------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut
http://www.muellersatomics.com/
(I'm not sure that I like the thought of having movies sound exactly like every top-40 FM radio station, personally, but I'm sure it has a use somewhere.)
------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut
http://www.muellersatomics.com/
------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut
http://www.muellersatomics.com/
------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut
http://www.muellersatomics.com/
Just for reference, 99% of the new video monitors/TVs have a setting that boosts the dialog and/or center channel so it is understandable by using some sorta compression. Also, while limiting/compression is lightly used in FM it is the STANDARD in AM broadcasting. Many theaters do not have the audio amplifier watts (and speakers) to reproduce high-level sound without clipping.... you know, when those pesky "clip" LEDs on the amps light up on the loud passages. I hope that will change in the future. (The systems I have designed have 27 to 35 kW of audio power which seems like an over-kill, but they do not distort and clip and are kick-ass clean)
Anyway Greg, a lot can be said for compression. The old tube-type compressors like the Gates "Level Devil" go for buco bucks and are used in many soundtracks.
While I agree it is desirable to reproduce both the image and the sound as originally intended, there has to be a compromise based on the available venue and media...both in film and video...but the goal is the best it can be.
>>> Phil
David
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.
------------------
Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.
oscar@smartdev.com
------------------
Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.
oscar@smartdev.com
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.
I don't know the cost of the Smart unit (as described, it is really being used as a hard threshold limiter rather than a compressor), but buying the three studio type compressor/limiterss would probably cost the same or more than the Smart unit, although more than likely they will would give you a lot more control. You can fine tune the threshold level, the compression ratio above threshold, the attach and release times, etc. Problem is, unless you are pretty much the only one in the booth who is allowed to touch anything, this kind of unit in your audio chain could REALLY mess stuff up if some dumbass decided to "adjust" it. The Smart, I imagine, is a simpler IN or Out affair with minimum controls exposed to booth monkeys.
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
------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut
http://www.muellersatomics.com/
"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.
I am not sure I am adequately explaining the action, but having heard compressors that do as you describe, I can assure you that this unit does not have the problem you have mentioned.
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.
------------------
Evans A Criswell
Huntsville-Decatur Movie Theatre Information Site
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?
--jhawk
------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut
http://www.muellersatomics.com/
quote:
"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."
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.
How are the acoustics of the room? It isn't too "live" is it?
------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut
http://www.muellersatomics.com/
------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut
http://www.muellersatomics.com/
"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."
Ganging of compressor channels in a stereo system is standard practice throughout all facets of the audio industry for one very, very good reason. Almost all stereo sound tracks (BTW "stereo" means multi-channel, not just two-channel) make use of what is termed a "sound field". A sound field means that each channel does not only contain it's own signal, but also varying proportions of signals which are also present in adjacent channels. This creates the "stereo effect" where you are convinced that sounds are not only coming from each individual speaker but also from the area in between.
Now if a multi-channel limiter/compressor is placed in the signal path without ganging the channels together, the sound field floats back and forth sideways between speakers, whenever the compression threshold is exceeded more in any one channel than any other. A typical example is a two-channel stereo system in which a vocalist is panned mid-way between left and right (as in probably 90% of all popular music). Whenever one channel compresses more than the other, the vocal shifts sideways towards the channel with the least compression. The result is that the vocal floats back and forth sideways and depending on the severity of the compression, the effect can be serously annoying. Ganging the compresors together ensures that the sound field remains positionally stable, regardless of how unbalanced the dynamics of the soundtrack may be.
A properly designed and setup limiter/compressor will not produce "ducking" as Frank calls it. This is a characteristic of cheap AGC circuits that are not used in modern professional audio systems. In a 6-channel system, a loud explosion in one channel which causes the limiter/compressor to compress will indeed cause compression of all the other channels if they are ganged, however a signal which is loud enough to cause significant compression in only one channel will also be loud enough to mask the compression effects in the other channels. (Psycho-acoustic masking is the basic principle upon which the various Dolby processes are based, from Dolby A through to Dolby Digital).
