What is auralization? Definition and examples

Auralization (conceived as a counterpart to ‘visualization’) is a process which simulates how an audio file would sound when played in a particular space. The term was first used in an article by Kleiner et al., published in the Journal of the Audio Engineering Society in 1991.

Producing an auralization requires:

• An anechoic audio file – that is, one recorded in a sound-absorbing anechoic chamber, where unwanted sound-wave reflections aren’t produced. This means that the resulting auralization isn’t “contaminat[ed]” by reflections from somewhere other than the target space. (Recordings made in an acoustically ‘dry’ room, like a recording studio, can be a suitable alternative to fully anechoic ones)
• The impulse response of the target space (either measured or simulated), the dynamics of which are to be replicated. 

The impulse response of a closed or semi-closed space, “a short signal that fully represents [its] acoustics”, is based upon the ways its geometry and the material/s from which it is constructed affect the behavior of sound in that space. An impulse response is generated in response to an impulse such as “a short burst of a broad-band signal” in a space (such as a sine sweep, which begins at a low frequency and pitches up through the audible frequency spectrum); recording the reverberations of this impulse reveal the reverberant characteristics of the space. (Brief, percussive sounds, like those of a clapperboard or a balloon bursting, can also be used as an impulse.) 

Via a digital signal processing operation known as convolution – the “combin[ing] [of] two time-varying signals in[to] one” – the audio file and the impulse response are integrated together. Processing audio through a space’s frequency response renders the audio to sound as it would if played in that space. 

Though acoustic simulation software was developed towards the end of the 1960s, the technology to convolve sounds in this way has only been widely available since the early 1990s. ‘Multiplying’ the spectra (frequency content) of both the audio file and the impulse response, through convolution, will strengthen “frequencies that are shared between the two sources” and weaken any that are not shared. In so doing, convolution “impart[s] the characteristic timbres of spaces and objects on[to] other signals”.

The resulting auralization generally takes a binaural form: a type of audio which replicates the way that we hear via two ears, creating an immersive, three-dimensional experience; an “out-of-head localization”.

Auralization techniques have applications as an architectural design tool (enabling “direct […] experience [of] the aural implications of design decisions”); within room acoustics (the study of sound behavior within enclosed or semi-enclosed spaces); for noise control (“the process of managing and reducing noise levels”); and for creating sound environments within video games and virtual reality.

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