how to cite?
All hardware documentation and design is released under the CERN OHL v.1.2. There are no patentable mechanical components or special production techniques involved in our design and we live in the insightful part of the world that regards software patents as unreasonable. The design however is protected against patent trolls with a defensive publication which renders any patent filing by a third party invalid due to prior art.
Hanspeter Portner. Chimaera - the poly-magneto-phonic theremin - an expressive touch-less hall-effect sensor array. In Baptiste Caramiaux, Koray Tahiroglu, Rebecca Fiebrink, and Atau Tanaka, editors, Proceedings of the International Conference on New Interfaces for Musical Expression, pages 501--504, London, United Kingdom, June 30 -- July 03 2014. Goldsmiths, University of London. [ bib | .pdf ]
what is it?
The Chimaera is a poly-magneto-phonic-theremin (we had to come up with this new subcategory in the domain of electronic instruments, as the Chimaera did not fit anywhere else). Other terms that would describe it well could be: a general-purpose-continuous-music-controller, a multi-touch-less-ribbon-controller or a possible offspring of a mating experiment of a keyboard and violin.
Think of it as an invisible string that is excitable by an arbitrary number of magnetic sources. Depending on where the magnetic sources are located on the string and depending on how strong (or how near) they are, the device outputs different event signals. These general-purpose event signals then can be used to e.g. drive a synthesizer, an effects processing unit or some other hardware.
Chimaera S128: 8 sensor units (128 sensors) embedded in a beech case.
where does the inspiration come from?
We dreamed about a fully hackable music controller that would be as expressive as the violin, the theremin, the trautonium and the continuum fingerboard, as versatile in its usage as the Monome, as open as the Arduino and all that at an affordable price. As there was no such thing, we had to come up with something by ourself.
what were its design goals?
The main design goals for the device were to have a music controller that gives the player optimal control on musical expression. Now what is music in the first place? Our favorite definition is: music is structured sound. And the most prominent three parameters that distinguish sounds from each other in turn are pitch, time and volume. To have full control over music, therefore a player needs to have full control over pitch and volume of generated sounds and their temporal progression. And full control in this setting specifically means that pitch and volume can be controlled over continuous ranges with a high temporal resolution.
The points therefore that had to be fulfilled were:
- playable with fingers (those are the body parts that we have a very fine grained control on)
- design should qualify for do-it-yourself production
- entirely based on and released as free/libre and open source software and hardware design
- adhere to the KISS principle (were our favorite wording is: keep it simple and smart)
- highly sensitive, e.g. has to react to subtle changes in input (a prerequisite for an expressive play with vibratos, tremolos, ...)
- high update rates (>2kHz)
- low latency (<1ms) and low/no jitter (<0.25ms)
- driver-less communication and integration into any setup or operating system
- possibility for network performances via UDP and TCP inherently included
how does it work?
The chimaera consists of three parts: the sensory part, the computing part and the communication part.
Up to 160 linear hall effect sensors aligned on a straight line form the sensory part. Each single sensor can sense the magnetic field it is in and outputs a corresponding linear analog signal. Assuming a known constant source of a magnetic field, such as a permanent magnet, the sensors signal can be used to decipher the distance of such a magnet to each individual sensor. As the sensors are narrowly spaced apart (5mm), a single magnetic source is always sensed by several adjacent sensors. By doing some interpolation, we are able to not only decipher the distance of the magnet from the array, but also its exact location along the sensor array to a high accuracy (down to less than 1/100 of the inter sensor distance). For each magnetic source, the device therefore can output two signals, one is the position of the magnet in the sensor array (X), and the other is the distance from the sensor array (Y). As the sensors work independently from each other, an arbitrary number of concurrent magnetic sources can be measured at the same time (actually, the maximal number of concurrent events amounts to number-of-sensors/order-of-interpolation-polynomial).
The communication part connects the device to the outer world, e.g. to your computer and provides communication channels in both directions, both to transmit the gathered data to you and to receive configuration commands from you. As opposed to most other electronic musical devices out there that are using USB protocols, we use networking protocols instead. This has several advantages in respect to open-ended usage scenarios, e.g. full operating system independence.
The actual work of connecting the two parts is done by the computing part, which consists of a micro controller that reads all the sensors, detects the magnetic sources, interpolates their locations and prepares the data for handing it over to the communication part. Simply speaking, it is a digital signal processor, translating analog sensory input into digital event signals.
Dump of sensor array consisting of 144 hall effect sensors. Two magnetic fields were recognized as touch events #14 and #15. The two magnetic fields have different polarities.
how does it sound?
It does not make any sound by itself, it is just a controller. It is up to you to decide how the controller data is converted to sound, you are in full control.
Have a look at the media page for some video and audio samples.