[opendtv] DTV Audio
- From: dan.grimes@xxxxxxxx
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 7 Aug 2008 09:57:22 -0700
There are other "problems" with ATSC in comparison to NTSC, in my opinion.
One is the fact that the audio bandwidth is greater so now the audience
hears more origination quality problems. One thing I notice is the low
frequency content that did not used to be there in NTSC. Evidently, the
broadcasters do not have subwoofers in their audio control rooms to hear
the problems. The equalization and mic placement cause a tremendous
amount of vocal rumble and plosives which are overbearing to a home
theater sound system that is set for movies. The NTSC broadcast filtered
this out but with ATSC, they are overbearing and annoying.
So just like HD cameras created problems because of the detail, so, too,
the enhanced audio transmission is requiring a new level of quality in the
production chain.
Of course, I've noticed the problems listed in the below article, too. I
especially hate having to lower the volume dramatically when changing
channels.
Dan
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DTV Still Plagued by Hearing Problems
By Jim Barthold
TVNEWSDAY, Aug 7 2008, 8:35 AM ET
You hear few complaints about the pictures delivered by the ATSC digital
standard. But audio? That's another matter.
For the most part, the ATSC audio standard, based on Dolby Digital, is
delivering TV sound with the promised CD quality, providing a rich, new
aural dimension for consumers seeking the theater-like experience in their
homes.
But the standard continues to be plagued by loudness spikes and, what's
worse, lip sync troubles.
Engineers throughout the TV production and distribution food chain are
working on remedies. Dolby believes some of them lie in better education
and closer adherence to the protocols for using the system.
"Sometimes [engineers] run out of time to address all these little things
and figure it's just the audio," says Dolby Labs application engineer Ken
Hunold.
"We don't want that to happen. With the added capabilities of the audio
system come some added responsibilities in getting it right," he says.
Disturbing variations in loudness are cropping up from one channel to the
next and even within channels.
The Dolby system has built-in loudness normalization parameters that
producers can set with metadata so that decoders, be they high-end audio
systems, digital TVs, Dolby-standard digital cable set-top boxes or even
older analog TVs, recognize and adjust sound to proper levels.
According to Hunold, all Dolby signals, regardless of their source and
regardless of how loud they are, are controlled by the parameters.
Ideally, he says, this means that one channel would sound the same as
another and sound within a channel would not spike or drop.
But it's up to the program producers to set those parameters, he says.
"The programmers are slowly coming to grips with having to do this and are
learning to use the tools that exist in the digital audio system," says
Hunold.
Dolby is also working with cable companies and broadcasters to help them
understand the different parameters.
"It's something new to them that they didn't have to do before," says
Hunold, recently returned from a trip to speak with broadcasters in the
Carolinas.
"The [instructional] information is provided; it's in the manuals they get
with the equipment, but as we all know sometimes you don't have the time
to read the manuals when you're putting the stuff in."
Mostly, he says, problems occur through "omission" where something is set
incorrectly.
Common sense is usually enough to avoid those omissions, says Rich
Paleski, director of broadcast operations and engineering at CBS's
Philadelphia O&O, KYW.
The easiest thing is to simply match the station settings with those of
the network and "adhere to it and make sure that all the audio operators
understand and make sure that's the level we fix," he says.
Eric Small, founder and chief technology officer of Modulation Sciences,
concurs.
"The Dolby solution, which is very well thought through, is typical
Dolby," he says.
"The problem is the program originators, especially, won't play [and] it's
like a chain letter; if one person doesn't play, it all falls apart."
According to the experts, close attention to detail is also the key to
taking advantage of the standard's extra wide dynamic range — an ability
to reproduce sound with significant differences between the loudest and
quietest parts. It's a quality that audiophile prize.
"In the old days when people had compressor limiters and squashers and
stuff sitting on their transmitters, they compressed everything together
and that addressed everything including dynamic range and loudness. You
ended up with a one-size-fits-all mix" that sounded just fine on a
two-inch television speaker, Hunold says.
"We wanted somebody to be able to listen to a primetime program in their
home theater with all the dynamic range that a producer intended to go
into that program," he says.
"We didn't want to force everybody to mix to the same loudness level and
dynamic range; we wanted to give them the artistic flexibility to do
that," he says.
Lip sync is a problem that's been around ever since Hollywood introduced
the talkies, but it seems to have gotten worse in the shift to digital TV,
perhaps because the improved pictures make it easier to detect or more
difficult to ignore.
Unlike loudness, there is no standardized approach that will eliminate the
problem, the experts say.
"That's one of the most intractable issues related to digital television,"
says consulting engineer Merrill Weiss.
"When you start talking about lip sync, it not only covers the entire
production and distribution chain, but you're also into issues in
receivers, issues in the presentation devices, be they displays or audio
systems. It is a much more difficult problem to get your arms around,"
says Weiss.
Paleski does his part at the station level, seeing to it that everything
that comes in is in proper sync when it leaves.
"You want to make sure that every remote, satellite, microwave, fiber,
even off-the-Internet and computers ... all those remote sources arrive at
the routing switcher in perfect lip sync," he says.
"That's no different than the same practices we had in place with a
completely analog plant; it's just more difficult."
For tweaking the sync, Paleski says he uses the same gear he always has.
"As far as I know there aren't any really good tools for adjusting
high-definition lip sync," he says.
Even when delivered perfectly to the home, the audio can go out of sync in
the home when delay is introduced by a settop box or digital TV. The
problem is especially prevalent with cable.
"Set-top boxes introduce problems; the set itself introduces problems,"
says Small. "It's really a horror show. It's driving everybody crazy. The
problem is like a balloon in a box. You fix it here and it pops out
there."
It even pops out in places that don't directly affect the audience.
"Once you've delayed the audio in your plant [for sync], you can no longer
send that audio back out to the talent in the field on the normal
communications channel," says Paleski.
A station needs a "very good mix-minus IFB system" so that the reporter in
the field cannot hear himself, he says.
"If you're trying to talk and you hear your own voice come back to you a
tenth of a second later, it will really confuse you."
The ATSC, through several working groups, including the Specialist Group
on Receivers, is tackling the lip sync problem.
"But ATSC can only deal with certain parts of it; other organizations have
to deal with their parts of the problem," says Weiss.
It's not easy, he says. "It has sucked in most everyone who has tried to
deal with it."
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