Voice based information systems

Railway stations are examples of large and noisy areas to which voice announcements are to be made and were one of the early users of amplification to produce public address systems. Changes to station staffing arrangements have led to the need to provide voice information to unstaffed stations. This has resulted in the development of transmission and remote control systems that tandem link several stations specifically for this purpose. These systems have to operate on existing trackside cables, using only one or two pairs, over considerable distances in a fairly hostile electrical environment, whilst providing good quality audio at the remote stations. These systems are known as long-line public address systems (LLPA)