Below the threshold nothing happens. So soft and subtle material is not altered. Above the threshold, there is a 2 to 1 gain reduction in dB. If the signal increases 10 dB, for example, then the output increases only 5 dB. For a 20 dB input change, the output changes only 10 dB. So if the threshold was set to 85 dB spl, then a signal that would normally hit 105 dB spl only goes to 95 dB spl.

The effect is without any noticeable artifacts, at least none that I can hear, and certainly none that have been reported to me. It is so smooth in its operation that you don't really notice it is doing anything until you turn it off and suddenly things are louder.

Originally it was introduced to address the problem of digital mixes gone wild with dynamic range that the vast majority of cinemas simply could not handle. We took a lot of heat for daring to mess with someone's artistic discretion, but let's face it, most cinemas simply could not handle the extreme dynamic range in some mixes. Sound leakage between screens and painful levels were not acceptable. Blown drivers and amps were not acceptable. The inability to hear dialog because the overall level had to be turned down was not acceptable. This product filled a need at the time.

Since then, mixes are a little less "enthusiastic", and the problem is not as severe although it still does exist. Systems have been improved with more powerful amps and more capable speakers.

Then the problem of loud trailers began to get a lot of attention. So the latest ploy with the Afterburner is to put it just in front of the amps so that it catches everything including optical and digital sound. Loud trailers are tamed down, too-loud digital or optical mixes are softened a bit, and the overall result is good.

It has a DISABLE switch on the front panel to turn off compression if you don't need it for a particular film, and then easily enable it when you do need it.

The product serves a definite need, and I understand that not everyone would want to use it, but those who have used it would not do without it.

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Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.

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Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.

Then there's the question of ganging the channels (most pro units are designed to be ganged and have a loopthru option -- that wouldn't be a problem). BUT, ganging presents its own set of very audible artifacts -- namely, you don;t necessarily want ALL the channels to duck just because one has reached the threshold. That is a bad thing even in a two channel stereo system; I contend it could REALLY sound disturbing in a 6 channel system -- get a loud explosion in the left channel and the rest of the fronts channel and the surrounds drop 10 dB. for a second. That kind of pumping will be quite noticeable. To avoid this, using multiple stereo units would have the advantage that you could gang whichever channels you choose -- for example, the system could be configured so that this kind of "everybody duck" artifact is minimized -- if one stereo unit is set up to limit L&R independent of the other channels and another for the Surrounds and a third for the center channel and subs (this one can be decoupled so that the stereo channels are running independently), you would get better sonic results. I don't imagine the Smart unit will be that flexible.

I use a Valley People compressor, limiter and expander unit in the booth, not to limit dynamic range, but it is set as an expander for mag prints on the surround channel to quiet any hiss and edge noise (caused by uneven mag stripes) when no sound is present -- it pretty much replaces the old relay that originally would turn the surrounds on when the 12k trigger tone was present. The VP is set as a gentle expander and it is much more effective. The same unit can be set as a compressor or a limiter, whatever the user needs.

Exactly my problem.
The incredible amount of dynamic range offered by DTS, Dolby Digital, even SR are wonderful. But if I get the subtle whispers audible, then when a crescendo in the music takes place, (or that type of enunciation) its actually painful, the spl is so great. So I figure just a smidge of compression would allow me to bring up the whispers and bring down the explosions and be able to hear the intent of the mixer, without my ears bleeding. Maybe I can get the dial up to 7 and be able to enjoy the artistic intent of the soundtrack!
Thanks for explaining your gizmo Oscar, I think I'm gonna try one.
I'll let y'all know how it works out

"BUT, ganging presents its own set of very audible artifacts -- namely, you don;t necessarily want ALL the channels to duck just because one has reached the threshold. That is a bad thing even in a two channel stereo system; I contend it could REALLY sound disturbing in a 6 channel system -- get a loud explosion in the left channel and the rest of the fronts channel and the surrounds drop 10 dB. for a second. That kind of pumping will be quite noticeable."

Frank, I am no expert on all the different types of compressors/limiters out there, and I know there are many. Our unit does not work exactly like you are describing. The control path is what I would term a feedforward design. The control signal is NOT being derived from the output and fed back. The control is being derived from the input signal. Therefore, there is no sudden 10 db drop as you mentioned in your example. There is really not any audible pumping at all. What happens is that as any channel or combination of channels increases above the threshold level, the level at the outputs simply does not rise at the same rate as the input level. There is no ducking involved (assuming I am thinking of ducking as you are), just a lesser increase in level as compared to the input.

Case 1: Listening to music in an automobile: When I first tried listening to a CD player or tapes that I'd made on a high-end tape deck through my car's audio system, I found that quiet sections were inaudible if the louder portions were played at a reasonable volume. I found that when I heard these same songs on the car's FM radio, this problem did not occur.

Case 2: Listening to music in my office at low volume: The same thing occurs. Quiet portions of songs get lost with only the loud portions audible.

Case 3: Playing movies with large dynamic range for people like my parents: If I set the volume so that dialogue is clear and understandable, the special effects and music bother them and my mother will ask "Can you run it down?" Then guess what, when the effects or music is over, they can't hear the dialogue. I have to constantly adjust the volume up and down during the entire movie.

Dynamic range compression can be very useful in situations like the above, so I can see that it would be very useful in theatres in cases where there was a lot of ambient noise or when a theatre is crowded with more than average noise from customers.

Of course, the budget for booth monitors is more limited; does anyone have experience deploying compression in this sort of budget-limitted less-than-top-quality environment?

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"But if I get the subtle whispers audible, then when a crescendo in the music takes place, (or that type of enunciation) its actually painful, the spl is so great."

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I still have a feeling your high frequency rolloff is not tapered to the room quite right. This should not be a problem. If you experienced it on one or maybe two films, then ok, but if you are experiencing it on every film, your system needs tuning.