Optimod-AM 9400 V1.2 Operating Manual - Orban

OPTIMOD-AM DIGITAL OPERATION 3-33
cal maximum, unless source material is primarily from compact discs of recently recorded
material. In several of our presets, we use this equalizer to boost the presence
band (3 kHz) slightly, leaving broadband HF boost to the receiver equalizer.
Receiver Equalizer
HF Gain (“High Frequency Shelf Gain”) determines the amount of high
frequency boost provided by the 9400’s receiver equalizer.
HF Curve (“High Frequency Shelf Curve”) determines the shape of the
curve produced by the 9400’s receiver equalizer.
The high-frequency receiver equalizer is designed to compensate for the high frequency
rolloff in average AM radios. The typical AM radio is down 3dB at 2kHz and
rolls off at least 18dB/octave after that. The HF equalizer provides an 18dB/octave
shelving pre-emphasis that can substantially improve the brightness and intelligibility
of sound through such narrowband radios. The HF equalizer has two controls: a
gain control that determines the height of the shelving curve (dB), and a curve control,
calibrated with an arbitrary number that determines how abruptly the shelving
equalizer increases its gain as frequency increases. 0 provides the most abrupt curve;
10 provides the gentlest. The HF CURVE control is used to trade-off harshness on
wider-band radios against brightness in narrow-band radios.
An HF CURVE of 0 provides the same equalization that was originally supplied as
Figure 3-1: HF Receiver Equalizer Curves