S2 vs. S2 DT Video Quality

"Bill Kearney" wrote in message
t...
The television is an LG 37LC2D. The source is Time Warner cable, 72 ohm
coax. The video is pretty clean when tuned using the television's tuner.
I
am comparing coax - TV tuner to coax - Tivo S2 - AV1 input on the TV
using composite cables.

It is true that you get better video through S-video, and I tried S-video
in
place of the composite connection. What you see better is the artifacts.

Whoa, you're mixing things up here. If you're using plain old coax, on
channel 3, that's the crappiest possible signal you can give to the Tivo.
If you're talking composite video, you're using yellow RCA connector.
That's "less worse" than the RF channel 3 coax signal. S-video is the
best
you're going to get out of that gear. Try to feed s-video through the
whole
process. And do NOT run things through the TV. Run it direct from the
cable box to the Tivo. If you're trying to use the cable tuner in the TV
to
watch some channels live while the Tivo is recording, that's fine. Just
don't run the video cabling through the TV. Just split the RF coax before
the cable box and run that to the TV's tuner. There's no sense in putting
other devices inbetween the Tivo and the cable box; they'll just add the
risk of degrading the signal.

Um, Bill, thanks for taking interest.

What am I mixing up?

I didn't say anything about channel 3. That would imply rf from the Tivo to
the TV. I am using composite from Tivo to tv, not rf.

The coax is split. One side goes to the TV, the other to the Tivo. There
is no "cable box".

coax - TV tuner
coax - Tivo S2 - AV1 input on the TV using composite cables.

There is nothing between the coax and the TV tuner.
There is nothing between the coax and the Tivo. The only thing between the
Tivo and the AV1 input on the TV is a composite cable.

I tried s-video from the Tivo to the TV, and that seems to make the
artifacts more visible resulting in a lower quality picture, from the
viewer's perspective, than when using a composite connection.


I think the composite connection has a smoothing effect on the artifacts
making them less apparent. So while S-video is technically better (and
it
absolutely is), the composite connection results in a more appealing
picture. I am not the first to say that here.

Based on the input's artifacts that might be true. You're at the mercy of
how poorly the cable company or the broadcast network has encoded the
picture. You may want to investigate the merits of the cable box you're
currently using. Some are worse than others (although I'm no expert).


No cable box.

The video using the TV's tuner, directly from the cable is very good. So
the cable company is delivering a good signal.

I am trying to decide whether to replace the S2 with an S3. The S3 is a
little pricey, but after a month I might be glad I made the switch. I
(we)
really like watching television Tivo-style, with time shifting,
wishlists,
et al.

You still haven't said which cable company you're using, and in which
market.

It's up there. Time Warner cable. No "cable box" or STB. Sachse TX.

There may be options possible on how to improve things but they're
likely to be dependent on the local cable quality. Even an S3 won't help
if
the cable company's known to do a crappy job in your market, right?


The cable company's signal is good. If the cable company's signal was
crappy then I would get a crappy picture on the TV when using coax - TV.


--
Rusty

Um, Bill, thanks for taking interest.
What am I mixing up?

I didn't say anything about channel 3. That would imply rf from the Tivo
to
the TV. I am using composite from Tivo to tv, not rf.

It wasn't clear from your posting how the wires were set up. Now you've
clarified it.

The coax is split. One side goes to the TV, the other to the Tivo. There
is no "cable box".

Ah, so you're just attempting to record from analog cable channels.

The video using the TV's tuner, directly from the cable is very good. So
the cable company is delivering a good signal.

Well, analog cable and good signal aren't found together very often... But
I get what you're saying.

The cable company's signal is good. If the cable company's signal was
crappy then I would get a crappy picture on the TV when using coax - TV.

Ugh, then there's not much else I could suggest. Sorry, seems like a wasted
thread then.

-Bill Kearney

"Bill Kearney" wrote in message
t...
snip

Ugh, then there's not much else I could suggest. Sorry, seems like a
wasted
thread then.

