage level of a channel's knob can be patched to any analog port of the channel, or any of the 16 or 32 analog endpoints available.

Optional Grid Controller

While the module can be used with any USB controller, it is being developed jointly with a grid controller, the ISHIZENO g4. This experimental grid is made of 324 keys and 10 knobs. Keys are illuminated by RGB leds and are sensitive to pressure, tilt, and velocity. Knobs use rotary encoders with 24 detents and 24 PPR resolution, as well as SPST momentary switching.

The controller can be used for both playing and sequencing. In playing mode, 8 rows of keys are used for playing, while the top row is used for sequencing. In sequencing mode, 8 rows of keys are used for sequencing, while the top row is used for note selection. The grid supports playing across 4 octaves and 8 channels, as well as 36-step sequencing. When a note is added to a sequence, the 4 potentiometer settings related to the note's channel can be set from the knobs located on the left side of the grid, while the 6 analog levels of the note's channel can be set from the knobs located on the right side.

Power Supply

This module is likely to consume quite a bit of power. While a lot more work remains to be done in this particular area, the current thinking is to provide separate power buses for every pair of polyphonic channels (1-2, 3-4, 5-6, 7-8). The module should not require a dedicated power supply.

Software

This module is designed to be as open as possible, across all layers of the stack:
- Web user interface implemented using Node.js and famo.us
- Mixed signal middleware implemented using Arduino
- Online services implemented using the Google Cloud Platform

Future Upgrades

The built-in Raspberry Pi is replaceable and can be upgraded with future versions. All switches used for dynamic patching are mounted on PLCC sockets so that an entry-level 8-switch module can be upgraded to a 16-switch configuration later on. The first module will offer 8 polyphonic channels, but future modules might offer only 2 or 4.

Project Status

This module is at the early prototyping stage. Specifications will vary. No release timeframe yet.

Open Design

• All hardware designs will be released under a Creative Common license.
• All software will be released under an open source license.

Additional Resources

• List of Parts

Feedback needed!

https://ishizeno.wordpress.com/

• ? mA +12V
• ? mA -12V
• ? mA 5V

No info about availability.

$995