Don't the Cable Boxes Degrade HDTV?

wrote in message
...
On Mon, Sep 22, 2008, 4:55am (EDT+4) (Alan)
wrote:

"...Digital channels can be SD or HD."

Standard definition refers to 480 vertical lines, but how about
*horizontal* lines?

No. The verticle RESOLUTION is 480 'lines' of horizontal scan.

Transmitted NTSC has a theoretical maximum of 328 horizontal lines, but
digital SD *can* be up to 600 horizontal lines. In reality, what is the
average horizontal resolution of 8VSB and of QAM?

No. The actual maximum # of lines is (by NTSC Standard) 512.

--
SoCalCommie
http://so-la-i.com/

George W Bush, WORST pRESIDENT EVER!!!

Yes, but you will need a fairly large screen to detect the difference.

Viewing them same program, best is OTA, slightly degraded is QAM (internal
TV cable tuner), and last is cable via Comcast DVR (SA 8300 HD).

"jim evans" wrote in message
...
My TV just cratered and I'm about to buy an new one. I know nothing
about HDTV but in reading reviews they talk a lot about the purity of
the image. I have to to go through a Comcast DVR which has to be a
super cheeeeep box. Don't these boxes clobber an otherwise good
signal?

Morph wrote:
Bill R wrote:

The same applies to SD channels (which many cable channels still
are) and they quite often look worse on a HDTV because a lot of
cable boxes (and HDTVs) don't do a good job displaying SD signals.

Are you referring to SD digital channels, or to analog channels?

Digital channels can be SD or HD. Analog channels are just that -
analog NTSC. Please don't refer to analog channels as SD.

I was referring to DIGITAL SD channels since the question was about
digital cable boxes. Don't read something into my post that wasn't
there.

Newsflash, ace. Many, if not most, digital cable boxes tune analog
channels as well.



On our cable system digital cable boxes will NOT tune analog channel and
the cable company no longer supplies analog converter boxes. The cable
company still has the analog tier for people that don't use the cable
company's box and they said that tier is going to be available to (at
least) 2010.
--
Bill R.

Remove nospam_ and x in e-mail address to reply by e-mail

I had originally posted:

Standard definition refers to 480 vertical lines,
but how about *horizontal* lines?


On Mon, Sep 22, 2008, 5:08am (EDT-3) (SoCalCommie)
responded:

No. The verticle RESOLUTION is 480 'lines' of horizontal
scan.

I know that. "480 lines" and "480 lines of horizontal scan" mean
exactly the same thing. The number of horizontal scan lines determine
vertical resolution.

I further posted:

Transmitted NTSC has a theoretical maximum
of 328 horizontal lines, but digital SD *can* be
up to 600 horizontal lines. In reality, what is the
average horizontal resolution of 8VSB and of QAM?


(SoCalCommie) responded:

No. The actual maximum # of lines is (by NTSC
Standard) 512.

Let me rephrase my question: "Transmitted NTSC has a theoretical maximum
horizontal resolution of 328 lines, but digital SD *can* be up to 600
lines. In reality, what is the average horizontal resolution of 8VSB and
of QAM?"


If you're correcting my "600" to be "512," then fine, but that does not
answer my question: What is the horizontal-resolution specification of
an 8VSB and a QAM signal? I'm talking horizontal resolution, NOT the
vertical resolution of horizontal scan lines.

SoCalCommie wrote:

No. The actual maximum # of lines is (by NTSC Standard) 512.

But those lines include are top/bottom margins that for decades were
solid black bars between frames, Those were more familiar in the past
when aging TVs needed an occasional adjustment to synchronize the
vertical scan of the electron beam with the signal source. If the scan
rate was off, the TV produced an effect that resembled pulling a motion
picture film slowly across a lighted background. Eventually electronic
technology improved to the point where the adjustment was automated and
late model TVs don't even have user accessible adjustments for that
function. Now that portion of the signal is used for closed captions and
some other text information.

Digital channels can be either SD or HD, but not analog. Analog
channels are always Standard Definition, never High Definition.

Let me rephrase my question: "Transmitted NTSC has a
theoretical maximum
horizontal resolution of 328 lines, but digital SD *can*
be up to 600
lines. In reality, what is the average horizontal
resolution of 8VSB and
of QAM?"


If you're correcting my "600" to be "512," then fine, but
that does not
answer my question: What is the horizontal-resolution
specification of
an 8VSB and a QAM signal? I'm talking horizontal
resolution, NOT the
vertical resolution of horizontal scan lines.


I guess as long as people are jumping in he

NTSC has 328 lines of horizontal resolution PER PICTURE
HEIGHT so for starters, you need to multiply that by 4/3 for
a full line.

ATSC has 18 profiles for encoding video. The main SD
profiles via ATSC are defined as 640 x 480 or 704 x 480
pixels interlaced. Also do not confuse pixels with lines of
resolution. They are two entirely different measurement
concepts. Digital SD via a DVD is usually 720 x 480 with non
square pixels.

David

jim evans wrote:
My TV just cratered and I'm about to buy an new one. I know
nothing about HDTV but in reading reviews they talk a lot
about the purity of the image. I have to to go through a
Comcast DVR which has to be a super cheeeeep box. Don't
these boxes clobber an otherwise good signal?

If anything, some digital cable boxes - especially HD-DVRs, will
improve received 480i video. There is no reason for a cable box
to modify HD signals in any way whatever.

If the STB has user settings available regarding its output,
rest assured that the average users who have tweaked them, will
have done it incorrectly.

There is much talk about cablecos reducing the quality vs. OTA
digital. I see no verifiable evidence here, where I actually
capture both. The max bit rate for an OTA channel is 19 mbps,
while the max rate for a cable channel is 38 mbps. In both
cases, the broadcaster places multiple streams in the channel.
No channel carries merely one stream.

Some precise evidence: I just edited two 59 second clips from
morning CBS-HD, one OTA - one QAM, recorded simultaneously (with
about a 3 second start variation).

OTA 97.544 MB
QAM 97.370 MB
or slightly above 13 mbps each with only a 0.2% variance.

Whether I capture from ATSC or QAM, the bit rate of the material
varies widely. An observed average of about 1 GB per ten
minutes, with some shows being 25% less and others 25% more.
PBS tends to supply the lowest bit rate. CBS seems to be more
consistently high.

Some samples from recent cable recordings at hand:
Source/play time/file size
CBS 0:41 @ 4.9 GB "Flashpoint"
NBC 0:43 @ 3.5 GB "E.R."
CW 0:41 @ 5.2 GB "Smallville"
FOX 0:42 @ 3.4 GB "House"
PBS 1:24 @ 4.8 GB "Live from Lincoln Center"

Even on the same channel/stream individual shows arrive at quite
different bit rates.

Also, some shows on HDTV - especially among movies - are aired
in DVD quality (less than 10 mbps).

Alan wrote:

Digital channels can be SD or HD. Analog channels are just that -
analog NTSC. Please don't refer to analog channels as SD.

Actually, analog channels are SD. Admittedly, that confuses some folks.

HD, ED (archaic), and SD are ATSC terms - not NTSC.

wrote:

Transmitted NTSC has a theoretical maximum of 328 horizontal lines, but
digital SD *can* be up to 600 horizontal lines. In reality, what is the
average horizontal resolution of 8VSB and of QAM?

Since both 8VSB and QAM are *modulation* specifications, not actual video
signal specifications, I'd say they're the same. The ATSC standard allows
for anywhere from 352 to 1920 lines of horizontal resolution. An average?
Well, I guess that depends on the number and type of video signal sampled.