Emma Margetson / Spatial Materiality : A Little Backstory with Markus Noisternig 2/2
To give some background on Emma Margetson’s artistic research residency, researcher, sound artist and deputy director of the STMS labMarkus Noisternig guides us through the long research journey that involved the development of IKO – an icosahedron-shaped speaker that has become the focus of attention.
The story of IKO started with a dream: that of recreating the true sound radiation from an acoustic source – from an instrument or a voice, for instance – or synthesising any type of acoustic radiation. Indeed, an instrument does not work the same way a speaker does, and vice versa. We can easily imagine that, taking into account the shape of the instrument and the body of the musician (considering only that), the way a soundwave travels in a given space is far from simple. And that also changes depending on the height of each note, each timber … To draw a maritime analogy, a long swell will not hit the cliff the same way a stormy sea would, depending on its amplitude and its wave length. No matter how perfect it is, a speaker will only ever give a poor approximation of the sound radiation from an instrument.
Scientific research on the subject started long ago. At IRCAM, it goes back almost to the beginnings of the institute. “To do it properly, we have to explore two dimensions simultaneously”, explains Markus Noisternig. “On the one hand, we need to make measurements of the instruments’ directionality. This approach was first tried out by using a pair of microphones and moving them around the sound source (ideally around the surface of a sphere) in order to measure out the pressure and the speed of sound. More advanced devices were used later on, including spherical microphones arrays surrounding the sound source, in order to make simultaneous recordings of the sound field at multiple points. In an anechoic chamber, we don’t need to use more than one microphone for each position, which helps reducing the required number of sensors and makes it easier to develop microphones arrays at a very high spatial density. All these measurements then allow us to model the sound radiation as equations. On the other hand, we need to develop sound diffusion devices capable of reproducing that directionality.”
“The first experiments at IRCAM started in the 1980s, initially with only a single cube equipped with six speakers – one on each side – then with three cubes piled on top of each other, each covering a specific range of frequencies. This configuration aimed at reproducing the three-dimensional radiation from a complex sound source, taking into account the directional properties of each frequency range. In the 2000s-2010s, this approach led to the creation of Marco Stroppa’s « Speakers Tower », which he used in several works. Meanwhile, similar research was conducted in other academic institutions, such as Stanford, Princeton, Berkeley or Aix-la-Chapelle, where research teams made several attempts with structures arranged on the surface of a sphere – reaching up to 120 speakers.”
“Every scenario faces the same challenges: first, for the device to resemble an instrumental source, it needs to be fairly compact. Second, there needs to be enough speakers on its surface, in order to cover the space as completely as possible: that is what we call spatial sampling. In theory, that would require an infinite number of impossibly tiny speakers distributed on a minuscule sphere that matches the source. In practice, that is impossible to do, as speakers require a minimal size in order to produce a sufficient acoustic pressure level, which consequently limits how many can fit on a sphere. We therefore need to find a compromise between the size, the number of speakers and how they are distributed on the surface, in order to reproduce the directional characteristics the best we can without generating interferences or sacrificing sound efficiency. IKO was conceived at the Institute for Electronic Music and Acoustics of the University of Music and Performing Arts Graz. The first version dates back to 2007, when it was made up of two icosahedrons, one on top of the other (each corresponding to a specific frequency range). The technology was picked up by the startup Sonible, who developed IKO into where that we know today.”
Emma Margeston conducting tests with the IKO in the Projection Room
However, structure isn’t everything. While the icosahedron, with its 20 speakers (one on each face), is a good compromise, we cannot directly feed the signal that was captured back into the instrument, due to several technical barriers, both internal and external. “Within the structure itself, the proximity between the twenty speakers creates interferences between the soundwaves they are emitting. These soundwaves can also make interferences outside the device. These are as many phenomena that we need to assess, so that we can anticipate them and integrate them into our algorithms and therefore minimize the risk of potential disturbances. Lastly, we need to model how IKO behaves at every frequency – which we can do in IRCAM’s anechoic chamber. The acoustic radiation of each speaker is measured individually using microphones arrays distributed all around the sound source, in order to model their sound behaviour with accuracy. To measure diaphony, that is to say interferences between speakers, so that we can reduce it later on, we need to use a laser vibrometer. Another method consists in digitally modelling the radiation of each speaker. The only thing left to do then is to write algorithms that take into account all these constraints, so that we translate the sound radiation that was captured into the emitted signal.”
Accurately recreating an instrument’s acoustic radiation remains a legitimate and stimulating ambition, but it does not fully exploit the possibilities IKO offers. “Why not imagining other, more artistic, uses for this unique device?”, suggests Markus. Creating tracks – a technique used to project sound in a specific direction – is an accessible example, which already opens new expressive possibilities. More experimental approaches, such as spatial granular synthesis, suggest manipulating the sound space, just like any other malleable material. That is precisely where artistic research takes over, inventing new listening and creative modes. IKO’s potential is generating a growing interest among a vast network of artists, including at IRCAM, where we have collaborated on these topics with a wide range of composers, such as Yan Maresz,François Nicolas or Aaron Einbond. Using IKO in open field however does not showcase its full potential and isn’t particularly exciting – still, the device offers very interesting possibilities in terms of materialisation of the surrounding space. It allows us to play with the acoustics of a room, by sending the wave in different directions to trigger specific, sometimes unexpected acoustic feedback.”
“Nadine Schütz, who has a background in music, architecture and psychoacoustics, has been working for a few years now with the STMS lab on spatial composition techniques that showcase the architecture of a venue. By playing with the structure of a building or a room, we turn them into proper musical instruments. That is also the approach chosen by Emma Margetson, who is seeking to develop with IKO a new kind of spatial writing, as part of her artistic research residency. To manipulate the space, she places reflectors or similar objects that reflects soundwaves. This technique allows us to create sound illusions or masking effects. It’s all about the interplay between the device and the space. For instance, by placing several reflectors all pointing in the same direction, we can create additive synthesis – just like mirrors with coloured lights.”
“For us scientists, these musical studies explore use cases of technologies we are working on, which are interesting from a compositional/artistic standpoint. Artists constantly push us to our limits, and raise new challenges, that we try to answer to by developing the right tools to bring to their ideas to life and control the outcome.”
Jérémie Szpirglas