-Bill Kearney


Maybe you see it as a wasted thread. I'm sorry you wasted your time.

What I am talking about is the delta (the difference) between the signal
that Tivo is given to record, and the signal that the Tivo provides when the
recording is played back. I don't see how the source makes any difference.

--
Rusty

Maybe you see it as a wasted thread. I'm sorry you wasted your time.

No, just the opposite. I wasn't clear on how you had it wired up, thus the
'wasted' was my fault.

What I am talking about is the delta (the difference) between the signal
that Tivo is given to record, and the signal that the Tivo provides when
the
recording is played back. I don't see how the source makes any
difference.

On the fly compression that's done during recording alters the signal. It
will always introduce "some" differences from the original source signal.
That's just the nature of digital encoding. Some encoders do it better than
others but in consumer DVRs the Tivo's "Best" mode is about as good as
reasonable money can afford. If you give it a fuzzier picture to start with
it may produce a visually more appealing result. If only because the
encoders do a better job 'smoothing' less of a picture. Go figure.

The only way to get an artifact-free recording is to not encode it. There's
no way to avoid this other than using digital cable, via an S3 Tivo and a
CableCard, or a DirecTV Tivo.

From plain analog channels there's not much can be done other than what's
been pointed out, use a dual tuner Series 2 Tivo or a Series 3.

Rusty wrote:

What I am talking about is the delta (the difference) between the signal
that Tivo is given to record, and the signal that the Tivo provides when the
recording is played back. I don't see how the source makes any difference.

A weak signal, one with significant amounts of noise, is much harder to
digitize and compress cleanly. (Solid blocks of a single color compress
very well. A block with a bunch of red and blue speckles does not.)
Lower compression + limited bitrate = more artifacts.

-Joe

In article [email protected], "Rusty" wrote:
"Bill Kearney" wrote in message
et...
snip

Ugh, then there's not much else I could suggest. Sorry, seems like a
wasted
thread then.

-Bill Kearney


Maybe you see it as a wasted thread. I'm sorry you wasted your time.

What I am talking about is the delta (the difference) between the signal
that Tivo is given to record, and the signal that the Tivo provides when the
recording is played back. I don't see how the source makes any difference.

Wel it can, "Garbage in, Garbage out"

"Rusty" shaped the electrons to say:
What I am talking about is the delta (the difference) between the signal
that Tivo is given to record, and the signal that the Tivo provides when the
recording is played back. I don't see how the source makes any difference.

MPEG encoding is lossy - that's true for MP3 music files or MPEG-2
video like on the TiVo - or DVD. *How* lossy varies depending on many
factors, but the biggest is the bitrate of the encoding. That's why a
192Kbps MP3 sounds better than an 128Kbps MP3 encoded from the same
source. Given the same source, more bits means losing less data
during the encode, which means a more accurate reproduction of the
original.

But MPEG is never 100% accurate on reproduction, even with no bitrate
cap, it is never lossless.

That's also why, on TiVo, Best looks better than High which looks
better than Medium which looks better than Basic. Each higher tier
has a higher max bitrate for encoding.

There is another difference - resolution. On a standard S2 TiVo Basic
and Medium are encoded at 352x480, while High and Best are 480x480. A
higher resolution encoding means better reproduction - but it also
means more data to encode, so for a given bitrate a higher resolution
can be more lossy.

You can see it gets complex because there are different kinds of loss
and it is a tradeoff.


And then it gets even more complex because there are other issues.
TiVo, and basically all home recording devices like DVRs and DVD
recorders, do real-time, single-pass recording. They encode the video
on the fly. So they used fixed MPEG settings for all video.

But what is best for fast action isn't best for animation, which isn't
best for a talk show, etc.

