15kHz on LCD monitors

15kHz monitors

Most PC monitors made for VGA and later graphics adapters have a horizontal sync of 31.5kHz or higher, but most home computers including the Commodore Amiga line, as well as CGA and EGA for PC, have a hsync of about 15kHz as standard (PAL or NTSC). Many ‘recent’ monitors therefore do not properly show an image from those computers.

The Amiga has different video modes, and for example my A1200 can also output 29.29kHz hsync @ 58Hz vsync (Multiscan:Productivity) over a VGA cable (with a fairly common “DB-23” to DE-15 D-SUB converter).

Here’s my experience with monitors and the signals they take. Note that even within the same model numbers, the electronics can be different so there’s no guarantee that you’ll have the same experience with another monitor of the same brand and model.

Dell P2416D

A very nice WQHD (2560×1440) monitor with Displayport, HDMI and VGA. No ‘tv-like’ inputs, so I was surprised that mine does work with 15kHz signals. Not perfect (upscaling artefacts, interlacing looks wrong) but very usable. I suppose a real ‘flicker-fixer’ would be better, but glad it works.

On A1200:

Multiscan:Productivity (656×480, 58Hz, 29.29kHz) works fine, looks a bit ‘anti-aliased’ probably due to the upscaling.

PAL:High Res (640×256, 50Hz, 15.60kHz) and Low Res (320×256) works great, obvious sharpening artefacts (adjustable).

PAL:Super-High Res (1280×256, 50Hz, 15.60kHz) same as the other PAL resolutions, except that the aspect ratio is a bit weird. Workable on 16:9 setting.

Interlace (‘laced’) modes flicker, and are almost unreadable. Not recommended for use.