Since a variety of tape decks and test equipment exist commercially, it
would not be practical to generate a procedure applicable to all such items.
The procedure defined has, therefore, been tailored to a particular tape deck
and equipment set-ups and will serve as a guide in establishing procedures for
2-3.1.1 Equipment. The following equipment shall be used
to evaluate a tape deck:
a. Sweep Oscillator: provides a constant output voltage from 20-2000 Hz
(Spectral Dynamics, Model SD104A-5) or equivalent.
b. Precision Attenuator: provides a convenient method of decreasing
oscillator output voltage in even 10 dB increments from 0-40dB.
(Hewlett-Packard, Model 350D) or equivalent.
c. A.C. Digital Voltmeter: indicates the rms output voltage of the
oscillator at the reference frequency. (Fluke, Model 8800A) or
d. Frequency Counter: sets the reference frequency of 1000 Hz and adjusts
the sweep limits of the oscillator. (General Radio, Model 1192B) or
2-3.1.2 Recording The Reference Tape. Figure 2-1 depicts,
in block diagram form, the set-up required to record the reference tape. The
following step-by-step procedure defines the requirements necessary to perform
a. Enter all the manufacturers information on the
Tape Deck Data Sheet, Figure 2-2
, including the maximum line input voltage established by the
b. Establish the rms reference voltage representing
the OdB signal and enter this value on the Tape Deck Data Sheet (Figure 2-2
). (A level of
approximately 85% to 90% of the manufacturer's maximum line input voltage is
c. Connect the sweep oscillator output to the attenuator input and set
the attenuator to 0 dB.
d. Connect the counter and A.C.-DVM to the attenuator output.
e. Set the oscillator to the manual mode and adjust the frequency to 1000
Hz (± 1 Hz).
f. Adjust the oscillator output voltage to the reference level
(established in b.) while monitoring the attenuator output. After adjustment
is made do not change the oscillator output controls.
g. Place the oscillator in the linear sweep mode, set a sweep rate of 6
Hz/sec (+2, -0 Hz/sec.) and then reset the frequency to 20 Hz.
h. Set the oscillator to automatic sweep and alternately adjust the lower
limit to 20 Hz ( + 0 Hz - 5 Hz) and the upper limit to 2000 Hz ( + 50 Hz, -
i. Connect the attenuator output to both line inputs of the tape
j. Insert a cassette in a Position which will record on side "A"
k. Set the tape deck switch selectors to the proper
"Record" positions. Verify that the tape deck equalization (if selectable)
matches the cassette tape type and record this information on the Tape Deck
Data Sheet (Figure
l. Set the following tape deck selector switches to the "OFF"
(1) MPX Filter (2) Memory (3) DOLBY 'NR'
m. Rewind the tape deck to start and reset the counter to zero.
n. Reset the oscillator to the manual mode, preset to 1000 Hz in step
o. Record the reference voltage and adjust the tape deck's "record level"
potentiometers until both VU meters indicate OdB (+OdB, - 1 dB). Record at
this level for 10 seconds. (After performing this adjustment do not alter the
"record level" potentiometer positions).
p. After completing this 10 second recording enter the
counter number on the Tape Deck Data Sheet (Figure 2-2
) and reset the oscillator to the
automatic sweep mode.
q. Record approximately 10 seconds at the lower limit of 20 Hz and then
activate the sweep up mode.
r. After the upper limit (2000 Hz) has been attained,
stop recording and enter the counter numbers on the Tape Deck Data Sheet (Figure 2-2
s. Reset the oscillator to the lower sweep limit (20 Hz) and set the
attenuator for -10dB.
t. Repeat steps q. thru s. for attenuator levels of -20dB, -30dB and -
u. An oscilloscope can be used to verify the data taken by observing the