BW Broadcast technical manual
Page 19
Installation and setup
There are altogether twelve jumpers on the board which can be set - at the time of installation - to establish the way
the board operates.
The board leaves the factory with default settings which should be suitable for most locations and requirements.
Nevertheless, it is worth familiarizing yourself with all the options available, and checking that the settings are appro-
priate, as part of the installation process.
Jumper 1: MPX loopthrough
The default position is ON.
This is where you want the audio left and right XLR sockets on the back of the board to be the signal source,
duly limited and stereo coded internally. Only when you want to use the rear BNC socket for a complete
multiplex (MPX) input for the broadcast should you change the position of this link.
If the link is in the OFF position, only signals from an external encoder or processor will be accepted, unless
the internal coder has been ‘loop-throughed’ (see later).
Jumpers 2 and 3: Pre-emphasis 0 / 50 / 75 µs
The default position is 50 µs (75 µs/Japan).
What is pre-emphasis?
Pre-emphasis is the treble boost that must be applied to all FM broadcasts to compensate for the treble cut
(de-emphasis) present in every receiver. The aim of this process is to reduce noise in the broadcast path
without degrading the audio.
The precise nature of the treble boost is defined by a time-constant in microseconds, which describes the
resistor/capacitor network that will produce the appropriate 6dB per octave treble boost curve.
There are two different standards in use worldwide.
In Europe and Africa, the standard is normally 50 µs. This represents a lift of about dB at kHz, and
10dB at 10 kHz. In the Americas, and in Japan, more boost is in use with a network of 75 µs, about dB
up at 2 kHz.
Jumpers 2 & may either link the 50 µs pins, the 75 µs pins, or not link any pins, but be fixed to just one of
them for safekeeping, producing no pre-emphasis - ‘0’.
The effects of pre-emphasis
The absence of any pre-emphasis will result in a broadcast sounding noticeably lacking in treble. Applying
50 µs pre-emphasis will correct the situation in European receivers (75 µs in Μs/Japan). If you apply 75 µs
pre-emphasis when 50 is called for, the received sound will have some dB shelved treble boost above kHz.
This is undesirable. Conversely, if you only apply 50 where 75 is required, there will be dB treble loss, which
is also undesirable. You should not have to change the pre-emphasis setting from 50 to 75 or back unless
you are relocating the installation abroad where the standard is different.
However, whenever pre-emphasis is deliberately applied to your audio at some point before it enters the XLR
sockets on the back of the board, by an external processor for example, then you must set the pre-emphasis
to ‘0’, because pre-emphasis must only be applied once.
Double pre-emphasis must be avoided
because it
will make a signal sound far too bright and toppy.
Both Jumper 2 and Jumper should be in the same position at all times because both left and right audio
channels should have the same treatment. These jumpers do not affect the operation of the board when
external MPX is used with Jumper 1 off.
Jumpers 4 and 5: Limiter loud/pure
The default position is ‘Loud’ (hard limiting).
