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Re: Video Converter
<andrew.s.kochera@gmail.com> wrote:
> On Wednesday, July 18, 2012 11:40:54 AM UTC-5, andrew.s...@gmail.com wrote:
>> On Monday, July 16, 2012 1:02:29 PM UTC-5, andrew.s...@gmail.com wrote:
>>
>>> I have tried two composite to vga converters.
>>
>>>
>>
>>> One is a generic that successfully converts to monochrome, but loses
>>> the color signal. It's hard to describe here... if I get my act
>>> together, I will post some photos next weekend of how it looks and
>>> operates. It does successfully give color on an Atari 2600 modern reproduction.
>>
>>>
>>
>>> The other is the MyGica Gamebox HD. I returned one and got another,
>>> but no improvement. Tried all the settings -- no deal. On NTSC
>>> setting the screen freezes, on other settings (what the heck) you get
>>> crazy shadowing and green bands across the screen. It also did not
>>> work on a modern reproduction of the old Atari 2600. It did work for a TV box though.
>>
>>>
>>
>>> I have a third variety on order... I'm crazy determined.
>>
>>
>>
>>
>>
>> Most recent order cancelled by seller. He tested the unit for me before
>> shipping, and found it didn't work. Vexing. The search continues. In
>> the meantime, I saw this (link came from an old usenet post):
>>
>>
>>
>> http://user.xmission.com/~egan/vgatests/
>>
>>
>>
>> ... but haven't found this box for sale anywhere...
>
> Okay, I finally posted my experience with 3 inexpensive converters here:
>
> http://youtu.be/GM9pXpqovpk
>
> I welcome any comments.
In your video you suggest that an LCD TV would provide better results
through its composite port.
I think you will find at least as much variability in results as with
converter boxes.
The reason for the dichotomy between color response and sharp monochrome is
that the Apple II video signal has a very wide bandwidth luminance signal
(up to 25MHz)--far beyond the NTSC standard of about 4MHz--and the color
signal is, in fact, an artifact of switching the luminance signal at the
color subcarrier frequency of 3.58MHz with a phase corresponding to the
desired hue and an average luminance corresponding to the desired
brightness.
Converters expecting standard NTSC will usually filter the luminance
signal, eliminating frequencies (and therefore sharp edges) above 4MHz.
Some apparently don't recognize the presence of color and instead do their
best to represent the luminance with bandwidth in excess of 4MHz.
The AppleColor Composite monitors are unique in switching between filtered
color rendition (and blurry, color-fringed text) for graphics modes, and
higher bandwidth monochrome for text modes.
What we need in a VGA converter is something akin to these two modes,
automatically switched by the presence or absence of the color burst
signal. Given the market size, I expect this will only happen if an Apple
II enthusiast does it.
-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon