The Polyphonic adds extra PCM channels so the 000 matches the 030.
So the X68030 had more PCM channels (ADPCM?) than the original X68000?
Since the late '70s actually (see Mitchell Waite's Computer Graphics Primer, a copy is available online.)
Ed, is this a joke? Macs hadn't been developed yet in the '70s.
that 24khz signal has always mystified me. What is its vertical resolution? In PC monitor terms what would be the equivalent resolution?
PCs never used 24KHz, the closest thing would be the EGA 640x350 mode which is 21KHz. On the X68 24KHz mode is 424 lines or 848 interlaced.
The X68000 monitor in 15 and 31khz as well as CRT televisions have a "native" vertical resolution of ~480 raster lines which was something that stems from the rasterization process. So far as I understand for 31khz signals the electron beam makes ~480 progressive horizontal swipes across the screen to rasterize a full frame. For 15khz it makes ~240 swipes for 240p, and makes ~480 swipes for a full 480i frame but broken up into two passes, called fields, which each rasterize either the ~240 odd or even raster lines. That is why 480i looks so flickery.
Anyway, I do not care about what resolution the display can "resolve" as that is a subjective matter. what is for certain is how many horizontal swipes the electron gun makes during the raterization proces. That is what I call the native resolution.
To better understand what's going on you need to forget about the number of raster lines for a minute and consider how the horizontal and vertical frequencies are related. It's a bit complicated to explain because of differences between the official specs and the real-world usage, but here goes.
What the NTSC spec says: 525 lines * ~30 frames = 15750hz
This is called "480i."
What comes out of classic game consoles (and some computers): 262 lines * 60frames
This is called "240p."
There is enough TIME for 262/525i lines but part of that time is used for the vertical retrace so nothing can be displayed. Despite the 240/480 designations, generally the number of lines visible on the screen is not even that many, hence why a lot of systems didn't bother to generate more than 224 lines.
Now for PAL. Spec says: 625 lines * ~25 frames = 15625hz
This called "576i."
What comes out of classic systems in PAL region: 312 lines * 50frames
This is called "288p."
Again, 312/625i but that includes vertical retrace and overscan.
Notice how NTSC and PAL are both 15KHz but have different resolutions? One trades framerate for number of lines. Some TVs/monitors could display either resolution out of the box.
X68000 31KHz modes are pretty close to the 640x480x60hz VGA mode (BTW, 640x400x70hz is also a standard 31KHz mode) but with slightly lower vertical frequency and a few more displayed lines.
I don't own an X68 but if the behavior of the emulator is to be believed, when using 15KHz modes instead of 31KHz it goes back to a standard 60Hz NTSC timing and no longer displays the full 256 or 512 lines.
On the plus side my own Towns has regular video output so nothing special is needed to get a picture. Good to know that X68000 and NEC PC are close. FM Towns is the odd man out then.
