BOC-L Digest / Still in the Shadows

[Paul Mather]

On Tue, Jun 01, 2004 at 11:27:31AM +0200, Henderson Keith wrote:

=> As Paul alluded to...I believe the problem stems fundamentally from
=> the power difference between the US and Europe.  Not so much the voltage,
=> but rather the frequency.  Again, I'm speaking as a half-wit layperson,
=> but I've understood it to be the case that the scan rate of a PAL TV
=> matches in some way the 50 Hz frequency of the AC power.*  And likewise
=> 60 Hz for NTSC TVs.  And I think maybe even the total number of pixel
=> lines is different between PAL and NTSC TVs.

Yes, the number of scan lines differs too between NTSC and PAL: 525
lines for NTSC and 625 for PAL.  (This means you get greater spatial
resolution with PAL, but greater temporal resolution with NTSC due to
its higher field rate.  Given that film is shot at 24 fps, I'd take
the increased spatial resolution of PAL, personally...)  But, not only
that, the way the picture is encoded is different between the two
systems (leading some to say NTSC = "Never Twice the Same Colour" and
PAL = "Perfection At Last!":).  And, amongst other things, PAL
allocates more signal bandwidth to luminance than chrominance, which,
given the human eye is more sensitive to luminance than chrominance
differences, can yield perceptually better picture quality with PAL.

This different encoding of the analogue TV signal is a big reason why
you can't take analogue programme material on a common carrier like a
VHS tape and play it on the "other" format VCR.  Even though the tape
is physically the same, the way the picture is encoded is different
(and gibberish).  The same goes for DVDs.  If the DVD is modulating
the output analogue picture for a PAL TV, this will be "gibberish" to
the demodulation circuitry of a NTSC TV (and vice versa).  The
analogue output of the DVD player has to be speaking a compatible
"language" that the viewing TV understands.  (Some DVD players are
smart enough to be "multi-lingual" in this respect.)

=> *does this give a sharper picture, or eliminate 'resonance' patterns,
=> if the frequency matches?  I would *guess* this must be the case...

Not that I'm an expert, but I believe it does eliminate resonance
patterns (rolling hum bars) and gets rid of flicker problems with TV
cameras in the studio.

=> One question I have though...why don't they have *all* the features of
=> these chips activated for every model?  My guess is that it would be
=> harder for them to sell more expensive models, if the cheaper ones had
=> all the same features.  Which means the companies are basically making
=> their products "inferior" intentionally, so that you will pay more for
=> something that isn't really any more advanced, but just has been 'turned'
=> on.  OK, I'm a professional cynic when it comes to mega-corporations,
=> but what other answer is there?

The reason the cheaper models have all the functionality built in (but
selectively enabled) is because it's cheaper for, say, a Far-East DVD
player manufacturer to design and build a single unit they can
mass-produce out the wazoo and sell in all the world markets (Europe,
North America, Asia, etc.) than to have several specialised units that
can only be sold in a particular geographic area.  It's a matter of
economies of scale.

I believe there are several reasons they don't enable all the
features.  One reason is legal compliance.  For example, it may be
legal to disable macrovision in some countries but not others, so
obviously they'd have to enable macrovision in those countries that
had it as a legal requirement.  Big corporations may also be more
afraid of being sued if they make it easier for the end-user to defeat
said legal requirements, e.g., changing the region code, etc., so they
may "lock down" that kind of feature in hardware rather than making it
programmable (mutable) via software.

The other main reason would be to cut down on pilot error.  If it were
easy to, say, switch to PAL-encoded output, then there'd be lots more
people messing up their units and losing picture on their NTSC TVs by
playing around with the settings.  I believe that's why a lot of the
features are accessible only via these hidden "engineer" codes.
They're ostensibly "for experts only."

Cheers,

Paul.

e-mail: paul at gromit.dlib.vt.edu

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