Comparing Encoders - AVS Forum
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post #1 of 5 Old 03-16-2005, 03:47 AM - Thread Starter
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I have a Scientific Atlanta 8300HD DVR from TW running the SARA firmware. Picture-quality-wise the DVR works perfecfly for digital feeds. However, I am not at all happy with the quality of the recordings it makes from analog channels. The "Sa 8000" thread in this same forum has some discussion on this topic (in particular, the distinction in picture quality performance based on whether the feed is analog or digital).

As far as I am concerned, the recordings my SA DVR makes from analog feeds are substantially inferior to what I can make at EP speed with a decent VHS tape recorder - which is not very good to start with. In practice, I continue to record any show transmitted in analog on tape - usually at SP speed with Super VHS, in which case I can perceive practically no degradation compared to live. (For all my playbacks, I have a high-end JVC VCR which has a frame buffer and which does processing which eliminates most of what I call "VHS color noise". It can almost always play back a tape from another VCR with better picture quality than can the VCR which recorded the tape.)

I had been intending to buy a DVD recorder for recording analog channels, as I thought I would be happier with one of those than I am with my VCRs. However, having experienced the inadequacy of the encoders in SA's settop boxes, I am wondering if I will be happy with anybody's encoder in non-professional equipment.

The things that bug me are the compression artifacts. If you are watching an action sport like boxing or football, it is the things that are moving fast (fists, balls) that are most important things to watch. Yet it is these things which become blocky because the encoder cannot keep up. I am also distracted when the background goes blurry because the camera is panning. Things get even worse if the analog signal the box is trying to encode is noisy, as it is hard for the compression algorithms to know which differences are significant. My cable provider fails to provide a noise-free signal on many of the analog channels I watch, and SA DVR recordings from the noisy channels are extremely ugly with dynamic graininess - much uglier than live or a tape recording.

I am somewhat surprised by the fact that my concern about encoder quality and my conviction that tape remains a superior medium for recording analog TV are not things that I see others talking about much when discussing digital TV recording devices. Perhaps I am more sensitive to compression artifacts than most. But I do know that, with their professional equipment, the TV broadcasters can do a vastly superior job of encoding an SD digital data stream from analog than can my DVR - and at the same data rate.

What I hope to learn here is if others who are sensitive to digital compression artifacts can point me to DVRs and DVD recorders that have superior encoders. Are there any principles (specifications, key words) that would allow one to know about relative encoder quality issues without actually trying a product? Are there any reviews out there that concentrate on the encoder 'component', and can one determine whose encoder a box uses?

A related issue: A VCR can do fast and slow motion effects much more smoothly than can my SA DVR. Are there any DVRs which can do these effects smoothly? (Given the nature of the technology, I doubt it; but I hope to be surprised.)
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post #2 of 5 Old 03-19-2005, 07:06 PM
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How big is your TV? When you get a DVD recorder (or stand alone tivo or replay), you can change the bitrate to change the qualiy. The trade off is that at high qulity you can record 1 hour on that DVD, and at low quality you can record 4 hours. Most reviews will tell you you will not want to record at low quality! If you buy a stand alone Tivo or Replay to record the analog channels, which would work great since it would not need to be hooked up to your cable box at all, then you could record at "high" quality and it would look great. But your 30 hour tivo or replay would then only be able to record 10 hours at high quality... You digital channels look so good because they are compressed with encoders that cost more then your whole DVR on the original signal before it gets re-transmitted. The only easy solution I see would be to switch to a directivo (you would have to get directv of course) then all the channels would be digital. Or buy a stand alone tivo or replay which would be $400-$500 with activation to use with your current cable set-up.
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post #3 of 5 Old 03-20-2005, 03:02 AM - Thread Starter
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Originally posted by FarmBubba:
How big is your TV?

How could that be relevant? It is big enough for me to see compression artifacts that I do not like.

When you get a DVD recorder (or stand alone tivo or replay), you can change the bitrate to change the qualiy.

I know that. Clearly, in this context, I would only be interested in the highest quality.

If you buy a stand alone Tivo or Replay to record the analog channels, which would work great since it would not need to be hooked up to your cable box at all, then you could record at "high" quality and it would look great.

OK, this bears on the question I am asking, but with inadequate detail. I think I am a more severe critic of encoding quality than most. Are you saying that the encoder in a TiVo in "high quality" mode does a much better job of encoding analog programs than does the encoder in an SA 8300? If so, what other encoders are similarly or even more capable?

You digital channels look so good because they are compressed with encoders that cost more then your whole DVR on the original signal before it gets re-transmitted.

Given that I wrote, "But I do know that, with their professional equipment, the TV broadcasters can do a vastly superior job of encoding an SD digital data stream from analog than can my DVR - and at the same data rate.", I cannot figure out the point of what FarmBubba wrote above. Actually, I believe that those top-end on-the-fly encoders cost $thousands.

The only easy solution I see would be to switch to a directivo (you would have to get directv of course) then all the channels would be digital.

That is clearly not a solution to any problem I was asking about. What good is any encoder if all channels are digital? I am seeking information that would allow me to make a good choice on a digital recorder for recording analog channels.

Or buy a stand alone tivo or replay which would be $400-$500 with activation to use with your current cable set-up.

How does this make sense? Why is the price range you mention so high? Why would I use my cable box when recording analog? The DVR actually makes it extremely awkward to record analog outside the box (eg., to a VCR) anyway.
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post #4 of 5 Old 03-20-2005, 04:22 PM
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The size TV make great difference. If you have a nice 40"-70" HDTV and see artifacts from compressing analog channels, that is normal, there is no getting around it. If you have a nice 32" TV and you picture is still terrible then you might see some improvement from going with different hardware. Go buy a DVD recorder where you can return it, if you don't like the results, then return it.
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post #5 of 5 Old 03-21-2005, 12:15 AM - Thread Starter
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Quote:
Originally posted by FarmBubba
The size TV make great difference.
And, unless the set just has inferior resolution for its screen size, how far you sit from it makes an equally great difference - with the result that the TV size issue remains a red herring. As it happens, my set is an HDTV and we are talking about the appearance of recorded analog SD television. There is little chance that my set is poor enough to disguise SD compression artifacts.
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