[George Be]

Here's a little head-scratcher I'm trying to deal with:


The video output from my cable box is "composite" video only (i.e. one RCA jack for video, and two for audio). It would be ideal if the cable company offered an S-video version of the cable box; however, they don't, and I do not expect them to offer one any time soon.


My Replay 4320 has an S-video input, as well as a composite-video (RCA) input. It also has a Y/Pr/Pb output, which I am routing directly to my Sony 40XBR700 (monster 40" Sony TV, which supposedly has the best 3-D comb filter Sony makes.)


I want to split the signal from the cable box three ways:

(1) Directly to my Kenwood receiver, for playback of DMX music (i.e. video quality not important)

(2) To my Replay, for recording.

(3) To a VHS recorder, which does not have an S-video input. (i.e. S-video doesn't matter, and composite is all that's needed.)


I have figured out that I need to use a buffer/distribution box in order to split the signal three ways without degradation. Extron makes such a box, but they make it in either a composite-video or S-video version.


Extron also makes a "YCS Transcoder" box, which will convert composite video to S-video. It does this by means of its own 3-D comb filter, much like a TV set has. I have no way to assess the quality of their comb filter versus Sony's, but I think it's safe to assume that they are very similar in quality; therefore, I wouldn't expect to see any difference in picture quality between running the cable box's composite output directly to the Sony (i.e. using the Sony's comb filter) and running the cable box's output through the Extron YCS Transcoder and thence to the Sony's S-video input (i.e. using the Extron's comb filter instead of the Sony's.)


Have I got it right so far?


Now, the bigger question: would I see any improvement in the quality of the Replay recordings by feeding it with the "transcoded" S-video signal? This would seem to depend on the Replay's internal recording mechanism: if it combines chroma and luma information before it records (essentially converting S-video BACK to composite-video), then I wouldn't expect to see any improvement in recording quality. However, if it processes and records the chroma and luma separately, then I might see some improvement in recording quality. The Replay does provide both S-video outputs and the aforementioned Y/Pr/Pb outputs; however, I don't know if the "native" output from the Replay is Y/Pr/Pb (which they would "downconvert" to S-video and composite), or if the "native" output is composite (which they would "upconvert" to S-video and Y/Pr/Pb, in the same manner as the Extron box does.)


Presumably, if I put S-video quality INTO the Replay, I would expect to get S-video quality OUT. However, this may not be exactly the case. Additionally, I have to consider that the origin of the S-video signal in this case is in fact a composite source; therefore, the quality of the S-video source signal (from the Extron box) will be dependant on the quality of the composite-video, which may already have color smearing, etc.


Anybody know anything about this?


George

 

[KenL]

Quote:

Originally posted by George Be ...Anybody know anything about this?

Well I know something about it and you are onto something here. Unfortunately it's hard to predict how all these will interact, without actually trying them each way, and on a variety of channels.


I'd say if you are going to that much trouble to get the best signal why not try to get a better cable box (somehow) or change companies (or move )? I've only plugged in the replay composite in/outs summarily... never really tested much but it looks worse. I'd be inclined to convert the cable box to S before mpegging then feed it all out from the Replay box as needed? Keep in mind any mpegging introduces a quality all it's own that can behave unlike you may be used to with top notch comb filters.


The Y/Pr/Pb outputs are always up-converted (surprisingly well in my experience) from whatever you feed into the Replay.

 

[lonetreejim]

IMHO component or s-video signals generated from analog channels on any cable box would be little better than composite video. Once the chrominance and luminance have been combined you're beat... the "damage" is done and then the mod/demod adds even more degradation.


That being said, Radio Shack has a 4-Way A/V Distribution Amplifier (Cat.#: 15-1172) for $40 that you could use to split the composite output of the cable box to your 3 target devices.


Jim

 

[George Be]

Quote:

Originally posted by lonetreejim IMHO component or s-video signals generated from analog channels on any cable box would be little better than component video.

I'm assuming you meant to say "composite" here? (It's OK, I do that all the time myself!)


And does that imply that digital channels from the same cable box might garner some benefit from a conversion from composite to S-video?


Quote:

Once the chrominance and luminance have been combined you're beat... the "damage" is done and then the mod/demod adds even more degradation.

That's pretty much what I thought at first, but then I thought about "scalers" (line quadruplers); they pretty much create "resolution" where before there was none (yes, I know, they can only duplicate existing bits of data, but it DOES look better!) For all I know, maybe a similar thing can be accomplished with composite-to-S-video.


Quote:

That being said, Radio Shack has a 4-Way A/V Distribution Amplifier (Cat.#: 15-1172) for $40 that you could use to split the composite output of the cable box to your 3 target devices.

Unfortunately, I already purchased and tried one of those Radio Shack Distrib boxes. A WORD OF WARNING: the Radio Shack box did some very strange things with my setup. The off-air channels on my cable system are sometimes marginal; but where the channel would ordinarily show a tiny flicker or blip, the Radio Shack box somehow stretched this out and messed up the sync on the picture for several frames!! When I took the RS box out, the problem went away. I'm assuming the Extron box will not exhibit this behavior (for $250, it BETTER not!!!)


Although the RS box has both S-video and RCA inputs and outputs, I find it hard to believe that it does the same type or quality of "upconversion" (composite to S-video) that the Extron does.


George

 

[lonetreejim]

I agree that some heavy duty signal processing may improve the quality of the picture (cablecos do it all the time). I was more speaking about typical consumer products. I keep forgetting about the level of expertise that is exhibited by the readers of this forum!


I do think digital channels from a cable box would benefit from an S-Video output because, in many cases, those channels have never been composite therefore should be more salvageable.


Thanks for the input on the RS A/V box. I've considered one in the past and now I think I'll pass.


Jim