junger D*AP8 FLX Manual page 83

D*AP8
But as the increased high frequency energy adds to the MPX power, it needs to be considered within
the FM Conditioner. There are two facilities to deal with Pre-Emphasis. First a Pre-Emphasis
Headroom parameter reduces the maximum wide band level by lowering the true peak limiter
threshold. This results in lower overall audio levels, but increased high frequency transparency. Second
a process called Pre-Emphasis Limiter reduces the high frequency amount of the audio signal
dynamically and thus creates 'space' for the additional Pre-Emphasis shelving. When activated the
Pre-Emphasis Limiter prevents high frequency over-modulation. To reduce its effect the Pre-
Emphasis Headroom needs to be increased. If the signal structure requires permanent Pre-Emphasis
Limiter action, the system automatically reduces the input gain of the True Peak Limiter to improve
sound quality. Please note that very short transients may not be 'catched' by the Pre-Emphasis
Limiter. This however happens by principle and has no practical relevance for the
FM transmission.
When activating the FM Conditioner it takes over control of the True Peak Limiter algorithm.
Important Note! The True Peak Max value cannot be set by the user, as it is automatically calculated and
set to the Ceiling level minus the Pre-Emphasis Headroom. With no Pre-Emphasis Headroom
True Peak Max equals Ceiling.
The MPX Limiter algorithm
The most important part of the FM Conditioner processor certainly is the MPX Limiter. As MPX power
is a value that is calculated with one minute of integration time, limiting is a very complicated task.
In theory 60 seconds look ahead time seems appropriate but of course not practically applicable for a
real time processor. Thus the Junger Audio MPX Limiter works with a complex prediction algorithm
that adapts to the incoming signal structure. Still the limiter reference level is a brickwall threshold and
considered sacrosanct. In case of 'emergency' the MPX Limiter will reduce the signal level drastically
to prevent any threshold violation. Chances are that the MPX Limiter of the FM Conditioner is the best
MPX brickwall available today.
Please note that the MPX Limiter Reference can of course be violated when the incoming levels are
high and the MPX Limiter was just switched on. By measurement principle it may take up to one
minute for the MPX Limiter to settle.
The MPX Limiter Profile influences the speed and range of the process and in consequence the
neutrality to the incoming sound quality. With softer settings the system needs to apply a buffer zone
between the MPX Limiter Reference and the measured MPX power of the audio signal. Though this
buffer zone is always very small, with harder settings it becomes even smaller and a higher MPX power
can be transmitted. The optimal setting depends on the type and style of program that is broadcast.
A very handy feature of the FM conditioner is the visualization of the development of
MPX power over time:
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