at require isochronous service. The Advanced Television Systems Communications. This group was formed by the Joint Committee on Inter-Society Coordination (JCIC) to establish voluntary technical standards for advanced television systems, including HDTV. In April 1995, the ATSC approved the Digital Television Standard for HDTV Transmission. ATSC A/53 The digital television standard for HDTV transmission proposed by the Grand Alliance and approved by the Technical Subgroup of the Federal Communications Commission (FCC) Advisory Committee. The standard specifies the HDTV video formats, the audio format, data packetization, and RF transmission. New television receivers will be capable of providing high- resolution video, CD quality multi-channel sound, and ancillary data delivery to the home. attenuation The decrease in the amplitude of a signal. In video communications this usually refers to power loss in electromagnetic signals between a transmitter and the receiver during the process of transmission. Thus, the received signal is weaker or degraded when compared to the original transmission. Advanced TV. Any system of distributing TV programming that results in better video and audio quality than that offered by the NTSC standard. ATV is based on digital signal processing and Video Communication: the Whole Picture transmission. HDTV can be considered one type of ATV but systems can also carry multiple pictures of lower quality. audio In video communications, electrical signals that carry sounds. The term is also describes sound recording and transmission systems-speech pickup systems, transmission links that carry sounds, amplifiers. audio bridge Equipment that mixes multiple audio inputs and feeds back composite audio to each station after it removes the individual station's input. This equipment may also be called a mix-minus audio system. auto focus In a camera, a device for measuring the distance of the lens from a given object is included to automatically set the lens-film distance. In videoconferences when th