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What is the proper aspect ratio adjustment of the IBM 5153 CGA monitor?

Unless you actually measure, it's hard to tell if a circle is ellipsoid until it gets pretty far out. The exception to that is if there's bad linearity.
 
That's almost as bad as the CD Red Book failing to adopt a uniform loudness standard, leading to the loudness war.

A uniform loudness standard has no place in the Compact Disc specification. Even if it had included one it would've just been ignored anyway. Also, the loudness war predates the CD by decades.
 
#1: Created an even-size border all around and

#2: Happened to make the circles drawn by the BASIC command (which used an easy mathematical shortcut for scaling) square.

From what I understood, the 5153 does only one of these at a time, not both.

I'd think that anyone who was anal about having their circles perfectly circular would mess with that to adjust the monitor to the CIRCLE command rather than vice-versa. (I know I did that myself even on my Tandy Color Computer, messing with the TV to try to make the circles round.)

The interesting question for me is: what did the person who wrote the CIRCLE command in BASIC use as a reference?
It clearly implements correction for a non-trivial pixel-aspect ratio (not just 1:1 or 2:1).
So what is the exact pixel-aspect ratio that the author used as a basis, and where did he get that number from?
Since BASIC was developed by MS/IBM during design of the 5150 PC, and BASIC was installed in the ROM of every PC, I think there would have been close contact between the software and hardware developers.

So in my opinion, BASIC is probably 'the absolute truth', regardless of how many programs do it differently.
Mind you, BASIC was written a few years before the 5153 was on the market.
 
From what I understood, the 5153 does only one of these at a time, not both.



The interesting question for me is: what did the person who wrote the CIRCLE command in BASIC use as a reference?
It clearly implements correction for a non-trivial pixel-aspect ratio (not just 1:1 or 2:1).
So what is the exact pixel-aspect ratio that the author used as a basis, and where did he get that number from?
Since BASIC was developed by MS/IBM during design of the 5150 PC, and BASIC was installed in the ROM of every PC, I think there would have been close contact between the software and hardware developers.

So in my opinion, BASIC is probably 'the absolute truth', regardless of how many programs do it differently.
Mind you, BASIC was written a few years before the 5153 was on the market.

Looks like spot on 5:6 to me:
basic_circle_aspect.png


(The smaller circle, radius parameter 180, is 300 pixels tall and 360 wide when I measure it in Paint Shop Pro).

Combined with the VGA evidence, it's pretty compelling that IBM meant for the DAR of the CGA to be 4:3 at least for composite. If they meant 5153 to have a different DAR then I'm mystified as to why they would have done so.
 
Looks like spot on 5:6 to me:
basic_circle_aspect.png

Also looks like DOSBox gets it completely wrong.

If they meant 5153 to have a different DAR then I'm mystified as to why they would have done so.

Yes, but I guess there are too many open ends for that.
From what I understand, the width of the screen is set at the factory, whereas the user gets control over the height of the screen.
We can't rule out the possibility that the people responsible for adjusting the width at the factory used a wrong setting because of some kind of miscommunication.
This would preclude the user from dialing in the proper DAR by varying the height of the screen.

It could also be that the circuit design is somewhat flawed, and it cannot generate the required DAR within safe working parameters, so the factory decided to use safe settings rather than accurate settings.
 
Also looks like DOSBox gets it completely wrong.

Yes, DOSBox (at least in the default configuration, without any fancy scalers/shaders) uses a 2:1 (1:1 for low-res) PAR, so it's way off what it should be. That doesn't matter for figuring what PAR is programmed into the software, though.

It could also be that the circuit design is somewhat flawed, and it cannot generate the required DAR within safe working parameters, so the factory decided to use safe settings rather than accurate settings.

It can generate a DAR of 4:3 or 48:35 or even wider just by adjusting the image height...
 
A uniform loudness standard has no place in the Compact Disc specification.

Movie theaters have had an industry standard audio playback level for over 40 years. U.S. TV stations are required by law to limit the volume of commercials (the "CALM Act"). European FM radio stations have a mandatory audio loudness level (ITU-R BS.1770). iTunes and YouTube both use ReplayGain-based uniform loudness levels. Similar efforts could and should have been done with CDs.

Even if it had included one it would've just been ignored anyway.

There are always some rogues who smash their levels on purpose, but most recording studio engineers know what a VU meter is and how to keep an eye on it during recording. With analog recording you always needed to reserve some "headroom" due to the physical limitations of the media. The problem is that during the transition to digital, no one could agree on how much headroom to reserve, if any, because physical limitations were no longer a problem. A uniform standard headroom level for digital audio would've gone a long way to preventing the drastically different audio playback levels of early CD releases, which led to artists and consumers complaining that some CDs were too quiet and that future releases needed to be louder, exacerbating the loudness war.

