Junger Audio d07 - Digital Transmission Processor - Manual (Page 63)

B 7 FM-Transmission d07
To enhance the signal to noise ratio for FM transmission, Pre-Emphasis on the
transmission end and De-Emphases on the receiving end is used. Higher
frequency signal components are raised following a standardized filter curve and
leads to an increased drive of the transmitter. This level pull up must be considered
for the limitation of peak levels.
In the d07 the signal reaches a dynamic filter after a broad band limiter. The cut-off
frequency of this filter is controlled adaptive and time depending. The attenuation
of the filter for high signal components is controlled in a way that it compensates
exactly the increase of high frequencies by Pre-emphasis on the transmitting end.
This alteration of the frequency response is only effective temporarily and will
practically not be recognizable for normal program material because the
processing time is below the integration time of the human ear.
The threshold of the limiter can now be set in a way that maximum deviation is
achieved for low frequencies. Higher frequency components will be reduced if
necessary and do not cause an overshooting of the peak deviation.
If the program material has a lot of high frequency components the activity of
the adaptive filter is of course more frequent and will eventually be audible.
If the threshold of the peak limiter is not set to maximum but some dB’s below the
resulting headroom can be used for higher frequency components.
By using the parameter CEILING, the operating point for the control of the filter can
be set. Caused by this mode of operation this value can only be higher or equal to
the threshold of the peak limiter.
Due to the different adjustable thresholds for peak limiter and adaptive pre-
emphasis, an optimisation in regard to maximum level and sound balance can be
achieved. This optimisation should also be done under consideration of the
multiplex power because higher frequency components caused by a level increase
on the transmitter side will make a higher contribution to the overall power.
7.3.
Pre-
emphasis
Ceiling
Pre-emphasis
Set up hint
-20
-0
-19
-18
-17
-16
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
d
B
F
S
-20
-0
-19
-18
-17
-16
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
d
B
F
S
10 20k 20 50 100 200 500 1k 2k 5k 10k
Hz
D07 Parameter : Ceiling
Limiter Tresh. = -4.0
Ceiling = -4.0 Ceiling = 0.0