S-Video vs Composite Question

I just signed up for Comcast cable a couple of weeks ago and am
sending the signal, from the Motorola 6412 Digital Comcast Receiver,
to a standalone Philips Tivo.

After checking and double checking, it seems to me that I'm getting a
better picture, from the Tivo to TV, on composite video than on
S-Video.

Is that normal? I always thought the picture quality would be better
on S-Video.

Definitely not normal. Resolution, contrast and color should all be clearly
improved on SVHS. Replace the cable first.


wrote in message
...
I just signed up for Comcast cable a couple of weeks ago and am
sending the signal, from the Motorola 6412 Digital Comcast Receiver,
to a standalone Philips Tivo.

After checking and double checking, it seems to me that I'm getting a
better picture, from the Tivo to TV, on composite video than on
S-Video.

Is that normal? I always thought the picture quality would be better
on S-Video.

wrote in message
...
I just signed up for Comcast cable a couple of weeks ago and am
sending the signal, from the Motorola 6412 Digital Comcast Receiver,
to a standalone Philips Tivo.

After checking and double checking, it seems to me that I'm getting a
better picture, from the Tivo to TV, on composite video than on
S-Video.

Is that normal? I always thought the picture quality would be better
on S-Video.


I've seen this sometimes, it depends on the particular equipment.

wrote:
I just signed up for Comcast cable a couple of weeks ago and am
sending the signal, from the Motorola 6412 Digital Comcast Receiver,
to a standalone Philips Tivo.

After checking and double checking, it seems to me that I'm getting a
better picture, from the Tivo to TV, on composite video than on
S-Video.

Is that normal? I always thought the picture quality would be better
on S-Video.


You may want to look into changin out that S-Video cable w/ a new one.


Keith
Http://www.eHDMI.com

wrote in message
...
I just signed up for Comcast cable a couple of weeks ago and am
sending the signal, from the Motorola 6412 Digital Comcast Receiver,
to a standalone Philips Tivo.

After checking and double checking, it seems to me that I'm getting a
better picture, from the Tivo to TV, on composite video than on
S-Video.

Is that normal? I always thought the picture quality would be better
on S-Video.

Resolution, contrast and color are not significantly
improved with an S-Video interconnect. On an analog NTSC set equipped with
a low quality filter to separate the brightness from the color signal,
S-Video interconnects will avoid the need for the filter since the color and
brightness is not mixed to begin with. With a composite interconnect and a
poor filter you will see artifacts. Typically, moving worm like artifacts on
bright vertical lines. This is not an issue with S-Video interconnects or on
sets with a decent filter. On most decent sets you will see little
difference.

Richard.

On Sun, 12 Mar 2006 05:30:59 -0600, wrote:

I just signed up for Comcast cable a couple of weeks ago and am
sending the signal, from the Motorola 6412 Digital Comcast Receiver,
to a standalone Philips Tivo.

After checking and double checking, it seems to me that I'm getting a
better picture, from the Tivo to TV, on composite video than on
S-Video.

Is that normal? I always thought the picture quality would be better
on S-Video.


It is a fairly common misconception that a S-Video connection will
always give a better video signal than a composite video connection.

Given an equivalent quality video source, then it is usually true that
the quality of the video signal passed will improve as one goes from
composite video , to S-Video, to component video to digital video (
DVI or HDMI). However, this order may change depending on the length
and quality of the particular video cable and in some cases it will be
very hard to notice any difference.

The other reason the generalization is not necessarily true is that
the quality of the source is not always the same. In particular,
cable boxes often have a problem with analog cable channels. The
S-Video, component video and digital video outputs of a cable box
require processing of the analog video signal which would otherwise be
done in the TV or, in your case, by the Tivo. Cable boxes have been
notorious for their poor processing of the analog video channels and,
in a lot of cases, it is better to have the necessary processing of
these signals done in devices with better quality processing such as
the better quality TVs or recorders. This will depend very much on
what devices you have, their video processing capabilities and the
type of video connection you use.

Another factor in this equation is that analog TV displayed on large
screen TV's from the same distance that one would view a smaller TV
means that the large screen will show imperfections in the TV picture
quality more than a smaller screen does. Your cable box is for HD
pictures so if you have a large screen TV then you will be bothered
more by the poorer inherent quality of Standard Definition TV
exasperated by noise introduced by the poor video processing in the
6412 cable box.

Note there are reports that the newer model 6412 cable box with the
HDMI output has better processing of the analog channels so this
problem is eliminated or less significant for those cable boxes.

Unfortunately, you really have to try the particular combinations you
have available to see which connection has the least problem. There
is also the ease of use factor to consider. I have my 6412 cable box
connected with component video and composite video. I use the
component video for SD and HD digital channels and composite video for
analog cable channels. This gives me the best video quality. However
it is a nuisance to change the video source on my TV so I often will
not bother to switch video sources when changing to a analog channel
from a digital channel unless it starts to bother me too much or
unless I know I going to stay on an analog channel for a long time.

