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US 4,342,104 AGranted
Helium-speech communication
AssigneeThe University Court of the University of Edinburgh
InventorMervyn A. Jack
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AssigneeThe University Court of the University of Edinburgh
InventorMervyn A. Jack
Estimating the term…
The invention relates to a novel helium-speech unscrambler which can be located at a diver's location, and enables the helium-speech voiced by the diver to be subjected to waveform time expansion to reduce the bandwidth of the helium speech (e.g. to 2 to 3 KHZ) prior to transmitting the speech signals to a distant location on a carrier wave selected for optimum transmission through the water.
A method of through-water communication of helium speech in which the bandwidth of a leading part of each pitch period of a diver's helium speech is reduced by waveform time expansion to provide a signal bandwidth acceptable for modulating a carrier wave of a frequency selected for optimum through-water transmission, the carrier wave being modulated and fed directly into the water to a listening station, the degree of waveform time expansion effected at the diver's location being preset and the listening station including means to modify the time expansion of the received signal to optimise intelligibility of the received speech.
A method of through-water communication of helium-speech in which a leading part of each pitch period of a diver's helium-speech is subjected to a waveform time expansion to reduce the signal bandwidth to a level acceptable for use with a carrier frequency selected for optimum transmission through the water, a carrier wave at the said carrier frequency is modulated with the reduced bandwidth signal, the modulated carrier wave is fed via a first transducer into the water, the modulated carrier wave is received by a second transducer at a distant location, the output from the second transducer is demodulated, the demodulated output is operated on to reduce the waveform time expansion applied at the transmitter and the so operated-on signal is fed to a sound generator in the vicinity of a listener, said reduction in waveform time expansion being controlled by said listener.
Apparatus for through-water transmission of helium-speech voiced by a diver comprising transmitting equipment for the diver comprising a microphone, an analogue speech unscrambling device to subject a leading part of each pitch period of the diver's speech received from the microphone to waveform time expansion and thereby to reduce the bandwidth of the helium-speech signals, and means to transmit the reduced bandwidth signals to a listener location, the transmitting means comprising a through-water communications transmitter to receive the reduced bandwidth signals and a transducer to feed the output from the transmitter directly into the water to the listener location, and at the listener location a receiving transducer, a further analogue helium-speech unscrambling device of variable expansion ratio, which is adjustable by a listener at said listener location, and a sound generator, for said listener, receiving output signals from the said further unscrambling device.
A method of transmitting a diver's helium-speech to a remote listening station which comprises subjecting an initial portion of each pitch period of the helium speech to waveform time expansion to reduce the bandwidth of the helium-speech and transmitting the reduced bandwidth signals to the listening station via an electrical line connecting the diver to the listening station, and adjusting the time expansion at the listening station to optimize intelligibility.
Apparatus for transmission of helium-speech voiced by a diver to a remote listener location comprising transmitting equipment for the diver comprising a microphone, an analogue speech unscrambling device to subject a leading part of each pitch period of the diver's speech received from the microphone to waveform time expansion and thereby to reduce the bandwidth of the helium-speech signals, and means to transmit the reduced bandwidth signals to a listener location, and at said listener location,
Dependencies are inferred from the claim text.
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No related US applications are recorded in the indexed filing history.
Speech or voice signal processing techniques to produce another audible or non-audible
Speech analysis techniques or speech synthesis
Term ended 30 Oct 2000 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
This invention relates to a method of, and apparatus for, improving communications when life-supporting atmospheres other than air are in use.
When divers are required to operate at a great depth under water, the normal oxygen/nitrogen atmosphere encountered at the earth's surface is no longer acceptable as a life-supporting atmosphere. This arises because of the blood's increased absorptivity for nitrogen under the pressures encountered. It has thus become accepted practice for deep sea divers to use a nitrogen-free atmosphere (usually a helium/oxygen mixture). The fundamental pitch of a diver's speech signal is little affected by the changed life-support atmosphere, since it is set by muscular properties of the larynx, due to the different speed of sound in the gas mixture used as compared with air at NTP, the band width of the speech signals is dramatically altered, (typically increased by a factor of 2 to 3), thus rendering the speech unintelligible to an ear accustomed to speech encountered on the earth's surface. Throughout this specification the phrase "helium-speech" will be used to indicate the distorted speech resulting from breathing a nitrogen-free (or substantially nitrogen-free) atmosphere. The use of that phrase should not however be taken to mean that the invention is limited to applications where the atmosphere used contains helium.
Helium-speech typically has a bandwidth of 12 to 16 KHZ (compared to normal voiced signals in air at normal temperature and pressure (NTP) which have a bandwidth of 3 to 4 KHZ).
The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:
FIGS. 1a and 1b are graphs indicating the form of helium-speech voiced signals received by, and the output from, a helium-speech unscrambling device according to the invention,
FIG. 2 is a block diagram of a communication system for helium speech, and
FIG. 1a shows the basic form of a voiced helium speech waveform where the amplitude peaks correspond to the start of the pitch intervals. This pitch interval which is determined by muscular properties of the larynx, shows minimal change from normal air to high pressure helium/oxygen mixture.
The helium speech waveform suffers a shift in (vowel) formant frequencies and the rate of decay of the inter-pitch wavefrom is corresponding more rapid than for normal speech. The unscrambler technique to which this invention relates consists of storing the initial sections of each inter-pitch waveform which contain useful information and subsequently time-expanding this stored waveform to the general form expected in normal (air) speech, FIG. 1b. FIG. 1b shows that in the long term there is no time-base change (the pitch intervals on input and output remain equal) however, in the short term, between pitch peaks, the time-base is expanded. The discarded sections of the input waveform cause little degradation to the speech intelligibility.
The maximum duration of the stored segment is governed by the maximum expected pitch for the input helium speech. The design considered here stores a segment of duration 3 ms corresponding to a maximum voiced fundamental frequency of 300 Hz.