MIRAGE MK III - Broadcast Audio Processor
AEV Broadcast Srl via della Tecnica 33, 40050 Argelato Bologna ITALY
www.aev.eu
9
Configuration and in/ out connections
MIRAGE has been designed to offer the follwing features:
1.
analog inputs and outputs.
2.
composite stereo output (MPX)
3.
user input/output for addition external audio effects.
The construction of the MIRAGE allows optional boards to be inserted in a card frame within
the unit. The configuration ordered by the user will determine which boards are fitted.
Connections
It is recommended that input/output connections be made with high quality, flexible cable,
incorporating a good screen.
Special attention should be paid to the grounding of the unit and the quality of the line supply
ground connections. GROUND and CHASSIS connections between units should be kept
separate in order to avoid interference caused by earth loops.
Inputs / Outputs
The female XLR inputs have an impedance selectable between 600
_
and 10 k
Ω
.
The range of input levels is from -20 dBm to +10 dBm.
The male XLR outputs are active balanced with an impedance of 100
Ω
.
The range of output levels is from 0 dBm to +12 dBm.
The adjustment of input and output levels is made with trimmers situated on the rear panel.
Encoder board inputs / outputs (*)
The stereo encoder features an unbalanced output on a BNC connector situated on the rear
panel. This output can drive an impedance of 50 or 75
_
at a distance of upto 10m via RG 58
cable without noticeable degradation of the MPX signal.
Also present are two inputs that can accept SCA and RDS signals which can be adjusted
with trimmers and are added to the MPX output signal.
Furthermore an output provide synchronization to an external systems: SYNC 19 KHz OUT 1
Vpp SW for the synchronizing of external encoders.
Positioning the MIRAGE
The audio processing circuits of the MIRAGE produce a signal that is pre-emphasized with
curves of 50µs or 75µs and processed in a precise manner to avoid overmodulation; the signal
is then filtered at 15 KHz to protect the 19 KHz pilot tone.
If the two-channel output signal of the processor is input to an external stereo encoder, it
is advisable not to introduce any other apparatus that could alter the bandwidth and increase
modulation peaks with respect to the average value.
Frequency response errors and variable delays are introduced typically by equalizers, line
transformers, low-pass 15 KHz filters and pre-emphasis networks in stereo encoders.
It as advisable, therefore, first of all, to by-pass all low-pass filters and pre-emphasis circuits
present in normal stereophonic encoders.
Low-pass filters, high-pass filters, transformers, distribution amplifiers and long transmission
lines can all alter the signal with the consequences outlined above.
It is clear then that the criteria for the optimum level of peak modulation outlined above,
can be most easilty met when the audio processor feeds directly an internal stereo encoder.
In the MIRAGE there are no active circuits or components between the audio processor
and the internal stereo encoder that could distort the waveform. It is thus strongly
recommended that the MIRAGE is used with its own internal stereo encoder wherever
possible.
