DARING DOLBY TACKLES TV LOUDNESS
We’ve intermittently used
this space in the past to discuss the problem of raging audio levels over
broadcast television. Whether the
problem is caused by a global conspiracy of producers of super-loud
commercials, a cabal of broadcast engineers that just can’t get all the
machines to output the same level, or a bunch of moviemakers that want to blast
the crap out of your woofers during the shoot ‘em up for maximum dramatic
effect, the advent of digital delivery systems doesn’t seem to have helped …
actually the problem seems to be getting worse.
One of the interesting
technical papers presented at last fall’s WABE convention was from Dolby
Digital Labs, discussing some of their efforts to rein in HDTV audio levels
using metadata embedded in the digital bitstream. It became apparent that Dolby has done a lot
of research and thinking about audio levels, and how to control them without
destroying the program producers’ efforts to achieve a specific dramatic
effect. The Dolby approach centres on
the viewer adjusting her audio gain to get a comfortable level for spoken word
programming in her environment. In
essence, by so doing, she is calibrating the receiver level for what is to
follow, and audio processing upstream will be set to tell the receiver how many
dB above or below that reference level the current audio
level should be.
Well, I say hats off, as far
as that goes, but there are still a couple of gaping related loopholes. First, while we can all appreciate the 100dB
or so of dynamic range afforded by the digital streams, mostly we don’t want
that much when we’re watching TV in our living room, particularly if we share
walls with neighbours. While getting
that reference level set by using conversations is clever and intuitive, and
according to Dolby it’s also quite accurate (generally within a couple of dB),
reference level is only half of the problem.
Their idea is that the audience can tolerate levels x number of dB above that
reference for explosions and shotguns, etc.
I can’t help thinking that the individual viewer might want to have some
say in the value of x.
But the greater problem is
that the metadata setting is in the hands of the program producer, and as far
as I can see, this is on the honour system, which frankly hasn’t served us very
well so far. If an (unscrupulous)
commercial producer wants to crank the level for his audience, he now has a new
handy tool with which to do that (the metadata control), with consequences
probably greater than with the old analog system… because in the HDTV world
there’s little or no processing downstream to try to moderate levels even a
little bit from source to source. I’m
left with the sinking feeling that this system belongs in the same world where
the producers of music CD’s don’t clip, compress, equalize and distort their CD
masters to achieve maximum loudness.
This imaginary world sounds like a good place to live, but it bears
little resemblance to where we are right now.
But maybe I’m selling
Dolby’s cleverness short. At the same
time that they’ve been doing all this research and marketing at the broadcast
end, they’ve launched Dolby Volume at the set
manufacturers. Dolby Volume is a new
proprietary DSP chipset to be installed in television receivers. It will do to audio levels what Dolby
ProLogic did to surround sound:
it will analyze the audio (analog or digital), and adjust levels to
prevent those commercials from sending us diving for the remote, while making
quieter passages audible. This is a
brand new product, so of course we haven’t heard it yet, but the reviews have
been encouraging. The demonstration that
was reviewed allowed for differences between TV channels of 30dB or so, yet
there was no jarring transition between them.
And, depending on how clever the chips are, it may preserve the
illusion of dynamic range. Maybe
that’s the best we can hope for…