NTSC 4.43 and PAL-60

[d***@postmaster.co.uk]

Following the excellent insights I received to my previous question
about PAL-M, can I throw this one open as even more confusing...?

Any website will tell you that NTSC 4.43 and PAL-60 are 525-line ~60Hz
(actually 59.94Hz) formats with the colour subcarrier at 4.43MHz ("the
same as standard PAL, rather than ~3.58MHz as would be normal for
NTSC/525-lines").

Is this strictly true? Is the PAL-60 and NTSC 4.4.3 subcarrier
_exactly_ 4433618.75Hz (like PAL), or is it adjusted slightly to give a
certain number of cycles per line (plus a 1/525 offset?).

I ask, because I've tried PAL-60 with 4433618.75Hz, and it makes many
TVs flicker at the top. I wonder if the video encoder I'm using is
re-setting the phase every 8 fields (but the flicker looks faster than
that). I could try to disable that, or I could use a different
subcarrier frequency.

I will continue to experiment, but if anyone has any insight, I'd
really appreciate it.

Cheers,
David.

P.S. I have read one newsgroup posting that every manufacturer decided
on their own version of PAL-60, and quite a variety of versions exist.
I can't imagine the "plays NTSC on PAL TV" VCRs are intelligent enough
to line or field-lock the subcarrier, but some of the PAL-60 DVD
players may be.

[Roderick Stewart]

Post by d***@postmaster.co.uk
Any website will tell you that NTSC 4.43 and PAL-60 are 525-line ~60Hz
(actually 59.94Hz) formats with the colour subcarrier at 4.43MHz ("the
same as standard PAL, rather than ~3.58MHz as would be normal for
NTSC/525-lines").
Is this strictly true? Is the PAL-60 and NTSC 4.4.3 subcarrier
_exactly_ 4433618.75Hz (like PAL), or is it adjusted slightly to give a
certain number of cycles per line (plus a 1/525 offset?).

These non-standard formats are typically used for replay of VHS, where a
particular number of cycles per line would be meaningless because syncs
are not stabilised, and the nature of VHS removes any relationship between
subcarrier and sync. The aim is to simplify circuitry by using most of the
same chroma decoding circuits, including the crystal, so nominally it must
be the standard PAL frequency.

Rod.

[d***@postmaster.co.uk]

Post by Roderick Stewart

Post by d***@postmaster.co.uk
Any website will tell you that NTSC 4.43 and PAL-60 are 525-line ~60Hz
(actually 59.94Hz) formats with the colour subcarrier at 4.43MHz ("the
same as standard PAL, rather than ~3.58MHz as would be normal for
NTSC/525-lines").
Is this strictly true? Is the PAL-60 and NTSC 4.4.3 subcarrier
_exactly_ 4433618.75Hz (like PAL), or is it adjusted slightly to give a
certain number of cycles per line (plus a 1/525 offset?).

These non-standard formats are typically used for replay of VHS, where a
particular number of cycles per line would be meaningless because syncs
are not stabilised, and the nature of VHS removes any relationship between
subcarrier and sync. The aim is to simplify circuitry by using most of the
same chroma decoding circuits, including the crystal, so nominally it must
be the standard PAL frequency.

Thanks Rod.

I agree, and I doubt the VHS machines are doing anything clever - quite
the opposite.

However, some DVD players will output PAL-60, and some will output NTSC
4.43.

As digital devices with complex digital>analogue video encoder chips
inside, things will be tied down to the last pixel.

I'm just trying to find out what the most common "standard" is in this
case, because the one I have tried is not working as well as expected.

Cheers,
David.

[Roderick Stewart]

Post by d***@postmaster.co.uk
I agree, and I doubt the VHS machines are doing anything clever - quite
the opposite.
However, some DVD players will output PAL-60, and some will output NTSC
4.43.
As digital devices with complex digital>analogue video encoder chips
inside, things will be tied down to the last pixel.

They probably could be made to much greater precision with today's
electroncs, but originaly PAL-60 and NTSC443 were simply bodges to enable
playback of a "wrong" standard tape on a VHS machine. The heterodyne
correction system in the VHS electronics would stabilise the subcarrier
frequency, but without a timebase corrector it wasn't posssible to
stabilise sync frequency, so there was no relationship between them.
(Subcarrier decoding circuitry is much more fussy than timebase circuitry
about frequency stability, which is why the subcarrier had to be
stabilised while it was possible to get away without bothering to do
anything to line syncs).

Subcarrier frequencies of *broadcast* signals were very carefully chosen
but couldn't be simultaneously optimal for two different line standards,
so even with the use of modern circuitry with the required stability, it
wouldn't be possible for any meaningful subcarrier to line sync
relationship to exist on the "wrong" line standard. These non-standard
"standards" really were bodges, and in their day it was remarkable that it
was possible to play back foreign tapes at all. Thankfully it no longer
matters with disk recorders producing RGB or YUV components.

