PROCESSING OF AUDIO TAPE FOR BUREAU OF NARCOTICS DANGEROUS DRUG DIVISION

• Document Type: FOIA
• Collection: FOIA Collection
• Document Number (FOIA) /ESDN (CREST): 01430480
• Release Decision: RIFPUB
• Original Classification: U
• Document Page Count: 2
• Document Creation Date: December 28, 2022
• Document Release Date: August 7, 2017
• Case Number: F-2007-00094
• Publication Date: May 1, 1973

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� 1. On 13 April 1972 Mr. Charles Gaskins of the Bureau of
Narcotics and D:Ln:Y.z-.�.,-ous Diu rsted. SAW/An/ORD nCC
to improve the intelliz;ibility of an audio tape that had been ac.cuired
by 1311 DD agents.
nrelin--in=r�kf assessmentmost of the signal
� vc:?iee ) riztgradatior: as .the result of clistortiorvof the t:-..-avaform rather
than additive noise. A detailed analysis showed that the preliminary
� assessment was correct in that the signal had been clipped (peak
limited) somewhere in the collection process. Long term averaging
of the recordinc! also indicated that an undetermined source had caused
some unut.o..tal shaping of the spectrum. 1 explained to Mr. Gaskins that
the clipping is a nonlinear process and is not reversible by any known
means. (Clipped speech con-imunication systems have been under in-
vestigation for several decades..)
3. The particular r=.rordint-, was taken via a radio tc1ephon links
that distortion from an irnpro:"erly tuned receiver also needed to
be considered. Several spectra with well defined voice harmonics were
examined by e::trapolating the voice harmonics to zero fresmency.. In
all cases the spectra showed a proper relationship to zero Hertz. We
concluded that L-nproper demodulation had not occurred.
Approved for Release: 2017/01/18 C01430480
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Approved for Release: 2017/01/18 C01430480