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Mounting standoffs are already in place, just plug the accessory
board squarely onto the header strip so that the screw holes
line up. Fasten the board down with the screws that came with
it. The DAVID IV will recognize the board when it boots, and
you can then access and set up the delay menu.
NOTE:
HD Radio Delay functions appear on the menus only if
the accessory board is installed, and installed correctly.
Adjusting
the Delay
HD Radio delay is available over a much wider range than re-
quired, in the expresses hope for improvements in the encod-
ing/decoding process of the HD Radio system to lessen the de-
lay substantially. Although this adjustment can be ‘earballed’
to a fairly close match, a seamless crossfade between analog
and digital reception requires a better technique.
An HD Radio receiver in its normal operating mode will fade
from analog to digital within a few seconds after the station is
tuned. Tune away from your station and then tune back again.
The transition should be ‘seamless,’ with no echo, gaps, stutter-
ing or level shift as the radio cross-fades from analog to digital
reception.
The delay may be set with fair accuracy using an HD Radio re-
ceiver that can be put into the “split” mode, where the analog
program is heard in one stereo channel and the digital program
in the other. Best to use headphones for this to home-in on re-
ducing phase displacement between the programs.
Despite one’s best effort to synchronize the analog and digital
program channels, it has been found that the encoding equip-
ment ‘slips’ over time, even when locked to a GPS time stand-
ard. For various reasons, some yet unknown, the HD Radio en-
coding process will allow the digital signal timing to wander
back and forth over the broadcast day.
This yet-to-be-solved shortcoming in the HD Radio system jus-
tifies a shameless plug for the Inovonics JUSTIN 808, a fully au-
tomatic time-alignment processor. The JUSTIN constantly mon-
itors your station off-air and makes incremental adjustments in
the delay and in r.m.s. audio levels to keep the two programs in
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