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9.5 ADVANCED PROCESSING
This section has more detailed information on setting up the DSPXtra-AM Encore’s
processing.
9.5.1 HIGH PASS FILTER
The high-pass filter has five selectable cut off frequencies and a bypass option. Modern
AM transmitters can accommodate low frequencies, however older AM transmitters
may suffer from AFC bounce and overshoot when driven with high levels of very low
frequency 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-AM Encore can cure this problem by removing the very low frequency content
from the program material.
Additionally, some AM receivers can't handle low frequencies (<30 Hz) properly and
may produce distortion. Another reason 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 20 Hz than say 50 Hz where most people can here and speakers reproduce bass. The
processing stages will respond to this amplified 20 Hz content even though most people
won’t ever hear it when listening to your radio station.
Taking everything into account we recommend setting the filter to 30 Hz (or higher if
necessary).
9.5.2 BASS ENHANCEMENT
The frequency contouring effect of multi-band audio processors often leaves the bass
lacking a little. The summation of the bands tends to give a boost to the presence
frequencies and leaves the bass sounding a little thin. This effect can be compensated
somewhat by enhancing the bass prior to multi-band processing.
The DSPXtra-AM Encore has a pseudo parametric style bass equalizer control that allows
you to sweet tune the bass. Four frequencies, amplitudes and Q's are provided giving
you 6 different bass curves to select from. Frequencies selectable: 60Hz, 76Hz, 95Hz and
120Hz. Q's selectable: 0.4 , 1, 2 and 4. Gains selectable: 0, 1.5dB, 3dB, 4.5dB, 6dB. A
starting setting of 95Hz, Q of 1 and gain of 4.5dB warms the bass up quite nicely but you
are free to experiment to get the bass sound you're after.
9.5.3 MULTIBAND AGC
The multi-band AGC in the DSPXtra-AM Encore employs an RMS based level detector for
superior performance. This enables the DSPXtra-AM Encore to control input level
variations based on the true loudness of the input waveform unlike other simpler
average responding peak detectors used in other digital audio processors. When you
couple the advanced detector with the user adjustable and hidden intelligent controls
you really do have a powerful levelling tool.
The Multi-band AGC stage of the DSPXtra-AM Encore has two main functions: