Mephisto: an Open Source WIFI OSC Controller for FaustApplications

Romain MICHONCenter for Computer Research in Music and Acoustics

Department of Music,Stanford, CA 94305-8180,

USA,rmichon@ccrma.stanford.edu

Abstract

Mephisto is a small battery powered open sourceArduino based device. Up to five sensors can beconnected to it using simple 1/8” stereo audio jacks.The output of each sensor is digitized and convertedto OSC messages that can be streamed on a WIFInetwork to control the parameters of any Faust gen-erated app.

Keywords

Faust, Arduino, Controller, OSC

1 Introduction

In the past few years, the Faust1 [Orlarey andLetz, 2002] programming language has beenused increasingly by researchers and developersto implement new algorithms for real time audiosignal processing. As a result, dozens of opensource Faust effects and synthesizers are nowfreely available. For example, Julius Smith’s li-braries [Smith, 2012] and the Faust-STK [Mi-chon and Smith, 2011] provide a large array ofobjects ranging from the simplest lowpass filterto complex feedback delay networks and physi-cal models of musical instruments.

However, we observed that these technologiesremain relatively inaccessible to musicians whodon’t have the knowledge (and the desire) tocompile a Faust object on their laptop. Inother words, these elements are not “plug andplay”.

One of the tool already at our disposal to fa-cilitate the sharing and the use of Faust objectsis the Online Compiler2 [Michon and Orlarey,2012]. This web app contains an interactive cat-alog of Faust programs that can be compiledto any of the available Faust architectures andthen downloaded. Users can easily add theirown Faust codes to the catalog or modify ex-isting elements. Even if this very high level toolmakes the creation of plug-ins, etc., very easy, it

1http://faust.grame.fr.2http://faust.grame.fr/compiler.

targets users who have some knowledge in com-puter music and who know how to use a VST3,an external audio interface, etc.

Thus, to make things even easier we startedto think about a Faust stomp box that could bebased on an embedded Linux system such as aRaspberry Pi4. It would have been able to con-nect to the online compiler to provide its user alist of the objects stored in the catalog. A down-load button to cross compile and then downloadthe effect or the synthesizer in the Faust boxwould have made the use of this system veryeasy.

However, even though Raspberry Pis aregreat prototyping platforms, their computationpower is quite limited. Also, their bootingtime can be a problem for impatient musi-cians. We then realized that a smartphone ora tablet could do a similar job and would bemore user friendly. While there already existeda faust2ios architecture, Apples product werepresenting a huge disadvantage over Androidphones: in order to be installed, an app hasto be approved by the Apple Store which wasmaking our concept of a customizable stompbox impossible to implement. Thus we optedfor Android and created a faust2android [Mi-chon, 2013] architecture.

Another key component of our project wasto provide an easy way for musicians to con-trol the different parameters of a Faust objectduring a live performance. While smartphonesoffer built-in basic controllers: touch screen, ac-celerometer, etc., these elements are not verypractical to interact with if the user is playingan instrument and processing its sound with hisphone. Indeed, many instruments require theuse of both hands, making it inconvenient tointeract with another interface.

Mephisto was created to solve this problem.

3Virtual Studio Technology.4http://www.raspberrypi.org/.

Figure 1: View of Mephisto from its top.

It is a small battery powered device that can beeasily attached on someone’s belt (cf., figures 1and 2). Up to five sensors can be connected to itusing simple 1/8” stereo audio jack plugs. Theoutput of each sensor is digitized and convertedto OSC5 [Wright, 2005] messages that can bestreamed on a WIFI network to control the pa-rameters of any Faust generated app. As OSCis a standard protocol, Mephisto can be usedwith faust2android apps but is also compat-ible with most of the Faust architectures andprograms enabling OSC communication.

As a “DIY”6 open source project, Mephistoonly uses open source hardware (Arduino, etc.)and was designed to be easily built by anyone.A web page giving the instructions to build yourown Mephisto has been created7.

2 Hardware

Designing small scale open source hardware canbe a rather complicated task. Indeed, whilesoftware can be easily deployed and shared,in many cases hardware requires a productionchain, etc. For this reason, Mephisto has beendesigned to be easily and quickly built by any-one.

2.1 The Case

To make it as easy as possible for users, the caseof Mephisto is 3D printable. It has been de-signed with Blender8 which is an open sourceprogram for 3D design that has some CAD fea-tures.

5Open Sound Control: http://opensoundcontrol.org/.

6Do It Yourself.7http://ccrma.stanford.edu/~rmichon/mephisto.8http://www.blender.org/.

Figure 2: Use example of Mephisto.

Figure 3: 3D model of Mephisto’s case as itappears in Blender.

We’re perfectly aware that not everyone has a3D printer at home, but 3D printed models cannow be ordered very easily online for very cheap.Moreover, Mephisto’s case has a very simpledesign and can be printed on almost every 3Dprinters.

2.2 Electronics

Mephisto is based on an Arduino Uno9 anda WIFI Shield10 (cf., figure 4). The Arduinoprovides five analog inputs that are used in

9http://arduino.cc/en/Main/arduinoBoardUno.10http://arduino.cc/en/Main/ArduinoWiFiShield.

