Reproduction formats

Multi-channel and surround sound
Multi-channel audio production is a standard in many areas, like TV, film, digital radio, computer games, and of course music production released on different commercial available media like SACD, DVD-A, Blu-Ray, etc. Often these multi-channel formats are called “surround sound”. This is mainly due to the fact that loudspeakers positioned behind the listener reproduce some of the audio channels. Hence the listener is “surrounded” by the sound. 

Number of channels
The standard format for discrete multi-channel surround sound is configured with five full bandwidth main channels. For some purposes also a band limited channel for low frequency effects or low frequency enhancement (LFE) is added. These formats are referred to ad 5.0 or 5.1 depending on the LFE-channel being present or not.  

However, in film production you may find formats like 6.1 and 7.1 

Loudspeaker arrangement for 5.0 / 5.1
The loudspeaker arrangement for the reproduction of 5.0 / 5.1 is depending on the application. The international standard ITU-R BS.775-1 is widely accepted for music production.

In this set-up all loudspeakers are positioned in equal distance from the listener. A centre speaker (C) is placed right in front of the listener. The left and the right front speakers L, R) are positioned at angles plus and minus 30 degrees off the centre axis (as is for standard stereo listening). The surround channels (LS and RS) are positioned at angles between 110 and 120 degrees.  This configuration is also called 3/2 because there are three front channels and two rear channels. If the front speakers are arranged on a straight line, it is suggested that the centre speaker is given a time delay. 

The LFE (or “.1”) channel has not been taken into account in this arrangement. The subwoofer can in principle be placed anywhere with appropriate regard paid to distance and the acoustic conditions of the room (especially standing waves). It should be mentioned that the LFE-channel is not a sub-woofer channel or the like, because all primary channels exhibit a frequency response all the way down to 20 Hz and all the low frequency contents related to the main channel in general are reproduced in these channels.  The LFE channel is gained 10 dB more than the main channels to provide additional headroom. It may only be used for a bang that occurs once half an hour into the programme material. This channel is included due to regard for the better utilisation of the dynamic range of the primary channels. In general, it can be said that it is used mostly in films and only extremely rarely in music.