44 lines
3.3 KiB
Plaintext
44 lines
3.3 KiB
Plaintext
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Phile 4 of 4 Audio Surveillance
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---------------========SANctuary=========----------------------
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Audio is the most common surveillance method in use. Most listening devices depend on some form of electronics, and it is important to understand the
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usual steps to audio electronic surveillance. It is basically a 5 step process.
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1) Input- usually a microphone
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2) Preamplifier- used to boost the nominal signal of a mic to usable levels
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3) Processing- eliminates excess noise and unwanted sounds from teh output
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4) Output- headphones, recorder, transmitter, etc.
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5) Post-processing (sometimes)
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This is the last phile in this series. It deals with the output, and what you should do with it. We can, and usually do monitor in realtime, but
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most intelligence work is recorded for later review. Small tape recorders introduce a LOT of noise, and don't have very long playing times. Open
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reel recorders correct this, but high fidelity VHS have longer recording times and better frequency response. A T-160 tape in extended play records
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for more than 8 hours. In addition, if the mark is under video surveillance, that can be recorded simultaniously. Pulse Code Modulation is a true
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digital format with better dropout compensation than VHS, and they can input to a video recorder. Digital Audio Tape also exists, and an encoder
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could be used easily to make your tapes useless to anyone who confinscated them. Solid state digital recorders have applications as well. Currently,
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the limitations are in memory only, but, with 1 megabit chips and 4 megabit chips coming into play, long play is possible. There is a device called
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"Memo-me" that records 32 seconds of low resolution sound on 512K. The recording time could be doubled or quadrupled without suffering much loss, and
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a high-memory device could be used to record for hours. Digital tape and solid state digital recording equipment is still quite a bit out of the
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budget of the average hobbyist, and VHS gives sufficient quality. Someday, however, the average spook will be able to feed a bad recording with
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unintelligable speech through his digital processor and get crystal clear sound out of it. For now, however, open reel tape offers about the best
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quality for the price, though most people do own a video recorder...
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This was a lot shorter than I had planned. Oh, well. Anyway, watch for more philes by,
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The Gaurdian
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P.S. If response is good, I will write some files with schematics for building an amp that incorporates all the processing and amplification in this
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series. E-mail Dave #40 on Hellfire or write to me at
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The Gaurdian
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P.O. Box 483
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Lincroft, NJ
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07738
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-----------------------------------------------------------------------------
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=======================SANctuary=====================================
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----------------------------------------------------------------------------
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Oi! Damn, 4 great philes in 1 day! This is some kind of record!
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If you like these kind of philes, let us know... the Guardian is writing at a mile a minute!
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----------------------------------------------------------------------
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CALL HELLFIRE!!! (908) 495-3926!
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-------------------------------- ---------------------------------
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