These are compression algorithms from the Dolby Laboratories. The AC-2 coding is an adaptive transform coding that includes a filterbank based on time-domain alias cancellation (TDAS). The AC-3 is a dedicated multichannel coding, which like AC-2 uses adaptive transform coding with a TDAS filterbank. In addition, AC-3 employs a bitallocation routine that distributes bits to channels and frequencies depending on the signals, and this improves the coding efficiency compared to AC-2. The AC-3 algorithm is adopted for the 5.1-channel audio surround system in the American HDTV system.