Surround Sound


Introduction

Surround sound, or “multichannel audio”, as it is sometimes known, is the technology employed to reproduce audio – from the soundtrack of a DVD (“Digital Versatile Disk”) film, or a digital television broadcast, for example – on more than two loudspeakers; typically, nowadays, 6, 7, or 8 speakers positioned at specific locations around the listener. The technology has actually been in existence, in one form or another, since 1940 – Walt Disney and conductor Leopold Stokowski collaborated on a sound system that involved 8 music tracks, for the film “Fantasia”, in that year – but the advent of digital technology within reach of the typical domestic consumer means that surround sound is, today, commonplace in home entertainment systems.

Surround Sound Formats & Features

Dolby® Digital is the recognised industry standard for multichannel sound for commercial DVD releases, for example, although for full, 5.1 channel surround sound – that is, 5 discrete main channels of audio, plus a sub-channel for low frequency, bass effects (the “.1” in the designation) – Dolby® Digital 5.1 is required, specifically. Dolby® Digital actually refers to a format that supports up to, but not necessarily, 5.1 audio channels. Extended surround sound formats do, of course, exist. DTS-ES (“Digital Theatre Systems – Extend Sound”), for example, is a 6.1 channel format, supporting an additional discrete rear channel, completely independent of the left and right rear channels. Dolby® TrueHD, as an alternative, offers a total of 7 discrete, full bandwidth audio channels, 1 discrete LFE (“Low Frequency Effects”) and “bit-for-bit” reproduction that is identical, in every respect, to the original recording.

To experience digital surround sound to its full extent, therefore, a total of at least 5 main loudspeakers – usually arranged as front centre, front left and right and rear left and right – and a specialised loudspeaker, known as a “subwoofer” – which is typically positioned in a corner of a listening space, and reproduces low frequency (3Hz to 120Hz) bass and rumbling effects – are required. The sound that emanates from a subwoofer is typically less directional than that from other speakers, so the precise positioning is less critical. 6.1 and 7.1 channel surround sound systems require an additional main rear speaker, or two, respectively.

One important characteristic of speakers and surround sound components is the matching of the speakers for tonal quality, or “timbre”. If you are considering an HTIB (“Home Theatre In a Box”) surround sound system, speakers are typically matched for timbre by the manufacturer, but, if not – and particularly if you choose speakers from different manufacturers – this may become more of an issue. If speakers are not matched, when sound changes, or “moves”, from one to another, the source of that sound will become immediately identifiable, and the overall effect will be ruined.