Determining the capture area of a capture card [Archive]

Arachnotron

4th December 2003, 20:45

edit dec 6th 2003
I found some inaccuracies in these numbers. Some are 1 or 2 pixels off.
for example:
25, 9-712, 704, 10.2, 52.15, BT878, BTWincap v5.3.6.1
this should be 702 ITU pixels, 52 µs.

I will re-check them and be back later with corrections if needed.

For convenience I repeat my own earlier measurements

PAL:

25, 9-712, 702, 10.2, 52.0, BT878, BTWincap v5.3.6.1
23, 15-710, 696, 10.7, 51.56, BT878, Hauppauge WDM v3.35 b 21125
23, 15-710, 696, 10.7, 51.56, BT878, Iulabs universal WDM v3.1.28.36
23, 13-708, 696, 10.5, 51.56,CX23881, Hauppauge WDM v2.75.21070
23, 3-722, 720, 9.8, 53.33, SAA7113, Terratec Cameo Grabster 200 USB v3.05
22, 10-713, 704, 10.3, 52.15, SAA7134, Terratec Cinergy TV 400 WDM v1.2.0.5

NTSC:

23, 2-713, 713, 9.3, 52.80, BT878, BTWincap v5.3.6.1
23, 17-704, 688, 10.4, 50.96, BT878, Hauppauge WDM v3.35 b 21125
23, 17-704, 688, 10.4, 50.96, BT878, Iulabs universal WDM v3.1.28.36
24, 16-703, 688, 10.3, 50.96, CX23881, Hauppauge WDM v2.75.21070
22, 0-719, 720, 9.1, 53.33, SAA7113, Terratec Cameo Grabster 200 USB v3.05
22, 8-711, 704, 9.7, 52.15, SAA7134, Terratec Cinergy TV 400 WDM v1.2.0.5

PAL-60:

290?, 16-714, 699, 10.3, 51.78, BT878, BTWincap v5.3.6.1
22, 8-711, 704, 9.71, 52.15, SAA7134, Terratec Cinergy TV 400 WDM v1.2.0.5

Wilbert

6th December 2003, 21:20

I did my measurements:

http://www.geocities.com/wilbertdijkhof/SAA7108.rar

PAL: 1-720, 720 (720x576 and 704x576 are scalings, hence not ITU compliant)
NTSC: 1-720, 720 (all three are scalings)

1) I captured with vdub using the nvidia WDM 30.82 drivers.

2) I couldn't capture at 768x576.

3) Why aren't the vertical lines 1-4 captured?

Arachnotron

7th December 2003, 00:42

1:
I think this card might be 'ITU compliant with scaler' at 720x480/576, but the sampling frame is slighly shifted compared to the output of your DVD player. Which one of the two is or isn't compliant is difficult to say.

Note that the gray pattern in the 'unscaled' 720x480 cap is the same for all vertical lines, but changes if you do 704x480, which is scaled from the 13.5 MHz base. In fact, I think that it should be possible to calculate back the base sampling rate from the interference patterns

Did you use a composite lead by the way?

This is the first DVD player I saw which actually outputs all pixels without cropping.

2: this is probably a driver issue. I remember reading a driver .inf file in which the revision comments mentioned limiting the allowed horizontal resolution to a maximum of 720.(can't find it back though)

3. They are captured, but your DVD player has cropped them, so they are black. It seems all DVD players crop lines, mostly 4 but which ones vary.
Your DVD player only does this in PAL mode.

The end result is that there is a 4 line variation in which lines a DVD player puts the center of the image.

edit

Notice by the way your card starts capturing below line 23, since the WSS signal is not visible in your PAL cap. A WSS line looks like this (http://www.arachnotron.nl/videocap/download/WSS%20demo.JPG) in the top of a capture.

Wilbert

7th December 2003, 14:02

I think this card might be 'ITU compliant with scaler' at 720x480/576, but the sampling frame is slighly shifted compared to the output of your DVD player. Which one of the two is or isn't compliant is difficult to say.
Hmm. I always thought that 'ITU compliant' meant "the 4:3 picture is given by the 702x576 part of the image (thus active area is 52 µs)". How can the one at 720x576 be ITU compliant?

Note that the gray pattern in the 'unscaled' 720x480 cap is the same for all vertical lines, but changes if you do 704x480, which is scaled from the 13.5 MHz base. In fact, I think that it should be possible to calculate back the base sampling rate from the interference patterns
How do you suggest to do that?

Did you use a composite lead by the way?
Yes. I couldn't get s-video to work a while ago (image remains grey). I guess both scarts of my tv are composite.

