The AGC (Automatic Gain Control) regulates the signal level of the audio output. A good AGC function normalizes broadcast signals to the standard output level in spite of the changes in the amplitude. The amplitude control includes a function for eliminating signal overload during static crashes, followed by a quick restore back to the standard level immediately after the overload burst.
Typically, all changes in the gain are bad when listening to weak signals as every gain change also modifies the "raw audio" a bit and this is why many experienced DXers keep the AGC disabled, especially when studying some specific ID. Consequently, in each individual case, the gain is being set manually. Also, when creating an audio clip, one of the rules of thumb is to disable the AGC unless there is some specific reason to use it.
The AGC in Jaguar has three different modes: AGC ON (default), AGC OFF, and AGC OFF+. When the AGC is OFF, the gain level is fully controlled by the user.
AGC OFF+ is a special, "semi-locked average" mode which combines the best of the ON and OFF modes. Normally, AGC OFF would require constant tuning to reach the optimal gain level for each frequency. This is where the semi-locked gain values come into the picture. When the user tunes in to a new frequency in the AGC OFF+ mode, JAGUAR will determine a "semi-lock gain value" within the first 500 ms of the playback. Then, the gain value is kept fixed during the playback of this frequency until an amplitude overload happens, or a new "semi-lock" is created.
A new semi-lock value is calculated (the gain value can also remain the same) in the following cases:
* SSB mode is changed
* Frequency is changed
* Filter is changed
* File is changed
The AGC should not be mixed with the CLICK REMOVER (CR) even though both handle amplitude overflows. The CR is good for recovering clicks caused by e.g. electric fences, i.e. very short audio bursts.
By default, the AGC is always ON. You can change the AGC status by clicking AUDIOBAR > AGC button, or clicking AGC on AUDIO APPLET.
If you scroll (with the mouse wheel or left/right arrow keys) instead of clicking, you will always enter into the manual gain control and will increase/decrease the gain value by yourself. If you had AGC ON, the mode will change to AGC OFF, and you can return from AGC OFF back to AGC ON by clicking the AGC button.
The behavior of the AGC can be followed by monitoring the "gain value". The gain value is displayed
- on STATUS BAR (between the Y and S service buttons): Click on this area to toggle the QSA and GAIN values
- on WAVE APPLET: in this example, the numeric value of 0.58 on the bottom of the applet is the current gain value
The WAVE APPLET also shows when the AGC performs a major elimination ("AGC hit") of any abrupt signal burst (such as a lightning struck): the background of the WAVE applet will flash as red.
Note that there is a "magic connection" between the "LO noise" function and the amplitude: the "LO" not only filters audio frequencies below the speech but also flattens the output waveform dramatically. Normally, there is a lot of power on those low frequencies; you can see the effect in the WAVE applet. This may reduce "AGC hits" in many cases. However, please note that the LO/HI options are not available in the pre-versions of Jaguar V6.
Finally, also using the Jaguar audio equalizer (the TINYEQ applet) has a similar effect on the gain.