junger d07 Operation Manual page 79

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 low path 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 for 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.
The operation of the adaptive pre-emphasis filter also happens in this case only
when the maximum value is exceeded, i.e. depending on the headroom at higher
frequencies only. By using the parameter PRE_EMPHASIS THRESHOLD, 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.
0
-2
Limiter Threshold -4dBFS
-4
-6
-8
-10
-12
-14
-16
-18
200 500
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.
1
Parameter:
Preemphasis Threshold
1
- 4,0dBFS
-2,0dBFS
2
3
0,0dBFS
1k 2k
2 3
5k 10k 20k
d07 Pre-Emphasis
B 7 FM-Transmission d07
7.3.
Pre-
emphasis
Pre-emphasis
Threshold
0
-2
-4
-6
-8
-10
-12
-14
-16
-18
Pre-emphasis
Set up hint