Tuning to Multicast
Multicasting Is Embraced Quickly, But
There Is Still Much to Learn
by Skip Pizzi
 Last
time we started a discussion on next steps for IBOC, and focused
on multicasting as a potential killer app for HD Radio broadcasters
on the FM band. This time we'll consider the receiver marketplace
in that regard.
Of the relatively few HD Radio receivers in the market, even fewer
handle multicasting, but this is about to change. Numerous new HD
Radio receivers are expected to hit the market soon, and most of
these will include multicast reception capability.
How these receivers display and navigate among multicast channels
is not necessarily uniform, however. This creates a potential problem
for consumers' accessibility to any new multicast services. It also
makes broadcasters' promoting of these services difficult.
For this reason, the NRSC has established a Supplemental Identification
Task Group, or SIDTG, which may ultimately provide the industry
with some guidance in this regard.
(Note that Supplemental Program Service or SPS is the official
title given to an IBOC multicast channel in the NRSC-5 standard,
distinguishing it from Main Program Service or MPS, which in IBOC
Hybrid Mode is the name given to the digital simulcast of the analog
program.)
Meanwhile the industry is considering various elements of what
the consumer experience of multicast services could soon be like.
Tuner behavior
The first commercial multicast-capable receiver was produced by
Kenwood in 2004, and its designers made their own decisions on how
to tune and display multicast channels. Initially the Kenwood design
used the pause button of the CD player (which has no function when
the tuner is selected, of course) as a method of selecting supplemental
program audio.
Kenwood radios also displayed "-HD1" after the station's frequency,
once the receiver switched from analog to MPS digital signal. If
a multicast channel was selected, the display showed "-HD2" or "-HD3",
etc.
Other HD Radio receivers will use a similar approach, but generally
with only numerals "-1," "-2," "-3"... instead. Some units will
display these subchannel identifiers in a highlighted circle or
other geometric shape, to better distinguish them from the frequency
numbering. More variation is expected on how to access the multicast
channels (e.g., buttons with differing labels, menu-driven operations,
etc.).
Then there's the "scanning problem."
If an HD Radio user is scanning upwards through HD Radio-enabled
channels, typical tuning behavior is to first access a station's
analog FM signal, and after about 5 seconds of acquisition time,
to switch to MPS digital. Seeking or scanning any multicast services
on that channel can then take place without difficulty (assuming
the user knows what button to push).
When scanning down the dial, the user might intuitively expect
the process to be essentially reversed. In other words, if you are
listening to MPS on 107.3 MHz and push the scan-down button, the
first signal you'd expect to encounter would be the highest-numbered
supplemental service on 106.5 MHz, for example. But because this
is a supplemental channel, which has no analog acquisition/back-up
signal, the radio has to do one of several things - none of which
are particularly pleasant or expected by the listener.
First, if the radio wants to take the intuitive approach of going
to that highest numbered supplemental on the next station down the
dial, there will be at least five seconds of muting, while the tuner
acquires the channel (in silence), buffers the digital signal, checks
for the presence of multicast services, then switches to the highest-numbered
SPS signal. (The receiver might display some kind of "acquiring
signal" sort of visual message during the silence.)
Alternatively, if the receiver wishes to avoid a long mute time,
the station's analog (main channel) signal could be played while
the digital buffering took place, and the radio could switch to
the highest-numbered SPS signal when it became available a few seconds
later. The abrupt but delayed content change is likely to cause
seriously negative listener reaction, however.
A final alternative would be to scan (at least in the downward
direction) only MPS services, ignoring SPSs until the user actively
called for them on each station. In other words, if a multicast
service were desired by the listener, it could be accessed by another
separate command (e.g., pushing the up-scan or some other button)
after acquiring MPS on a newly tuned station. To aid in this, some
visual display element could indicate the presence of any SPS on
the channel.
Among automotive radio manufacturers, particularly the major car
companies' OEMs (Delphi and Visteon), resistance to addition of
any new hardware buttons is expected to be high. Equally problematic
is anything that encourages drivers to take their eyes off the road
to read in-dash displays. (An increasing number of new vehicles
now include scan and volume buttons on the steering wheel for this
reason.) Therefore one-button scanning may be the best way, at least
initially, to access a multicast channel, so just how the scanning
of multicast channels is handled becomes critical for supplemental
services' access to mobile audiences.
Latency hurts
A related SPS latency problem will be encountered in any radio
that allows direct access to a multicast channel (for example via
a memory location). Broadcasters seem to like the idea that a new
multicast service could be stored to a preset button like any other
station, but no one likes the fact that when that service is recalled,
there would be several seconds of dead air before the channel's
audio is heard.
And of course, when the IBOC signal fails, an MPS service will
blend to analog, while an SPS service simply mutes. If the digital
signal is reacquired while still tuned to an SPS service, there
will likely be an additional few seconds of reacquisition time before
SPS audio is played.
Perhaps listeners' reaction to this problem will be blunted by
increasing exposure to tuning latency in satellite radio and digital
TV, or from buffering delays on digital music playback devices and
PCs, but those delay times are typically shorter than the ~5 seconds
expected for direct-tuning of an IBOC-SPS service.
Note that this issue doesn't go away in the all-digital IBOC era.
Then, too, the MPS service will maintain low-latency acquisition
and backup via a low bit-rate, robust digital signal, while SPS
services will not benefit from such assistance.
Marketing challenges
As mentioned earlier, in order for broadcasters effectively to
cross-promote their multicast services on-air, or to advertise their
presence in print or other media, there will have to be relatively
consistent display and navigation for multicast channels in HD Radio
receivers. Meanwhile, however, broadcasters themselves may be introducing
another element of inconsistency in how they position their multicast
services.
So far, most stations offering multicast services are leveraging
their analog/MPS service's existing brand and adding a related service
(e.g., programming a second service with "Deep Tracks" or "New Releases"
from the same musical genre as their main service). Other broadcasters
have hinted they will offer weather and/or traffic services, once
sufficient multicast receivers proliferate - perhaps even airing
these as narrowband third services.
Yet some broadcasters would like to at least reserve the right
to provide new multicast services with no connection to their existing
brand - perhaps even offering services that run counter to their
existing brand, such as country and classical, or conservative and
liberal talk. Therefore they feel it's important to be able to maintain
a fully separate identity on multicast channels. How these divergent
views eventually are accommodated remains to be seen, and will likely
be one of the key discoveries of the early multicast era.
Finally, how ratings services deal with multicast channels will
also be critical to their success. Both diaries and PPM systems
will have to be adjusted to include multicast services, and broadcasters
will need to establish effective and memorable on-air identification
styles to encourage accurate diary reporting of multicast-channel
listening.
HD Radio multicasting seems to have caught fire with broadcasters
and receiver makers, with both sectors acting to enable this fundamental
shift with relatively high speed. All this early activity is based
on initial assumptions, however. As the transition continues, the
industry should remain agile and open to adjusting its strategies
to those that resonate most strongly with the audience, but it should
act in a uniform and consistent fashion. Confusing listeners with
widely divergent methods of accessing multicast services could obstruct
success for one of HD Radio's most promising components.
Next time we'll look at some other areas of IBOC that will mature
in coming years, and how they might also change the future landscape
of radio broadcasting.
Skip Pizzi is contributing editor of Radio World.
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