Figure 4: An Arduino Uno and its WIFI shield.

WIFI Shield

Smartphone, Laptop, etc.

Sensors Jack Inputs

Mephisto

Template ArduinoFirmware

JAVA Interface

Ino

Interface Program

Arduino

USB

Compilation &Upload

LCD Screen

Nav Buttons

OSC

User Interface

Figure 5: Mephisto flow chart.

Mephisto to digitize the output signals of thesensors. Simple 1/8” stereo audio jacks (threepins) are used to bring power to the sensors andto retrieve their output signal (cf., figure 1).

Users can configure basic parameters such asthe WIFI network to connect to or the IP ad-dress of the host using an LCD screen and anavigation button interface.

Mephisto can be powered with any DCpower adapter between seven and nine voltsor with a simple nine volts battery. We con-sidered using lithium ion batteries instead butthese are more expensive and need a specialcharger. With five simple sensors plugged toit, Mephisto can run for about four hours onthe same nine volts battery. Moreover, it is veryeasy and quick to replace it.

Figure 6: Example of sensors that can be con-nected to Mephisto with their 1/8” jack plugs.

Dozens of sensors have been tested and can beeasily prepared to work with Mephisto. Ourwebsite explains how to set up an accelerometer,a pressure sensitive and a flex sensors, trim pots,etc.11.

3 Software

3.1 Arduino Firmware

The Arduino firmware carries out a large num-ber of tasks. It retrieves and digitizes the outputsignals of the sensors and scale them in functionof the parameters specified in the interface pro-gram (cf., §3.2). Then it converts them to OSCmessages using oscuino12. The OSC address ofeach sensor can be configured in the interfaceprogram (cf., §3.2).

The firmware also handles the user interfaceimplemented through the LCD screen and thenavigation buttons.

3.2 Interface JAVA Program

Even though Mephisto provides its own verysimple interface to configure it by the mean ofits LCD screen and navigation buttons, a JAVAprogram13 that can run on both Linux and Ma-cOSX was created to carry out this task moreprecisely.

This simple program allows to configure theOSC address and the range of the OSC messagessent by Mephisto for each jack input. It is alsopossible to choose which sensor is connected towhich jack in order to carry out some scaling ontheir output signal (even if the Mephisto web-site explains how to do basic electronic scaling

11http://ccrma.stanford.edu/~rmichon/mephisto.12http://cnmat.berkeley.edu/oscuino.13https://github.com/rmichon/mephisto/.

Figure 7: Screenshot of the interface programused to configure Mephisto from a desktop.

on sensors, it is often necessary to adjust theiroutput range computationally).

The Mephisto configuration program alsomakes it possible to pre-configure the WIFI net-work to which mephisto will connect as well asits password if it is protected, the IP address ofthe host and the rate at which the messages aresent.

This interface program formats and cus-tomizes the Arduino firmware in function of theprovided parameters. It then compiles it anduploads it to the Arduino if it is connected toone of the USB port using ino14. As this pro-gram only works with Linux and MaxOSX itmakes the interface only usable on these plat-forms even though it can also be executed onWindows.

4 Conclusion

Mephisto is an open source project that im-proves and simplifies the control of sound ef-fects and synthesizers running on a mobile de-vice. Any kind of sensor can be connected to itand used as on OSC controller for live perfor-mance.

The Faust online compiler together withMephisto, faust2android and the Faust cat-alog of sound effects and synthesizers greatlysimplifies the use of Faust objects by musi-cians.

The use of 3D printing in the framework ofopen source hardware projects makes things alot easier than in the past. Indeed users don’tneed to have any background in manufacturingand only have to take care of putting the differ-ent components together.

Similarly, Arduinos are relatively self con-tained environments that significantly reducethe size of electronic circuits making projectslike Mephisto easy to build at home.

14http://inotool.org/.

References

Michon and Orlarey. 2012. The faust on-line compiler: a web-based ide for the faustprogramming language. In Proceedings of theLinux Audio Conference (LAC-2012), pages111–116, Stanford University, USA.

Michon and Smith. 2011. Faust-stk: a set oflinear and nonlinear physical models for thefaust programming language. In Proceedingsof the Conference on Digital Audio Effects(DAFx-11), pages 199–204, IRCAM, Paris,France.

R. Michon. 2013. Faust2android: a faustarchitecture for android. In Proceedings of16th Int. Conference on Digital Audio Effects(DAFx-13), pages 301–304, National Univer-sity of Ireland, Maynooth, Ireland.

Fober Orlarey and Letz. 2002. An algebrafor block diagram languages. In Proceedingsof the International Computer Music Con-ference (ICMA), pages 542–547, Gothenburg,Sweden.

J. Smith. 2012. Signal processing libraries forfaust. In Proceedings of the Linux Audio Con-ference (LAC-2012), pages 33–38, StanfordUniversity, USA.

M. Wright. 2005. Open sound control: anenabling technology for musical networking.Organised Sound, 10(03):193–200.