Introduction to Spatial Audio

The spatial dimension in natural sound

width
height
depth

Natural sound ‘scene’ outdoors

many sources with their own location and attributes
source blending

Indoor environments

reflections strongly effect sound
gives the size of the space

Guess the environment?

Sound sources in space

Sound sources in a free field

Sources in reflective spaces

Introduction to the spatial dimension in reproduced sound

What is the aim of sound reproduction?

From mono to surround sound and 3D audio

Early sound reproducing equipment

The first stereo transmission?

Bell Labs in the 1930s

Early consumer stereo

Binaural stereo

It could well be argued that all sound reproduction is ultimately binaural because it is auditioned by the two ears of a listener. Nonetheless the term binaural stereo is usually reserved for signals that have been recorded or processed to represent the amplitude and timing characteristics of the sound pressures present at two human ears

Documented examples of interest in this approach go back over much of the twentieth century. When reproduced over headphones such recordings can recreate a remarkable sense of realism, including height cues and front–back discrimination. Unfortunately the variables in such signal chains, particularly the differences between the recording head/ears and the listener’s, the headphone response and coupling to the ears, and any distortions in the signal path, can easily destroy the subtle spectral and timing cues required for success.

Cinema stereo

Quadraphonic sound

Ambisonics

History

Ambisonic sound was developed in the 1970s by a number of people including Gerzon, Fellgett and Barton, and many others influenced its development both in the early days and since. Much of the work was supported by the NRDC (National Research and Development Council) and the intellectual property was subsequently managed by the British Technology Group (this was eventually transferred to the British record company, Nimbus). It was intended as a comprehensive approach to directional sound reproduction, involving any number of reproduction channels, based partly on an extension of the Blumlein principle to a larger number of channels. The system can be adapted for a wide variety of loudspeaker arrangements, including (more recently) the ITU-standard five- channel configuration. Enabling fully three-dimensional sound fields to be represented in an efficient form, including a height component, it remains an elegant technical toolbox for the sound engineer who believes that accurate localisation vector recon- struction at the listening position is the key to high quality spatial sound reproduction.

The home cinema and ITU-standard surround sound

Applications of spatial audio