Audio theory 3: Listening blog 1
UnderEden WALKMAN *Explorers Edition* is a series of audio adventures currently showing at Melbourne Fringe Festival, and created by artist collective STRANGEkit that I have the delight of being composer and sound designer for. Each episode guides the listener through a transformation into different beings and alien worlds.
UnderEden WALKMAN *Explorers Edition* discs (STRANGEkit 2021).
In the fourth episode, the listener is transformed into Ryan, a humanoid fish in a box in space. To create a reverb for Ryan’s voice, I approximated the reverb of a wine carton with a digital plugin and by performing tests with my own voice, a clap impulse response, and playing recorded dialogue from a speaker. In this small space, reflections are almost immediate and sound energy builds up due to the parallel walls on all four sides encouraging axial reflection of sound. Sound waves reflect off the walls until the energy dissipates through a combination of absorption into the cardboard walls and dispersing in the air. Both mechanisms involve transforming sound energy into heat through dispersing structured waves into disorganised vibrations (Physics Central 2021, para. 5).
Using a clap impulse response inside the box resulted in a sound with pronounced mid-range frequency resonance and less resonant high end. Since it is fairly difficult to fit a speaker and microphone into the box for a sine sweep I approximated one by singing ‘oooooo’ from the lowest to highest boundaries of my vocal range with my head in the box. I identified a resonant frequency around 300Hz which has a wavelength of 1.144m, approximately four times the length of the box. At ¼ wavelength a standing wave forms in the box as reflections coincide and reinforce once another (Russell 1997, para. 5).
Comparatively, a vocal sweep in my room did not yield any particular resonance around 300Hz, and the clap had much more high end. The time it took for reverberant energy to attenuate by 60dB was also greater in the room than inside the box. This measurement is known as RT60, the ‘reverberation time, or the time it takes for sound to decrease by 60 dB in a room’ (Long 2014 p.301). The larger size of the room allows more time between reflections off the wall, however more factors affect its reverb quality. Diffusion is created from the irregular angles of furniture and blinds dispersing waves both spatially and temporally which ‘reduc[es] the sense of localisation’ (GIK Acoustics 2021, para. 3). Sound energy is also absorbed by carpet and cushions ‘which reduces or eliminates reflections by removing the sound energy from the room’ (GIK Acoustics 2021, para. 4)
Reflection, absorption, and diffusion diagram (Sound&Vision 2021).
After becoming familiar with the reverb characteristics of the box came the task of creating a reverb for Ryan’s voice. I chose the smallest room setting possible on the reverb plugin, set a pre-delay of 1.2ms, decay time of 600ms, and attenuated the diffusion network above 500Hz. The reflections were also boosted by 4dB, and the reverb was EQ’d to boost around 300Hz and attenuate above 1kHz with a shelf. In comparison with playing the dry recording into the box and listening to my voice inside the box, the reverb plugin was fairly similar yet slightly exaggerated for dramatic effect.
At the end of the episode, Ryan escapes the box and drifts into space. The box reverb is removed and an artificial long reverb is added with a delay. Obviously in space there is no air and thus no sound let alone reverb, however most of us have never been there and the human imagination can only be informed by familiar input. Therefore creating a sense of vastness in a vocal effect was best achieved by imitating large reverberant spaces in our world, such as a large canyon with a long echo. Sometimes a feeling is more important than realism. After all, Ryan is a fish in a box in space.
Listen with headphones for the full binaural experience!
Long M 2014, Architectural Acoustics, 2nd edn, Elsevier Science Publishing Co Inc, San Diego
GIK Acoustics 2021, Decoding Diffusion, viewed 12 October 2021, https://www.gikacoustics.com/decoding-diffusion-acoustic-solutions/
GIK Acoustics 2021, How Diffusion (audio) Works, viewed 12 October 2021 https://www.gikacoustics.com/how-diffusion-works/
Physics Central 2021, How long would you have to yell to heat a cup of coffee?, viewed 11 October 2021, https://www.physicscentral.com/explore/poster-coffee.cfm
Russell K 1997, Resonance, viewed 11 October 2021, https://home.cc.umanitoba.ca/~krussll/138/sec4/resonanc.htm
Sound&Vision 2021, Acoustic Surfaces, online image, viewed 12 October 2021, https://www.soundandvision.com/content/room-acoustics
STRANGEkit 2021, Initiation : TOMORROW, online image, viewed 12 October 2021, https://www.facebook.com/strangekitperformance/photos/a.118849659773227/388396949485162/