Dictionary additions and dialog normalization

Rod, mentioned in the post below, has also suggested I include ‘dialog normalization’ in the Dictionary of Home Entertainment. Good point, and it was something I shouldn’t have overlooked, so here it is. Naturally this required some other additions, so in went metadata and dynamic range control. Plus I’ve added slightly to Dolby Digital, and corrected a mistake (I had said it was originally developed for film, but of course it was originally developed for digital TV, but became famous through film).

My treatments of these subjects in the dictionary are necessarily short, but there’s some interesting Webbed stuff. In particular, this Secrets of Home Theater and High Fidelity piece is excellent while this SMR Home Theatre A/V Magazine piece also provides useful background, and raises the interesting issue of calibration.

If you read formal treatments of setting up home theatre systems, you will find that they always ask you set the channel levels using the test tone for an indicated 75dB on your SPL meter. This is something I never do. I usually use 70dB or 80dB. Why? Because the good old Radio Shack meter has +6dB on the extreme right of the scale, so if you set the dial to 70 and try to get everything at 75, the meter needle will spend a lot of its time pushed against the stop on the right hand side. I suppose it can take it, but I believe in respecting equipment (I have two of these meters, the first one I purchased some time in the 1970s and it still works fine!)

Also, because I don’t think that calibration to an absolute volume level is especially useful. For me the important thing is to have the channels calibrated properly relative to each other. What level I actually watch a movie on depends upon my mood, the circumstances and the equipment I’m using. If properly calibrated to an absolute level then, as the SMR piece makes clear, program peaks may reach 105dB. Actually, that’s 105dB per channel! Let’s do some arithmetic. If I’m reviewing some DynAudio speakers (which, as a rule, I simply love for their sound), I have to take into account their lower than average sensitivity. They typically come in around 85dBSPL (1 metre, 2.83 volts average pink noise bandwidth limited to 500-2,000Hz). Let’s say that the receiver I’m using can deliver 100 watts per channel. At my listening position of 2.7 metres from the front speakers, the volume for one watt (which is what 2.83 volts into eight ohms is) is actually less than 85dB. One hundred watts is 20dB more than one watt. So there’s no way that this system can reach the 105dB peak. Absolute calibration is not a good idea in such cases.

Or I might be watching a movie with gear that has plenty of headroom (say some Klipsch speakers with a sensitivity of 96dB driven by a Sony digital receiver producing 170 watts per channel), and the guy next door is mowing the lawn. So I turn it up louder than the absolute calibration level. Or I might be watching late at night and I need to have it down (two of my daughters came rushing out to my backyard office the other night from their rooms on the other side of the house, worried about the shooting and screaming they heard — but it was just me playing the start of Runaway Jury).

The SMR piece also mentions some calibration problems with some test DVDs. I did a quick check on some of mine. I agree with the piece that all calibration tracks really ought to be set for the official calibration level of -31dBFS (0dB dialog normalization). Here’s what I found:

  • Video Essentials: -27dBFS (-4dB)
  • The Ultimate DVD Platinum: -31dBFS (0dB)
  • DVD Spectacular (both program and test tones): -31dBFS (0dB)
  • Pearl Harbor (Region 4) THX Optimizer and program: -31dBFS (0dB)
  • Alien (from the new Quadrilogy set) (Region 4) THX Optimizer: -31dBFS (0dB), but -27dBFS (-4dB) for the movie
  • Manhunter (R1) THX Optimode and program: -27dBFS (-4dB)

The question is, though, whether those -27dBFS settings have any practical effect. Because everything is relative. If the test tones on Video Essentials, for example, were recorded at a 4dB higher level than those on the Ultimate DVD Platinum, then what difference does it make? The decoder should just turn them down 4dB. That’s something I’ll have to check when I have a spare moment.

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