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COMPOSITE CLIPPING
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Processing / Composite Clipper
:
At the user’s discretion, up to 3dB of composite clipping may
be introduced. This is brute-force, flat-topped clipping of the
baseband signal, but before the 19kHz stereo pilot and RDS
subcarrier (if used) are added. Baseband clipping invariably in-
troduces harmonic components that ‘clutter’ the spectrum
above the program signal to a greater or lesser extent. Compo-
site clipping does provide some degree of loudness advantage
with somewhat less harshness than program signal clipping in
the L/R audio domain. Nonetheless, exercise this advantage
with care.
Composite Clipping
has no effect on either the analog or digital
line outputs, even when they are programmed for the FM mode.
HD RADIO™ DELAY
The HD Radio digital broadcasting system, employed principal-
ly in the U.S., is a ‘hybrid’ broadcasting system. This means
that the all-digital signal carrier is transmitted ‘on-channel,’
simultaneously with the traditional analog FM (or AM) carrier.
Legacy radios are thus able to receive the program in the usual
manner, and new HD Radio receivers can recover both the ana-
log and the digital versions of the program.
Because there is an obligatory delay of some 8 seconds(!) in the
digital program encoding and decoding process, the analog sig-
nal must be delayed by this same amount to arrive in sync with
the digital signal. The HD Radio receiver first tunes and plays
analog audio to the listener, but then it cross-fades to digital
reception when the digital signal is acquired. If this were not
the practice, then using pushbutton presets would be an ago-
nizing process, much as digital-TV channel-surfing can some-
times be frustrating, though to a lesser extent because of its
shorter delay.
This time-aligning “diversity delay,” as it is called, is enabled in
the DAVID IV with an optional accessory circuit board that is
simply plugged into a header strip on the main board.
Installing
the Delay
Subassembly
If you are adding the HD Radio delay option in the field, first
disconnect power from the unit. Then remove the top cover
and install the accessory board as shown in the snapshot at the
top of the next page. Mounting standoffs are already in place,
just plug the accessory board squarely onto the header strip so
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