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martinlw

Audiophyte
Will an HDMI cable connected to a TV HDMI and a cable tuner's DVI transmit the analog signal of standard programming as well as the digital signal of HD? Isn't HDMI preferable to a component video connection?
 
U

Unregistered

Guest
No. HDMI and DVI are digital only. If you have a cable box that tunes digital channels and/or HD channels, they arrive in digital form and are simplyl passed over DVI or HDMI to the display (which will process it and convert it to analog for display).

If you tune to an analog channel on the cable box, it will convert it to digital and send it via DVI or HDMI to the display. If for some reason you actually want to send an analog signal to your tv via component (perhaps because it looks better than using DVI) you will have to connect component cables from the cable box to the tv (and switch inputs on the tv). This assumes that your cable box will allow you to have both analog and digital video outs connected at the same time. Probably will and will have a menu choice for you to choose which one should be active.
 
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martinlw

Audiophyte
Did you mean to say that the picture quality of standard programming using component video cables might be superior to that provided by HDMI? Would component be the way to go if most programming viewed is standard definition? Maybe you can clear up something else for me. Is a standard definition signal from a cable box 480i whether sent by component or HDMI and then converted to 480p by a digital progressive scan TV? Thanks for your input.
 
U

Unregistered

Guest
I have no personal experience with DVI or HDMI (yet!) but have seen many discussions about it and the consensus is decidedly mixed. Some say there is definitely an improvement with DVI but most I've seen say the improvement, if any, is negligible.

For SD, component is likely better simply because you avoid an additional analog to digital conversion by the cable box. A digital tv is going to process the signal anyway (scaling, noise reduction, etc) so might as well let it do the analog to digital conversion.

480i can be "deinterlaced" to 480p by either the tv or the source device. If the source (cable box, dvd) is set to interlaced, the tv will do the deinterlacing. If it is set to output progressive, it will do the deinterlacing and pass it directly to the tv. Lots of room for debate here as well. If your tv does a better job of it, it is sometimes better to set the dvd player or cable to interlaced and let the tv do the deinterlacing.

Note also that most digital tvs scale any signal to their native resolution. If you send a 480i signal to a tv with a native resolution of 720p, it will scale it to 720p. That's why digital connections like DVI are theoretically better. The signal is untouched until it gets to the tv vs using analog connections where the tv has to first convert analog to digital, then scale it, and then back to analog for display.
 
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martinlw

Audiophyte
If the cable that's run from the outside to the cable box is low quality, is it too much to expect a quality TV picture even if using component or HDMI cable from the box to the TV? Am I wrong to be thinking that the coaxial cable the cable company uses can only carry an analog signal? I've read that RF, composite and S-Video are all analog cable.
 
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U

Unregistered

Guest
Certainly the quality of the source signal has a large impact on the resulting quality. However, analog signals that are poor quality to begin with from the cable company or deteriorated further by a low quality cable that is susceptible to RF/EMI interference will be FAR worse than a digital signal.

RF, composite, and s-video (and component too) usually carry analog signals, but there is no reason you couldn't use the same cables to send digital signals. I have digital cable and it comes to my box over the standard RF cable from the wall. You could use a composite video cable to send digital audio to your receiver. You could take that RF cable and solder on rca jacks and use it for digital audio too. The only real requirement is that the cables meet the specs for the transmission method; ie Video cables and digital audio cables need to be 75 Ohm.

This gets confusing, but I'll elaborate. Would it shock you if I told you that digital signals are analog too? Everyone knows that digital means 1s and 0s, right? But how do you send a 1 or a 0 over a wire that carries electricity?

You modulate the signal using any one of a number of techniques: PCM, PWM, PAM, Bi-Phase mark, etc. The fundamental difference between analog and digital is that analog is a continuous waveform (it is ANALOGous to the real world) whereas digital is discrete ("countable"). Naturally since we use the binary number system for digital, there are only 2 discrete steps: 0 or 1. How a 0 or 1 is represented is governed by the aforementioned modulation schemes. PWM (pulse width modulation) is the easiest to understand. The 'width' of the pulse determines whether it is a 1 or a 0. Say a 50 us pulse is a zero and a 100 us pulse is a 1. The amplitude of the pulse won't be anywhere near the amplitude of the corresponding analog signal - in fact it is constant for pwm - the 0 or 1 is encoded in the width of the pulse.

So... for an analog signal that is 4.7Mhz (480i cable signals) the wire has to be able to carry that frequency exactly, which is why a poor quality cable could introduce noise or attenuate the signal and result in a lousy picture.

For digital signals, bandwidth is in terms of bits per second and has nothing to do with the actual frequency of the signal you want to reproduce, except that the original analog signal was sampled at a frequency twice the highest frequency you need to reproduce (Nyquist theorem). So a digital transmission of 480i signals would result in 4.7 million bits per second and the amplitude of the pulses are low in comparison to the analog signal where they are exactly the original waveform. Thus, even a low quality cable will handle digital audio and video respectably. And of course, now that you have the signal in a digital form it can be more easily manipulated to do things like scaling or applying noise reduction techniques or changing color to greyscale, etc. For audio, it can be normalized, compressed, or have reverb added. All things that are more difficult to do with an analog signal.
 
M

martinlw

Audiophyte
Thanks for the explanation. I think I'm starting to get it. I was going to have my mother upgrade her cable box to the Motorola 5100 HD so I could use component cable between the box and her new HD-ready TV to improve picture quality. I read this Q&A from another site. What do you make of it?

Q: Is there anything I can do to improve the picture quality on the non HD channels through the component outputs? (The Motorola DCT's (non-HD) seemed to have a better picture)

A: Not really. This is a problem that is being worked on by Motorola. The 5100 is ?upconverting? the analog signals to the Component (Y/Pb/Pr) Outputs, and there is formula being used that contains an algorithm that controls compression & conversion of these signals. The first part of possibly multiple firmware updates was released recently (2.48). This was to make changes to this algorithm that should make the Analog PQ better, and there are more updates planned to ?fine tune? the overall PQ.
 
U

Unregistered

Guest
It is deinterlacing the 480i signals, not technically 'upconverting'. Sounds like they are saying that the algorithm they use isn't working as well as they'd like. Perfect example of how it's sometimes better to let the source device (in this case, the cable box) do the deinterlacing and sometimes to just tell it to pass the 480i signal to the display and let it do the deinterlacing.

You would have to just try it and see if it does a good enough job for you. If its deinterlacing algorithm doesn't work that well, set the box to output interlaced (if it allows that). If it's still not good enough, just use s-video. I still use s-video on one of my tvs and I really don't notice that much difference between that and component, but then I'm more interested in audio than video.
 
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martinlw

Audiophyte
That all makes sense. I'll try component cables with the HD STB and see what happens. I've seen a good illustration of the setup options for the Motorola 5100 and I think it is possible to have it send the TV 480i if the other doesn't work out. Here's another simpleton question. What kind of audio cable should I use with the component video cables? I suppose I would use the same with S-Video if need be.
 
U

Unregistered

Guest
The audio and video are unrelated so use the best connection available. You must use a digital cable, either optical or coaxial, to get Dolby Digital from the STB.

The majority of channels are still analog audio so unfortunately you have to also hookup up analog audio cables.
 
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martinlw

Audiophyte
OK. I should be able to figure that out. Thanks for all of your help. Now I know enough to get a job as a Comcast tech support rep. :)
 

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