An early device designed to interface analog PBX or central office (CO) voice circuits to a DS-1 circuit. Channel banks perform two functions, in sequence. First, they multiplex up to 24 analog signals on a common pulse amplitude modulation (PAM) electrical bus. Second, they encode the individual PAM channels into a digital format, using pulse code modulation (PCM), for transmission over a DS-1 circuit. Channel banks place each voice conversation on a separate channel. A given channel can support a digital data transmission, rather than a voice transmission. For example, a data transmission at 9.6 kbps or 19.2 kbps originally occupied a full DS-0 channel of 64 kbps, just as does a 56 kbps data transmission or a digitized voice conversation. Later, sub-rate multiplexing allowed as many as 5 channels of 9600 bps to share a DS-0 channel. See also bus, DS-0, DS-1, multiplexer, PAM, and PCM.