HELIUM SPEECH:
RELATIONSHIP BETWEEN FREQUENCY AND DENSITY
- Deep-sea diving to depths exceeding about 140 feet of sea water
requires the use of heliox (a mixture of helium and oxygen) as a
breathing gas, rather than compressed air.
- Heliox eliminates the danger of nitrogen narcosis and reduces
the risk of decompression sickness which would otherwise be present.
- Heliox presents another risk. The diver's speech is rendered
unintelligible because the higher velocity of sound in the diver's
vocal tract shifts the frequency components of the diver's speech to
much higher frequencies - an effect that has been likened to the
"Donald Duck" voice.
- Heliox is less dense than air or pure oxygen. Hence, the speed
of sound is greater, so the resonances occur at higher frequencies.
- The excitation remains largely unchanged since flesh in your vocal
folds still vibrates at the same frequency, so the
harmonics occur at the same frequency.
(There could be a small change because the less dense Helium loads
the vocal folds a bit less than the air, but this effect is
slight.)
- Examples
of helium speech are always
fun to listen to.
-
Descramblers are available that will perform real-time
spectral shifting.
- Such systems use real-time
spectral shifting.
The information on this page comes from two sources:
and,
Work on real-time frequency scaling can be found in several journals
including the IEEE Transactions on Speech and Audio Processing
(formerly Acoustics, Speech, and Signal Processsing), and
the Journal of the Acoustical Society of America.