Professional encoders who do DVD, or encode MPEG for broadcast, use
multi-pass encoders. Since they don't have to work in real-time, the
systems analyze the video and can tweak the MPEG settings scene by
scene. And for DVD they'll make a number of passes over the video,
doing test encodes, analyzing the results, and feeding that back into
the settings to improve the results. And in the end the professional
encoders can make manual tweaks based on their expertise.


So, anyway, MPEG encoding has many variables and it is always lossy to
some degree. Even DVD, which supports bitrates up to 10Mbps, with
high-end, multi-pass encoders, can show artifacts. A normal TiVo
maxes out around 6Mbps and it is using a single-pass encoder.


And then you have the source. Everything in the source signal is data
to be encoded. And the encoder doesn't know what is 'noise' and what
is picture. So it is all just data. MPEG-2 works by encoding key
frames and then encoding the changes between frames from that key
frame, until the next group. So the less that changes between frames,
the less there is to encode, and the less loss there is - the higher
the quality of the end result. This is why shows with a lot of slow
pans and static backgrounds encode better than fast action like sports
where the camera is always moving and the frames change rapidly.

Well, a noisy analog signal is like fast motion. All that noise is
perceived as changes in the image frame to frame, which greatly
increases the amount of data to encode. Since the noise and real
picture are both just image data to the encoder, it can't throw out
noise to preserve the data. (Side note - there are filters that can
do some of this, but they aren't that common in consumer grade gear.)
So the baby gets tossed out with bath water - since the encoder needs
to 'lose' information to fit the encoding into the bitrate, image data
is tossed out along with noise data. This can produce an image that
is noticably poorer than the source, because now you have reproduced
analog noise along with digital artifacts like macroblocking. With
enough noise, or a combination like noise with fast pans, this can
completely destroy the image, producing nothing but digital artifacts.

So a clean source is important. The cleaner the source fed to the
encoder, the better the encoding will be. Not just because of the
obvious fact that higher quality in is higher quality out, but the
multiplication effect of having less to encode means less loss in the
process.

-MZ
--
URL:mailto:megazoneatmegazone.org Gweep, Discordian, Author, Engineer, me.
"A little nonsense now and then, is relished by the wisest men" 508-852-2171
URL:http://www.megazone.org/ URL:http://www.eyrie-productions.com/ Eris

The coax is split. One side goes to the TV, the other to the Tivo. There
is no "cable box".

You could try removing the splitter and not routing the coax to the tv
at all. We found that helped us get rid of some artifacts, as it
improved the signl-to-noise ratio. We still get some artifacts, but
fewer.

-Chris

"Chris F Clark" wrote in message
...
The coax is split. One side goes to the TV, the other to the Tivo.
There
is no "cable box".

You could try removing the splitter and not routing the coax to the tv
at all. We found that helped us get rid of some artifacts, as it
improved the signl-to-noise ratio. We still get some artifacts, but
fewer.

-Chris

Thanks Joe, MegaZone, and Chris for the highly informative and educational
posts.

It is sounding like I really need to upgrade to a digital service. Digital
is available here from Time Warner who is supplying my analog cable now.
FiOS is also available at this address. And I am kind of leaning toward a
Tivo S3.

--
Rusty

It is sounding like I really need to upgrade to a digital service.
Digital
is available here from Time Warner who is supplying my analog cable now.
FiOS is also available at this address. And I am kind of leaning toward a
Tivo S3.

The only downside to using an S3 with cablecards, in comparison to the
providers "house brand" DVR, is not getting the bidirectional "features".
That is, their house brand units (comcast, verizon, directv, etc) have some
features for interacting back/forth with the network for added
functionality. Stuff like Pay-Per-View and some interactive fluff mainly.
Those features are not (yet) available for use on an S3 Tivo, even with
cablecards added. But if you're like me you won't really care about those
features and will instead focus on the Tivo aspect. But it's a valid point
and one to be aware of before making a switch. Personally, I'd go for
FiosTV, but that's only because I really despise Comcast...