Also, the loudness war predates the CD by decades.

But as I mentioned above, the transition to digital meant that loudness was no longer bound by physical limitations. A record will cause the needle to jump out of the groove if you cut it too hot, and a loud LP will have less playback time per side than one cut at a more conservative level. A loud, overmodulated CD will still play fine and for the same amount of time as a quiet CD; it'll just sound bad.
 
65535 isn't a physical limitation?

If loudness standards are good, everything should be mostly the same colour and most things should taste pretty much the same too.

The limited dynamic range of CDs stifles creativity enough as it is.
 
The limited dynamic range of CDs stifles creativity enough as it is.

The dynamic range of 16-bit signed samples, as used on CDs, delivers far more dynamic range than any mainstream analog media that went before it (such as compact cassette, 8-track, vinyl, reel-to-reel etc).
So while it was a physical limitation, as stated, the amount of headroom to preserve was not commonly agreed on. There suddenly was so much more headroom than what went before it, and more importantly: there was basically no noise. Historically the point of loudness was to cram as much signal and quality into a very limited bandwidth, where signals that were too soft would disappear under the inherent noise of the media, and signals that were too loud, would clip/distort.
With CD, you suddenly had so much more room to play with, that it became quite arbitrary where you would draw the exact line. Aside from that, recording/mastering for digital media was still in its infancy, and it was not that easy to explore the limits of the media, so better safe than sorry.

I agree that 'loudness' should not be defined by the media (and standardization thereof) itself. No more than a specific level of 'brightness' or such should be defined for pictures/videos.
It is up to the artist to experiment with it, and find the levels that express his meaning best (not that this is actually what is happening in the loudness war, but that's another story).
 
A uniform standard headroom level for digital audio would've gone a long way to preventing the drastically different audio playback levels of early CD releases, which led to artists and consumers complaining that some CDs were too quiet and that future releases needed to be louder, exacerbating the loudness war.

If anything has exacerbated the loudness war it has been the incremental improvements in technology which have allowed the perceived volume of audio to be steadily increased year over year whilst keeping the distortion due to this processing from reaching a point where it became unacceptable to the masses. The desire to make recordings as loud as possible goes right back to the beginning of recording itself and this desire combined with the tools to actually achieve it are what have really driven the loudness war. I think the Compact Disc and digital audio in general have been made the scapegoat for this escalation. They didn't start the loudness war so why should they be expected to end it? And as I mentioned before any loudness standard included in the CD specification would've just been ignored anyway, since as you point out the playability of them is unaffected by exceeding any imposed volume limit.
 
There's also the possibility that Microsoft took a naïve approach to circle drawing - "hey, it's 320x200, we're rendering to a 4:3 display, that means we've got a PAR of 1:1.2" (or for 640x200, a PAR of 1:0.6) - and didn't consider the hardware, figuring that they'd #1 actually be rendering to a 4:3 display, and #2 the hardware would fill the display or would tell users to adjust V size appropriately.

I will say that this means that for BASIC code specifically, this means that correct adjustment is for 4:3. But, that doesn't mean that other code, even from the pre-5153 era, makes that particular assumption.
 
as I mentioned before any loudness standard included in the CD specification would've just been ignored anyway, since as you point out the playability of them is unaffected by exceeding any imposed volume limit.

But if an official loudness/headroom rule was written into the Red Book, then a CD would need to meet that standard in order to get the official "Compact Disc Digital Audio" logo stamped on it, and CD pressing plants could reserve the right to reject master discs that were not Red Book complaint. (Even without an official loudness standard, allegedly the Red Hot Chili Peppers had to sign a waiver to get their "Californication" album made, because it was so loud and distorted that it didn't meet the CD pressing plant's quality standards.)

Red Book compliance did become an issue in the 2000s when rootkit-virus-laden "copy protected" CDs and dual-sided CD/DVDs and CD/SACDs were pushed on the market -- none of which were Red Book compliant. These discs did not work in some CD players, resulting in the common disclaimer that "if you don't see the Compact Disc logo on the CD, then it's not guaranteed to play".
 
There's also the possibility that Microsoft took a naïve approach to circle drawing - "hey, it's 320x200, we're rendering to a 4:3 display, that means we've got a PAR of 1:1.2" (or for 640x200, a PAR of 1:0.6) - and didn't consider the hardware, figuring that they'd #1 actually be rendering to a 4:3 display, and #2 the hardware would fill the display or would tell users to adjust V size appropriately.

