PROJECT MONITOR AT (SANITIZED)

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78-03300A001900110002-6
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 11
• Document Creation Date: December 22, 2016
• Document Release Date: May 3, 2011
• Sequence Number: 2
• Publication Date: August 6, 1958
• Content Type: MEMO

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tll~t rat TBS Int. =
6 August 1958
TDSZ A1? Pi ACZ or ) Ifl11G: The sleeting was held 24 July 1958
3. DISCUBSIOA:
a. The following hardware program covering several varieties
of item was worked out:
(1)F---~ill run response curves ~at-the BK-6B micro-
-A 'k- AM
They will also run response curves of the 1C-l4
microphone with the probe housing supplied by
APD. It should be noted that these probe attach-
ments were obtained Ergs ASD as representatives
of a program done in Frankfurt.
(2)L--`i l deliver, by 30 September, the reining
items called for under Task Order 6 with the
exception of the composite stmarary report. Rvery
effort will be ride to finish the report as soon
thereafter as practical.
(3) The hardware schedule under Teak Order 7 was
changed to call for delivery of the following:
Six Type F microphones of 75 otars, six FA micro-
phones (Type F with integral preaaplifisrs), and
three Type F microphones at 2000 ohms output
impedance. In addition, six Type AP units to
remotely power the FA microphone will be built.
It should be noted that the first Type F proto-
type was returned too to check its charact-
eristics. Tests conducted by the undersigned
indicated that the microphone was not up to its
earlier performance level.
25X1
25X1
25X11
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(b) svaluate a foreign microphone given to the
undersigned by AM.
b. U was asked to consider the design reQuirements for a 25X1
non magnetic type of microphone that would have the follmwing parameters:
(1)
Have an absolute minimm of metal associated
with its construction
(2) Be able to operate in an environment of 100%
relative humidity and a temperature of lkO? T
(3)
(4+)
(5)
(6)
Have a probe capability
Be relatively small in volume (The also of
BA-110 was used as an example.)
Frequency response of 200-6000 cps
Maxi- output consistent with the above parameters
This microphone design would probably use Barium Titanite as the active
element. The undersigned asked that preliminary thought be given to the
subject and that further discussion would be held in the near future.
C# upon the request of the undersigned, displayed
the latest model of a condenser microphone they are presently working on.
For possible consideration by APD, its pertinent characteristics are
outlined below:
(1) Size - 5/8" dig. x 2-1/2" long
(2) Output - appraximstely -50 dbm (note output of
BK-6B under same conditions is -67 dba)
Output Impedance - 250 ohms
Frequency Response - at least 200-7000 cps
Tube used is a CK547MK
~EERE~-
ID F
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-~NTIAL
-3-
This microphone represents a high output, high quality ~y micro-
consistent with reasonable sine. is one serious drawback wback is that
a vacuum tube is needed integral with the microphone. (Bse attached
circuit diagram for circuit details.) This tube is necessary because
of the high input impedance necessary for use with a condenser aicro-
phone.
The undersigned believes that some possible use could be
made of a microphone of this general type and believes that we or
nodeL should be obtained for evaluation. It is proposed that
asked to he two models under existing task orders (it is net
-believed that too tuck money is involved as cost of the design work
is accomplished) and that their usefulness be further discussed with
TSB/A6D.
d. Attached to this assoarandua are two L_] reports covering 25X1
studies recently conducted by One deals with additional 25X1
data obtained concerning the audio noise reduction problem while the
second deals with a discussion of the articulation index of 3 micro-
phones with different response characteristics.
TB$ APD
Attachments:
1. Circuit Diagram
2. Report -Articulation Index Calculations
3. Baport-Audio Note* Reduction Circuit
Distribution:
Orig. - P-189 v/ette 1 & 2
1 - P-185 w/att 3
1 - Chrono
BPKsis (6 Aug 58)
25X1
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Work
Covering the Period
March 15, 1958 to June 30, 1958
Report Date: July 1, 1958
AUDIO NOISE REDUCTION CIRCUIT
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During the period since the final report was prepared, several additional tests have
been performed using the threshold noise reducer. The following circuit conditions have
been used.
1A. 110 channel band pass filters with bandwidths similar to the sample shown in
upper part of Figure 32 of the Final Report were used with a square law non-
linear characteristic. Refer to Figure 1A.
2A. 110 channel band pass filters with bandwidths similar to the sample shown in
the lower part of Figure 34 of the Final Report were used with a square law non-
linear characteristic. Refer to Figure 1A.
3A. 110 channel band pass filters with bandwidths similar to the sample shown in
the lower part of Figure 34 of the Final Report were used with a fourth power non-
linear characteristic. Refer to Figure 2A.
4A. 11 chassis band pass filters as shown in Figure 14 of the Final Report were used
with a square law non-linear characteristic. Refer to Figure 1A for this charac-
teristic.
5A. 11 chassis band pass filters as shown in Figure 14 of the Final Report were used
with a sharp cut-off non-linear characteristic. Refer to Figure 3A for this char-
acteristic.
In cases 4A and 5A the 110 channel filters were by-passed; only the 11 chassis filters
were used. These five additional circuit conditions were tested in the same manner as de-
scribed in the Final Report. Oscillograms of the test results are shown in Figures 4A through
6A.
The square law and fourth power characteristics provided an increase in the signal-
to-noise ratio as is evident in the oscillograms. They also eliminated the sharp switching
transients or "birdies" caused by sharp non-linear characteristics. I t was felt that some
words were heard very clearly through the noise reducer with the 4th power characteristic,
but none of these additional circuit conditions provided a substantial improvement in intel-
ligibility over the signal as heard through the by-pass circuit.
The tests reported here conclude the presently scheduled evaluation measurements.
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SPEECH THROUGH
BY-PASS
SPEECH THROUGH
NOISE REDUCER
SPEECH & NOISE
S/N'=,0 DB
THROUGH BY-PASS
+ IO DB
SPEECH & NOISE
THROUGH
NOISE
REDUCER
I SEC.
+15 DB
BANDWIDTH = - 3 DB
THRESHOLD SETTINGS-FLAT
NOISE SPECTRUM -FLAT
NON-LINEAR CHARACTERISTIC=' 2nd POWER
FIGURE 4A
OSCILLOGRAMS SHOWING EFFECTIVENESS
OF NOISE REDUCER, CONDITION 2A
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A ~MmT :,? SPEECH THROUGH
BY - PASS
-I SEC.
SPEECH THROUGH
NOISE REDUCER
SPEECH 81 NOISE
THROUGH BY- PASS
SPEECH S NOISE
THROUGH
NOISE
REDUCER
+ 15DB
BANDWIDTH = -3DB
THRESHOLD SETTING-FLAT
NOISE SPECTRUM -FLAT
NON- LINEAR CHARACTERISTIC= 4th POWER
FIGURE 5A
OSCILLOGRAMS SHOWING EFFECTIVENESS
OF NOISE REDUCER, CONDITION 3A
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4~--- I SEC.
SPEECH THROUGH
BY - PASS
SPEECH a NOISE
THROUGH BY- PASS
+ I0DB
SPEECH &
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THROUGH
+ 15 DB NOISE
REDUCER
II CHASSIS FILTERS
THRESHOLD SETTINGS - FLAT
NOISE SPECTRUM-FLAT
NON -LINEAR CHARACTERISTIC = SHARP CUTOFF
FIGURE 6A
OSCILLOGRAMS SHOWING EFFECTIVENESS
OF NOISE REDUCER, CONDITION 5A
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