Intercommunication system with several subscriber stations - has filters separating speech signals from noise and threshold circuit varying with noise level

摘要

Each subscriber station of the intercommunication system has a transmitter (microphone) and a receiver in the form of headphones or a loudspeaker, and a signal processing unit, such as an amplifier, radio link etc. The signal processing unit has frequency filters, to which signals from the transmitters of subscriber stations are applied. They separate the speech band of 300 Hz to 3000 Hz from the noise band outside the former. The speech signal is applied to a threshold circuit whose threshold value increases with increasing noise. The transmission of speech signals is stopped in detected pauses.