How film measures up.
A modern photographic emulsion is extraordinarily efficient at capturing light, with each grain of silver bromide only requiring three or four single photons to expose it. (Think of a photon as an 'atom' of light.) There's a simple relationship between film speed and grain. Bigger grains (crystals of silver bromide) capture more photons of light, so they become 'exposed' more easily. Thus grainy film is fast film. Over photography's lifetime, the main struggle has been to make the grains more efficient at catching photons, giving more speed for smaller grains. At first, cinematography wasn't possible, as photographs needed exposures of many minutes. Only when exposures came down to 1/50th of a second--around the 1880s--could moving images be recorded. By present standards though, film was still very slow--less than 10 ASA to begin with.
By the mid 1970s, when video cameras first appeared, colour negative film stock was a modest 100ASA. There was no choice of emulsion type. Last year, Kodak released the first of its Vision 2 series of emulsions, rated at 500EI (the old ASA scale), with grain generally agreed to be finer than older, slower stocks. Three more stocks have just been announced. The new chemistry in Vision 2, in practice, doubles the effect of each photon, and there is the potential for it to double again. This can add up to ever-faster film emulsions, or it can lead to ever-finer-grained images. It's quite realistic now to rate film at 1000 EI and expect an excellent image, even on a large cinema screen.
The human eye is capable of responding to brightness over a range of about a thousand billion to one. That's not all at once, and it allows for things like dark adaptation, when the eye adjusts to dark or bright environments. Even so, we can see a range of fifteen stops--that's about 30,000 to one--at any given time. Film doesn't quite measure up to this range (hence the need for lighting, even with the most sensitive stocks); but it is possible to record about eleven stops using the latest emulsions. The older ones managed about ten stops. Traditional analogue video cameras by contrast could respond to a range of about 100 to one (or six stops), with high-end digital cameras now achieving up to eight stops.
The BBC's early television service using the Baird system had thirty lines; it was replaced by the world's first 'high resolution' system using 405 lines in 1936. When High Definition TV was first mooted, around 1979, the various research groups all set their target at around 1100-1200 TV lines. This was double the existing TV standard, and thought to be sufficient to match film for image quality.
But by the time the film Digital Intermediate came into the research arena, the Cineon developers (Kodak and Philips) announced that film couldn't be properly reproduced with less than 4000 pixels per line (which is around 3000 TV lines).
Every frame of 35mm film captures the equivalent of about twelve million pixels of image information, nearly fifty Megabytes of digital data. It's hard to record electronic data that quickly. But because the information is stored on the film right where it is captured, there is no limit to the frame rate except the mechanical one of pulling the film through the camera; so film cameras can run at up to 300 fps for extremely slow-action shots: bullets, bees in flight, or car crashes, for example. By comparison, at present, some digital systems are able to record equivalent detail in real time; but there is simply too much data coming in too fast to be able to record at anything approaching the high speeds reachable by film cameras. Meanwhile, Imagica is developing a film scanner capable of 10K pixel resolution--the digital world is running to catch up with film!
Quieter is louder
Audiences know how loudly people speak: close up in a room, shouting across a car park, or in bed; and film dialogue has traditionally been mixed at this realistic level. We have less experience of the sound of an angry Orc, or of a planet exploding--there is no 'realistic' level. Newer digital sound systems allow effects to be played louder than before, simply because there's no reason for them not to be. At the same time, in keeping with the way it is played at concerts, music is louder than before.
Fortunately, people have a remarkable ability to separate out different sounds coming from different places, and digital sound systems are good at reproducing the source direction of sounds. A good mixer can take advantage of this, putting very loud effects around the edges without drowning out the dialogue in the centre.
Mixing theatres are calibrated so that a standard Dolby reference 'pink noise'--a carefully selected and standardized mix of noise at all frequencies--is reproduced at a sound level of 85db. In turn, cinemas are set up so that the correct sound level is heard when the fader on the Dolby unit is set to 'seven'. In earlier times, that was an end to the matter; no one complained that films were 'too loud'.
Now it's different. Not only do digital soundtracks permit louder effects, but trailers and commercials are often compressed (bringing the average sound level up, grabbing attention), and so audiences frequently complain about the excessive loudness. Faced with unhappy customers, the cinema manager has an obvious recourse: turn it down! Many cinemas now set their fader down to 'five' (six decibels less) for commercials. Few of them bring the level right back to normal for the main feature.
Turning it down may solve the overall problem of 'loud' tracks. But in reducing the overall level, the dialogue is pushed down to below its normal level. Now the audience can't understand what's being said!
Worse, some producers complain that their commercials or trailers now fail to grab the audience's attention. In response, some mixers mix their soundtracks louder (sometimes under protest) to restore the previous levels. This of course is the start of a slippery slope, as cinemas and mixing rooms chase each other down the scale.
In recent years a modified loudness metering system has been developed and used to control Dolby licensed mixes. It uses a weighted frequency range, and measures not just peak levels, but a scaled measure of sound energy over a period of time. Despite this, the perception remains that commercials and trailers are too loud, and many cinemas continue to play them at a lower level.
The moral? Ensure that you choose to mix in a facility that has its monitor levels calibrated and set correctly. THX certification guarantees not just the monitor levels, but strictly standardized frequency response and reverberation characteristics, as well as minimal background noise. And remember--if you want the audience's attention, mix the sound quietly so they have to listen.
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|Title Annotation:||Technical Section|
|Date:||Sep 22, 2004|
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