Submodular Synthesizer

Introduction

The ISHIZENO ONE is a submodular synthesizer. It decouples faceplate from electronics in order to provide fine-grain modularity. It is built around an iPod Touch used as touchscreen, 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 analog ports is supported by a matrix of analog crosspoint switches.

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
• Experimenting with Low-Frequency Patching (think LFO, but for patching)
• Using fully digital controls so that patches and settings can be recorded and replayed

8 Polyphonic Channels

Each of the 8 polyphonic channels provides:

• 6 analog ports (A0, A1, A2, A3, A4, A5)
• 8 virtual knobs
• 8 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 (48 of them), 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. 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 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 graphical user interface provided by the iPod Touch, by downloading a patch from the Internet through the iPod Touch's WiFi connection, by scanning a QR code with the iPod Touch's front-facing camera, or by using a dedicated controller like the monome grid.

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 iOS operating system of the module's iPod Touch. For example, the iPod Touch 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.

Multi-Channel Shields

By default, a shield is attached to a single channel, through a single Arduino Uno. That being said, some applications might require more than 6 analog ports, more than 8 potentiometers, or more PCB real estate. For such a scenario, a multi-channel shield can be used, spanning any number of channels.

Arduino Uno

Every polyphonic channel is controlled by a dedicated Arduino Uno. 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.

16-channel Oscilloscope

The module includes two AD7606 8-channel 24-bit analog to digital converters. This allows the built-in iPod Touch to be used as a low-frequency 16-channel oscilloscope. The 16 channels of the oscilloscope can be dynamically patched to the 48 analog ports of the module's 8 polyphonic channels through a series of 3 AD75019 analog crosspoint switches.

Virtual Knobs

8 physical knobs are logically associated to the 8 polyphonic channels. These knobs use rotary encoders with 24 detents and 24 PPR resolution. They also provide SPST momentary switching and RGB led illumination. Pushing a knob selects the corresponding polyphonic channel, making all 8 physical knobs available as virtual knobs for the channel's configuration.

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 64 virtual knob settings (8 settings for each of the 8 channels) are converted into analog voltage levels through 16 built-in AD5254 quad digital potentiometers (2 per channel). From there, the voltage level of a channel's virtual knob can be patched to any analog port of the channel, or any of the 16 or 32 analog endpoints available.

Additional Features

• 2 spinner control knobs driving rotary encoders
• 1 USB port connected to the iPod Touch's lightning connector
• 1 stereo headphone output connected to the iPod Touch's headphone jack

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:
- User interface implemented using iOS
- Mixed signal middleware implemented using Arduino
- Online services implemented using the Google Cloud Platform

User Interface

The iOS user interface will be the most complex component of the architecture, and the one that is the least open. In order to work around this limitation, the iOS application running on the iPod Touch will be implemented in Swift with a domain specific language (DSL) and a set of packaged components. Developers will then be able to create custom user interfaces for their shields by simply using meta-data elements that are dynamically interpreted by the application framework, without having to write any Swift code or re-deploying the app on the iPod Touch. These software shields will be downloaded from the Internet through the iPod's WiFi connection.

Arduino Middlware

The Arduino software stack is a lot more open and suitable to interfacing with various hardware components than the iOS platform. As a result, it will be used to implement most of the mixed signal middleware that will be needed between the user interface running on the iPod Touch and the various hardware components of the module. In a perfect world, we should be able to push Arduino applications from the iPod Touch, thereby enabling the following code flow: Internet > iPod > Arduino.

Online Services

Some online services might be eventually developed for facilitating the distribution of firmware updates, software shields, and dynamic patches. In such a case, the Google Cloud Platform will be used, but this project will be undertaken at a later stage. In the meantime, all developments will be done using GitHub.

Future Upgrades

All switches used for dynamic patching are mounted on PLCC sockets so that an 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.

Pricing

Once in production, this module is likely to retail for $1,495, but we are currently considering the release of a barebone beta-tester model with no iPod and only 16 dynamic patching ports. A small batch of such models could probably be sold for $995. The iPod Touch would have to be added separately.

Additional Resources

• List of Parts

Feedback needed!

https://ishizeno.wordpress.com/

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No info about availability.

$1,495