‘dynamic contrast’

Just went away for a couple of days, and the house we were renting had a typical flat-screen LCD TV. For a while I found it difficult to watch, and then I realised that it still had the default menu setting of ‘dynamic contrast’. I believe that this ‘feature’ is included to increase the perceived dynamic range of a TV, and it allows the manufacturer to quote a really impressive figure like 15000:1, when in fact the brightness ratio between the screen’s deepest black and whitest white is only 100 or some such. By dimming the backlight in response to the ratio of dark to light in the scene, the greyness of the black is disguised. The upshot is that the screen looks bright and vivid on many scenes (when the bright parts mask the greyness of the blacks), but in dimly-lit scenes where the grey blacks would be obvious, the picture dims down even more, with a time constant of some fraction of a second. It’s horrible! It has nothing to do with revealing more information, and everything to do with trying to make an average piece of hardware look slightly better cosmetically. Once I had disabled this in the TV’s menu settings, it was an amazing relief, and the non-black blacks really weren’t a problem.

Effectively this is a variety of dynamic range manipulation, and it is analogous to dynamic range compression or manipulation in audio. A ‘spongy’ system, constantly shifting, is fatiguing for the ears and brain even if it is not noticed consciously. If it can be turned off, the relief is palpable. Dynamic range compression can be an intentional recording effect, a necessary evil such as in vinyl mastering, or a by-product of hardware limitations such as the ‘turbo lag’ of bass reflex, power compression, passive crossover non-linearities and so on. You may not realise it is there until it is turned off.


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