5
noise or audio signals, which are clearly background effects, the GGS inhibits gain "recovery"
during those intervals when the input level drops below a preset threshold.
The GGS threshold has been factory set to inhibit gain increase when the incoming signal has
dropped approximately 14 dB below the normal line level. This figure has been established after
extensive field experience, and represents a satisfactory value for typical broadcast use. For
special applications the GGS threshold may be move upwards towards normal program level by
decreasing the value of R45A or lowered by increasing the value of this resistor. The following
table gives suggested values:
GGS Threshold
R45A
-4 dB
120 ohms
-8 dB
220 ohms
-11 dB
430 ohms
-14 dB
680 ohms
-17 dB
2.4 k
-20 dB
open
Sine wave verification of the GGS threshold level may be accomplished by the following
procedure:
a. Feed a sine wave input to cause the front panel meter to read 0 dB gain reduction.
b. Remove the signal and wait at least 15 seconds for full stabilization to occur.
c. Reapply the input signal at a level below the required threshold and slowly increase the
signal until the front panel meter just begins to deflect towards the right. The input level at
this time should be approximately 5 dB less than that indicated by the above table. (This
5 dB difference is a special factor and must be considered when sine-wave calibration of
the GGS threshold is performed.)
3-4 FUNCTION SWITCH
Audimax III is in operation performing automatic level control when the FUNCTION switch is at
NORMAL position. Turning the switch to the TEST position causes the gain to hold constant at
the same level as for normal operation. The function of the TEST position is to provide for
overall system performance measurements.
3-5 LIMITED DYNAMIC RANGE APPLICATIONS
The gain control action of the Audimax has been designed to provide a precise degree of control
with a minimum of noticeable change in the original dynamic range. As a tool for the
broadcaster, it provides maximum modulation consistent with artistically acceptable
performance for a wide variety of program material. In some applications, however, it is practical
and desirable to further limit program dynamic range. This is commonly done for the purpose of
achieving higher average modulation, or a more uniform sound as in the case of public address
systems. This effect may be achieved by decreasing the Audimax recovery time.
Although the total gain-reduction action of the Audimax is a complex function of many variables,
one phase of the recovery characteristic may be modified by changing R76. This normally is a
10 megohm resistor mounted on lugs on the Logic Board. By decreasing its value, the speed of
recovery is increased. Typically, the resistance may be decreased to 5 megohms, although
values as low as 1 megohm can be used in special applications.
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