Furthermore, in a properly designed and setup multi-channel limiter/compressor, the compression caused by that explosion will follow the envelope of the explosion closely, in fact as closely as attack and decay times will allow whilst keeping distorion inaudible. This results in an inverse envelop or "hole" in the other channels that closely matches the envelop of the explosion and this actually aids the masking process. Anyone who doubts this effect only need to listen to any Dolby soundtrack where acoustic masking is constantly busy at work hiding all manner of horrors from your tender ears.
If ganging was not employed, the soundfield would shift away from the channel with the explosion and then suck back again as the explosion subsides. (Recall that classic footage of the nuclear blast as it first blows the house in one direction and then in the other).
Of course if you go out and buy a whole bunch of studio compressor/limiters as Frank suggests, then you are bound to end up with horrendous results, unless you are an audio professional and know how to set up and optimise the many variable parameters these devices offer. So the Smart device has already been setup and optimised for you and provides a useful degree of dynamic range compression with minimal audible artefacts.
BTW I am not advocating (or otherwise) the use of compression in cinemas.
------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
You are partially right about ganging compression channels -- depending on the program material, the parameter settings, especially the way the compressor attacks and releases the signal, you certainly can create very audible, undesirable artifacts, specifically the distortion of the stereo soundstage. But these can be just as bad with ganged compression. With regard to film sound, I was talking about threshold limiting rather than linear compression. Soft threshold limiting, correctly and minimally set can be applied to non-ganged channels without causing noticeable artifacts, again, depending on the program material.
In recording sessions I have used this type of limiting for the sole purpose of preventing tape saturation. Done judiciously, it is very effective and practically transparent with no audible shift in the stereo soundfield. In fact, I used it on an album that I engineered, RUBBER NICKELS (which won the Phoenix Award in 1975 for Best Quadraphonic Recording of an Original Musical). ANY kind of compression, ganged or non-ganged, would be most apparent on matrixed (4-2-4) material as was this album. The trick is to use your ears. Compression of any kind is always a dubious, although sometimes necessary, distortion of the original signal; a good engineer uses his ears as the ultimate tool to determine what parameters and what mode of compression works best and least intrusive for any particular sound source.
Personally, for film sound, I would not recommend ANY tampering with the soundtrack -- whatever signal processing needs to be done on the tracts should have already been done in the mix. But if there HAS to be additionally processing because of shortcomings in the playback system, as you point out and as I agreed, the Smart single button would be the best bet.
Frank
"With regard to film sound, I was talking about threshold limiting rather than linear compression"
So was I.
"Soft threshold limiting, correctly and minimally set can be applied to non-ganged channels without causing noticeable artifacts, again, depending on the program material".
It would have to be VERY minimally set. Maybe the album you mixed was very mono heavy, or had exceptionally even dynamics, or maybe you were just lucky, who knows, but you cannot raise a single specific instance and apply it as a generalisation. The fact is you cannot change the laws of physics, and reducing gain in one channel MUST shift the position of the soundstage. If the reduction is subtle then the shift is subtle, but there is a shift none the less.
"The trick is to use your ears".
Using your ears is not a trick, just common sense.
"Compression of any kind is always a dubious, although sometimes necessary, distortion of the original signal;"
If compression is dubious distortion then so is equalisation, so do we remove all the equalisers and dynamics from mixing consoles?
"a good engineer uses his ears as the ultimate tool to determine what parameters and what mode of compression works best and least intrusive for any particular sound source".
Couldn't agree more. But good sound engineers are not normally employed in cinemas.
"Personally, for film sound, I would not recommend ANY tampering with the soundtrack --"
Frank I would agree with you, except when your patrons start walking out of the theatre en-masse and ask for a refund because the loud parts of the movie are deafening, you do have to start to question the director's judgement. There are no doubt times and circumstances when the "judicial" use of compression in a cinema may be warranted, particularly when your continued viability depends on it. Under those circumstances it is important to chose a system that is discrete and as free from artefacts as possible. To simply say "don't do anything because that is what the director intended" is like saying the director also intended to put my cinema out of business because no normal human being can stand the loud parts of this film.
Somewhere along the line you may have to decide if playing a film the way the director intended is more important than going broke. And if you do have to modify the performance, then do it correctly and discretely with a product properly designed for the purpose. That is all I am saying.
------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
Rolling stock ads (on video) -- loud.
MovieTunes to accompany slides -- loud.
Trailers -- loud. Some distortion in the trailer for Road to Perdition.
"Blade Runner" snipe (original version) -- loud with the dynamic range all but taken away.
Feature -- sounded perfect. Turns out the movie is heavy on dialogue (Sunshine State).
This was in a 281-seat hall with 200+ taking in a Fourth of July matinee.
that would be funnyCheers!
Rory!
------------------
Greg Mueller
Amateur Astronomer, Machinist, Filmnut http://www.muellersatomics.com/
With the afterburners on, I never had a single problem. Not one. I never noticed a sound rolloff of any kind, and my ears never bled.
I give kudos to smart on this particular product.
Dave
I am very pleased that you are having good results with the Afterburner. You said, "There is no sign of volume riding or other objectionable byproducts, in fact, it is quite transparent in operation." This has been the general experience with this product from many customers.
As you have noted, yours is in line between the DTS and the CP. This is the original intention for the Afterburner, to be used on digital soundtracks. It is now more commonly placed between the CP and amps so that ALL material, whether digital or optical (especially loud trailers) can pass through it.
Thanks also to Dave and Gordon for the very nice comments.
------------------
Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.
oscar@smartdev.com
Since this is a topic on limiting and compressing, i will get back on topic.
www.behringer.com
When feeding audio to a radio transmitter, there is a volume level "ceiling", over which you either can't (in the case of AM) or shouldn't (for FM) exceed. The problem with an improved drive-in sound system is that now you have a much greater dynamic range to your sound. Things like heavy bass content and hot passages (like explosions) can either cause your transmitters to distort OR force a single-channel compressor/limiter punch huge holes in your sound. The dynamics (the difference between the loudest and quietest sounds your system will pass) may also be too wide for car radio listening... causing your customers to turn their radios up when things are quiet, then back down when "the dinosaur roars"! FM transmission poses an additional challenge, in that high frequencies are designed to pass through the system at higher levels than mid & low frequencies. Many theatres address these issues by using single band compressor/limiters. These are certainly much better than nothing. However, a single-band unit may add its own audible artifacts to the sound you're sending to your customers. Consider that the operation of a single band processor is very much like manually adjusting your volume. Imagine that you have your hand on the master volume control knob in your booth. You've turned the volume up because the actors are whispering at each other. All of a sudden, here come the hot bass beats of a rap song. Since you absolutely can not allow your volume to go above a certain level you would have to (quickly) turn your volume control down far enough to let the bass pass at or below the 100% level. Unfortunately, you just turned everything else down as well. This is basically what a single-band compressor is... a single automatic volume control. They can be effective, but can also punch big enough holes in your sound that your customers CAN hear!
Most modern radio stations have moved away from single band processors for much the same reasons described above. In their place has emerged the Multiband Processor. These devices are something like taking a multiband equalizer and putting a compressor on each band. If a hot bass beat goes through one of these systems, the channel that handles low frequencies reduces the bass while allowing the mid and upper bands to continue at their own preset levels. In effect, instead of one automatic volume control over the whole audio spectrum (bass to treble), these multiband processors chop the spectrum into a number of channels (6). Each channel is "in charge" of a portion of the audio band. It's something like automatic bass and treble controls on your stereo, except in this case we have 6 controls instead of two. It is a bit technical to set up, but is extremely stable & can be left alone, once you have it sounding the way you like.
------------------ http://www.autoramadrivein.com
come on out to the drive-in and spend a night out with the stars"