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Discussion Starter · #1 ·
I notice my dvd recordings from my Zenith 901 are relatively "soft" looking, do these boxes output the full resolution of sdtv atsc (isn't it close to 500 lines?) over the composite video jack, or is it reduced?
 

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All CECB's are supposed to output 480i only.
 

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I hope this explanation isn't too pedantic.


You will be getting 480 (vertical) lines, interlaced, with the NTSC aka analog video. This is where 480i comes from.


I believe the composite inputs/outputs are limited to around 330 (horizontal) lines of resolution, and since the chroma (color) and luma (black and white or brightness) are combined into one signal, your dvd recorder must then separate them with some signal processing, further degrading the quality.


So, your tuner is taking a mpeg-2 stream from the ATSC signal, and converting to a composite analog signal, then your dvd recorder comb filters to get the luma and chroma separated, then I'm guessing these signals are further processed to get the component values, usually made up of three signals.


This is then compressed into a new mpeg-2 stream to be recorded on the disc. As you can see, the original tv signal has gone through a lot to be recorded onto a dvd-r, its not surprising that the picture looks a bit soft after all that.


The recorded picture might improve if you used a converter box that has an S-video output, and connecting that to the S-video input on the dvd recorder. I believe S-video connections can support around 440 (horizontal) lines of resolution. Plus, with S-video, the luma and chroma are carried over separate wires, so there will be less processing needed in the dvd recorder, giving better quality than composite video.


With your composite lines, you are getting 330 (h) X 480 (v) lines of resolution, and S-video getting 440 (h) X 480 (v) lines.
 

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Quote:
Originally Posted by Roger Lococco /forum/post/15458917


I notice my dvd recordings from my Zenith 901 are relatively "soft" looking

Hi there


The recordings look "soft" compared to what?

If the recording looks soft compared to a direct connection of the CECB to the TV, then the output "resolution" of the CECB is not an issue. Try a test: record the composite video output of another DVD player (another source of clean analog video), and see if the recording of a DVD is also "soft". As Popeetheus mentions, there's a lot of processing to record and play back analog video on a digital medium (and using lossy compression to boot).




Quote:
This is then compressed into a new mpeg-2 stream to be recorded on the disc.

Actually before the MPEG encoding and compression happens, the analog video has to be digitized. And when lossy compression is applied, how much video information is being lost (i.e. what is the "recording mode")?

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With your composite lines, you are getting 330 (h) X 480 (v) lines of resolution, and S-video getting 440 (h) X 480 (v) lines.

The horizontal "resolution" of the analog video signal is not guaranteed to be displayed by an analog device. This is not like a fixed-pixel display with N horizontal pixels. The bandwidth of the CRT and its electronics determine the horizontal "resolution" that can be seen.


Is the recorder's A-to-D sampling at a rate fast enough to take advantage of the high quality signal (esp compared to a typical NTSC broadcast) from the CECB?



Regards
 

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Quote:
Originally Posted by Popeetheus /forum/post/15460728


I believe the composite inputs/outputs are limited to around 330 (horizontal) lines of resolution, and since the chroma (color) and luma (black and white or brightness) are combined into one signal, your dvd recorder must then separate them with some signal processing, further degrading the quality.

I really doubt that the boxes will give you this. If the chroma and luminance are output separately from the internal processor then recombining them requires a very sophisticated interleaver: then the TV's comb filters will separate them again. The method used in VCRs has been to cut the luminance at 3Mhz and tack the chroma on (at 3.58Mhz center frequency) leaving you with about 270 lines horizontal resolution. (which was more than acceptable for small, under 40", analog TVs)


An analog tuner puts out a detector output signal that is still interleaved so a full resolution signal is easy to produce. If the ATSC signal is separated into chroma and luminance at any point in the receiver, then the output will be limited.
 

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Discussion Starter · #6 ·

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Originally Posted by blue_z /forum/post/15461082


The recordings look "soft" compared to what?

They look softer compared to recordings made from my Radio Shack Accurian, not surprising since the Accurian has S video out.
 

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Try the CM-7000 with s-video out - it has the best PQ of any CECB out there.


Many of us here are using it with our old recorders, and it looks excellent, even on a 50" HD display.
 

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Quote:
Originally Posted by Popeetheus /forum/post/15460728


With your composite lines, you are getting 330 (h) X 480 (v) lines of resolution,

Your numbers are only correct for a square image. Since the screen is rectangle shaped, you need to multiply by 4/3. The S-video connection has no bandwidth limitation, so it can carry the full resolution of the digital signal. And finally the overlaid color bandwidth is limited by the NTSC tuner. Therefore:


Composite == ~440 x 480

Separated-video == ~720 x 480

Overlaid color image == ~160 x 480


Since this is analog the horizontal resolution is variable, however I will say this: My Channel Master's S-video connection looks just as good as a DVD player.
 

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Quote:
Originally Posted by electrictroy /forum/post/15527318


Your numbers are only correct for a square image. Since the screen is rectangle shaped, you need to multiply by 4/3. The S-video connection has no bandwidth limitation, so it can carry the full resolution of the digital signal. And finally the overlaid color bandwidth is limited by the NTSC tuner. Therefore:


Composite == ~440 x 480

Separated-video == ~720 x 480

Overlaid color image == ~160 x 480

I think you're talking about pixels and I'm talking about lines?
 

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720x480 is NOT high definition. 720x480 is standard definition, and an NTSC analog set is fully capable of displaying standard definition, so long as you use a cable with the ability to carry the required 7 megahertz bandwidth (which S-video can do).
Quote:
Originally Posted by Popeetheus /forum/post/15529500


I think you're talking about pixels and I'm talking about lines?

No. When you hear a figure like "VHS tapes output 3 megahertz bandwidth and 240 lines horizontal resolution, per picture height" they are only talking about the number of lines that fit inside a square image.


In order to get the number of lines from one edge to the other edge, you need to multiply by 4/3 which yields 320 lines horizontal resolution, across the entire screen. Super VHS can do about 560 lines across the entire screen, and DVD of course can do 720 lines edge-to-edge.
 
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