Monday, February 12, 2007

5.1 Sound is not 3D

Surround sound, for movies or for music, is wonderful.

5.1 was developed as a minimum configuration that could deliver 360 degree full-range sound, and it works well. Tony Grimani and Tomlinson Holman, then at Lucasfilm's THX division, coined the phrase and researched the concept.

Every sound we hear arrives from a sphere around us. Unless we are in an anechoic chamber - a room with no reflections - we can tell where a sound source is from just about anywhere in the room. Our ear/brain mechanism evolved so this system could help us survive.

Dimensionality of Sound Systems:

Mono - one-speaker sound comes from a point, and a point has no dimension.

Stereo (two or more reproduction channels can be called Stereo) - Two-channel Stereo is single-dimension: Width. Instead of a point, the sound source is a line, which again mathematically has no dimension, but two-speaker Stereo provides a sonic image of a certain width and can provide an image of a center source.

Surround - 3.x Stereo (adding at least one channel of reproduction behind the listener) can provide a dimension in addition to Width: Depth. This makes 5.1 Surround two-dimensional.

A height channel, as used in Tomlinson Holman's TMH 10.2 system and some IMAX presentations, would be the next dimension to add to Stereo sound reproduction. Eight channels or more are available in surround distribution platforms such as Blu Ray disc, HD-DVD disc, Dolby Digital Plus, Dolby TruHD, Windows Media, Quicktime... Perhaps a mono Height channel could be commonly used with these platforms. The Center Surround should probably be implemented with the last of the eight channels - this is already commonly mixed for distribution with Dolby EX and DTS-ES, and can overcome our lack of ability to hear a phantom image well from behind us. The Right Wide and Left Wide channels should probably be next on the list, to compensate for our difficulty in hearing a phantom image from directly to the right or left of us.

The addition of a Height channel would be the minimum necessary change to be able to make any audio system three-dimensional.