This is the first DVD player I saw which actually outputs all pixels without cropping.
Pioneer DV77.

2: this is probably a driver issue. I remember reading a driver .inf file in which the revision comments mentioned limiting the allowed horizontal resolution to a maximum of 720.(can't find it back though)
I could you can change this in your registry. But I don't know what to change ...

erratic

7th December 2003, 14:04

@Arachnotron, regarding that WSS line:
I read in this PALplus document (http://tallyho.bc.nu/~steve/palplus.html) (section 5.0) that a WSS line can also flag the format as Letterbox 16:9 Center. I was wondering if such a line can be inserted into a letterboxed MPEG-2 file to make a TV zoom in automatically when you play a letterboxed (not anamorphic) DVD.

This question doesn't really belong in this thread but I think the answer will be short: No, it's impossible. :(

Arachnotron

7th December 2003, 14:33

@ Wilbert,

I always thought that 'ITU compliant' meant "the 4:3 picture is given by the 702x576 part of the image

Your card puts 720 DVD pixels in 720 grabbed pixels when you grab at 720x576;
so, 720x576 grabs 53.333 µs, which means 702x576 does 52.0 µs after cropping the 720.

How do you suggest to do that?

I don't know the math for it, but the resulting patterns in the vertical lines is the result (harmonic) of the interference between the requested sampling frequency and the base sampling frequency of the card. Theoretically if you know the one you should be able to deduce the other, but I don't know how myself. Just a thought.

Yes. I couldn't get s-video to work a while ago (image remains grey). I guess both scarts of my tv are composite.

I thought so because of the extra blurring and rainbow artefacts caused by the comb filter of the card.

could you can change this in your registry. But I don't know what to change

I'll check. I just remembered which driver it was: the new drivers for an Asus SAA7134 based TV card. But many options are compiled into the driver and cannot be changed from the registry.

@ Erratic:

You might fake the pattern, but the resulting line would have a colorburst in it, which the original signal doesn't have. Also, you would have to be certain which line, if any, from the MPEG2 your DVD player puts out in TV line 23. Last, most DVD players crop a few lines, and since this would be the first line it is a sure thing to go. And of course, any DVD player would output it's own WSS signal in line 23, overwriting your WSS.

But I think you can set AR info when you author a DVD. I remember ripping a DVD with a wrong AR and burning it back with an adapted menu once. Unfortunatly, that was a while back and I don't know how I did it or where the option is. Something for a DVD forum I guess.

trevlac

9th December 2003, 15:08

Originally posted by Arachnotron
I don't know the math for it, but the resulting patterns in the vertical lines is the result (harmonic) of the interference between the requested sampling frequency and the base sampling frequency of the card.

Hey,

So many interesting things ....

Does this mean that the card's resize causes an interference pattern in the picture? Would it be better to cap at full size and then resize? Maybe I should learn more about this, instead of looking at post cap processing.

You can never really know enough ...

:(

Arachnotron

9th December 2003, 16:02

@Trevlac,

This remark is based upon something I noticed when I was making my series of captures. When I captured using the Terratec grabster at 720x576 or the Terratec Cinergy at 704x576 I got really beautifull captures that looked almost identical to the original DVD. A 1 pixel vertical line in the DVD would result in a 1 pixel wilde line in the capture.

When I did the same with the BT878 or the CX23881 the resulting lines were blurred. I was very surprised by this; the sample rate of those cards is higher than those of phillips.

Untill I realised that the phillips card were working at the same base sample rate as the DVD player, 13.5 MHz AND that the horizontal sync happened at the same time. So every pixel in my cap was positioned exactly under the analogue peak which in turn resulted from a matching pixel on the DVD.

Basically, the system was genlocked and as a result the Kell factor no longer applied.

This was a happy coincidence; the other 13.5 MHz devices in this thread had a slight offset. As a result, the peak resulting from a white pixel on the DVD is 'hit' by at least two pixels in the capture. But because the sample rates still match, the resulting gray pattern is the same for each horizontal line. This is how I know Wilberts cap was unscaled and 13.5 MHz. (this (http://www.arachnotron.nl/videocap/site/capwindow_edge.jpg) picture illustrates some of this effect)

The moment your card has another sampling rate than 13.5 (as I suspect is the case for the ATI theater range and certainly the case for the conexant cards), you will get an interference pattern. The gray pattern changes going from left to right, but after a certain interval will start to repeat itself.

From this interval you should - in theory - be able to calculate back what the sampling rate was; the pattern is caused by interference between the 13.5 MHz of the DVD peaks (or, to be more presize, the cycle time of the repeating white pixel/19 black pixel sequence) and the sample rate of the card.

