Damping ratio equalising circuit for two wire speech transmission - uses compressor amplifier and speech recognition circuit for each direction

摘要

The two wire speech transmission system using compression and expansion, uses a two way return, so that the required counter speech can take place. At a junction point, each line incorporates a compressor/amplifier (KVI, II) for the two directions. These are controlled by a number (ST) such as an A/D converter, with inputs connected to a speech recognition circuit (SPI, II) for each direction, so as to obtain the required damping for all frequencies. The sum of both amounts of amplification does not exceed logarithmically twice the min. value of the damping for the junction. The transmission ratio of an amplifier in one direction matches the amplitude of its input level, and the transmission ratio of the other amplifier is adjusted according to a given formula.