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EVP's and radio interefence


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#1 perpetualstudent

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Posted 24 October 2011 - 10:08 PM

Hey guys!

I noticed a post on a youtube video referencing the possibility of EVP being radio interference and thought to myself "I never considered that." So I did a little bit of digging around and haven't found anything that really was conclusive regarding the amount of interference a recorder receives and the odds of picking up entire words or phrases.

So can anyone point me in the right direction for some solid information on the subject? If I were in a better financial position I would just buy a recorder and find out for myself. Also, when I ask I am speaking more abound the standard digital or cassette recorders that people will pick up to investigate with.

Looking forward to some responses!

#2 CaveRat2

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Posted 25 October 2011 - 09:00 PM

Which is why the "standard" digital and cassette recorders are not recommended for EVP work. Period.

Better quality recorders are shielded against outside EM Fields must more effectively than cheaper recorders. A method called single point grounding will be employed in the design. It's more expensive, requires better grade of design, but will help to minimize this interference.

Another design improvement is the recorder will incorporate a Faraday shield in its design. Maybe not something obvious, but close examination will show how component placement and layout uses various techniques to provide both real and virtual shielding of crucial front end components.

Actual design of equipment involves extensive work and the theory behind ground loops, common mode rejection, and impedance matching are quite complex. However it is attention to these details which separate the good equipment from the junk.

Labs can test for the effectiveness of such shielding as well. I do these tests on equipment I build under contract. The method involves using an EM generator, and a modulated RF source. The tests involve exposing the DUT (Device Under Test) to these fields while monitoring its operation. If the shielding is working the EM sources will not in any way be detected by the device. But if the shielding is faulty it will interfere. And in the real world, if the device can be interefered with by these signals it can also be influenced by real world signals like radio stations, power lines, stray audio, or any number of culprits. Most cheap equipment will fail these tests miserably. Thus any supposed EVPs captured cannot be trusted to be legitimate; instead they are assumed to be this outside interference.

#3 perpetualstudent

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Posted 26 October 2011 - 03:22 PM

Thanks for the response caverat. I was hoping you would chime in! :weeee: I'll be delving farther into the information in your post, and in the meantime I do have a question. Is there any out of the box recorder that you could recommend for teams to avoid the majority of external interference? Or is there a simple modification that can be made?

Thank you once again,

Perpetual Student.

#4 CaveRat2

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Posted 26 October 2011 - 05:28 PM

Thanks for the response caverat. I was hoping you would chime in! :clap: I'll be delving farther into the information in your post, and in the meantime I do have a question. Is there any out of the box recorder that you could recommend for teams to avoid the majority of external interference? Or is there a simple modification that can be made?

Thank you once again,

Perpetual Student.


I can only recommend what I have tested and to date the cheapest digital recorder that meets specs is the H2. And only when used in its HQ setting. I also recommend using external mics spaced apart so you can do spatial analysis, the internal phased array simulates stereo but does not provide true diversified pick-up. There may be other recorders but I have not tested them so obviously I can neither recommend nor reject them. I have tested the H2 in my lab so it is on my tests that I can say it meets specs. If cost is not a factor I can also recommend the Fostex FR2 as I have also used that one. But at around $1,000 most people balk at the $$$.

#5 perpetualstudent

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Posted 26 October 2011 - 06:18 PM

Good to know, I'll put that on the list just in case I get any questions and I'll be putting some items on my one day I'll have the money list.

Thanks a ton!

#6 OMPRDave

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Posted 27 October 2011 - 08:16 AM

The late founder of the first team I trained with had a wonderful example of radio interference and how it can impact audio recordings. He left a standard cassette recorder running on the hood of his car while he and a few others toured a local cemetery here in Massachusetts. On review later on, there was a twenty minute recording of what sounded like a fire and brimstone minister preaching in a distinctly non-New England accent with clear responses from his congregation. A friend of mine examined the recording and was able to match up the preacher to a Baptist minister that broadcast his services all the way from Georgia on AM band radio, and it was theorized that the car acted as a antenna that focused the broadcast in a way that the recorder could interpolate.

I'm still trying to find a copy of this recording as his old website has gone the way of the Dodo so I can post it as an example of interference on my own site.
"There is a principle which is a bar against all information, which is proof against all arguments and which cannot fail to keep a man in everlasting ignorance - that principle is contempt prior to investigation." Herbert Spencer

#7 perpetualstudent

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Posted 27 October 2011 - 04:08 PM

O.O Wow. That's terrible! And hilarious!

It is also a darned good example of what I was asking about.

Thanks for that!




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