Dropping a scaler over this adds a third sample rate to the mix.

And of course, if you use composite (as wilbert did) you blur the original signal throught the comb filter. It migth turn out that Wilberts card WAS genlocked, and that with a svhs leas the cap would be sharp.

In analogue caps this may not be important, unless the source came from a digital master. If that is the case, there might be a capturing 'sweet spot' where the sampling matrix matches the source.

Edit: explanation of the pic

# A. line 130 of the 720x480 mpeg file. Pixels 1-7 are white, the following ones are 50% gray
# B. On playback, the DVD player crops the first 3 pixles and replaces them with horizontal blanking.
# C. The analogue signal produced by the DVD player. The signal rises from blanking level to white level, stays at white level for about 0.2 µs and drops down again to 50% grey level. Note the rise time going from blanking level to white level (rise time is the time it takes to go from 10% to 90% of maximum signal). This is almost 0.06 µs which equals 0.8 DVD pixel! This is why a vertical change from black to white on a DVD will always result in a grey pixel in the capture. To increase the precision, the test DVD uses white lines on a 50% grey background, since going from white level to 50% grey takes less time.
# D. Theoretical capture card with the capture window coinciding with the signal resulting from DVD pixel 7.
# E. Theoretical capture card with the sampling grid 'out of phase' with the pixelgrid on the DVD. The first pixel captured contains signal from DVD pixels 6 and 7, and is white, but capture pixel 2 contains signal from the flank and results in a grey color between white and 50% grey.
# F. Theoretical capture card with the capturing window beginning before the start of the active part of the DVD signal. Because of this, two black pixels are captured on the left. The third pixel is grey, since most of the analogue signal in this area is on a slope between black and white

The above is a bit of a rambling story, but I hope you understand what I am getting at? It's just a bit of speculation on the side, but interesting. It might be complete nonsense of course. :D

edit2 Looking at it, the pic may not be the best illustration if what I am talking about, but it is the only illustration of a shifted sampling frame I have

trevlac

9th December 2003, 20:45

@Arachnotron

For some strange reason I love this stuff. :D

Some observations form a guy who has no formal education in electrical engineering.

1) I don't see why a 13.5MHz card could not represent either the perfectly in phase line and (D), and the out of phase line (E). Depends on how the card locks on the sync, and considering it may not be working with a full lenght signal, I'm suspecious of an insync capture. *** Forget this. I re-read your post. You got 1 of these not all the time like I thought you said. ***

2) A higher sample rate card should have more 'pixels' in it's line. 17.74MHz is about 25% more for PAL. *** Hence the pattern you mention *** I may try 754 NTSC and look for the pattern. No scaler here.

3) I have never seen kell used when refering to horizontal. At least in a reliable source. Here is an example of many articles. No horizontal kell that I see. http://broadcastengineering.com/microsites/searchresultsnext_mag.asp?qry=kell&return=20&record1=1&sort=1&searchparams=qry%3Dkell%26return%3D%26Magazine%3D158%26Magazines%3Don%26bg%3D%26bizcom%3Don%26newsfeatures%3D&idlist=158&SiteID=15&magazineID=158&codeID=&srID=11249&PageID=5126

Also, It is my understanding that you should not be able to 'see' a single DVD pixel. The best you can do is see 1 pixel for every 1.333 pixels using a 6.75MHz bandwidth s-video connector. This assumes everything thru the DVD player supports this bandwidth. Composite is most likely less.

4) I am following your tests and information. I think it is great. I plan on doing a test on the drivers for my MSI CX card, when I get a chance.

Thanks

Arachnotron

9th December 2003, 21:43

For some strange reason I love this stuff.

Yep, me too :) (including the no formal training part ;)

I will re-do some caps using my new test DVD's. See if I can reproduce it again. But the "in phase" pattern for 13.5 MHz caps without scaling is clearly visible and not only in my caps.

@3:
As to Kell: I am talking about verical lines here. The pattern can be seen in a horizontal band consisting of repeating single pixel vertical lines in my test DVD's.

But I took Kell as an illustration of the principal behind this, not as something that applies in the strict sense.
My understanding of Kell and Nyquist is that both are based on the same thing: if you are trying to sample /display a signal that has random lines in it, how narrow should your grid be to be sure to 'catch' an event which happens at a certain speed (line-width). The key here is random. A DVD player is a synthetic signal, produced from a perfect 13.5 MHz clock. Not random. So you loose the Nyquist/Kell like fudge factor if you cap it at a fixed sampling rate.

