| 摘要 |
Two avoid nitrogen imbalance in the blood stream of deep sea divers and very high altitude pilots, a helium-nitrogen-oxygen mixture is used for breathing. This presents difficulties in understanding speech transmitted over intercommunication systems due to the acoustic velocity in the mixture being some 1.8 times that in air. To avoid such problems and improve the quality of speech transmission an electronic sampling technique is adopted. Instead of transmitting the output of the microphone to the receiver it is bypassed to a low pass filter, limiter and gate that is pulsed in such a way that 50% of a given signal duration is sampled. The sampled signals are transmitted to a shift register and are stretched to the original period duration before transmission to the receiver loudspeaker. Either a detector is used to gate the sampling clock signal or an analogue converter may be used. |
