The DSPX And It's Processing Structure
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couplings and complex gating features afford the user with full control of this important re-equalisation stage
of the processor.
Multi-band Limiters
Each band has its own dynamic peak limiter. Multiple time constant based detectors with built in adjustable
hold and delay functions significantly reduce distortion.
Mixer
The four bands are 'virtually' mixed together at this stage. In truth, the four bands have become three. The
three bands are fed off into the two peak processing paths.
Distortion controlled clippers (PEAK CONTROL PATH 1)
The DSPX clipping algorithms peak limit (clip) and linear phase filter the audio in three bands for maximum
distortion control before being fed to the final clipper stages.
Look-ahead limiter (PEAK CONTROL PATH 2)
The DSPX look-ahead limiter is one of the most sophisticated available in a broadcast processor. Processing
is performed in three bands for maximum transparency and clarity. A cut shelving filter is provided to compen-
sate for the effect of pre-emphasis when the DSPX is used to process FM signals at the same time.
Output selection, processing and routing
The DSPX allows the user to select where each processing path is routed to and provides output level con-
trols. A de-emphasis option is provided on both the analogue and digital outputs. The digital output sample
rate can also be configured to a variety of settings.
The analogue output also has one extra path that can be routed to its outputs. This is a lower latency (delay)
path that bypasses the final clipper stages and reduces delay by more than 4mS. This can be used to help
with talent (DJ's) who can not get to grips with the delay of the main processing path. This output if selected
should only be used as a studio monitor signal and should not be used ‘on the air’ as the peak clipping stage
in the monitor processing path is not over-sampled or anti-aliased.
The analog and MPX outputs will be affected by the ITU limiter, if it is engaged. The purpose of this limiter is
to comply with the ITU BS.412 standard. The standard calls for limiting of the power of the composite signal
being broadcast. When activated, the ITU limiter will drastically reduce the loudness of your signal.
Stereo encoder
The DSPX's DSP stereo encoder takes its inputs from the FM path of peak processing. The audio fed to the
stereo encoder does not pass through any de-emphasis circuits. The stereo encoder is highly over-sampled
and offers superb stereo performance. A composite clipping function is provided for those who wish to use it,
as well as a pilot protection filter.
