[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Apple video bandwidth question



vladitx wrote:
On Aug 29, 12:55 am, Alex Freed <alex_n...@mirrow.com> wrote:

BTW the 80 col mode uses 14 MHz pixel clock and so it doesn't look good
on a color TV but looks OK on a monochrome monitor with a bandwidth of
about 6 MHz or so.

Monochrome monitors' bandwidth must be about 8 MHz, or you wouldn't be
seeing some patterns like $5 and $A in Lo-Res (7 MHz).

Not quite. "Bandwidth" is not a "brick wall" filter. Think analog.
If we have a 14 MHz pixel clock and a $55 pattern it's a 7 MHz square wave that can be represented as a sum of the 7 MHz fundamental sine wave plus odd harmonics. Suppose we have a 7 MHz "bandwidth". Then by definition 7 MHz is a "corner" frequency that will be passed at -3 dB compared to low frequencies. If the bandwidth is say 5 MHz, if will have a level below that but definitely visible. Just blurry.

-Alex.