November 18, 2009 • 27 mins
Inspired by listener mail, Jonathan and Chris discuss the difference between DVD and Blu-ray in this episode of TechStuff.
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Speaker 1 (00:00):
Brought to you by the reinvented two thousand twelve camera.
It's ready. Are you get in touch with technology with
tech Stuff from how stuff works dot com. Hello there, everybody,
and welcome to tech stuff. My name is Chris Poulette,
and I am the tech editor here at how stuff
(00:22):
works dot com, sending across from me as usual as
senior writer Jonathan Strickland. We're living in a material world.
You know, I'm not going there. It's because our our
guest producer, Liz called me a prima madonna, just because
I said that I can't work like this and I
would be in my trailer. By the way, my trailer
(00:44):
is underneath my cubicle. That explains the trash. Yeah, it does,
lots of trailer trash. You know what, Before we get
into a total rat hole here, I think we could
talk a little bit about some pumpkins. Pumpkins, Yes, all right,
what do you like to when you look at a pumpkin?
What do you think? I'm thinking I prefer it that
way and not as a pie. Really, I think I
(01:06):
would love to see that move at a high velocity
and splat into the ground as hard as possible, preferably
as far away from its origin possible. In fact, I
spend hours thinking of ways to propel a pumpkin through
mechanical means, through the air, onto the ground and splat
into a thousand pieces. Alright, then, so what is the
(01:27):
best way to achieve that? Well, it turns out the
best way to achieve it is to watch people who
already know what they're doing. And you can do just
that because the Science Channel has two television shows, the
Road to Punkin Chunkin and punkin Chunking, that are airing
on Thanksgiving Day, which would be November at eight p
(01:48):
m on the Science Channel. Yes, eight p m is
the Road to Punkin Chunkin. Nine pm is punkin Chunkin.
You two can watch as pumpkins do what they were
born to do, fly through the air and smash into
the ground. Ah. Yes, and hopefully noone will make pie
out of them afterwards, I would hope, not sowing the
seeds of destruction. You might say, yes. Indeed, I wouldn't
(02:10):
say that, but you might I would. All right, Well,
let's move on. Today's topic actually comes to us courtesy
of a little listener mail. This listener mail comes from
Brian in Vegas, Viva Las Vegas, Brian, He writes, Hey, guys,
love the podcast. Got a question for you, guys, what
(02:32):
is the difference between Blu ray and DVD? I own
both but can't tell the difference by looking at them.
Is that the way they encode the disks? Brian and Vegas. Well, Brian,
we're going to talk a bit about DVDs and a
little bit about Blu ray and what the differences and uh,
and you know why there's two different sets of all
the movies that you want to see in your local
movie store. And if we're lucky, we can manage to
(02:55):
get through the entire thing without quoting an Austin Powers movie,
because it all comes down to one simple thing. Freaking lasers.
Just get it all the way. Look, I got the
hairstyle for Dr Evil, so I'm just gonna go with it. Yeah, lasers,
Yeah exactly. So first of all, before we before we
(03:18):
really dig into it, let's talk a bit about digitally
encoding information onto a disc format. This applies to compact discs, DVDs,
blue rays, and even the limited HD DVD, also DVD audio, yeah,
other other formats as well, but really, any kind of
digital encoding upon a disc um So it's sort of
(03:42):
similar in a way to the analog way of encoding
sound on a vinyl disc, only in the sense that
you have to spend the disk and and a reading
mechanism goes across the disc and picks up information. Now
in the case, yeah, I wouldn't say that's completely that
(04:02):
that's the only way. Well, maybe not, but we're talking
the difference between digital and analog. There's a lot of
There are a lot of differences. Well actually yeah, I
mean the main one being nothing actually touches the disk,
and in in the newer polycarbonate discs. But in both
cases it is the surface of the disk which is
uh has has has a texture. It doesn't look like
(04:25):
a DVD has texture, but it does, right, So the
DVD has these tiny little bumps. It's there. Usually you
hear about DVD pits. The pit is on one side
of the DVD, but the side that is actually read
by the freaking laser beam that side. It's more of
a bump. And these bumps are tiny, and I'm talking
(04:45):
tinier than microscopic. We're talking on the nanoscale tiny, which
is why they appear flat to us. Yeah, of course
you can. You can try to smash them out with
a hammer, but I wouldn't recommend it because that will
break your dvdsy So, um, we're talking that, like I said,
in the nanometers range. Uh, the I'll tell you right. So,
(05:07):
so a typical bump on a DVD would be about um,
three and twenty nanometers in width, like like wide, which
is pretty narrows long, which is also not that long.
These are tiny, tiny little bumps, and uh, a red
(05:28):
laser reads these bumps. Yeah. The DVD players and and
c D audio players use red lasers to read the disks. Yeah,
So here's here's what's happening. A laser gets the the
DVD player or CD players shoots the laser that gets
reflected by these different little bumps and by the smooth
(05:51):
spaces between the bumps, and the difference in that is
what is interpreted by the machine as bits and bites,
and that in turn is what ends up being converted
into the video and audio that you experience when you
PLoP a DVD or Blu Ray into a DVD or
Blue Ray player and you turn your TV. The difference
(06:11):
is a matter of size, right, because a Blu ray
player can read bumps that are much much smaller than
a DVD player. And why is that? It's because of
freaking lasers. Yes, the blue ray actually got its name
from the fact that it uses a blue laser. Yes,
that's the blue ray right right. And uh, it has
(06:34):
a shorter wavelength of light wavelength. So that's that's the
whole thing. Because it has a shorter wavelength, it can
read information in a smaller track. Right. So, um, we're
talking about like like when you think of the spectrum
of colors, that's what we're talking about, the wavelength. So
roy g Biv. Although I think they took out the eye,
(06:56):
didn't they. I don't think there's no longer an indigo.
I think it goes is blue to violet now because
there was a discussion about how indigo and violet are
too close to one another to be considered separate. I
might did the school that I am familiar with they
are still teaching. Yeah, but we're in Georgia. So Roy
g Biv. The the color what a what a dirty look?
(07:19):
I got the Uh? I went to school in Georgia too.
But the colors go from the longer wavelengths to the
shorter wavelengths, So a red laser has a longer wavelength
um than a blue laser. Uh. So the red lasers
wavelength is about six d and fifty nanometers or rnometers
if you prefer, I do prefer nenometers. I'm saying nanometers.
(07:42):
And then the blue laser has four hundred and five
four and five nanometer wavelength. So that means that the
blue laser can actually focus on a smaller bump than
the red laser. Thus you are able to fit more
bumps and uh and the flat tracks between bumps on
a blu ray DVD than you would on a regular DVD.
(08:06):
What this translates to for you and me mean is
the dig capacity of storing a high definition film versus
a standard definition film. Right, so high definition audio and video,
why should just say high definition video? High definition audio
doesn't really mean anything. High definition video takes up a
lot of space, so much space that I A. If
(08:30):
you want to try and pack more than an hour
and a half of of a high definition content greater
than seven lines of resolution, you're gonna need something besides
a regular DVD, because even with video compression, it just
can't do. Oh, I can't do it uncompressed, and um,
(08:52):
even with video compression, it can't hold that much information. Really,
a single layer DVD only holds four point seven gigabytes.
I love that. I love only because I'm that's a
lot of information. Yeah. I think back to I think
back to the days of CDs coming out and thinking, Wow,
on one disc, I can hold that much information? Who
(09:14):
would ever need more than? Right? I mean seven hundred megs.
I can't imagine filling up more than a hundred at
a time. My first hard drive was forty megs. Yeah,
I think mine might have been run around that same size.
And before that didn't have a hard drive at all.
It was all on floppy disks. But yeah, I mean
a single layer of Blu ray in comparison, holds twenty
(09:36):
seven gigabytes, and that's more than two hours of high
def video or standard. Yeah. But the thing, the thing is,
though DVD is only really equipped to do right well,
I mean it can do seven twenty, It can do
more than that or to, but it can't hold as
much information. So, in other words, it can it can
(09:57):
do it, it just has to. It's not gonna it's
not gonna have as much. So like you can do
the higher resolutions, but you have to. But you because
that requires more information or more storage space, you can't
store as much of it as you could on a
blue ray. So again, DVD four point seven gigs, Blu
(10:18):
ray twenty seven gigs. That's single layer on either case.
Now you can double layer these discs. Uh. So a
double layer Blu ray would hold up to fifty four
gigabytes of data. Um. Now, when you're double layering, it's
kind of an interesting thing. You've got two different tracks
going uh along a disc. And here's another interesting thing,
(10:41):
another thing that's different between uh, the digital discs and vinyl.
With vinyl, you put the needle on the outer part
of the record and it naturally works its way through
the groove to the center. All right. With these digital discs,
the laser, the freaking laser starts in the center and
works it's outward toward the edge. Now, can you think
(11:03):
of anything that could cause an issue as a laser
moves from the center of a disk toward the outer
part of a disk? I mean, other than like a
scratch or a dog here, right, I'm just talking about
a natural thing that will happen as you're moving from
the center of a disk to the outside of a disk. Like,
what happens to the speed of the data that's going
by as you as your laser moves outward, Because yeah,
(11:26):
it's it's gonna get slower. Well, the disk has to
move slower. See, the problem is that it's gonna the
data itself will actually move faster because you're talking about
revolutions per second. Okay, if you keep your revolutions per
second constant, then the data is going to stream by
much faster toward the edge of the disk than it
would towards the center. Say yeah, yeah, okay, that makes sense.
(11:48):
And if you guys are having trouble imagining this, uh,
just get a piece of paper, put something put like
a little coin around, like maybe towards the center of
the paper, and maybe another one toward the edge of
the paper, and turn it one revolution. Now, in that
one revolution, both coins just made one circle, but the
one on the outer edge had to go a greater
(12:08):
distance in that same amount of time. Therefore, the one
on the outer edge is going faster. Okay, then, so
in order to compensate for this, DVD players and Blu
ray players actually physically slowed down the spinning of the
disk as the laser moves towards the outer edge. Okay,
so it automatically knows where where the laser is reading
(12:29):
and adjusts the speed of the disc spinning. Right, because
the arm that holds the freaking laser is always going
to be in a specific location and that dictates how
fast the disk needs to spin. Now, um with a
double layer The reason why I brought this up is
because with a double layer disk, it is possible to
have one layer of information go from the inner edge
(12:53):
to the outer edge of the disk, right, or from
the center to the outer edge, I guess I should say,
And then the second layer could start at the outer
edge and work its way back into the center. And
in that case, you would need to speed up the
disk as it started getting closer and closer to the center,
otherwise it would not be turning fast enough for it
to read the information properly. Right. In other words, DVD
(13:14):
players and Blu ray players make my head hurt because
they require physics and I was an English major. And
Blu ray transfers information faster too. I mean, it has
a thirty six megabit per second data transfer rate as
opposed to just ten make a bit per second for
our DVD, right, which is also important to note. Right.
(13:36):
So let's see what we got here. We've we've discussed
the fact that since you are able to create smaller
bumps in a Blu ray disk, you therefore can fit
more bumps onto a disc than you could with a DVD.
That's why you can store more information on it. That's
why you can store high definition information on it, as
opposed to a DVD, where you just can't. It's just
not doesn't have the capacity. Here's another thing that the
(14:00):
manufacturing process for the two different discs, it's different. Oh yes,
Because the DVD is a sandwich. It has two pieces
of polycarbonate plastic about zero point uh six millimeters six
tenths of a millimeter um in thickness, and the material
that has the information on it is sandwiched in between them,
(14:20):
and the two halves are glued together. Um. Whereas the
information on a Blu ray disc is actually on top
um of a one point one millimeter thickness disc, which
is really amazingly thin, I would think, um, But it
does have a a plastic coating on top of it,
a hard coating on top of it to keep it
(14:42):
from I'm assuming its plastic. It has a hard coating
on top of it to keep it from getting scratched.
But it does also prevent distortion uh that you know,
the plastic would cause as the laser would travel through it,
which is called by refringence. It's it's kind of it's similar, Marty,
but you know, bifrage. It's similar to you know, if
(15:03):
you've ever if you've ever like looked at something through
a really thick pane of glass or or underwater, you know,
where you you look up through the water and you
see something beyond the surface, and then when you do
surface through the water, you realize that it's not exactly
where I thought it was. It's similar to that. It's
(15:23):
not the exact same thing, but you can think of
it as uh analogous to it. But yeah, that can
cause the uh, the red laser to have difficulty getting
the information and it may even actually cause it to
uh to skip right. Yeah, that and that's a that's
what we call a bad thing. Yes, it means that
you're not going to get the experience you want out
(15:43):
of it. Also, a DVD has to be has to
be flat for that reason. Has to be red flat,
and Blu Ray disks do not necessarily have to be flat.
I would assume though, that it would be preferable if
they were flat. And uh there, because one of them
is like one point one millim you're stick in the
other as one point two millimeters stick. A Blu ray
and a regular DVD look pretty much the same to us.
(16:05):
I mean, like you said, is it in the encoding. Yeah,
but it's also in the decoding, which would be the
freaking lasers. Um, I'm gonna get so much mail about
people who were tired of hearing freaking lasers. I expect
you to. Liz probably will as well. She's kind of
chuckling right now, but it's not gonna be as funny
when you're editing, is it? Is it? Liz? Ha um?
(16:27):
And of course you could always soundscape this to make
me sound like and even she wanted. Now. The other
interesting thing, we have articles, by the way, on both
DVDs and Blue rays on how stuff works dot com,
both of which I found incredibly informative while cramming for
this podcast. Yes, and they have some great illustrations as well.
So if you're having if you're having problems, imagining what
(16:48):
it is we're talking about. I do highly recommend you
guys check out these articles because it will give you
a visual sense of the things that we're explaining. But
one of the things I thought was interesting that they
pointed out um in these articles is that the manufacturing
process for the Blu ray disc, even though it's different
from the way DVDs are created, it is not more
(17:09):
expensive than the way DVDs are created. So then why
would you say Blu ray discs cost so much more
in the stores. I think there are a couple of
different reasons. One is that it's a premium product, so
you are buying a high definition products so that you
can the experience that you will get watching a Blu
ray disc using a Blu ray player on a high
(17:31):
definition television. All of that is important. If you don't
have a high definition definition television, this isn't gonna do
any good. So but the experience of watching one of
those on an HDTV with right cable connectors, using the
right equipment, it's gonna be It's gonna be noticeable. It
may not be as huge a leap as DVD was
from VHS, but it's still going to be noticeable. The
(17:55):
other reason is that because the Blu Ray has a
greater capacity, you could actually pack more specials and UH
and extras on a Blu Ray disc then you could
on a DVD. And a lot of companies do that.
And thirdly, a lot of companies that are making Blu
Ray players have made them Internet capable and you can
actually access extra content through the Internet on your Blu
(18:19):
Ray player and UH, a lot of companies are are
making this available where you get, you buy the Blue Ray,
you put it in your player, you started up, and
then you can access extra content online and things like
you know, new subtitles. Let's say that you um wanted
to get a film but there was no you know,
you wanted to You had a friend who was coming
(18:41):
and their English wasn't so good, but they spoke fluent
Portuguese and you don't have Portuguese normally on the disc.
But if you pop it in you find out, hey,
there's an option here where I can get Portuguese subtitles.
Or it may be extra commentary. It could be anything
from even extra content like deleted scene. Really pretty much
anything that they can think of that the movie studios
(19:03):
can think of could be part of this extra content
that you can access with your DVD player, your Blu
ray player, I should say, not DVD player. UM. Now
you're limited mostly by a couple of things. One, you
have to have a high speed Internet uh access point. Um.
If you don't have that, then you're not going to
be able to access all this content. Even if you
(19:23):
could access it, it would take you so long to
download any of it because it's it's high bandwidth stuff.
If it's pointless, right, So you have to have a
high speed Internet connection. And um, you also what was
that I had to I had to and now I
only have the one. Ah, it's gone. It's gone high
(19:43):
speed Internet access. If it comes back, I'll shout okay.
So one of the things I was hoping it would
come back immediately, but no, it's not coming back immediately.
You touched on something there though that I think uh
might answer the listener meal question. And then I wanted
to come back to because we were talking about why
(20:04):
might you not be able to see the difference in
a DVD and a Blu Ray or h D DVD
for that matter of disc And I think it comes
down to something we've talked about before. And that's the
screen size and resolution of your TV. Yeah, it turns
out that, uh, let's say that you if you have
a larger television, you will notice these these differences a lot.
(20:28):
They'll they'll they'll jump out out at you more. Um.
If you have a smaller TV, the difference in resolution,
UM isn't going to be quite as noticeable. But on
that plasma you'll be able to pick it out. Yeah, obviously, yes, yes,
but if you're talking about like a say, thirty inch television,
(20:48):
and uh, you know, a thirty inch television, standard definition
may look pretty good. High definition is gonna look fine.
But you know, anything beyond seven lines of resolution you
probably don't need. I mean, you probably wouldn't really know
the difference between seven twenty which or your your two
main kinds of high definition TV in the United States,
(21:08):
the seven twenty lines of resolution or the ten eight
lines of resolution. Um. Now, if you have and even
if you have a bigger TV, some would argue that
the difference is really not that noticeable. So when I
say bigger TV, I'm talking like in the fifty to
sixty inch range, which is that's pretty big. I mean,
there are larger televisions out there, and of course you
could get say a projector, which would you know, a
(21:31):
digital projector is going to make an even larger picture.
And in that case, yeah, you may need some sort
of equipment that will provide a ten a D resolution
or else it's just gonna look kind of blocky, and
you know that it's not gonna it will look muddy
and not as not as crisp. Right. That I think
is probably the the crux of the situation right there.
(21:53):
And also there are a lot of DVD players out
there now that up convert uh signals now an up
converting d v D. What that does is it tries
to add in some of the information that is lost
during the video compression process. Because again, to get a
movie onto a DVD DVD, I don't know where that
came from onto a DVD, I tell you it's because
(22:15):
this studio so hot today, so warm in here today. Um.
But in order to get the information on there, they
use a compression format and uh, and you tend to
lose information when you compress it, and so an up
converter tries to add in information to create a more
high definition experience, even if the source material itself is
(22:38):
not high definition. So if you have an up converting
DVD and a Blu Ray player, and you have a
copy of the movie on DVD and a copy of
the movie on Blu Ray, the differences maybe subtle. They
you should probably still notice them. I mean, it's it's
not like, uh, it's not like it's you know, it
would take a an expert to see the difference. But
(23:00):
it may be that they're not. You know, maybe the
colors are just a little richer on the Blue ray,
or that the the edges are look a little more natural,
not quite as sharp. I mean, it depends. It's a
very subjective experience. Yeah, I would imagine so. Uh yeah, gosh,
it never came back to me. I don't know what
it was that was in my brain that just decided
(23:21):
to escape. At least it got while the getting is good. Yeah. Yeah,
there's so much stuff in there that's still stuck screaming
to get out. Thoughts. Did you have anything else to
add on this discussion of blue ray versus DVD? Not really? Okay,
Well hopefully that answered your question. Um, And you know,
we could have even gone into the whole HD DVD thing.
(23:42):
The the failure of the of that format, which you know,
what's what's sad is I actually backed that format. I didn't.
I didn't purchase an HD DVD player. I didn't go
that far, but I expected that one to win out
early on in the race between the two formats. Was
one of our very first podcasts. Yeah, HD DVD versus
(24:04):
Blue Ray. Yeah, you know, and and blue ray technically
can store more information than HD DVD could. But because
HD DVD hit the market first, I thought that that
was gonna be the I thought that was that was
the death knell there that and it's less expensive, Yeah,
and it was. It was significantly less expensive than Blue Race.
(24:25):
Of course, now Blu ray players are in a much
more excuse me, a much more affordable range, especially the
PS three Slim ount. So you don't rest around with Slim, No,
you don't at any rate. I was having a gym
crochy momentum at any rate. So that wraps up our
discussion on Blue Ray versus DVD. I guess that brings
(24:46):
us to our second round of listener mail. This listener
mail comes from Christopher and he says, hey, guys, love
the podcast. The AI episode was great. I just wanted
to add a little bit into the part about the captions.
As you mentioned, they are used for preventing people from
making mass accounts all across the net. There's a company
that is making these called Recapture. What they do is
(25:08):
take a word that is known and bends it into
a typical capture and takes another unknown word that has
been scanned from a book or some other means of
creating digital copies of hard copy works and assumes that
you will get the unknown word correct if you get
the known word correct. It then takes the newly discovered
word and places that in the scanned book instead of
(25:29):
the unreadable by O c R mess. Also, that leads
into O c R which could be a pretty good topic.
I think. Thanks for a great podcast. Keep it up.
Um yeah, I kind of wrote a little bit about
this when I wrote how captures work. The The idea
is really interesting. Google does this a lot where it
actually crowd sources, uh your search when you're trying to
(25:51):
search information within a hard copy. Um, so you've got
the scanned document, you're let's say that your search algorithm
cannot recognize the text within that scanned document because it's
just a picture, right. What you do is you pull.
It identifies that you know a section as being this
has got to be a word. Pulls that puts that
picture as part of the capture. When you identify both
(26:14):
the the known capture and the unknown one, it then
stores the information for the unknown one in a database.
As more and more people are confronted with that word,
it looks for the greatest number of people agreeing on
what that word is. Okay, let's say the word is
is trumpet, all right, and the people who are answering
(26:36):
this capture say it's trumpet and the other five percent
say it's something else. The program then says, all right, well,
then chances are this word actually is trumpet. And that's
how it tags that that picture with the word trumpet
and makes it searchable within a scanned document. So yeah,
yet another way of making artificial intelligence a little more
(26:57):
of a reality. That's yep. If any of you have
any other cool things to tell us, or questions or
comments or criticisms that sort of thing, you can write us.
Our email address is tex Stuff at how stuff works
dot com. Remember every Tuesday, one pm E Stern we
do tech stuff Live with great special effects. Sometimes it
(27:18):
actually records the episode we're doing, not today, but usually,
so check that out. If you do miss it live,
most of the time you're gonna be able to get
a chance to see the recorded version. Yep. And Chris
and I will talk to you again really soon for
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(27:40):
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twelve camera. It's ready, are you
Brought to you by the reinvented two thousand twelve camera.
It's ready. Are you get in touch with technology with
tech Stuff from how stuff works dot com. Hello there, everybody,
and welcome to tech stuff. My name is Chris Poulette,
and I am the tech editor here at how stuff
(00:22):
works dot com, sending across from me as usual as
senior writer Jonathan Strickland. We're living in a material world.
You know, I'm not going there. It's because our our
guest producer, Liz called me a prima madonna, just because
I said that I can't work like this and I
would be in my trailer. By the way, my trailer
(00:44):
is underneath my cubicle. That explains the trash. Yeah, it does,
lots of trailer trash. You know what, Before we get
into a total rat hole here, I think we could
talk a little bit about some pumpkins. Pumpkins, Yes, all right,
what do you like to when you look at a pumpkin?
What do you think? I'm thinking I prefer it that
way and not as a pie. Really, I think I
(01:06):
would love to see that move at a high velocity
and splat into the ground as hard as possible, preferably
as far away from its origin possible. In fact, I
spend hours thinking of ways to propel a pumpkin through
mechanical means, through the air, onto the ground and splat
into a thousand pieces. Alright, then, so what is the
(01:27):
best way to achieve that? Well, it turns out the
best way to achieve it is to watch people who
already know what they're doing. And you can do just
that because the Science Channel has two television shows, the
Road to Punkin Chunkin and punkin Chunking, that are airing
on Thanksgiving Day, which would be November at eight p
(01:48):
m on the Science Channel. Yes, eight p m is
the Road to Punkin Chunkin. Nine pm is punkin Chunkin.
You two can watch as pumpkins do what they were
born to do, fly through the air and smash into
the ground. Ah. Yes, and hopefully noone will make pie
out of them afterwards, I would hope, not sowing the
seeds of destruction. You might say, yes. Indeed, I wouldn't
(02:10):
say that, but you might I would. All right, Well,
let's move on. Today's topic actually comes to us courtesy
of a little listener mail. This listener mail comes from
Brian in Vegas, Viva Las Vegas, Brian, He writes, Hey, guys,
love the podcast. Got a question for you, guys, what
(02:32):
is the difference between Blu ray and DVD? I own
both but can't tell the difference by looking at them.
Is that the way they encode the disks? Brian and Vegas. Well, Brian,
we're going to talk a bit about DVDs and a
little bit about Blu ray and what the differences and uh,
and you know why there's two different sets of all
the movies that you want to see in your local
movie store. And if we're lucky, we can manage to
(02:55):
get through the entire thing without quoting an Austin Powers movie,
because it all comes down to one simple thing. Freaking lasers.
Just get it all the way. Look, I got the
hairstyle for Dr Evil, so I'm just gonna go with it. Yeah, lasers,
Yeah exactly. So first of all, before we before we
(03:18):
really dig into it, let's talk a bit about digitally
encoding information onto a disc format. This applies to compact discs, DVDs,
blue rays, and even the limited HD DVD, also DVD audio, yeah,
other other formats as well, but really, any kind of
digital encoding upon a disc um So it's sort of
(03:42):
similar in a way to the analog way of encoding
sound on a vinyl disc, only in the sense that
you have to spend the disk and and a reading
mechanism goes across the disc and picks up information. Now
in the case, yeah, I wouldn't say that's completely that
(04:02):
that's the only way. Well, maybe not, but we're talking
the difference between digital and analog. There's a lot of
There are a lot of differences. Well actually yeah, I
mean the main one being nothing actually touches the disk,
and in in the newer polycarbonate discs. But in both
cases it is the surface of the disk which is
uh has has has a texture. It doesn't look like
(04:25):
a DVD has texture, but it does, right, So the
DVD has these tiny little bumps. It's there. Usually you
hear about DVD pits. The pit is on one side
of the DVD, but the side that is actually read
by the freaking laser beam that side. It's more of
a bump. And these bumps are tiny, and I'm talking
(04:45):
tinier than microscopic. We're talking on the nanoscale tiny, which
is why they appear flat to us. Yeah, of course
you can. You can try to smash them out with
a hammer, but I wouldn't recommend it because that will
break your dvdsy So, um, we're talking that, like I said,
in the nanometers range. Uh, the I'll tell you right. So,
(05:07):
so a typical bump on a DVD would be about um,
three and twenty nanometers in width, like like wide, which
is pretty narrows long, which is also not that long.
These are tiny, tiny little bumps, and uh, a red
(05:28):
laser reads these bumps. Yeah. The DVD players and and
c D audio players use red lasers to read the disks. Yeah,
So here's here's what's happening. A laser gets the the
DVD player or CD players shoots the laser that gets
reflected by these different little bumps and by the smooth
(05:51):
spaces between the bumps, and the difference in that is
what is interpreted by the machine as bits and bites,
and that in turn is what ends up being converted
into the video and audio that you experience when you
PLoP a DVD or Blu Ray into a DVD or
Blue Ray player and you turn your TV. The difference
(06:11):
is a matter of size, right, because a Blu ray
player can read bumps that are much much smaller than
a DVD player. And why is that? It's because of
freaking lasers. Yes, the blue ray actually got its name
from the fact that it uses a blue laser. Yes,
that's the blue ray right right. And uh, it has
(06:34):
a shorter wavelength of light wavelength. So that's that's the
whole thing. Because it has a shorter wavelength, it can
read information in a smaller track. Right. So, um, we're
talking about like like when you think of the spectrum
of colors, that's what we're talking about, the wavelength. So
roy g Biv. Although I think they took out the eye,
(06:56):
didn't they. I don't think there's no longer an indigo.
I think it goes is blue to violet now because
there was a discussion about how indigo and violet are
too close to one another to be considered separate. I
might did the school that I am familiar with they
are still teaching. Yeah, but we're in Georgia. So Roy
g Biv. The the color what a what a dirty look?
(07:19):
I got the Uh? I went to school in Georgia too.
But the colors go from the longer wavelengths to the
shorter wavelengths, So a red laser has a longer wavelength
um than a blue laser. Uh. So the red lasers
wavelength is about six d and fifty nanometers or rnometers
if you prefer, I do prefer nenometers. I'm saying nanometers.
(07:42):
And then the blue laser has four hundred and five
four and five nanometer wavelength. So that means that the
blue laser can actually focus on a smaller bump than
the red laser. Thus you are able to fit more
bumps and uh and the flat tracks between bumps on
a blu ray DVD than you would on a regular DVD.
(08:06):
What this translates to for you and me mean is
the dig capacity of storing a high definition film versus
a standard definition film. Right, so high definition audio and video,
why should just say high definition video? High definition audio
doesn't really mean anything. High definition video takes up a
lot of space, so much space that I A. If
(08:30):
you want to try and pack more than an hour
and a half of of a high definition content greater
than seven lines of resolution, you're gonna need something besides
a regular DVD, because even with video compression, it just
can't do. Oh, I can't do it uncompressed, and um,
(08:52):
even with video compression, it can't hold that much information. Really,
a single layer DVD only holds four point seven gigabytes.
I love that. I love only because I'm that's a
lot of information. Yeah. I think back to I think
back to the days of CDs coming out and thinking, Wow,
on one disc, I can hold that much information? Who
(09:14):
would ever need more than? Right? I mean seven hundred megs.
I can't imagine filling up more than a hundred at
a time. My first hard drive was forty megs. Yeah,
I think mine might have been run around that same size.
And before that didn't have a hard drive at all.
It was all on floppy disks. But yeah, I mean
a single layer of Blu ray in comparison, holds twenty
(09:36):
seven gigabytes, and that's more than two hours of high
def video or standard. Yeah. But the thing, the thing is,
though DVD is only really equipped to do right well,
I mean it can do seven twenty, It can do
more than that or to, but it can't hold as
much information. So, in other words, it can it can
(09:57):
do it, it just has to. It's not gonna it's
not gonna have as much. So like you can do
the higher resolutions, but you have to. But you because
that requires more information or more storage space, you can't
store as much of it as you could on a
blue ray. So again, DVD four point seven gigs, Blu
(10:18):
ray twenty seven gigs. That's single layer on either case.
Now you can double layer these discs. Uh. So a
double layer Blu ray would hold up to fifty four
gigabytes of data. Um. Now, when you're double layering, it's
kind of an interesting thing. You've got two different tracks
going uh along a disc. And here's another interesting thing,
(10:41):
another thing that's different between uh, the digital discs and vinyl.
With vinyl, you put the needle on the outer part
of the record and it naturally works its way through
the groove to the center. All right. With these digital discs,
the laser, the freaking laser starts in the center and
works it's outward toward the edge. Now, can you think
(11:03):
of anything that could cause an issue as a laser
moves from the center of a disk toward the outer
part of a disk? I mean, other than like a
scratch or a dog here, right, I'm just talking about
a natural thing that will happen as you're moving from
the center of a disk to the outside of a disk. Like,
what happens to the speed of the data that's going
by as you as your laser moves outward, Because yeah,
(11:26):
it's it's gonna get slower. Well, the disk has to
move slower. See, the problem is that it's gonna the
data itself will actually move faster because you're talking about
revolutions per second. Okay, if you keep your revolutions per
second constant, then the data is going to stream by
much faster toward the edge of the disk than it
would towards the center. Say yeah, yeah, okay, that makes sense.
(11:48):
And if you guys are having trouble imagining this, uh,
just get a piece of paper, put something put like
a little coin around, like maybe towards the center of
the paper, and maybe another one toward the edge of
the paper, and turn it one revolution. Now, in that
one revolution, both coins just made one circle, but the
one on the outer edge had to go a greater
(12:08):
distance in that same amount of time. Therefore, the one
on the outer edge is going faster. Okay, then, so
in order to compensate for this, DVD players and Blu
ray players actually physically slowed down the spinning of the
disk as the laser moves towards the outer edge. Okay,
so it automatically knows where where the laser is reading
(12:29):
and adjusts the speed of the disc spinning. Right, because
the arm that holds the freaking laser is always going
to be in a specific location and that dictates how
fast the disk needs to spin. Now, um with a
double layer The reason why I brought this up is
because with a double layer disk, it is possible to
have one layer of information go from the inner edge
(12:53):
to the outer edge of the disk, right, or from
the center to the outer edge, I guess I should say,
And then the second layer could start at the outer
edge and work its way back into the center. And
in that case, you would need to speed up the
disk as it started getting closer and closer to the center,
otherwise it would not be turning fast enough for it
to read the information properly. Right. In other words, DVD
(13:14):
players and Blu ray players make my head hurt because
they require physics and I was an English major. And
Blu ray transfers information faster too. I mean, it has
a thirty six megabit per second data transfer rate as
opposed to just ten make a bit per second for
our DVD, right, which is also important to note. Right.
(13:36):
So let's see what we got here. We've we've discussed
the fact that since you are able to create smaller
bumps in a Blu ray disk, you therefore can fit
more bumps onto a disc than you could with a DVD.
That's why you can store more information on it. That's
why you can store high definition information on it, as
opposed to a DVD, where you just can't. It's just
not doesn't have the capacity. Here's another thing that the
(14:00):
manufacturing process for the two different discs, it's different. Oh yes,
Because the DVD is a sandwich. It has two pieces
of polycarbonate plastic about zero point uh six millimeters six
tenths of a millimeter um in thickness, and the material
that has the information on it is sandwiched in between them,
(14:20):
and the two halves are glued together. Um. Whereas the
information on a Blu ray disc is actually on top
um of a one point one millimeter thickness disc, which
is really amazingly thin, I would think, um, But it
does have a a plastic coating on top of it,
a hard coating on top of it to keep it
(14:42):
from I'm assuming its plastic. It has a hard coating
on top of it to keep it from getting scratched.
But it does also prevent distortion uh that you know,
the plastic would cause as the laser would travel through it,
which is called by refringence. It's it's kind of it's similar, Marty,
but you know, bifrage. It's similar to you know, if
(15:03):
you've ever if you've ever like looked at something through
a really thick pane of glass or or underwater, you know,
where you you look up through the water and you
see something beyond the surface, and then when you do
surface through the water, you realize that it's not exactly
where I thought it was. It's similar to that. It's
(15:23):
not the exact same thing, but you can think of
it as uh analogous to it. But yeah, that can
cause the uh, the red laser to have difficulty getting
the information and it may even actually cause it to
uh to skip right. Yeah, that and that's a that's
what we call a bad thing. Yes, it means that
you're not going to get the experience you want out
(15:43):
of it. Also, a DVD has to be has to
be flat for that reason. Has to be red flat,
and Blu Ray disks do not necessarily have to be flat.
I would assume though, that it would be preferable if
they were flat. And uh there, because one of them
is like one point one millim you're stick in the
other as one point two millimeters stick. A Blu ray
and a regular DVD look pretty much the same to us.
(16:05):
I mean, like you said, is it in the encoding. Yeah,
but it's also in the decoding, which would be the
freaking lasers. Um, I'm gonna get so much mail about
people who were tired of hearing freaking lasers. I expect
you to. Liz probably will as well. She's kind of
chuckling right now, but it's not gonna be as funny
when you're editing, is it? Is it? Liz? Ha um?
(16:27):
And of course you could always soundscape this to make
me sound like and even she wanted. Now. The other
interesting thing, we have articles, by the way, on both
DVDs and Blue rays on how stuff works dot com,
both of which I found incredibly informative while cramming for
this podcast. Yes, and they have some great illustrations as well.
So if you're having if you're having problems, imagining what
(16:48):
it is we're talking about. I do highly recommend you
guys check out these articles because it will give you
a visual sense of the things that we're explaining. But
one of the things I thought was interesting that they
pointed out um in these articles is that the manufacturing
process for the Blu ray disc, even though it's different
from the way DVDs are created, it is not more
(17:09):
expensive than the way DVDs are created. So then why
would you say Blu ray discs cost so much more
in the stores. I think there are a couple of
different reasons. One is that it's a premium product, so
you are buying a high definition products so that you
can the experience that you will get watching a Blu
ray disc using a Blu ray player on a high
(17:31):
definition television. All of that is important. If you don't
have a high definition definition television, this isn't gonna do
any good. So but the experience of watching one of
those on an HDTV with right cable connectors, using the
right equipment, it's gonna be It's gonna be noticeable. It
may not be as huge a leap as DVD was
from VHS, but it's still going to be noticeable. The
(17:55):
other reason is that because the Blu Ray has a
greater capacity, you could actually pack more specials and UH
and extras on a Blu Ray disc then you could
on a DVD. And a lot of companies do that.
And thirdly, a lot of companies that are making Blu
Ray players have made them Internet capable and you can
actually access extra content through the Internet on your Blu
(18:19):
Ray player and UH, a lot of companies are are
making this available where you get, you buy the Blue Ray,
you put it in your player, you started up, and
then you can access extra content online and things like
you know, new subtitles. Let's say that you um wanted
to get a film but there was no you know,
you wanted to You had a friend who was coming
(18:41):
and their English wasn't so good, but they spoke fluent
Portuguese and you don't have Portuguese normally on the disc.
But if you pop it in you find out, hey,
there's an option here where I can get Portuguese subtitles.
Or it may be extra commentary. It could be anything
from even extra content like deleted scene. Really pretty much
anything that they can think of that the movie studios
(19:03):
can think of could be part of this extra content
that you can access with your DVD player, your Blu
ray player, I should say, not DVD player. UM. Now
you're limited mostly by a couple of things. One, you
have to have a high speed Internet uh access point. Um.
If you don't have that, then you're not going to
be able to access all this content. Even if you
(19:23):
could access it, it would take you so long to
download any of it because it's it's high bandwidth stuff.
If it's pointless, right, So you have to have a
high speed Internet connection. And um, you also what was
that I had to I had to and now I
only have the one. Ah, it's gone. It's gone high
(19:43):
speed Internet access. If it comes back, I'll shout okay.
So one of the things I was hoping it would
come back immediately, but no, it's not coming back immediately.
You touched on something there though that I think uh
might answer the listener meal question. And then I wanted
to come back to because we were talking about why
(20:04):
might you not be able to see the difference in
a DVD and a Blu Ray or h D DVD
for that matter of disc And I think it comes
down to something we've talked about before. And that's the
screen size and resolution of your TV. Yeah, it turns
out that, uh, let's say that you if you have
a larger television, you will notice these these differences a lot.
(20:28):
They'll they'll they'll jump out out at you more. Um.
If you have a smaller TV, the difference in resolution,
UM isn't going to be quite as noticeable. But on
that plasma you'll be able to pick it out. Yeah, obviously, yes, yes,
but if you're talking about like a say, thirty inch television,
(20:48):
and uh, you know, a thirty inch television, standard definition
may look pretty good. High definition is gonna look fine.
But you know, anything beyond seven lines of resolution you
probably don't need. I mean, you probably wouldn't really know
the difference between seven twenty which or your your two
main kinds of high definition TV in the United States,
(21:08):
the seven twenty lines of resolution or the ten eight
lines of resolution. Um. Now, if you have and even
if you have a bigger TV, some would argue that
the difference is really not that noticeable. So when I
say bigger TV, I'm talking like in the fifty to
sixty inch range, which is that's pretty big. I mean,
there are larger televisions out there, and of course you
could get say a projector, which would you know, a
(21:31):
digital projector is going to make an even larger picture.
And in that case, yeah, you may need some sort
of equipment that will provide a ten a D resolution
or else it's just gonna look kind of blocky, and
you know that it's not gonna it will look muddy
and not as not as crisp. Right. That I think
is probably the the crux of the situation right there.
(21:53):
And also there are a lot of DVD players out
there now that up convert uh signals now an up
converting d v D. What that does is it tries
to add in some of the information that is lost
during the video compression process. Because again, to get a
movie onto a DVD DVD, I don't know where that
came from onto a DVD, I tell you it's because
(22:15):
this studio so hot today, so warm in here today. Um.
But in order to get the information on there, they
use a compression format and uh, and you tend to
lose information when you compress it, and so an up
converter tries to add in information to create a more
high definition experience, even if the source material itself is
(22:38):
not high definition. So if you have an up converting
DVD and a Blu Ray player, and you have a
copy of the movie on DVD and a copy of
the movie on Blu Ray, the differences maybe subtle. They
you should probably still notice them. I mean, it's it's
not like, uh, it's not like it's you know, it
would take a an expert to see the difference. But
(23:00):
it may be that they're not. You know, maybe the
colors are just a little richer on the Blue ray,
or that the the edges are look a little more natural,
not quite as sharp. I mean, it depends. It's a
very subjective experience. Yeah, I would imagine so. Uh yeah, gosh,
it never came back to me. I don't know what
it was that was in my brain that just decided
(23:21):
to escape. At least it got while the getting is good. Yeah. Yeah,
there's so much stuff in there that's still stuck screaming
to get out. Thoughts. Did you have anything else to
add on this discussion of blue ray versus DVD? Not really? Okay,
Well hopefully that answered your question. Um, And you know,
we could have even gone into the whole HD DVD thing.
(23:42):
The the failure of the of that format, which you know,
what's what's sad is I actually backed that format. I didn't.
I didn't purchase an HD DVD player. I didn't go
that far, but I expected that one to win out
early on in the race between the two formats. Was
one of our very first podcasts. Yeah, HD DVD versus
(24:04):
Blue Ray. Yeah, you know, and and blue ray technically
can store more information than HD DVD could. But because
HD DVD hit the market first, I thought that that
was gonna be the I thought that was that was
the death knell there that and it's less expensive, Yeah,
and it was. It was significantly less expensive than Blue Race.
(24:25):
Of course, now Blu ray players are in a much
more excuse me, a much more affordable range, especially the
PS three Slim ount. So you don't rest around with Slim, No,
you don't at any rate. I was having a gym
crochy momentum at any rate. So that wraps up our
discussion on Blue Ray versus DVD. I guess that brings
(24:46):
us to our second round of listener mail. This listener
mail comes from Christopher and he says, hey, guys, love
the podcast. The AI episode was great. I just wanted
to add a little bit into the part about the captions.
As you mentioned, they are used for preventing people from
making mass accounts all across the net. There's a company
that is making these called Recapture. What they do is
(25:08):
take a word that is known and bends it into
a typical capture and takes another unknown word that has
been scanned from a book or some other means of
creating digital copies of hard copy works and assumes that
you will get the unknown word correct if you get
the known word correct. It then takes the newly discovered
word and places that in the scanned book instead of
(25:29):
the unreadable by O c R mess. Also, that leads
into O c R which could be a pretty good topic.
I think. Thanks for a great podcast. Keep it up.
Um yeah, I kind of wrote a little bit about
this when I wrote how captures work. The The idea
is really interesting. Google does this a lot where it
actually crowd sources, uh your search when you're trying to
(25:51):
search information within a hard copy. Um, so you've got
the scanned document, you're let's say that your search algorithm
cannot recognize the text within that scanned document because it's
just a picture, right. What you do is you pull.
It identifies that you know a section as being this
has got to be a word. Pulls that puts that
picture as part of the capture. When you identify both
(26:14):
the the known capture and the unknown one, it then
stores the information for the unknown one in a database.
As more and more people are confronted with that word,
it looks for the greatest number of people agreeing on
what that word is. Okay, let's say the word is
is trumpet, all right, and the people who are answering
(26:36):
this capture say it's trumpet and the other five percent
say it's something else. The program then says, all right, well,
then chances are this word actually is trumpet. And that's
how it tags that that picture with the word trumpet
and makes it searchable within a scanned document. So yeah,
yet another way of making artificial intelligence a little more
(26:57):
of a reality. That's yep. If any of you have
any other cool things to tell us, or questions or
comments or criticisms that sort of thing, you can write us.
Our email address is tex Stuff at how stuff works
dot com. Remember every Tuesday, one pm E Stern we
do tech stuff Live with great special effects. Sometimes it
(27:18):
actually records the episode we're doing, not today, but usually,
so check that out. If you do miss it live,
most of the time you're gonna be able to get
a chance to see the recorded version. Yep. And Chris
and I will talk to you again really soon for
moral this and thousands of other topics. Does it how
(27:40):
stuff works dot com and be sure to check out
the new tech stuff blog now on the House Stuff
Works homepage, brought to you by the reinvented two thousand
twelve camera. It's ready, are you
TechStuff News
Hosts And Creators
Oz Woloshyn
Karah Preiss
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