Question about Digital Cable Signal Processing (Cablevision) (1 Viewer)

[Doug_B]

Considering digital cable service from Cablevision. I currently have their analog service with a basic cable box - RF In and Out. Their digital service naturally requires a new box to decode the digital channels.

As I am unfamiliar with digital TV, I'd like to know whether it is a given that when digital signals are decoded by such a box, the chrominance and luminance are already separated, so that when the signal leaves the cable box via an S-Video or better output, there was no comb filtering function required by the cable box.

As of now, I do not know what Cablevision's digital cable box provides in terms of outputs, but I would guess at least S-Video and composite. My main concern is that I have only composite and component runs to my projector, as I didn't think I would have a source that didn't require comb filtering that also didn't have component outputs. My proj does a good job comb filtering my analog cable via composite, but I'd rather not have any comb filtering done on this digital source if the signal stays separated after the cable box decodes it.

Update: The cablevision dig. service web site has user guides for 2 different boxes (Sony and apparently Scientific Atlantic). Both have S-Video and composite video outputs.

Thanks.

Doug

 

[Joseph Dubin]

Doug, I just became a cablevision subscriber this month and have the digital package.

The Scientific America box has three video outputs that can be used at the same time - a S-Video jack and rca jack to play through monitors plus the standard F-type connection through channel 3. It also has a digital (RCA-type) jack for 5.1 and l-r jacks for surround sound. Audio through channel 3 is mono.

The picture through S-video is near DVD quality. The other video I have output to line 1 of my VCR which gives better quality recording than through channel 3.

While most stations are digital 2.0 a few channels (Starz, HBO, Fox Movie Channel, etc.) periodically broadcast in 5.1. Most local stations, even if surround, are analog. If you plan to use a vcr I suggest getting a pair of y-cables so the l-r channels can go directly to your receiver and vcr (thus not needing the receiver to be on for the audio signal).

Cable being cable, there are problems at times but overall I'm very happy with the digital quality of the picture and audio. It is definately worth the investment.

Let me know how it works out,

Joe

 

[JohnnyG]

As I am unfamiliar with digital TV, I'd like to know whether it is a given that when digital signals are decoded by such a box, the chrominance and luminance are already separated, so that when the signal leaves the cable box via an S-Video or better output, there was no comb filtering function required by the cable box.

Yes, but the problem is, if the chroma and luma are EVER combined, they can never be fully and completely seperated again. The vast majority of channels will have had this happen at some point in the production/delivery chain. As a result, if your TV has a top notch comb filter, feeding it a composite signal can sometimes provide superior results than using the s-video connection.

 

[Doug_B]

Thanks for the information.

I'm not surprised that a cable company's digital channels have likely gone through at least one "round trip conversion" (i.e., chroma/luma combining and then comb filtering) before being digitized and compressed for the last mile. Given my observation that my projector's comb filtering looks pretty good for my existing analog cable source, it would seem that I may not gain much, if anything, by running an S-Video connection from the cable box. Further support of this decision is that I don't currently or plan on watching much cable in my media room.

If you plan to use a vcr I suggest getting a pair of y-cables so the l-r channels can go directly to your receiver and vcr (thus not needing the receiver to be on for the audio signal).

I don't plan on keeping my VCR in the room. Only have it there now to convert my current cable box's RF out to composite for my projector (and audio l/r for my preamp). I think you meant "thus not needing the VCR to be on..."

Thanks again.

Doug