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Beware the Auto Gain Circuit!�

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PSI�s Dave Wood looks into why an annoying feature of most hand-held video and audio equipment � the Auto Gain Circuit � has ruined the results of many a paranormal investigation.

I�ve lost count of the number of times I�ve seen it. Be it on paranormal TV programs or be it on paranormal investigations, everyone seems to have �picked up� unusual sounds from a dictaphone left alone in a room or from a video camera �locked off� to record a scene.

Much excitement has resulted from the resulting anomalous noises, even described by some as �electronic voice phenomena� (EVP). Tragically the over-active Auto Gain Circuit probably renders many of these �results� as meaningless.

The Auto Gain Circuit was an invention of supposedly thoughtful developers. The role of the AGC is to keep a consistent level of sound: when a noise is too loud it �turns down� the volume and when the environment is silent it turns the volume �right up� in order to try to record something, anything!

The unfortunate by-product for paranormal investigators is that many of the sounds picked up during EVP sessions and video �lock offs� are likely the result of noises which, whilst they sound close, could be from some distance away. Even the voice of an investigator on a different floor could be amplified, recorded and heralded as fantastic �evidence�.

Professional media recorders have, of course, found ways around these problems: most of us will have heard producers �counting in� interviews, not just for timing, but also to ensure they don�t have a �noisy� start to the interview.
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So what should paranormal investigators be doing to overcome this problem? Generating a constant low level of background sounds during video �lock offs� may work, as might simply discounting auditory phenomena in �visual� experiments. The established practice of using a white noise background during EVP sessions should also be helpful.

The Auto Gain Circuit is just one possibly confounding factor that renders much paranormal �evidence� as useless. It�s worth remembering, also, that using recording equipment with moving parts (such as tape players or tape-based video recorders) also produce a lot of internal sounds which are picked up by the microphone.

The best tool in the paranormal investigator�s armoury, as ever, is rigour; studiously record the environment of any recording environment. Simply producing a piece of interesting �audio footage� without due care to confounds and environment doesn�t impress the wider world � and it should not impress you either!

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