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RT-EVP...15hHz?


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#1 Ten301

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Posted 07 December 2010 - 04:53 PM

I was reading the specs online for the RT-EVP digital recorder. While I would probably never use the "ghost box" feature, and agree that it does have some features of questionable value, it does boast the ability to record down to 15Hz, below the range of human hearing.

Does anyone know if it then converts what is recorded in that range to a frequency humans can hear, or is that feature only useful when used with a program such as Audacity? Come to think of it, is the ability to record down to 15Hz even useful at all in the context of recording EVP's, or is just useless marketing hype?

Thanks in advance for any replies.

#2 PhenomInvestigator

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Posted 07 December 2010 - 09:02 PM

The low end of some humans is actually right at 15Hz. Some people can hear a bit below that. When I worked at a national radio network years ago, most of the engineers could hear from about 15 Hz to up aroudn 22 to 25 Khz. This was a requirement for the job, and we were also fairly young!

It is not clear if lower recording frequency sensitivity is helpful or harmful when it comes to obstensible EVP recordings. While it might capture something other recorders would not, one could also say that it extends the noise band from which you might hear yet more artifacts.
Anomalous Phenomena is Unexplained not ImpossiblePsi is Subtle not AbsoluteAnything is possible, it's all a matter of Probability---------------------

#3 CaveRat2

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Posted 07 December 2010 - 10:46 PM

While I have not tested this recorder in my lab, I would seriously question its ability to record at those frequencies. Unless one were to use an external mic, I would doubt the small internal mics would pick up those longer wavelength signals very effectively.

Plus there are some other considerations when dealing with infrasound below about 20 Hz when it comes to amplifier design. One of these is stability regarding bias on linear stages. Compensation must be made to keep those in their linear operating areas, and that becomes somewhat complex. Not saying they didn't do it, but if I were wanting to do infrasound work I would choose a DC amplifier which I knew was properly compensated. This one is an unknown in that regard.

One more thing regarding low frequencies and EVPs. These can easily be mistaken for vocalizations due to the fact that the duration most phonemes of speech also occur over time periods of 10 -30 msec. This is very close to the wavelength of infrasound and unless you are careful the two can be easily confused. I can see this as a cause for false positives.

You would also want provisions to display those frequencies on a scope or other visual means. Again keeping in mind most headsets won't respond that low unless you go with professional grade equipment.

All in all, from what I have seen of this recorder literature it appears to be mostly hype aimed at wanna be ghost hunters. It does some things besides the white noise that really aren't beneficial to an investigator. Better to put your money into a decent, simple recorder that meets specs for EVP work instead of paying extra for a lot of superfluous stuff.
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#4 boatlesspirate

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Posted 10 December 2010 - 10:56 AM

Totally agree CR. I have questioned this on many forums. Even IF (big if) it can record down to 15kHz, play back is a whole 'nother issue. And then, actual "hearing" and understanding of anything at this frequency is a whole other issue. People should not confuse perception of sound as actually hearing and comprehending. And to your point, you would need a Freq Analyzer to even show you this waveform is there.

Now I would be impressed if a unit could pick up sub harmonic, or ultra sonic sounds and demux into the audible range. This can be done, but with lot's of $$ gear as you already know.
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#5 ourobouros2k2

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Posted 10 December 2010 - 11:14 AM

Cracks me up when I see websites that state that only genuine evp's are captured between xHz and xHz. I have captured evp of a broad range of frequencies, so no range can be definitively be stated as a primary home for evp frequencies.
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#6 CaveRat2

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Posted 10 December 2010 - 01:00 PM

Cracks me up when I see websites that state that only genuine evp's are captured between xHz and xHz. I have captured evp of a broad range of frequencies, so no range can be definitively be stated as a primary home for evp frequencies.


There actually is a limit to the frequencies for EVP. By definition, they are a voice phenomena, thus their limit is to the regions between approximately 100 - 3.5 kHz as this covers normal voice patterns.

That said it is also quite possible to pick up anomalous signals outside that range, however these would have to be considered something other than voice phenomena. Consider infrasound as an example. If a very low frequency such a 10 Hz for example were present it could modulate a higher frequency or even noise to simulate voice. The pulses of noise, 100 msec long would mimic the series of phonemes which comprise speech. That would be a very good source for pareidolia .

It would not be actual voice phenomena, but could easily fool one into thinking it was.
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