Line Doublers?

[Aaron N]

Does anyone use or know about line doublers? I'm pretty sure they work for doubling the lines of video to make sure no characters are missed, but do they work for audio as well? How do they work? Do they simply record the input signal and replace any missing pieces upon outputing the signal? Lastly, how much are they and are they worth the money? Any input is appreciated.

[Ray Garrison]

To quote from

http://www.getplugged.com/learn/GPLEARNPAGES_223191.html :

What is a Line Doubler?

In the quest to re-create the movie experience in the home, making the image appear more film-like is a high priority. And one of the main reasons normal video images don't look like film is because of the visible scan lines - if you look closely at a video screen, you can literally see the lines. A line doubler accumulates information from the image and paints twice as many lines on the screen in the same amount of time. This doesn't mean you see more lines, in fact, fewer lines are visible because the line doubler has drawn twice as many lines in the same space, basically filling in between the lines to create a solid image.

What You Need to Know

More and more line doublers are being integrated into projectors, digital TVs, and set-top boxes. That means that in years to come, you won't need to know anything about them at all. But for now, if it is not built into the projection TV you buy, an external line doubler can be added if your projection system meets a few requirements. The first requirement is a higher scan rate than standard TVs. For a line doubler to draw twice as many lines on the screen in the same amount of time, by definition it needs a scan rate twice as fast. Typical televisions and entry-level projectors have a scan rate of 15.75kHz. If you're adding a line doubler to your system, it will need to scan at twice that rate, or 31.5kHz, at a minimum - higher scan rates are okay, too.

Currently, there are also line triplers and line quadruplers on the market. Some can even do two or more of these processes and are called line interpolators. But for every step up in line manipulation, your projector needs a commensurate step up in scan rate. A line tripler requires a projector that has a minimum scan rate of 47.25kHz, and a quadrupler requires a minimum scan rate of 63kHz. Of course, these abilities come at incrementally steep prices. Entry-level line doublers can run from $2,500 to $8,000; triplers and quadruplers run as high as $30,000.

Besides offering one of the most satisfying film experiences in the home, these image processors - sometimes referred to as scan converters - offer a useful side benefit. Much of the technology investment you make in a projection system is spent in achieving a sustainable level of light output. Because they literally draw more lines on the screen, line doublers (and higher) increase the light output of the system. It's not double the amount of light, but every bit helps.

Line doublers, et al., can take the input signal from any video source in your system and convert it. They also offer a color-decoding chip that can often be an improvement over the one that comes in your system. The color decoder allows you to set your levels of color, tint, contrast, etc.

[dougdrake]

Isn't this also the function provided by Progressive Scan output in certain DVD players, at a much lower cost than an outboard line-doubler?

[Ray Garrison]

Short answer: yep. Line doubling gives many of the same enhancements to older video sources that progressive scan DVD players provide. Both require display devices that will support non-NTSC-standard input, and neither will work with your basic TeeVee set.

Long answer: progressive scan DVD players can actually provide a SUPERIOR picture to line doublers. The DVD player has access to the video data in its native digital format, and sufficient amounts of digital processing thrown at the signal with wild abandon can do some pretty wonderful things to the image prior to the D/A step.

Here's some verbiage courtesy of an enthusiastic manugacturer of high-end DVD products (Ayre at www.ayre.com ) and I quote:

"The VR2 video card for the Ayre D-1 DVD/CD player is the reference standard in video reproduction. Its progressive-scan outputs deliver an unprecedented visual experience that raises your involvement in home theater to a new level.

"Far more than a "line doubler", the VR2 represents an astonishing breakthrough in video performance. Through a complete re-thinking of each element contributing to the picture you see, the VR2 sets the benchmark for image quality, now and into the future. Here's how it works:

"The digital video signal read from the disc by the Ayre D-1 DVD/CD player is sent directly to the DVDO Image Enhancement Engine on the VR2 video card. This highly advanced digital processor provides automatic, seamless detection of each type of video source, distinguishing film, video, and graphic sources for optimized processing.

"Using patented Pure Progressive technology, film sources are perfectly reconstructed using a 3:2-pulldown inverse-telecine process to give you the true film experience, free of any artifacts. Video sources are deinterlaced using an advanced motion-adaptive algorithm that examines four sequential video fields. New pixels are calculated based on a sophisticated cubic equation for unsurpassed picture quality.

The progressive digital video signal is then fed to highest performance Digital-to-Analog Converters available. These are true 14-bit converters, with precision and linearity far exceeding conventional 10-bit devices. Three discrete devices are applied, one for each color channel, providing extreme image purity. These exclusive DACs provide balanced differential outputs to virtually eliminate digital switching noise from the video signal.

"In the analog domain, our proprietary differential current-to-voltage converters provide maximal linearity. Ayre's revolutionary zero-feedback video amplifiers give you the most natural picture possible, with stunning film-like clarity. True DC-coupled circuitry yields rock-solid black levels and unprecedented detail in low-light scenes. Extended bandwidth combined with near-perfect group delay yields the ultimate level of resolution, bringing your favorite DVDs to life.

"This exceptional combination of bold design innovation and superlative component quality brings a remarkable new dimension to your home theater. The Ayre VR2 is truly the Video Reference."

End of quote

Whether the Ayre DVD is really spif or not I can't tell you, never saw one, but it sure sounds good.

Ray

[Aaron N]

When I watch DVD's certain images appear to be "striped". For instance, during an opening shot consisting of flying over a city with numerous buildings the lines of the bulidings can appear to be striped. It seems to happen only with small, thin lines. Another example would be like the rails of a sailboat. The rails appear to be striped and as the boat moves up and down the stripes seem to move along the rails. I'm wondering if it's my DVD player. It's an entry level player, a Toshiba, and it may not be doing a good job at processing the picture. Do you guys think it's a fault with my DVD player or is it a natural characteristic of these devices? I hope Doug is right, if he is I'd like to find one of these players.

[Aaron N]

Ray,

You answered my question, but I was writing my reply as you posted yours. I think I'm going to go take a look at the website the Ayre machine is on.

[dougdrake]

Aaron - If you are looking at the Ayre, bring huge amounts of cash. I think Sterephile Guide to HT did a review on it a couple months ago, and the figure of around $5k comes to mind (but I could be wrong).

You can find a Toshiba or Pioneer with Progressive Scan for less than $500, I think.

As Ray quoted, though, be sure your "TeeVee" can handle the increased scan rate required!

The striping you are seeing with your player is often a product of the player -- many DVD players are challenged by shots that pan across horizontal and vertical lines (like stairs, masts, etc...). Don't feel bad if yours does it, too.

[mwiener]

You can get a DVDO IScan for $800 or less. They come in 3 models. You will find reviews are sites around the net.

Also the new DVD-2800 player from Denon has the DVDO IScan chip built into it for $800 list. This player was just released. They had some problems with the first shipment, but all indications are that it will be a great player. I would still wait a few weeks before ordering to verify all the kinks are worked out.

Mike.

[Ray Garrison]

I'd sure be nervous about dropping any significant dollars on just about ANY kind of technology related to multi-channel sound at this point. With multi-channel SACD finally rolling out, DVD-A finally hitting the stores, some vendors beginning to move towards a "universal" player (Phillips just released a player that does both multi-channel SACD, DVD Video, two channel SACD, "red bood" CD, CD-R, CD-RW, Abc, XYZ and QWERTY but STILLc> won't play DVD-A), companies like Perpetual Technologies driving down the cost of DSP processing and everything else that's going on, I'd expect to see an aggresive move towards more flexible, more powerful, less expensive toys building steam. Today's $3,500 super spiffy top-o-the-line player will be tomorrows Circuit City Buy of the Week at $299.

[avman]

progressive scan output WITH 3/2 film pulldown is an exceptional piece of equipment, the 450-500 dollar range prog. scan players don't do 3/2 pulldown, AND yuor tv/rptv/projector must also be compatable w/ 3/2 pulldown, THEN you get a picture just under high definition as far as appearence goes. we sell the integra dps-9.1 for around $1300. sony also makes an 'es' dvd/sacd player. i haven't seen one yet, but it's under consideration. hope this helps, avman

[WMcD]

I'm very intersested in how the new video systems work. Some discussion of the "old system" is warranted.

The "pull down" is interesting. I recall it is to allow a 24 frame per second film be shown on a 30 frame per second video system. Neat trick. (Bear with me, the video is actually 60 field per second.)

I set out the following of what I understand. It might be a little off. I tend to recall what I inferred, rather than the raw data.

Okay, we know that motion pictures are made up of a sucession of still pictures (frames) and they change every 1/24th of a second. We see 24 every second in the movie theater.

Video is said to be 30 still pictures every second. But we know they are painted line by line.

The video frame is interlaced, which is to say it is repeated in the video signal as two "fields." In a way, the transmission is 60 "fields" (which are sort of half video frames) every second. Odd numbered lines are traced in the first 1/60 of second then even lines, in the second 1/60th of a second. (Or maybe even then odd.) This is the "interlacing."

Line 1 (painted first sweep)

Line 2 (we'll come back after we're through with all the odd lines, in 1/60th of second)

Line 3 (painted in the second sweep)

Line 4 (painted after line 2, when we get to it, after 1/60 second)

Line 5 (painted in the third sweep).

It is a bit confusing without diagrams . . . however an appreciation of the tele-cine system is something else.

In real time, the video signal is really a 60 fields per second system. Yup there is the potential of painting 60 different pictures every second under the NTSC video system. They are "interlaced" together (per the above).

None the less, how to make the rates work together? This is the tele-cine system used to convert film (24 still pictures per second) to video (60 still pictures per second). Smart cookies came up with this half a century ago.

The conversion into video is"

Video Frame 1, Field 1 = Show Film Frame 1

(1/60th of a second, cumulative time.)

Video Frame 1, Field 2 = Show Film Frame 1

(2/60th of a second, cumulative time.)

Video Frame 2, Field 1 = Show Film Frame 1

(3/60th of a second, cumulative time.)

Video Frame 2, Field 2 = Show Film Frame 2

4/60th of a second, cumulative time.)

Video Frame 3, Field 1 = Show Film Frame 2

5/60th of a second, cumulative time.)

Wow. Look at the 5/60th second cumulative time figure. That is 1/12th of a second.

We've displayed 2 of the 24 frames per second film frames which each last 1/24th of a second. (1/12th second). We've done that in 5 fields of video, or 2.5 frames of video. 2.5 x 1/30 = 1/12th second. (Same for 5 x 1/60 seconds.)

The next transmission is

Video Frame 3, Field 2 = Show Film Frame 3

6/60th of a second, cumulative time.)

Video Frame 4, Field 1 = Show Film Frame 3

7/60th of a second, cumulative time.)

Video Frame 4, Field 2 = Show Film Frame 3

8/60th of a second, cumulative time.)

Video Frame 5, Field 1 = Show Film Frame 4

(9/60th of a second, cumulative time.)

Video Frame 5, Field 2 = Show Film Frame 4

(10/60th of a second, cumulative time.)

Okay let's check timing again.

10/60ths of a second is 1/6 second cumulative time. We've sampled 4 frames of film each lasting 1/24th of a second. (4 x 1/24 = 1/6) The samples have been put into 10 video fields or 5 video frames. 5 x 1/30 = 1/6 second.

Confused by these fractions? Me too, and I wrote them.

Let's look at the conversion in terms of film frames 1/24th second and video fields (half frames) 1/60th second. I'm going to sequentially number the film frames and video fields (half frames). This is the same information expressed above.

Video (half frame) <=Input from Film

1 < = 1

2 < = 1

3 < = 1

4 < = 2

5 < = 2

This is where we made our first break to look at the numbers. (Hey, look at the 3:2 ratio of film frames used as input!)

We continued:

6 < = 3

7 < = 3

8 < = 3

9 < = 4

10 < = 4

Hmm, we can conclude that the film frames are being sampled, but even numbered film frames are not being represented as much as odd ones. (Note, this is not interlacing.)

It seems to me that the video card is undoing the "pull down" system. Am I correct that the monitor is then running at 24 frames per second, or maybe 48 frames? I'd be happy to have some input.

Why is it called pull down? It may come from the mechanical mechanism in the film projector which pulls down the length of film to put a new little picture into position. As we can see, the new film frames are pulled down at at 3:2 ratio.

All comments, discussion, corrections, are more than welcome.

Regards,

Gil