S-video versus component out - AVS Forum
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post #1 of 5 Old 10-25-2000, 11:30 PM - Thread Starter
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Can any of you engineering einsteins help me?

As I wait for a decent STB before getting satellite, I am stuck with
"Digital" cable. The latest box I got (today-Motorolola 4000) did in fact have a digital dolby ac-3 out which makes the system sound noticeable better when viewing digital channels.

My question is: Will I do better getting a S-video cable and using that to rout the video out of the cable box, or is the single RCA-
type video out component connection usually better?
Thanks in advance !!
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post #2 of 5 Old 10-26-2000, 12:28 AM
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If it's a single RCA jack, it's "composite" not "component" video.

Composite video is NTSC format, which puts the luminance (b&w) and chrominance (color) on the same wire. The two signals overlap, and can never be perfectly separated. The chrominance ends up bleeding into the luminance, and vice versa. Higher-end equipment tries hard to do a good job of this with fancy comb filters, etc., but its difficult to do.

In S-video the chrominance and luminance signals are carried on separate wires, so the TV doesn't have to do the hard job of separating them. WIth analog cable this would yield no improvement, since all the channels are transmitted on the cable in NTSC format anyway, and the STB would probably have a very cheap color/luminance separator. But on digital cable, at least some sources, at least some of the time, may not have ever been in NTSC format, and you may notice a difference with the S-video output. However, on many of the DBS channels I see, NTSC artifacts are noticable, indicating that they started out in NTSC. It'll probably be hit or miss as to whether you see an improvement.

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post #3 of 5 Old 10-26-2000, 12:33 AM
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Standard answer: it depends.

For the channels that are transmitted digitally, S-Video will probably give a better picture. The luma and chroma in the video portion of the signal are already separated in the MPEG stream, so there's no sense in combining them into a composite video signal, only to have to separate them in your TV set (going through your comb filter with all the potential for introducing artifacts).

If your lower-numbered stations are transmitted as analog signals, you're probably better off with composite video. Your TV probably has a better comb filter than your cable box, so if you have to decode a composite signal, you want to do it on the component with the better comb filter.

-Jonathan
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post #4 of 5 Old 10-27-2000, 01:21 PM
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Quote:
Originally posted by BarryO:
If it's a single RCA jack, it's "composite" not "component" video.

Composite video is NTSC format, which puts the luminance (b&w) and chrominance (color) on the same wire. The two signals overlap, and can never be perfectly separated. The chrominance ends up bleeding into the luminance, and vice versa. Higher-end equipment tries hard to do a good job of this with fancy comb filters, etc., but its difficult to do.

In S-video the chrominance and luminance signals are carried on separate wires, so the TV doesn't have to do the hard job of separating them. WIth analog cable this would yield no improvement, since all the channels are transmitted on the cable in NTSC format anyway, and the STB would probably have a very cheap color/luminance separator. But on digital cable, at least some sources, at least some of the time, may not have ever been in NTSC format, and you may notice a difference with the S-video output. However, on many of the DBS channels I see, NTSC artifacts are noticable, indicating that they started out in NTSC. It'll probably be hit or miss as to whether you see an improvement.
BarryO,

Just to clear things up, Composite, S-Video, Component and RGBHV are ALL forms of the NTSC standard. They are just different stages of the encoding/matrixing that the video signal goes through to be transmitted. Over the air broadcasts are in the composite NTSC standard and S, component and RGBHV are what happens to the signal in the demodulator (TV receiver) to eventually be displayed on the screen. When passing video amongst components like DVDs to TVs, etc., you can bypass some of the encoding/decoding to avoid distortion from said processes.

Received broadcast NTSC signal flow:

1. RF modulated composite video (i.e.- CH 3/4 from VCR or a broadcast frequency)
2. Demodulated composite video (single RCA composite jack)
3. S-Video (Separated luminance and chrominance, as described above)
4. Component video (Luminance with syncs and color difference signals, Y,Pb,Pr...etc.)
5. RGBHV is the final stage delivered to your display device

They are all NTSC video, just at different stages in the decoding.


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post #5 of 5 Old 10-28-2000, 07:34 PM
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Quote:
Originally posted by chalucky:
Can any of you engineering einsteins help me?

As I wait for a decent STB before getting satellite, I am stuck with
"Digital" cable. The latest box I got (today-Motorolola 4000) did in fact have a digital dolby ac-3 out which makes the system sound noticeable better when viewing digital channels.

My question is: Will I do better getting a S-video cable and using that to rout the video out of the cable box, or is the single RCA-
type video out component connection usually better?
Thanks in advance !!
I haven't seen a 4000 before, I know of the new 5000 and 2000, anyway the S-video cable is the way to go if your set has a s-video input it usually allows up to 700 lines of resolution depending on the TV set. The new 5000 box also has a IEEE 1394 connection for HDTV's

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