@4
As far as I have seen, composite is less.
But under optimal conditions, you can see a single DVD pixel. Only those conditions don't apply to a normal video signal.

For example: If you try alternating black and white single pixel vertical lines from a DVD, In your cap you will probably see an alternating light gray/dark gray pattern. This is not a capture artefact; the peaks resulting from the white pixels are fusing, resulting in a signal that oscillates somewhat between white and blacklevel. edit but alternating double pixel lines you can separate, which sounds about right for the limit you mentioned. /edit

This is I think the bandwidth limitation you are talking about. You cannot have an ordinary picture, cap it from DVD and then reproduce it. Because of bandwidth limitations, the finer details will fuse an come out blurred.

But I was very carefull to avoind this on my test DVD. I have single pixel lines on a background that is already on about 25-30% gray level. The resulting peaks can be picked up in a single sampling period of a 13.5 MHz card. But once again, not anywhere near standard.

But I have made some Oscilloscope caps of what the signal looks like. It will take me a few days to process (they are CSV files, I have to plot them first) and I think this will explain a bit why this works.

Arachnotron

10th December 2003, 01:01

@ Trevlac
I did some tests. The results are in this pic (26k):

http://www.arachnotron.nl/videocap/download/strips.rar

it shows a cutout of the center 7xx x 16 pixels of a cap, aligned under each other for easy comparison.
the strips are:

1. original BMP source of the DVD
2. SAA7113 cap 720x576 (ITU device, does not have a scaler)
3. SAA7134 cap 704x576 (13.5 MHz device, does have a scaler)
4. BT878, IUlabs, 696x576 (17.2 , scaler)
5. BT878, Iulabs, 704x576

All show a pattern around a white center line except the last cap.

So, as long as the samplerate is 13.5 all vertical lines look the same. wether you get 13.5 directly or through scaling does not matter.

The moment the sample rate is not exactly 13.5 you do get interference patterns.

I found out the pattern you see is caused by the first and second harmonic on the sides of the main peak. This again is caused by the high 'offset' caused by the light gray background. An effect I hadn't considered when I made this testDVD. :). When the oscilloscope pictures are finished I can show this more clearly.

What this does make me suspect though is that these devices sample at 27 resp. 35.44 MHz, 9bit resp 8 bit and from these raw samples (27/35 MHz IRE values) directly interpolate the desired number of pixels. If there was (for the BT878) a 921 pixel intermediate that was resized to 696 there WOULD be a different pattern around the white lines between the unscaled 13.5 and scaled 17.2 devices.

trevlac

10th December 2003, 20:11

@Arachnotron

I don't really have anything to add. I just wanted to thank you for the test pic and all of the work you have been doing on this. I havn't been able to run the test myself (busy time of the year), but I'd like to. Have you ever seen the AVIA pixel cropping test pattern. This might give you some ideas on yours. They stagger the lines on a grey background. I'll try to post a link in a few hours.

Cheers.

Edit:

Here are the pics. The first is the pattern they use. The second is some instructions they provide. I thought this might be helpful as a contrast to your approach. As to the merrits, you'd know better than me. It appears they avoid the issue of high frequency events by staggering the vertical lines. Also, they include markers in the corners that can be used on a scope (they say).

http://pics.trevlac.us/img.htm?crop.jpg

http://pics.trevlac.us/img.htm?cropinfo.gif

Arachnotron

11th December 2003, 12:06

@Trevlac

Hi Trev,

Thanks for the info. reading back my last two posts in this thread I realize they are a bit messy, partly because my understanding of these effects changes/increases while writing and discussing them.

Once I have a firmer grip on these things and have some scope pictures to go along with this I'll do a short webpage on the sort of artefacts/phenomena you see in captures.

It will take some time since I have two other pages to write first. :-)

Thanks for the test pattern you mentioned. I'll look into it. Your links didn't work by the way, but from the descriptions on the web I get the inpression it is a tespattern you can use to find out which pixels are cropped by the DVD player on the edges.

trevlac

11th December 2003, 14:17

Originally posted by Arachnotron
Your links didn't work by the way, ....

They work for me on different machines. They use javascript to show the image because my provider does not allow direct links to images.

The direct links are below. To use them you have to paste them into a new browser window.

pics.trevlac.us/crop.jpg
pics.trevlac.us/cropinfo.gif

Arachnotron

11th December 2003, 16:05

Thanks, I got them. I am using Mozilla, perhaps that is the problem. I get a red smily that appears to give me the middle finger (or is it thumbs up ? :D)

By the way, do you own this test DVD? Is it any good?

trevlac

11th December 2003, 17:45

By the way, do you own this test DVD? Is it any good?

