The inert gas helium is used to dilute the oxygen that saturation divers breath so that,
under the great pressures in which they live and work, excess oxygen will not be absorbed
into their body tissues, causing illness or death. However, because the speed of sound
in helium is three times that in air, sound reverberating in a HeO2 mixture produces
higher frequencies--perhaps 2.7 times higher. Most of the frequencies in speech
comes from reverberation of vocal cord sounds in vocal tract of the speaker. Thus, the
speech of a saturation diver working at considerable depth sounds like
this.
Working for the United States Navy, Oxford Signal Processing has developed a
new generation of helium-speech unscrambler (HSU). This device translates
helium speech back into normal sounding speech. The speech sample, above,
becomes this.
The new HSU consists of three circuit cards (pictured on the right):
an analog-to-digital card (ADC),
a central processing card (CPU),
and a digital-to-analog card (DAC).
The CPU card employs two state-of-the-art digital signal processors (DSPs) that support
more sophisticated algorithms than was previously possible. Besides the voice
translation function, the new HSU also supports a noise reduction function. One
DSP is dedicated to each function.
Since algorithm improvement is an ongoing process,
provision was made for updating the software without removing the CPU card from the
communication system. The operator connects a PC's parallel printer port to the DAC card.
Th then powers up the communication system and the CPU card boots on data from the PC.
It burns the new software into its flash memory and signals completion with five tone bursts.
The operator powers down the system and removes the cable. When the system is powered up
again, it runs on the new software. With this arrangement, new software can be sent to
users on any portable medium, or even attached to email messages.
The developer, Jim Hendrix, has filed a patent for device and anticipates producing commercial versions in the near future.
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Analog-To-Digital Card
Processor Card
Digital-to-Analog Card
(click for larger image)
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