Re: [Discuss-gnuradio] Comb Filter (OT tangent)

[Cory Papenfuss]

On Wed, 5 Jan 2005, Dave Dodge wrote:
> I don't know much about the signal-level details, but some things that
> immediately come to mind:
>
>  - since (if I understand this correctly) you're talking about using an
>    RGB framebuffer and the RGB signal lines to generate YPrPb signals,
>    are the RGB voltage ranges going to be what you need?

	I believe the video signal levels are the same 0.7v.  I doubt that 
the RGB could do "blacker-than-black" except with the sync pulse, but it's 
not really necessary for regular video.

>  - it would most likely work for progressive scan.  Do you also need
>    the interlaced component formats?

	Both will work... I've already cooked up modelines to generate 
NTSC-spec frequencies interlaced.  I've even done sync-on-green and used 
that for a monochrome signal on a TV's Y-component and it worked fine. 
Pretty phsycho colors if you connect the other two to R and B... :)

> There are some simple circuit designs floating around for DIY
> RGB->component converters, so you could probably figure out
> from those whether the signal itself will present any problems.
>
>  http://www.epanorama.net/links/videocircuits.html#rgbyuv
	Thanks... I've already seen that and built one.  I've even built 
one that will generate composite/s-vid.  It works, but it'd be nice to not 
even have to build hardware for it.  This is of particular value to people 
on the mythtv list I subscribe to looking for cheap, high-quality tvout of 
their HTPC.  It's silly to spend money on a good video card that will to 
XVideo well ($50-100), and then spend more good money ($100) on a 
transcoder.  The XVideo is necessary to do YUV->RGB, and the transcoder 
does RGB->YCrCb.  If the vid card is just three fast DACs, why bother 
converting and unconverting for a single-use settop system such as mythtv?

-Cory

*************************************************************************
* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
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