I do own it. It's a bit old. There is a newer/cheaper one at Amazon.co.uk (http://www.amazon.co.uk/exec/obidos/ASIN/B00009WW03/qid=1071161361/sr=1-1/ref=sr_1_10_1/026-5855084-6082055).

I have found it to be helpful. It probably has 100 test patterns. However, it doesn't really provide great instruction on their uses. The more I learn, the more I go back and say 'oh, thats what you use that for.'

Red smilies? How did they get there?

http://www.dvdrhelp.com/forum/images/smiles/toma.gif (http://www.dvdrhelp.com/forum/images/smiles/toma.gif)

NOTE:The link I gave was not to the product I have. The one I have is older and costs more. You should read reviews of the newer one before you buy.

Arachnotron

11th December 2003, 20:55

Red smilies? How did they get there?

Yep, that is the one I am getting. In IE6 the pics display ok, in mozilla I get the finger :)

I have found it to be helpful. It probably has 100 test patterns. However, it doesn't really provide great instruction on their uses. The more I learn, the more I go back and say 'oh, thats what you use that for.'

OK, thanks for the info. I have been thinking about ordering it, but wasn't sure about it's usefullness.

Arachnotron

13th December 2003, 01:39

@trevlac

Look here (http://www.arachnotron.nl/videocap/site/peak_dvd.jpg)

Small pic showing DVD pixels, resulting oscilloscope trail and resulting pixels in BT878/btwincap 720x576 cap. (gray values taken from actual cap).

Kinda explains the 'interference' pattern, and the bandwidth limitations you mentioned.

trevlac

14th December 2003, 04:42

@Arachnotron

I've been reading a bunch and here is what I am guessing on this stuff today. :)

1) Sampling Theorem says "A signal can be reconstructed from its samples without loss of information, if the original signal has no frequencies above 1/2 the sampling frequency. (Nyquist)"

This tells me there is no such thing as Kell in captures. I think the 'missing link' is that a signal is (and can be) broken down into sin or cosine waves. Even though the samples may not line up with the signal peaks, they can be reconsturcted because the interpolation between samples is not a straight line, it is a sin curve that matches the orignial peak. Hense, "without loss".

This makes the "perfect sync" capture a mystery. I believe you had it, I'm just not sure what it was.

2) The less than exact samples are not due to the cards, but due to the dvd player. A single pixel is higher in frequency than is supported by DVD. The player filters this and the result is the curve you posted. It looks like a "sinc function". Here is where I really can't connect the dots. A sinc function is a representation of a low pass filter.

This has been great fun. However, some of the reading does make my head hurt. ;) I found I lacked knowledge of things like "periodic trigonomic functions". But I think I am beginning to muddel thru.

Here (http://www.cs.princeton.edu/courses/archive/fall00/cs426/papers/hanrahan95.pdf) is a paper I read about 20 times before I started to 'get it'. I might still not get it. :)

Arachnotron

14th December 2003, 23:22

1) Sampling Theorem says "A signal can be reconstructed from its samples without loss of information, if the original signal has no frequencies above 1/2 the sampling frequency. (Nyquist)"

This tells me there is no such thing as Kell in captures.
Agreed. Kell is about TV lines/ CRT apertures. Wrong example :)
I think the 'missing link' is that a signal is (and can be) broken down into sin or cosine waves. Even though the samples may not line up with the signal peaks, they can be reconsturcted because the interpolation between samples is not a straight line, it is a sin curve that matches the orignial peak. Hense, "without loss".
Agreed. When I had worked out the pic in my previous post, it dawned on me I was barking up the wrong tree. But I hadn't found the right explaination yet. More reading! Oh Joy :D :D
This makes the "perfect sync" capture a mystery. I believe you had it, I'm just not sure what it was.
I have a theory. I have not been able to reproduce the cap, but I noticed that when I juggle with different capture cards, sometimes the device settings are not reset. My guess is I unknowingly made a cap with a limited contrast/brightness range, which resulted in only the white 'peak' values showing and the oscillations at the sides disappearing in the background. With a grayscale cap, the result looks perfect.
2) The less than exact samples are not due to the cards, but due to the dvd player. A single pixel is higher in frequency than is supported by DVD. The player filters this and the result is the curve you posted. It looks like a "sinc function". Here is where I really can't connect the dots. A sinc function is a representation of a low pass filter.
Is it pixel frequency versus Y carrier frequency ? (everything is grayscale and s-video in my caps, so no chroma or comb filtering)
I will read the pdf you posted. From a quick look at the graphs in it, you are correct thet the results originate from something like this..
For comparison here is the same graph from a SVCD, so with a lower pixelrate. Notice the oscilations are much less pronounced. SVCD peak (http://www.arachnotron.nl/videocap/site/peak_svcd.jpg)

If you look at the figure on page 7: those are exactly wat the signal resulting from 1 white pixel, 2 pixels, 3 pixels....10 pixels look like. (but more streched out horizontaly of course)

This has been great fun. However, some of the reading does make my head hurt. I found I lacked knowledge of things like "periodic trigonomic functions". But I think I am beginning to muddel thru.

