Listener Experience Is Key to Proper HD
image of JVC’s KD-HDR52 CD receiver with HD Radio tuner.
the world of HD Radio, we have the opportunity to “wow” our
listeners with the quality and features of the digital signal, or to
irritate them with tune-out factors. There are several things that
every HD Radio station engineer should pay close attention to in
order to hold listeners.
analog/digital time alignment is a big deal. A little misalignment
creates a stutter or skip, depending on which direction the
misalignment is in and whether the station is blending into or out of
digital. I’ve heard some stations in big markets with apparently no
time alignment at all, and the signals eight or more seconds out of
alignment. Something like that will drive a listener crazy as the
blend occurs. While we as engineers at least recognize what’s
happening, Joe Listener does not, and he no doubt thinks that the
station has some real technical problems (and it does).
MONITORS ARE ESSENTIAL
learned over the last 10+ years of HD Radio that digital/analog time
alignment does occasionally drift. Such slip can occur wherever the
delay of the analog signal takes place (in the audio processor or in
the exporter). The important thing is to monitor it, and for that, we
have several tools available, starting with the ones affixed to the
sides of our head.
think every HD Radio station chief engineer should have an HD-capable
radio in his or her vehicle. That CE should listen to the station and
pay attention to what happens during the blend. If there’s a
problem, it should be readily apparent.
least one manufacturer produces an HD monitor equipped with a
time-alignment monitor and alarm. Having one of those around
constantly monitoring the status of the time alignment sure wouldn’t
THE SOUND RIGHT
tune-out factor is when there is a noticeable level jump between the
demodulated analog and digital signals. I was recently in
Philadelphia and noticed in my HD Radio-equipped rental car that one
HD Radio station had enough of a level difference between analog and
digital that I had to make a volume adjustment after the blend to
maintain a comfortable listening level. That was aggravating,
especially when I drove through an area where the station had some
signal issues and the digital was in and out.
exporters or HD exciters have some adjustment for this. It is
sometimes called Digital Gain, and in other exporters/exciters it’s
called Analog Level. Depending on the setup, this can sometimes also
be adjusted in the audio processor. However it’s done, the levels
should be adjusted for proper analog modulation depth with a good
match, within a dB or so, between demodulated analog and digital
some audio processors contain separate digital and analog
equalization controls. One manufacturer provides a control called HF
Shelf EQ. Get it set too high, and the resulting digital audio can be
unnaturally bright and sibilant, even irritatingly so. While it’s
good to exploit to some degree the capabilities of the digital signal
to provide higher audio quality, the hybrid world we live in dictates
that we don’t get carried away. Equalization and processing should
be adjusted so that the blend sounds natural and the digital signal
sounds perhaps a little brighter and crisper than the analog but not
the end of the day, it’s all about “The Listener Experience.”
Provide content that the listener wants with good technical quality
and without irritations, and the listeners will stay tuned in, but
even high-demand content with a bunch of irritations will drive
listeners away. Pay attention to proper time alignment, level match
and equalization, and you will keep your listeners happy.
your HD Radio tips or column suggestions to
Alexander is the director of engineering at Crawford Broadcasting and
a past recipient of SBE’s Broadcast Engineer of the Year award.