Commonly used in theaters and at home.
5.1 surround sound specifies three front channels, two rear surround channels and a low frequency channel totaling 6 discreet channels. It is commonly provided on DVDs and is used in Digital Theater System (DTS).
The track layout:
LFE (Low Frequency Effects)
Ls (Left Surround)
Rs (Right Surround)
HD deliveries often require 5.1 audio mix in addition to Stereo Left & Right Composite Mix. In case M&E is required another set of 5.1 M&E tracks will be needed totaling the number of tracks to 16. Additional audio can be folded into a smaller number of tracks using Dolby E process or the tracks can be delivered on an audio tape such as DA88.