Not just the reading. Some of the pictures... The math is way beyond me, but I will nevertheless have a stab at it. A long, long time ago somebody tried to teach FFT to me, but I didn't get it at the time, and probably never will :(

Thanks for the great link!

trevlac

15th December 2003, 04:28

Originally posted by Arachnotron
Not just the reading. Some of the pictures... The math is way beyond me

You're not kidding on the math. I really did read that last one about 20 times before it started to sink in. Your pictures actually helped a lot. When I noticed they matched, I said "wow".

Here is another great link: http://www.snellwilcox.com/knowledgecenter/books/books/ecomp.pdf

This stuff starts on about page 18. They say the "little bumps" are Gibbs' phenomenon. Havn't read about that yet.

Another interesting thing in this one is that they say if you decimate the samples, it is exactly the same as simply reducing the sample rate. Appearently this is true because of what I mentioned about how the "dots" are connected. Using curves. Anyway, what this means is that "resizing" the samples like the scaling cards do, is theoretically exactly the same as changing the sample rate.

To further go along this line, the cards with a scaler, do have a variable sample freqency. :) Wierd. One of the 1st things I though I knew was that they sample at 1 and only 1 rate.

I'm gonna have to go back to that BT878a doc and re-read to see what I think today.

EditHere is another great link. Wish I could stay up and read it, but I need sleep: http://www.analog.com/Analog_Root/static/technology/dsp/training/materials/pdf/dsp_book_Ch3.pdf

Arachnotron

16th December 2003, 01:46

To further go along this line, the cards with a scaler, do have a variable sample freqency. Wierd. One of the 1st things I though I knew was that they sample at 1 and only 1 rate.

I think it is fixed, but sampling rate here refers to the basic sampling. I.E. converting the voltage at fixed intervals into a digital value. This is the first step in the whole dsp chain and must be Nyquist. Otherwise, if you sampled for a low, say QCIF resolution (176*144), you would not be able to separate colors any more since both colour and luma frequencies would be to high compared to your sampling rate.

But the second step, comb filtering and pixel engine, could be a dsp circuit running at the target sampling rate. After which you crop off the blanking bits you don't need and output the rest.

This would make the cards referred to as ITU run ADC's and the DSP at a locked 13.5 MHz frequency.

By the way, the clock part is the PLL, which is a circuit fed by the crystal and which can be programmed to deliver other frequencies.

So may fun things to play with, so little time to do it in....

I am struggeling with your reading list :D and trying to 'simulate' the DVD player's output signal to get a grip on the math. So far, no luck. But I still have some writing to do, so I have to put this on the back burner for a few days :(

EDIT That compression link is great! No mathematical background, but a lot of pictures really explaining step by step where the analogue signal comes from (p30-34). In my pics, I should have replaced the 'pixels' with single line sample spikes.

edit2 look at this (http://www.snellwilcox.com/knowledgecenter/whitepapers/papers/digital_arc.pdf) link. Not much depth, but it illustrates what I am trying to say. :) Note the remark on page 2 about separating chroma and luma beforehand. So: sample high, comb and interpolate (I think this had been incorporated in the same algorithm) and produce the desired number of pixels.

trevlac

19th December 2003, 21:50

I've still been reading on this stuff and I found a great quote on an older (not much older) thread right here at good ol doom9. :D

I pulled it out, because there is alot of false/confusing stuff in the thread. I think I know enough now to understand what Joe is saying. He doesn't provide all of the info, but he clearly knows the topic well.

Originally posted by Joe Fenton
I just read through this thread and it seems to me that a lot of people never learned traditional TV engineering.

Back when TVs were actually made from 100% analog parts (you know, transistors, tubes - that sort of thing) you didn't have dots or pixels, you had frequencies and bandwidth. The way they measured the resolution of a display was to actually draw a picture and display it on the TV. The picture was just a set of alternating vertical black and white lines. You made the lines thinner and closer together until you could no longer distinguish the lines on the TV. You then counted the number of lines drawn on the picture. It was found that you could discern about 80 lines per 1 MHz of signal.

Now a black line followed by a white line can be represented as a square wave - that is how it would look on an o-scope if you had lots of bandwidth. We are still talking ANALOG signals here. The fourier of a squarewave is a sine at the fundamental frequency plus a lower amplitude sine at the third harmonic plus an even lower amplitude sine at the fifth harmonic, etc. To see EXACTLY a black line followed by a white line would require the TV to handle a signal at a set frequency plus several odd harmonics. Since the TV has a limit or bandwidth, many of the odd harmonics are lost and the signal becomes less like a squarewave and more like a sinewave. At the limit of the TV to produce a discernable line, you have only the fundamental frequency and no harmonics. That is why if a TV has a bandwidth of 3 MHz, you can discern 240 lines which actually appear as a sinewave that goes from shades of black through shades of white.

Since a TV has a set number of scanlines, you would think that the vertical resolution would be exactly the same as the number of visible scanlines. However, the scanlines on a CRT are scanned (hence the name) and combined in the brain through persistence of vision. This reduces the number of horizontal lines that can be discerned to less than the number of scanlines drawn. Even more, TV displays are interlaced which affects the number of discernable lines even more. The general rule found with long persistence phosphores was that the number of horizontal lines discernable to be about 85% the number of visible interlaced scanlines. So a TV with 440 visible interlaced scanlines gives a vertical resolution of about 374 lines.

I would hope that clears that issue up a bit, but I imagine it has some folks even more confused than ever. :)

It was found that you could discern about 80 lines per 1 MHz of signal.

At the limit of the TV to produce a discernable line, you have only the fundamental frequency and no harmonics. That is why if a TV has a bandwidth of 3 MHz, you can discern 240 lines which actually appear as a sinewave that goes from shades of black through shades of white.

For a DVD player (on a 4:3 display) 720 pixels = 720/1.333 = 540 lines. 540 / 80 = 6.75MHz. 6.75MHz * 2 (Nyquist) = 13.5MHz.

conclusion:You can only see/sample a max of 540 distinct (black/white/black/white) pixels back from a DVD. That should be what the 6.75MHz test pattern is. I'll have to check it out tonight.

YMMV because the 6.75 signal may be low pass filtered.

Also, there is a link to another thread about someone who made a test pic for measureing overscan and cropping and resolution. May be of interest.

http://forum.doom9.org/showthread.php?s=&postid=378891#post378891

Arachnotron

21st December 2003, 11:24

Hi Trev,

I'm beginning to see where you are getting at. I am not at home at the moment, so will read the links later. But there is something here that is not clear to me.

Are we talking about going from the digital signal to analogue signal here OR about what you can still see AFTER playing it back on a TV screen.

I think those are two separate issues

issue 1 being: what does the analogue representation of alternating black and white DVD pixels look like considering the limitations imposed on it by bandwidth and Nyquist ;
This is what we are dealing with when converting VHS to DVD and when capturing.

issue 2: how much of the detail in an analogue signal can you actually discern with the human eye when played back on a TV screen (Which includes Kell).
This only comes into play when you are whatching it afterwards, and depends on the player and TV/screen/beamer/??? used.

point 2. is variable, and depends on the technology used, which nowadays isn't pure analogue/CRT anymore. Especially on a completely digital screen with LCD you might 'loose' Kell altogether and see every line at present in the signal.

edit

I think I can see where the number 80 comes from.
80 lines (40 black, 40 white) goes on a square piece of TV signal.

so, 52.65/1.333 = 39.5 µs. put 40 complete sinusses (sinus?) on it. That is about 1 complete sinus (period) per µs. That equals 1 MHz.

Which makes your calculation a circular argument I'm afraid.

edit2

As far as the analogue peak is concerned: that is indeed, as you sugested earlier, a sinx/x resulting from a 6.75 MHz low-pass filter.

Such a peak should be 2* 1/Fs at it's base, which is 2/13.5=148 ns. Which it is exactly in my pic. The other zero crossings should be 1/FS apart, or 74 ns. Also fit's.

Which would make the lines of horizontal resolution in the resulting analogue signal theoreticaly (2 * 52 * 6.75) / 1.33 = 528
provided of course the screen is not limiting.

