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UPDATE: On several occasions we
have used out ultrasound machines at Fort Mifflin however each
frequency used had created sound on put digital recorders. We plan
to start again from the beginning using only analog recorders.
(The details of
this experiment are being written up. More about the theory behind this study, data,
evaluation of that data, and explanations of the images below will be posted soon.)
Click top see larger images
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Detail
of instrument
we will be using |
Range for
high and low settings |
One of our ultrasonic wave generators
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Graph showing
Stochastic Resonance
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Graph of White Noise
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Graph of Pink
Noise
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Notes:
1. Ultrasonic sound waves cannot penetrate walls.
2. Humans can hear frequencies
up to abut 20 kHz. Frequencies above that are what we call
"ultrasonic waves.
3. Ultrasonic sound waves are not harmful to humans.
4. Ultrasonic sound waves are harmful
pets if they are above 25 kHz, so be careful in conducting
experiments with ultrasound.
Definitions
| Frequency |
The
number of repeating cycles of change in air pressure that
occur in one unit of time (usually a second. Frequency is
measured in units originally called cycles per second (CPS),
now called Hertz
(Hz). |
| Audio
Frequency |
The
range of frequencies
which a human being can hear. The range is defined as 20
Hz
to 20 kHz (20,000 Hz) for convenience; but in practice,
is realistically closer to 20 Hz to 17 kHz (17,000 Hz). |
| Ultrasonic
frequency |
Frequencies
above 20 kHz that can not be heard by humans. Some animals can
hear ultrasonic frequencies. Dolphins are believed to hear up
to 70 kHz. |
| Amplitude |
This
is the height of its waveform. This tells you its volume or
magnitude. |
| Decibel |
The
unit used to measure amplitude (how loud a sound is).
Normal speech is about 80dB. |
| Wavelength |
The
distance between two identical points on a waveform i.e. one
cycle of the waveform, or the spatial distance between two
identical points of an electromagnetic or sound pressure wave,
which have the same phase. In high frequency waves, there are
more cycles in a given unit of time than there are in low
frequency waves. |
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Amplitude |
Frequency |
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Important
to remember:
When we talk of amplitude (decibels), we are talking about how loud
a sound is. When we talk about frequency (hertz), we are talking
about the wavelength of a sound.
We can hear sounds between 20 and 20,000 Hz…. and we can
hear sounds about 10 decibels and higher.
Stochastic
resonance
Stochastic
resonance
is “a phenomenon in which a nonlinear system is subjected to a
periodic modulated signal so weak as to be normally undetectable,
but it becomes detectable due to resonance between the weak
deterministic signal and stochastic noise.” In other words…
Imagine a sound that is too low to be heard. (Very low decibels).
Add another sound to it (for example running water or rustling
leaves…what EVP experimenters sometimes call “white noise”).
When the two sounds mix (top graph a)
the amplitude of the inaudible sound can be raised to the audible
level (bottom graph b).
BEAT
BEAT
is
a phenomenon that takes place when vibrations at two
different frequencies are combined at a certain point in space. At
the meeting point, the two waves will act in a manner that causes
them to produce two new vibrations. That is, the point will vibrate
at a frequency that is the sum of the original frequencies and at
the same time, and at the same time, at a frequency that is the
difference between the two original frequencies. For Example, if two
frequencies are combined…20,000 and 25,000 Hz… the sum, 45,000
Hz, is not audible; however, the difference… 5,000 Hz… is
audible and can be recorded.
What
does this all have to do with EVP?
I
believe that the principle of stochastic resonance and the
beat phenomenon can be used in recording EVP's. Using
ultrasonic sound waves as ambient noise when recording can possibly raise the
amplitude and/or frequency of an inaudible EVP to the audible level,
thus increasing the number and and/or quality of EVP’s recorded during
an investigation.
More
coming soon
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