Rod.

[Alan Pemberton]

Post by Roderick Stewart
They probably could be made to much greater precision with today's
electroncs, but originaly PAL-60 and NTSC443 were simply bodges to enable
playback of a "wrong" standard tape on a VHS machine. The heterodyne
correction system in the VHS electronics would stabilise the subcarrier
frequency, but without a timebase corrector it wasn't posssible to
stabilise sync frequency, so there was no relationship between them.
(Subcarrier decoding circuitry is much more fussy than timebase circuitry
about frequency stability, which is why the subcarrier had to be
stabilised while it was possible to get away without bothering to do
anything to line syncs).

Even domestic digital equipment these days is stable enough for you to
record and play back a PAL signal generated by a digital satellite
receiver on a digital video recorder. Just tell the DVR that the
composite video is really the luminance component of s-video and it will
treat the subcarrier as hf luminance detail, inserting its own burst on
the output so a PAL decoder with work with it.

Of course the MPEG coding messes up all that hf somewhat but with a
10Mb/s recording it works reasonably well. There's a 1 in 4 chance of
the reinserted burst being in the same quadrant as the original, but a
little jiggery with the pause control soon finds the correct one.

However, using a VHS tape as the source demonstrates Roderick's point.
The luminance is nicely TBCed, but the clever way VHS stabilises the
subcarrier is then lost and the result is unlocked colour on playback of
the digital recording.

I've tried the above experiment using a 525/60 NTSC signal, but it
doesn't work for some reason. The reinserted burst is completely the
wrong phase (always out of range of the hue control on the decoder). I
used a Strong satellite receiver and Panasonc DVR feeding a UK Sony Wega
PAL/NTSC receiver (which decodes the NTSC direct from the Strong ok, as
well as NTSC generated normally by the Panny).

[Barney Wol]

I also tried to find out about this "standard" last year, without much
success. The people at Sony who devised this seem to have long-since
retired. As Roderick says, it presumably is to allow the same PAL
crystal to be used in the decoder. Professional kit checked last year
(several years old by then) just had free-running oscillators at about
nominal 625-PAL frequency.

TTFN, Peter

[d***@postmaster.co.uk]

Thanks to Peter and Rod for their replies.

I've solved my problem, and will pass on what I've found in case it
helps anyone else.

With a free running colour subcarrier, I'm sure any frequency within a
broad range will work (though different frequencies will give different
dot patterns - some maybe more subjectively objectionable that others,
though all look pretty horrible!)

However, it seems the hardware I'm using is set up to reset the
subcarrier phase every 4 frames (PAL), and presumably every 2 frames
(NTSC).

Using the exact PAL-I subcarrier frequency in a 525-line 59.94Hz system
means that after 4 frames the phase is _not_ back to where it started
(as it would be in a 625-line 50Hz system). In fact you get 591740.316
cycles of subcarrier in 4 525-line frames. So there's a jump of 0.3
cycles when the phase is reset which upsets the TVs, causing a nasty
visible flashing at the top of the screen.

Forcing it to have exactly 591740 cycles of subcarrier in 4 frames
yields a subcarrier frequency of...
4 433 616.38 MHz
...and cures the flashing, because there's no jump in phase when the
phase is re-set. That figure is even within ITU tolerances for all 4.43
PAL systems apart from PAL-I which has a +/-1Hz tolerance (though few
CE devices meet this in practice).

To prove that the phase reset really the problem, I changed the
subcarrier frequency to give 591740.5 cycles in 4 frames. This gives
the maximum possible 0.5 cycle jump at the phase re-set point, and did
indeed cause even nastier flashing at the top of the TV screen. Some
TVs even started to lose colour entirely for part of the frame.

PAL-60 has really nasty dot crawl from a clean digital source. Enabling
a PAL notch filter in the luma channel (within the video encoder chip)
helps dramatically, and reducing the chroma bandwidth helps a little
more. However, the Panasonic DVD player I have with a PAL-60 output
does neither of these things.

Finally, I am convinced that PAL-60 is quite pointless in this context.
It was compatible with fewer UK TVs overall (that I checked) than
standard NTSC, and RGB SCART gives a vastly superior picture without
the PAL/NTSC problems.

Still, all good fun.

Cheers,
David.

[Alan Pemberton]

Post by d***@postmaster.co.uk
I ask, because I've tried PAL-60 with 4433618.75Hz, and it makes many
TVs flicker at the top.

Presumably these non-standard PAL formats do not (or cannot) employ the
correct 8-field Bruch blanking sequence which was introduced to
eliminate the colour flashing at the top of the screen by making sure
the first line containing burst was of the same phase on each field.

[Roderick Stewart]

In article

Post by Alan Pemberton

Post by d***@postmaster.co.uk
I ask, because I've tried PAL-60 with 4433618.75Hz, and it makes many
TVs flicker at the top.