Well, with NTSC you *are* rendering to a 4:3 display, and most TVs won't allow the user to adjust H or V size (there's no point really, since it's all standardized. Set it up correctly at the factory and you're done).
You should be careful about deriving the PAR from only the resolution though, since especially these older systems had overscan areas (borders) of arbitrary width and size.
The use of these borders was mainly to align a particular grid of pixels to the colour clock (eg for CGA you have a resolution of 640 pixels horizontally, where every 4 adjacent pixels are used to generate a colour pattern).
So there's no reason why the horizontal border size should have any relation to the vertical border size, which means that the aspect ratio of your active display area (that which the resolution of 640x200 is based on) may not necessarily be the same as the total aspect ratio including horizontal and vertical overscan.
 
But if an official loudness/headroom rule was written into the Red Book, then a CD would need to meet that standard in order to get the official "Compact Disc Digital Audio" logo stamped on it, and CD pressing plants could reserve the right to reject master discs that were not Red Book complaint.

Sony defined a maximum allowable peak modulation with the Scarlet Book specification for SACD. A pressing plant will refuse an SACD master if out of any consecutive 28 samples more than 24 or less than 4 are “1”.
 
You should be careful about deriving the PAR from only the resolution though, since especially these older systems had overscan areas (borders) of arbitrary width and size.

Which is why I suggested that Microsoft's approach was naïve, NOT considering any of that, just saying "we're on a 4:3 display, we're outputting 320/640x200, that gives us how much we have to compensate".
 
Which is why I suggested that Microsoft's approach was naïve, NOT considering any of that, just saying "we're on a 4:3 display, we're outputting 320/640x200, that gives us how much we have to compensate".

Well, comparing a BASIC circle against an NTSC test card should answer that one :)
 
From what I understood, the 5153 does only one of these at a time, not both.

Doh, you're absolutely right. I looked again at the pictures in the OP, this time pulling them into an image editor and tracing out the rectangles created by the "Even all around" border and the "it looks too tall" border and the one that creates a 1.33 rectangle is the latter (which is the shape necessary for the 5:6 PAR to be correct.). Aspect ratio of the first one is even worse than 1.37, it's more like 1.43. I guess I was just sucked in by how nice it looks that way into thinking that's "correct". (And also I was under the impression that the rounder circle in the test pattern was being displayed with the tighter border, and, well, it looked pretty round to me. Maybe I just can't tell the difference between exactly right and 3% off, while the 15%-ish off 1:1 pixels is obvious.)

(It is notable that you can actually see a *little* bit of the inactive area in the upper left-hand corner of the tighter picture so maybe it should have the dial spun just a tiny bit more, making the "even all around" height more like 1.35-1.40-ish?)

Since BASIC was developed by MS/IBM during design of the 5150 PC, and BASIC was installed in the ROM of every PC, I think there would have been close contact between the software and hardware developers.

So in my opinion, BASIC is probably 'the absolute truth', regardless of how many programs do it differently.
Mind you, BASIC was written a few years before the 5153 was on the market.

Therefore... the 5153 is doing it wrong, or at least its bezel is the wrong shape for looking quite right when it actually doing it right, for the chosen-in-its-ROM PAR corrective ratio of 5:6. This could mean one of two things:

#1: IBM put a great deal of thought into it, decided that there was some compelling reason to make the 5153's aspect ratio different than the 5:6 they chose for BASIC, and then never really told anybody about it (and changed their mind again when they settled on the 5:6 ratio for displaying CGA doublescanned on VGA), or:

#2: When designing CGA IBM just put the number of pixels on the screen that would easily fit into 16k of memory and was an even multiple of their 8x8 character dimensions without really thinking about aspect ratios at all, and the 5:6 number was arrived at by Microsoft as an easy-to-compute approximation that looked fine on your average composite monitor. Later, when the 5153's plastics were being designed, the guy doing that job just made the hole a shape he thought looked good and called it a day. Since WYSIWYG wasn't really a "thing" back then nobody really cared that much that a CGA monitor adjusted to the letter of IBM's instructions (turn the knob until the black outside the borders goes away) made circles a wee bit egg shaped.

Still thinking #2 is substantially (overwhelmingly) more likely, but maybe there was some method to their madness of making that border a little squat for the PAR they settled on later. But I do think I've convinced myself that I ever have a 5150+5153 again I'll go for the stretched borders.
 
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Still thinking #2 is substantially (overwhelmingly) more likely, but maybe there was some method to their madness of making that border a little squat for the PAR they settled on later.

This is why I've been trying to track down people involved with the project. So far no luck, although I may have a few more people to try. My guess is that the guy responsible for the bezel dimensions messed up.
 
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