AGC OPERATION
ENG
Page 12
When the AGC level is getting close to its internal reference level when releasing, the AGC will enter a so
called WORK ZONE, where the AGC speed is reduced to the WZ Rel value stated in the AGC WINDOWS
menu.
The dimension of the WORK Zone is stated by the WZ Thr (Work Zone Threshold) parameter.
The WORK ZONE interval (which ranges from the negative level expressed by the WZ Thr parameter to the
0 dBr internal reference) has been introduced because high compression and high amplification speed on
the whole band could engender unpleasant pumping effects.
The Attack speed sets the speed the AGC will use to react to sudden and unaxpected transient of input
signal (exceeding 0 dBr), which could bring to improper, large increment of output level.
Basically, the Attack time should be set according to the music contents and type (Classical, Rock, etc) being
broadcast.
EXAMPLE 1 – SETTING AGC SPEEDS FOR GENERAL PURPOSE OPERATION
Having set AGC Release speed = + 2 dB/sec and WZ Thr = + 4 dB, an input signal of – 14 dBm will be
amplified to – 4 dB in exactly 5 seconds. Once entered the Work Zone, the approach to the 0 dBr threshold
will be slower, and equal to the WZ Rel speed. Having the latter set to 0.5 dB/sec, the whole travel will take 5
+ 8 = 13 seconds.
NOTE: this is a very theorically AGC operation. In fact, the MultiBand stage (featuring its own AGC control)
will also contribute to normalize the level.
EXAMPLE 2 – SETTING AGC SPEEDS FOR EXTREME OPERATION
This setting is indicated when large level gap should be compensate in the shortest time. Having set AGC
Release speed = + 5 dB/sec and WZ Thr = 1 dB, an input signal of – 16 dBm will be amplified to – 1 dB in
exactly 3 seconds. Once entered the Work Zone, the approach to the 0 dBr threshold will be slower, and
equal to the WZ Rel speed. Having the latter set to 1 dB/sec, the whole travel will take 3 + 1 = 4 seconds.
6.3 SETTING DRIVE, IDLE AND GATE PARAMETERS
The Agc stage may be considered as a Compressor stage with a positive Drive. The Drive value represents
the AGC Max Gain, i.e. the maximum amplification value attainable by the AGC system. Thus, a Drive not
null means AGC can increase low levels fed at its input.
EXAMPLES
Condition
Drive = 0
- having an input signal at + 8 dBr*, the AGC meter will read – 8 dB and the AGC stage will
output 0 dBr (the AGC stage is always capable to attenuate large signals)
- having an input signal at –2 dBr*, the AGC meter will read 0 and the AGC stage will output –
2 dBr (there is no capability to add Gain, as the Drive factor is null)
Drive = 3
- having an input signal at + 8 dBr*, the AGC meter will read – 11 dB and the AGC output will
be 0 dBr (the AGC stage is always capable to attenuate large signals)
- having an input signal at –2 dBr*, the AGC meter will read - 1 and the AGC stage will output 0
2 dBr (the Agc stage is able to compensate for low signal, as Drive factor is not null)
* if the input signal is rated at the same level of A/D Reference, this is also the level of the signal being fed to
the processor.
Drive parameter may be considered as the maximum amplification value attainable by the AGC system.
For instance, setting Drive = +12 dB means that maximum amplification is +12dB: thus a –12dB signal can
be compensated to 0, while a –15dB signal will reach a maximum of –3dB.