Alan Bealby
Remove no_spam from my E-Mail address

Good analysis, Alan.

My goal was to determine the best quality video source to the Tivo so
that I could record and store movies on large hard drives.

I have the newer version of the 6412, the Phase III, which has the
HDMI output, and has a much better analog tuner than the 5100 I just
replaced. However, I seldom view the analog channels.

I have the 6412 connected to a 30 inch Philips HDTV, with Component
cables, and get excellent HD and SD quality. The Composite or S-Video
is connected to the Tivo, which is connected to a 26 inch Samsung HDTV
for monitoring the Tivo.

I've tried several different S-Video cables, but results is the same.

Thanks to all for helpful suggestions.



On Sun, 12 Mar 2006 19:42:54 GMT, Alan Bealby
wrote:

On Sun, 12 Mar 2006 05:30:59 -0600, wrote:

I just signed up for Comcast cable a couple of weeks ago and am
sending the signal, from the Motorola 6412 Digital Comcast Receiver,
to a standalone Philips Tivo.

After checking and double checking, it seems to me that I'm getting a
better picture, from the Tivo to TV, on composite video than on
S-Video.

Is that normal? I always thought the picture quality would be better
on S-Video.


It is a fairly common misconception that a S-Video connection will
always give a better video signal than a composite video connection.

Given an equivalent quality video source, then it is usually true that
the quality of the video signal passed will improve as one goes from
composite video , to S-Video, to component video to digital video (
DVI or HDMI). However, this order may change depending on the length
and quality of the particular video cable and in some cases it will be
very hard to notice any difference.

The other reason the generalization is not necessarily true is that
the quality of the source is not always the same. In particular,
cable boxes often have a problem with analog cable channels. The
S-Video, component video and digital video outputs of a cable box
require processing of the analog video signal which would otherwise be
done in the TV or, in your case, by the Tivo. Cable boxes have been
notorious for their poor processing of the analog video channels and,
in a lot of cases, it is better to have the necessary processing of
these signals done in devices with better quality processing such as
the better quality TVs or recorders. This will depend very much on
what devices you have, their video processing capabilities and the
type of video connection you use.

Another factor in this equation is that analog TV displayed on large
screen TV's from the same distance that one would view a smaller TV
means that the large screen will show imperfections in the TV picture
quality more than a smaller screen does. Your cable box is for HD
pictures so if you have a large screen TV then you will be bothered
more by the poorer inherent quality of Standard Definition TV
exasperated by noise introduced by the poor video processing in the
6412 cable box.

Note there are reports that the newer model 6412 cable box with the
HDMI output has better processing of the analog channels so this
problem is eliminated or less significant for those cable boxes.

Unfortunately, you really have to try the particular combinations you
have available to see which connection has the least problem. There
is also the ease of use factor to consider. I have my 6412 cable box
connected with component video and composite video. I use the
component video for SD and HD digital channels and composite video for
analog cable channels. This gives me the best video quality. However
it is a nuisance to change the video source on my TV so I often will
not bother to switch video sources when changing to a analog channel
from a digital channel unless it starts to bother me too much or
unless I know I going to stay on an analog channel for a long time.

Alan Bealby
Remove no_spam from my E-Mail address

This is a common misconception. Actually, it is very typical. S-VHS
connections are often a poor choice.

S-VHS connections were designed for signals where the luma and chroma are
encoded discretely. Signals from cable, sat, and DVD sources do not get
video in the form of luma and chroma. These units have to filter the signal
to separate them to output at the s-video ports. Typically, the filters are
quite crude compared to those in the television and do a poorer job.

The specifics of processing are quite variable with equipment. I would
recommend trying both s and composite connections to see which is better.
When using VHS units which record the luma and chroma discretely there will
likely be an improvement. With the previsously mentioned sources, it
depends, but the set will usually have the better filtering.

Leonard

"Dan G" wrote in message
news
Definitely not normal. Resolution, contrast and color should all be
clearly
improved on SVHS. Replace the cable first.


wrote in message
...
I just signed up for Comcast cable a couple of weeks ago and am
sending the signal, from the Motorola 6412 Digital Comcast Receiver,
to a standalone Philips Tivo.

After checking and double checking, it seems to me that I'm getting a
better picture, from the Tivo to TV, on composite video than on
S-Video.

Is that normal? I always thought the picture quality would be better
on S-Video.

Leonard Caillouet wrote:
This is a common misconception. Actually, it is very typical. S-VHS
connections are often a poor choice.

