Periodic detector for the noise immune VOX Periodic detector for noise immune VOX

The conventional method of obtaining voice operated keying (VOX) depends on sensing energy level. This assumes that the speech signal will produce a signal level which is greater than the noise and the circuit would be set to actuate when the signal exceeded some preadjusted threshold. Under adverse conditions, such as encountered in diving, undesired noise signals may equal or exceed the speech signal and the level approach is unsatisfactory. A new approach has been developed which utilized the fact that vowel sounds in speech are generated by the vocal cords opening and closing in a periodic manner. Circuitry has been designed to detect the periodicity of the vocal cord vibrations when vowel sounds are uttered, but rejects random noise which may be present. Sources of noise might include gas turbulence around the microphone when the operator breathes or noises from associated life support equipment such as SCUBA gear. The new VOX has been successfully applied to a wireless acoustic diver communication system to provide "hands-free operation", and to a hardwire diver intercommunication system to provide reduction of breathing noise from divers on the line but not speaking.