DARING DOLBY TACKLES TV LOUDNESS
Weíve 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 canít 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 Ďem up for maximum dramatic effect, the advent of digital delivery systems doesnít seem to have helped Ö actually the problem seems to be getting worse.
One of the interesting technical papers presented at last fallís 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 producersí 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 donít want that much when weíre 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 itís 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 canít 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 hasnít 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 systemÖ because in the HDTV world thereís little or no processing downstream to try to moderate levels even a little bit from source to source.† Iím left with the sinking feeling that this system belongs in the same world where the producers of music CDís donít 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 Iím selling Dolbyís cleverness short.† At the same time that theyíve been doing all this research and marketing at the broadcast end, theyíve 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 havenít 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 thatís the best we can hope forÖ