S-VHS connections were designed for signals where the luma and chroma are
encoded discretely. Signals from cable, sat, and DVD sources do not get
video in the form of luma and chroma. These units have to filter the signal
to separate them to output at the s-video ports. Typically, the filters are
quite crude compared to those in the television and do a poorer job.

The specifics of processing are quite variable with equipment. I would
recommend trying both s and composite connections to see which is better.
When using VHS units which record the luma and chroma discretely there will
likely be an improvement. With the previsously mentioned sources, it
depends, but the set will usually have the better filtering.

Leonard


That's very interesting Leonard and I suppose it makes sense. You are saying
that the luma and chroma must be separated at some point before the image is
displayed by the TV monitor. And you are saying that a cable , sat or DVD source
does not contain this discreet luma / chroma information and the unit must
create this signal to output it at the S output connector. And I think you are
saying that if you use composite out of cable, sat or DVD and let the TV do the
luma / chroma separating that the end result is the same and that any
differences depend on the quality of the circuit that does this filtering. Be it
the cable, sat, DVD player or the TV.
I am aware that SVHS recorders do record this luma / chroma separately so there
would be an advantage to using S out of those devices.
I'm confused about DVD players though. Do they not contain luma / chroma signals
in the form of R-Y, B-Y, Y? Would it not be better to derive the luma / chroma
from that component signal instead of from a composite video signal? Or am I
wrong about the actual encoded data on a DVD?
A little off the main topic but I've had experience with cheap-o Radio Shack
devices that convert composite to S. They are nothing more than a capacitor and
resistor. I'm wondering if anyone makes high quality devices that do this trick.
You'd think there might be a good after market demand for something like this.
The thinking would be... don't let your cable box or TV do this necessary job...
let our SuperS Gadget to it.

"DanR" wrote in message
et...
Leonard Caillouet wrote:
This is a common misconception. Actually, it is very typical. S-VHS
connections are often a poor choice.

S-VHS connections were designed for signals where the luma and chroma are
encoded discretely. Signals from cable, sat, and DVD sources do not get
video in the form of luma and chroma. These units have to filter the
signal
to separate them to output at the s-video ports. Typically, the filters
are
quite crude compared to those in the television and do a poorer job.

The specifics of processing are quite variable with equipment. I would
recommend trying both s and composite connections to see which is better.
When using VHS units which record the luma and chroma discretely there
will
likely be an improvement. With the previsously mentioned sources, it
depends, but the set will usually have the better filtering.

Leonard


That's very interesting Leonard and I suppose it makes sense. You are
saying
that the luma and chroma must be separated at some point before the image
is
displayed by the TV monitor. And you are saying that a cable , sat or DVD
source
does not contain this discreet luma / chroma information and the unit must
create this signal to output it at the S output connector. And I think you
are
saying that if you use composite out of cable, sat or DVD and let the TV
do the
luma / chroma separating that the end result is the same and that any
differences depend on the quality of the circuit that does this filtering.
Be it
the cable, sat, DVD player or the TV.
I am aware that SVHS recorders do record this luma / chroma separately so
there
would be an advantage to using S out of those devices.
I'm confused about DVD players though. Do they not contain luma / chroma
signals
in the form of R-Y, B-Y, Y? Would it not be better to derive the luma /
chroma
from that component signal instead of from a composite video signal? Or am
I
wrong about the actual encoded data on a DVD?
A little off the main topic but I've had experience with cheap-o Radio
Shack
devices that convert composite to S. They are nothing more than a
capacitor and
resistor. I'm wondering if anyone makes high quality devices that do this
trick.
You'd think there might be a good after market demand for something like
this.
The thinking would be... don't let your cable box or TV do this necessary
job...
let our SuperS Gadget to it.

Your understanding is greater than I expected and I very much
oversimplified. All MPEG compressed video is encoded as YUV. While it is
true that the conversion to YIQ may preserve much information that can be
lost in the conversion to composite and the subsequent filtering to separate
luma and chroma, many systems seem to do a lousy job of the conversion and
likely just SAW filter it after it is converted to composite. In this case,
the (usually) much more elaborate comb filter in the television will do a
better job. I actually traced the signals in a SA cable converter recently
and this appears to be exactly what it was doing. Why would they do this
instead of taking the wider bandwidth earlier in the conversion? My guess
is that they are perfectly happy to limit the bandwidth of the chroma and
luma to minimize complaints about noisy signals. The bottom line is that
you just have to try it. Some DVD players do a much better job than cable
and sat boxes, but some look better with composite connections. As so often
is the case, it depends, and one should never underestimate the ability of
manufacturers to screw things up.

The simple passive filter that you described is a very crude conversion but
will usually work, just not very well. Some outboard scalers likely have
pretty good conversion to s-video, but I never paid much attention to it.

Leonard