Digital question

[Larryl]

For the past week I have been re-watching Roy Underhill's the Woodwright Shop videos. I started out with the current season and moved through the past three years. Finally my question; with each older year the picture quality becomes worse. Does the digital image wear out?

[herb fellows]

Are these home made, or professional dvd's?
My understanding is that they do, but you shouldn't be seeing any problem within 3 years.
Generally, I've heard about 10 years as a benchmark for any noticeable deterioration.
In fact, I have 7-8 year old home made dvd's that seem just fine to me. I would guess you've either got a storage problem (humidity, heat, cold?) or some faulty dvd's.

[LCHIEN]

your question does not provide enough information.
Quality loss can come from any step in the process chain from the camera to your playback system.

1. are you comparing original DVDs from the producers of the series or
2, are you comparing your own off the air recordings of these shows and if so, on what media - VHS (which is really analog) or home recorded DVDs.
The chain of possession is also important. Were they commercial DVDs on aanalog tapes stored for years before transferring to DVD or were they filmed with digital recorders and in digital format through the whole chain. More importantly, did the studio equipment change over the years, e.g. the first year were recorded in Analog equipment and years later transfered to DVD but the last years was filmed in high def digital from the get-go.

generally digital recordings are considered less likely to degrade than aanalog, and optical storage (e.g. DVDs are optical disks) are more permanent than magnetic. Age can cause the recorded bits to become less distinct leading to more noisy images on decoding, but this should last for many, many years unless you have faulty media. normally stored digital information has enough contrast or signal to noise ratio that very, very few errors are made in recovering the digital data. and satys this way even as the contrast degrades. Even then error correction allows lost bits to be replaced. Until the point where the contrast is so bad it exceeds the self-correction. Then the signal starts to break up and freeze as you see with digital television. On Analog recordings, degraded data recovery leads to worsening snow, a form of noise.

[Larryl]

Thanks Herb and LCHIEN for the explianations, obviously I didn't even know enough to ask the question properly. I was watching the videos on the PBS TV Woodright Shop web page. You both answered my question, but have to admit that I thought the media stored digital was ~permanent. Love this board, we have such a broad/deep knowlege base in our members.

[woodturner]

generally digital recordings are considered less likely to degrade than aanalog, and optical storage (e.g. DVDs are optical disks) are more permanent than magnetic.

Good explanation, just wanted to add that DVDs or CDs recorded at home are different than commercially produced disks.

Commercially produced disks are essentially permanent - the plastic used to make the disk is shaped to record the information. As long as the disk is not physically damaged, it should last forever. Note, however, that many plastics degrade when exposed to sunlight, so they should not be stored in sunlight.

Disks recorded at home use a different technology, since they have to be programmable. This technology is not permanent. Numbers thrown out for longevity are typically in the range of 5 years to 10 years. However, there have been bad batches of disks that have lost their data after a month or so.

As a bit of anecdotal experience, I have a DVD recorder I use instead of a VCR. When I use the RW disks, which can be written multiple times, I find that after I record over them 10 to 20 times, they no longer work correctly. When I record shows I want to keep, I record them on the R+ or R- media, not the RW media.

[cgallery]

As a bit of anecdotal experience, I have a DVD recorder I use instead of a VCR. When I use the RW disks, which can be written multiple times, I find that after I record over them 10 to 20 times, they no longer work correctly. When I record shows I want to keep, I record them on the R+ or R- media, not the RW media.

Ignoring the re-usability...

I once read that -RW media uses a metallic alloy, whereas -R media uses dyes.

I know that -R media can't be accidentally erased, but which will last longer if one is careful not to erase it, -R or -RW?

I've previously read an article by an engineer that said the -RW should last longer. But I've also read plenty of comments from people that said -R should last longer.

[herb fellows]

If you recorded them both one time, I don't know.
But the whole point of rw, which is more expensive, is to record over them, so this would not be a practical thing to do.
If you're recording 4,5,10 etc. times on a rw, I imagine it would degrade somewhat in quality, as Woodturner said, and the 'r' would be the better choice for longevity.
I believe they also sell a 'gold'(?) dvd for self recordings, which is supposed to last longer. It should by the price charged (I think they were 3x the regular dvd's), but I really don't know anything about it other than the claims made for it..

[pelligrini]

For the past week I have been re-watching Roy Underhill's the Woodwright Shop videos. I started out with the current season and moved through the past three years. Finally my question; with each older year the picture quality becomes worse. Does the digital image wear out?

It might also be a difference in how it was recorded and the process of encoding it to DVD over the years. Different codecs used, resolutions, original capture devices and recording medium, etc.

If you're streaming the shows it's probably their use of the compression codecs.