Julien Signolet sculpturist based out of Paris and musician Mathias Durand approached me for an interactive sound installation at Parc Floral in Paris for Nuit Blanche 2019.

The installation would be out door and I would not be present during the installation as I had commitments in India. I had to fabricate and make sure it runs unattendant with minimal requirement for it to be installed. So basically Plug and Play.

The basic Idea of this synthesiser is using the notion of Miyan ki Todi Raag (an Indian Classical Scale)

Generating Modulating sine wave using the principle of this raag.

In extremely simple explanation: Indian Classical Music the raag or something like scale has a structure where the feeling of the raag based on ascending and descending of notes not the root essentially. Certain notes can appear only in ascend while certain only in descend while certain note can only appear as combination. This defines feeling attached to the raag. Think something like Modes in western music. These structures can be put down mathematically and used in a generative sense. There are more elements which gives the specific feeling of the raag but I suppose here I will focus on 3d modelling, coding and design. Using this as fundamental ie the code and the concept you can model your own shape for the synthesiser or can make this one it self.

This synthesiser was built for site specific experience but can be used anywhere !

Supplies

Arduino

HCSR04 Ultrasonic Sensors

Fusion 360

3D Printer

3.5mm Audio connector

270 Ω and 10K resistor

100n capacitor

2.1mm DC barrel connector

Cables, solder Iron etc

Step 1: Fusion 360 Modeling

I needed something to mount the ultrasonic sensor around a tree in the park.

So I designed a Dodecagon - 12 sided polygon.

Effectively using 360 degree with 12 ultra sonic sensors. (not entirely true as the effective horizontal capability of these ultrasonic sensors are around 27 degree but this 6 degree difference between the two sensors is less than a normal human step (6 to 10 cm) so in human interaction sense these small dead zones are fine and in fact better as only one sensors gets activated by them so it seems like a continuous range)

Here I made a mounting screw holes for the sensors and just enough space for the arduino. Each section has a side hole for wire to go internally and bottom hole in 2 of the parts .. One for power and one for audio out.

In no time it became a mess of wires inside! And I could not get it printed in black . only white was option. So i Spray painted it Black after printing. And since the installation would be open only in night time ie in dark . Imperfect surface finish in my opinion was working great with the tree trunk

Look at the images above for Reference

Use M2 bolts and mount the ultrasonic sensor to the 3d printed part

Solder the cables to them.

Step 2: Arduino

For the Sound Generation bit I used Mozzi. I had crazy trouble with speed and refresh while using multiple ultrasonic sensor attached to one arduino. I was experimenting with Newping Library. Its an excellent library.

It was something to do with me and my approach or maybe atmega itself. (I would use teensy next time)

I could not get mozzi + new Ping using 6 ultra sonic sensors working in tandem

So essentially I ended up using 12 arduino nano and 12 HC SR-04.

So every nano also had a simple RC filter. RC filter means Resistor - Capacitor filter

This is to reduce aliasing at high frequencies at the pwm output of nano.

An RC filter with around 6kHz as roll-off frequency is fine. Here R is 270 Ω resistor while C is 100n capacitor,

Also since I am summing the audio of every nano I would need to attenuate the signal.

A Simple 10K resistor works well for this. SO effective after the RC filter a 10k is added so the signal can be summed to one output. That summing 12 audio out into one stereo out. OR 6 to left 6 to right.

For Powering the Arduino I connected a 2.1mm barrel connector.

Nano can withstand 9v into its Vin pin. I connect all the arduino in parallel Vin to the + of 9v and GND to the Ground of 9V.

Now its only uploading the code and testing.

parc-mozzi.ino
Download

Step 3: Sound Experiments

Mozzi is an Excellent Library !

In the above Synth. the Sound can be made more exiting by adding simple delay and reverb effect may be from a guitar pedal.

Yes I did use them for the installation. Mathias hooked up his Pedal Board to it. and it sounds fabulous !

Even though it rained in the night people had a really great time. And some crazy comments were passed as it felt like space, its like water ,etc :)

Essentially you can use this as a base to create something really different. Ultrasonic sensor and the attached code above is the fundamental ! You can really make some crazy devices out of this. Don't really have to stick to this specific form factor. Fire up your fusion 360 and model something crazy. With this code you can make a really personalise model of your own synthesiser. Your imagination and creativity is the limit !