Presumably these non-standard PAL formats do not (or cannot) employ the
correct 8-field Bruch blanking sequence which was introduced to
eliminate the colour flashing at the top of the screen by making sure
the first line containing burst was of the same phase on each field.

I thnk the bursts are treated like any other subcarrier on the signal,
i.e. separated by filtering and heterodyne converted to a lower frequency
for recording, then converted back to one of the broadcast frequencies by
the same method. As far as I know, there is no new burst blanking, so it
will have whatever burst sequence the original had, though of course any
phase relationships betweeen burst and syncs is completely lost. Something
that originated as kosher PAL would presumably still have the Bruch
sequence, but without its original reason, or any advantage in having it
in the new output signal. If anything, it probably *causes* a bit of
colour flashing at the top of the picture, rather than preventing it, but
VHS has so much flashing and flickering anyway it's hard to tell.

I used to wonder why nobody thought it a disadvantage that the Bruch
blanking sequence resulted in only one field in every four (Field 3)
having a colour burst for every picture line, but it seems to work.

Rod.

[Mike Hastings]

There is a standard called PAL-M which is used in South America. Uses 525
lines with a subcarrier of 3.575611 MHz. There used to be a 625 line NTSC
standard that used a subcarrier of 4.429 MHz this is now obsolete and was
only ever used for experimentation before PAL was developed. PAL N is 625
line PAL with a subcarrier of 3.582056 MHz.

Post by d***@postmaster.co.uk
Following the excellent insights I received to my previous question
about PAL-M, can I throw this one open as even more confusing...?
Any website will tell you that NTSC 4.43 and PAL-60 are 525-line ~60Hz
(actually 59.94Hz) formats with the colour subcarrier at 4.43MHz ("the
same as standard PAL, rather than ~3.58MHz as would be normal for
NTSC/525-lines").
Is this strictly true? Is the PAL-60 and NTSC 4.4.3 subcarrier
_exactly_ 4433618.75Hz (like PAL), or is it adjusted slightly to give a
certain number of cycles per line (plus a 1/525 offset?).
I ask, because I've tried PAL-60 with 4433618.75Hz, and it makes many
TVs flicker at the top. I wonder if the video encoder I'm using is
re-setting the phase every 8 fields (but the flicker looks faster than
that). I could try to disable that, or I could use a different
subcarrier frequency.
I will continue to experiment, but if anyone has any insight, I'd
really appreciate it.
Cheers,
David.
P.S. I have read one newsgroup posting that every manufacturer decided
on their own version of PAL-60, and quite a variety of versions exist.
I can't imagine the "plays NTSC on PAL TV" VCRs are intelligent enough
to line or field-lock the subcarrier, but some of the PAL-60 DVD
players may be.

[Tony Quinn]

Post by Mike Hastings
There is a standard called PAL-M which is used in South America. Uses 525
lines with a subcarrier of 3.575611 MHz. There used to be a 625 line NTSC
standard that used a subcarrier of 4.429 MHz

Better known as fNat

Post by Mike Hastings
this is now obsolete and was
only ever used for experimentation before PAL was developed.

[charles]

Post by Tony Quinn

Post by Mike Hastings
There is a standard called PAL-M which is used in South America. Uses 525
lines with a subcarrier of 3.575611 MHz. There used to be a 625 line NTSC
standard that used a subcarrier of 4.429 MHz

Better known as fNat

Post by Mike Hastings
this is now obsolete and was only ever used for experimentation before
PAL was developed.

Not quite. The BBC continued to promote NTSC, and carried on with tests,
as it was a developed and working system, long after PAL was developed.

[Derek ^]

On Sat, 03 Jun 2006 20:34:29 +0100, charles

Post by charles

Post by Mike Hastings
this is now obsolete and was only ever used for experimentation before
PAL was developed.

Not quite. The BBC continued to promote NTSC, and carried on with tests,
as it was a developed and working system, long after PAL was developed.

Perhaps it's no coincidence then that the BBC had already ordered the
equipment for a nationwide colour genlock system, Natlock" on the
assumption that a 625 line NTSC system would be chosen.

When 625 line PAL was chosen egg on face resulted and "Pal to Natlock"
converters were rapidly designed and installed all over the show.

DG

[Roderick Stewart]

Post by Derek ^
Perhaps it's no coincidence then that the BBC had already ordered the
equipment for a nationwide colour genlock system, Natlock" on the
assumption that a 625 line NTSC system would be chosen.
When 625 line PAL was chosen egg on face resulted and "Pal to Natlock"
converters were rapidly designed and installed all over the show.

Quite right. When I learnt all about this at Evesham, this was the
explanation for all the master oscillators in pulse generators being
4.4296875MHz instead of something a bit more sensible like 5MHz or 10MHz,
or even PAL subcarrier frequency itself. I wonder how much it cost to
design and build the frequency converters, compared with what it would
have cost to replace the oscillators and dividers with the right ones?

Rod.