Brushing II is a sound installation work for audio feedback by electronics and brushing tools. It aims to create a dynamic sonic space that interacts with the audience inside the feedback loop. At the center, there are brushing tools on the table. The interface installed on the table can detect the touch and pressure of the audience’s brushing activity, and the sound is synthesized based on this interaction. Below the table, there are two wood blocks with contact microphones mounted below. Whereas the space itself is ‘interactive’ due to the audio feedback, the brushing section in the center provides an instrumental characteristic to the piece and enables audiences to be more ‘expressive’ with the installation.
In this essay, I would like to focus on the audio feedback part of Brushing II. Audio feedback was used to create a sonic entity of the piece, which was the core element of forming the spatiality of the piece. A more detailed description of the background and design decisions of it will be discussed in the following.
When I was planning Brushing II, I had a massive interest in spatiality as a core element for sonic expression. For me, this didn't mean creating a timely constructed piece with spatiality as a key feature, such as fixed media acousmatic works. In this project, I wanted to create a sound artwork that does not follow the notion of time-based art. Rather, I wanted to create a type of sonic entity that resides in space and behaves/interacts in a certain fashion. To achieve this, audio feedback was used in this project.
In this project, audio feedback was created by facing multiple speakers with two sensitive condenser microphones with some realtime audio processing through Max. Theoretically, in this setting, every sonic event that occurred in between the speakers and the microphone will be captured and influence the sound of the audio feedback. How it sounds will be determined by the space's acoustic feature, the filtering algorithm of the realtime audio system, and the behaviors of audiences in the space. This idea fascinated me because it implies a possibility of creating a sonic interaction where the audience interacts with the sonic space directly through the sound they create. The sound created by the audience will be taken as input by the microphone and will affect the sound of the audio feedback, not by parameterizing the audience's action by using sensors or live image processing.
There are various approaches in using audio feedback for a sonic artwork, and how the artist does this treatment determines the characteristics of the audio feedback they are creating. For this project, I wanted the audio feedback to have the following features. First, the level of the feedback should not overkill the sound made by the audience, but it should be clearly noticeable at the same time. The motive behind this feature was to make the audio feedback coexist with the audience in the space, which enables the audience can perceive the audio feedback as an independent sonic entity. To achieve this, a bandstop filter was used where the center frequency is automatically adjusted to the strongest frequency bin of the input signal. In addition, if the strongest frequency bin is below a certain frequency threshold, it automatically moves the filter's center frequency to a high-frequency range. This method preserves more low-frequency signals in the feedback loop that prevents audiences from feeling fatigued by the high-frequency sound.
Second, the audio feedback should react to the sound made by the audience. As mentioned above, every sound produced by the audience will be reflected in the feedback. To make this more prominent, a spectral delay was added to the signal flow. Due to the spectral delay, a percussive sound like clapping creates a distinct 'watery' type of sound in the feedback, which adds an extra texture to the soundscape and creates a strong sense of interactiveness to the audience. This distinct interactiveness of the feedback makes the sonic space playable for the audience. For example, during the exhibition at the Center for Computer Research in Music and Acoustics(CCRMA), Stanford University, people clapped, stomped, and some even tap-danced inside the exhibition space.
Finally, the audio feedback should be dynamic on its own even when the audience doesn't create any sound. To achieve this, bit crunching and under-sampling were applied to the input signal, and the rate of each of them changed based on a random tempo. The bit crunching creates a distorted and glitchy sound, and the under-sampling creates a slight melodic contour due to the change of frequency caused by aliasing. These techniques provide liveliness to the soundscape, and it feels as if it is a living entity behaving on its own, not just a response created by the input from the audience.
The exterior look of the installation was also an important element. As shown in the image on the left, it was intentionally designed minimal and empty so that it creates strong contrast with the audio feedback, which is vivid and packed in the space. In addition, soft lighting was spread around the area to remedy the timidness caused by the audio feedback and create affordance for the audience to explore/play with the space.
In this piece, feedback was used to create a sonic entity that behaves and interacts with the audience through audio in realtime. This had been done by creating a space with a distinct sound with the right amount of amplitude that dominates the sound created by the audience and also applying realtime techniques that make the feedback dynamic by itself while interacting with the audience.
This interaction is done sonically as a whole, which operates in a way that does not parameterize the behavior of the audience such as using sensors. When integrated with other various audio/sound techniques, this can be developed into multiple directions for creating interaction between the space and the audience with sound. Therefore, utilizing feedback as another option to create interaction can be an interesting perspective for an artist who uses sound as the main medium.