BW Broadcast DSPXtra-FM, Operational Manual

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Setting Up The Processing
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S
EttInG UP thE
P
rOCESSInG On thE
dSPX
tra
-FM
This section has more detailed information on setting up the DSPXtra-FM’s processing.
Because the DSPXtra-FM contains another product in its own right, the Ariane, we have decided to start with
discussing that section of the processing and its setup. This also seems logical because it is the first part of the
processing chain after the audio has been routed through the high pass and phase rotating filters which we will
get out of the way below before moving on to the background, workings and setup of the Ariane.
High pass filter
The high-pass filter has five selectable cut off frequencies and a bypass option. Most users will bypass the high-
pass stage but there are several cases where enabling the high-pass has an advantage. The first of those is
stations that mainly play vinyl recordings. Vinyl recordings can suffer from low frequency rumble and the high
pass filter reduces the effect of these low frequency rumbles. Some processing experts believe that removing
the very low frequency content from the program material improves the rest of the bass sound from the proc-
essor. The theory is that most people can’t here or speakers can’t produce the very low frequency bass. They
believe that by removing this sub-sonic bass more room is made in the processed waveform for frequencies that
can be heard. Another reason that is given is that this very low frequency bass can dominate the band 1 AGC
and limiter, especially after bass enhancement has been carried out. The low frequency shelving filters used in
processors have much higher gains at 20Hz than say 50Hz where most people can here and speakers repro-
duce bass. The processing stages will respond to this amplified 20Hz content even though most people won’t
ever hear it when listening to your radio station.
Some radio transmitters suffer from AFC bounce and overshoot when driven with high levels of very low fre-
quency bass. If your transmitter suffers from this phenomenon you may need to turn your modulation down to
accommodate these overshoots. The high-pass filter in the DSPXtra-FM can cure this problem by removing the
very low frequency content from the program material
Phase rotator
This parameter if enabled will help to reduce vocal distortion in aggressive presets by reducing asymmetry in the
voice which would otherwise put more workload on the clipping stages. Human speech (particularly male) can
be very asymmetric compared to music and the phase rotator helps to bring symmetry to the audio waveforms.
We recommend enabling this option if you are after maximum loudness; Conservative formats such as classical
may prefer to leave it off as the phase rotation process does colour the sound slightly, although this coloration is
often used for artistic effect.
The Ariane RMS leveller
The first decision you need to make is which operating mode to use. The Ariane has three modes: Stereo,
Matrix and bypass. Each mode has its own capabilities and purposes.
Stereo In the Stereo mode, the Ariane is a traditional Left/ Right two channel AGC, with a single set of
adjustments for both channels. The two channels’ dynamic operation can be set such that control of both
channels is coupled together completely, allowed to operate independently, or with a user defined amount of
inter-channel control coupling.
Matrix In Matrix mode, the audio is converted before processing to a Left-plus-Right or ‘mono sum’ signal,
and a corresponding Left-minus-Right or ‘difference’ signal. Matrix mode allows for stereo enhancement and
optimization for any stereo broadcast medium (such as stereo FM, AM or Television) that ultimately is trans-
mitted in sum and difference. There are separate controls for the sum and difference signals. After process-
ing, the Ariane's matrix signals are reconverted to Left and Right stereo audio for output.
Once you have determined the appropriate operating mode to suit your needs, you could simply load one of the
Ariane’s factory presets to get rolling (there are several presets for each mode). You can then start your fine tun-
ing… and the fun begins!
Main Processing Controls
All three operating modes have a common set of controls that allow you to adjust the Ariane to best fit your
needs, plus a few controls that are unique to each mode, to further refine that mode’s operation.
The Ariane's basic processing adjustments are the IDR, Gate and Release settings, which are common to all
three modes. They set up the general static operating parameters which the Ariane will use to determine how
best to dynamically control your audio.