AC-3 ACM Codec 2.1

 

The codec can control up to six sound channels which cover the entire audible sound spectrum (20 Hz – 20,000 Hz). Five of the channels are dedicated to normal-range speakers (right front, center, left front, rear right, rear left) and one individual channel for low frequencies (20 Hz – 120 Hz) for the subwoffer.

Source : http://www.softpedia.com/get/Multimedia/Video/Codec-Packs-Video-Codecs/AC3-ACM-Decompressor.shtml