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| A DV(L)-FAQ [e] |  |
DVL-Digest 536 - Postings:
Index
Audio dynamic range: 12-bit Audio mode
PLUGE
Audio dynamic range: 12-bit Audio mode - Perry Mitchell
Adam Wilt posted:
>> Most consumer camcorders are limited to the 12bit 32kHz option of the DV
> format. This would give a maximum dynamic range of 72 dB with no headroom.
Ah, but the 12-bit mode uses a perceptually-coded nonlinear compression; its
dynamic range is still pretty much 96 dB.<
Adam (or anybody else), do you have any more information on how this works?
I did a quick Internet search with no luck.
Does the DV format actually use a non linear A/D or is this a Sony only
feature as somebody else claimed? Does it have any similarity to our NICAM
system that we use in Europe for transmitting stereo on 12 bits?
PLUGE - "Perry"
John Jackman posted:
>Perry, help out, what PLUGE values do you use for PAL monitor
adjustment? The SMPTE color bars are of course set up for NTSC and 7.5
IRE. I apologize for my relative ineptitude with PAL. If Perry comes
up with a downloadable chart for PAL monitor adjustment, perhaps we'll
put it up with instructions at GreatDV.com.<
PLUGE (=Picture LineUp Generation Equipment?) was invented at the BBC (hence
the acronym, the Brits LOVE acronyms). It relies upon a local feed of video
with 'superblack' (below normal black) which cannot be transmitted or
recorded. The idea is that you have 3 levels of near black centred on true
black. You then adjust the monitor so that the upper chip can be seen but
not the lower one.
NTSC allows super black to be transmitted courtesy of the set-up of 7.5 IRE
as John mentions.
Personally I distrust any artificial device and prefer just to use a well
known picture, although a test chart with a grey scale makes this easier.
If you can 'underscan' the monitor then you can set the 'brightness' level
with a black picture to match the blanking part of the video at the edge of
the picture. It is always better to err on the slightly sat up rather than
sat down and thus black clipping.
One problem still around is that a lot of so called monitors don't have a
proper black level clamp and the picture will drift up to a grey when the
average picture level is low (but this will happen to the blanking as well,
so the underscan trick still works). Cheap monitors also suffer black level
drift with age and temperature even when they have the clamp. A good
quality broadcast grade monitor very rarely NEEDS adjustment, although
engineers tend to get a bit AR about doing it on a daily basis.
Going back to the original query about poor 'blacks' on a PAL camera in
Indonesia, consumer cameras tend to 'core' out all the noise and detail in
the shadow areas, which may have something to do with the poster's problems.
Modern prosumer CCD cameras have automatic Black Level alignment at switch
on and so are unlikely to give a wrong value.
A last note on acronyms, my BBC colleagues swore to me that there used to be
a 'Engineering Information External Inquiries Officer'!
Perry Mitchell
Video Facilities
http://www.perrybits.co.uk/
(diese posts stammen von der DV-L Mailingliste - THX to Adam Wilt and Perry Mitchell :-)
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