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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:
