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Monster Media 1994 #1
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PAL_NTSC.TXT
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1994-03-06
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______________________________________________________________________________
What are PAL and NTSC modes, anyway?
There are different standards of broadcasting video signals around the
world. The two most common are known as PAL and NTSC. Pal is largely used in
Europe, while NTSC remains a North American standard. PAL typically gets
better vertical resolution, but at a sacrifice of only updating the screen
display once every fifty seconds, as opposed to the NTSC standard, which
refreshes once every sixty seconds. What does all that mean? This is going
to get a bit technical, so bare with me for a moment.
Inside every television set and monitor is what is called a Cathode tube.
The inside-front portion of this tube -- the part that faces you -- is coated
with tiny phosphors. These phosphors light up when struck by any form of
light; you may remember as a child having "glow-in-the-dark" toys of one sort
or another. These glowed because they absorbed the light energy and emitted
them much more slowly. This effect was visible when the lights were turned
out. Your television and monitor screens are similar in this respect, except
that the coating of phosphors on said screens is quite thin, and the energy
from a typical light is barely enough to energize the phosphors enough to
absorb. However if you look close enough in the dark you can see that it does
emit a small amount of light even though the set isn't on.
What the Cathode tube does is emit rays that strike directly at the
phosphors, which in turn light up and emits the image that you see on your
screen. These rays are emitted in a left-to-right, top-to-bottom fashion. The
left-to-right movement of the cathode rays is known collectively as a raster
line. In NTSC mode, this raster line moves from the top to the bottom of your
screen sixty times each second, and then returns to the top again to start the
process over. In PAL mode, this raster line goes from the top to the bottom
of your screen only once every fifty seconds, and therefore is slower. This
is how we percieve the effect of movement in images that display on our
televisions. Each time the raster line makes its trip from top to bottom, the
screen is "refreshed", and a new image is displayed on top (provided there is
a new image ready -- movies typically play at 30 frames per second, so in NTSC
mode, the raster line will spend half its time refreshing duplicate images).
This goes on so long as the set is on.
______________________________________________________________________________
So what do monitors and raster lines have to do with MODs?
This, also, is complicated.
For years, it has been typical programming practise to allow the computer
to take care of small routines and sub-programs itself while the main part of
the program does other things. This is what is known as Interrupt
programming; every computer has what are called Interrupt vectors. These
vectors normally remain empty, but programmers can put the address (the
location in memory) of their sub-program or routine there, and from that point
on, until the program tells it to stop, the computer will then take care of
running that routine so that whole program itself can go on about doing other
more important things. The most common interrupt vector that programmers use
is called a "Vertical Blank Interrupt", or VBI for short. This is where it
ties in with televisions.
A Vertical Blank is that small bit of time in which it takes the raster
line, explained above, to get from the bottom of the screen back up to the top
again. During this time, the computer doesn't have to worry about refreshing
the screen, and therefore has a bit of free time to take care of other things.
If there is an interrupt present in the VBI vector, the computer will then
execute that routine. In NTSC mode, it is able to execute that routine sixty
times each second. In PAL mode, it can only execute that routine fifty times
each second. Now this is where it ties in with MODs.
The MODule standard was originally created on the Commodore Amiga machine
in Europe with the advent of a program called Noisetracker. It gave the Amiga
the ability to create four track musical scores using standard PCM (Pulse Code
Modulation) sound samples. The programmer, like most programmers, used the
VBI to execute some of the smaller routines in his program while his program
did other things, such as wait for more input from the mouse or keyboard, or
whathaveyou. One of these routines was the routine to actually play the
musical score. Since, when being played, the musical score is constantly in
need of attention, it only made sense to put the routine that gives it that
attention (which included playing the sound samples and doing any effects that
were added to them, incrimenting the position it is currently at in the music
score, and so on) in the VBI so that the computer can take care of it. Since
then all programmers have put their play routine in the VBI since that's the
most logical and convenient place to put it.
Which brings us to why broadcast modes affect MODs, which you may or may
not have deduced by now. If you are in NTSC mode, the routine to play the
musical score, since it is in the VBI, will be executed sixty times each
second. In PAL mode, it will only be executed fifty times each second. And
that's the clincher: If you play a MOD that was originally designed to be
played in PAL mode on an NTSC machine, it is going to play too fast;
similarily, if you play a MOD that was originally designed in NTSC mode on a
PAL machine, it will play too slow.
On Commodore Amiga and Atari STE machines, the ability to switch between
real PAL and NTSC modes is simply a matter of loading a tiny program that will
do it. This is because said machines have these different broadcast signal
modes built in. The difference is that NTSC machines CAN synch down to PAL
mode (or 50Hz), but PAL machines can't synch up to NTSC mode (60Hz). This is
why most MODs done in North American on NTSC machines are still done in PAL
mode; it is the lowest common denominator between the two different standards.
IBM PC Machines, however, do not have the ability to switch, and more
importantly, most modern IBM PC monitors and video cards operate at a higher
video frequency -- usually 72Hz, as opposed to the 60Hz NTSC and 50Hz PAL
standards. The 72Hz refresh rate is still NTSC standard, however. You can,
however, buy Dual-, Tri- and Multi-synch monitors that have the ability to
synch down to these lower modes. But most people don't have these, so many
MOD players offer the ability to alter the speed of the MOD while it is being
played. Dual MOD Player, for example, allows you to alter the tempo and
"extended tempo" (ProTracker) settings to allow you to fine tune the speed of
the MOD you are listening to. This can be used to effectively simulate a PAL
mode. A good rule of thumb is that playing a PAL-based MOD in NTSC mode is
generally one speed slower than it is being played at. (That, however, is not
exact, so it may be necessary again to do more fine tuning with the "extended
tempo" settings of DMP -- this is especially important for MODs which use
whole sampled drum riffs in their songs, which may sound far too fast or slow
unless you edit the speed of the MOD itself)
So there you have it. That's the difference between PAL and NTSC, and why it
affects MOD playing. It's needlessly complicated, but now, at the very least,
you know about it. Have fun!
______________________________________________________________________________
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