Which, when I come to think of it, is also a circular argument. Oh well ;)

trevlac

21st December 2003, 20:52

edit As I re-read my original comments, I see I had a major misconception. 540 is not the limit to the # of black/white/black/white pixels you can see in a DVD line. 720 is. This is limited by the bandwidth of 6.75. If you have a bandwidth less than that somewhere along the line, the number is less. The BT878a limits captures to a 6MHz bandwidth or 640 pixels. Most DVD players probably do not reach the full 6.75 bandwidth. I think this is due to the fact that a Digital to Analog Conversion requires the 'signal' to be bandpass filtered on a 13.5MHz window. Filters are not exact and can clip some bandwidth or would let noise in if they were not tight enough. Anyway, that's what I think today.
tide <<== edit backwards hahaha.... :)

@Arachnotron

I think my point was that 'blurry' 1 pixel lines are due to what gets feed into a capture card by the dvd player, even with s-video. Past that, a BT878 limits the capture to 6MHz (640 pixels or 480 waves per microsecond). Of course, non of this invalidates the ability to measure the crop of a capture card. Just makes it harder. My thoughts on this enjoyable conversation are below:

Originally posted by Arachnotron

issue 2: how much of the detail in an analogue signal can you actually discern with the human eye when played back on a TV screen (Which includes Kell).
This only comes into play when you are whatching it afterwards, and depends on the player and TV/screen/beamer/??? used.

This is never what we are talking about. Kell has zero to do with horizontal. I finally read a good comment on 'Extended Kell' It just factors in the problems of interlace with Kell. You see, Kell said his stuff before interlace TV. Yes progressive came 1st. It was just not practical. Kell is vertical. For sampling, there really is no vertical.

I think I can see where the number 80 comes from.
80 lines (40 black, 40 white) goes on a square piece of TV signal.

so, 52.65/1.333 = 39.5 µs. put 40 complete sinusses (sinus?) on it. That is about 1 complete sinus (period) per µs. That equals 1 MHz.

Which makes your calculation a circular argument I'm afraid.

Wow! I never thought of it that way. Very nice. :D I'm not sure about the circle part. Seems if you up the bandwidth, you get more waves per microsecond. AKA more detail or resolution.

Which would make the lines of horizontal resolution in the resulting analogue signal theoreticaly (2 * 52 * 6.75) / 1.33 = 528
provided of course the screen is not limiting.

Again Wow! have you noticed that 2*52*6.75 = 702 PAL pixels? Also, 2*52.667*675=711 NTSC pixels? Or even 2*53.333*6.75=720 DVD pixels?

Talk about circular arguments :D

Given this info, I did some re-reading of the BT878 spec. I'm going to post some controversial remarks on this and see if Wilbert will respond. Please take a look.

Arachnotron

22nd December 2003, 11:42

I think my point was that 'blurry' 1 pixel lines are due to what gets feed into a capture card by the dvd player, even with s-video. Past that, a BT878 limits the capture to 6MHz (640 pixels or 480 waves per microsecond).

I am very curious where you got the 6 MHz from. Can hardly wait for your next post :)

I think my point was that 'blurry' 1 pixel lines are due to what gets feed into a capture card by the dvd player Yes, no argument from me.

This is never what we are talking about. Kell has zero ...

That was what I thought. But your Fenton quote trew me off. Lines of horizontal resolution is an empirical measurement dealing with how many lines from a test card you can see on your TV screen, which made me wonder. So I am glad we are talking about the same thing :D

From all this I get the impression that lines of resolution equals bandwidth 1:1 , but I don't think that can be true (gut feeling, no evidence).

For now, as a little side project I am trying to write a B&W DVD emulator.

about the 540 number: horizontal lines of resolution (which deals with vertical line spacing) is defined on a square area. so 540 * 1.333 = 720. It's all just a matter of how you define things. see
here (http://jkor.com/peter/tvlines.html)

trevlac

22nd December 2003, 15:18

Originally posted by Arachnotron
I am very curious where you got the 6 MHz from. Can hardly wait for your next post :)

I actually held off because I am not rock solid clear. I'd like more info on what a CX chip does, because it seems to have a higher limit, but It is not in the spec. But maybe I'll just post and not worry about my facts. :)

about the 540 number: horizontal lines of resolution (which deals with vertical line spacing) is defined on a square area. so 540 * 1.333 = 720. It's all just a matter of how you define things. see
here (http://jkor.com/peter/tvlines.html)

Yes, my mistake was think 53.333ms was square where 40ms is more like it. I read that link a little bit ago. I find the discussion to be a little confusing. I just ignore everything because I 'know' that the resolution of the width of the picture is the only thing to talk about. The resolution of the height is always the same because TV systems have a fixed number of scan lines. :) So what's the point in comparing or even worrying about Kell.

Resolution of height VHS=SVHS=Broadcast=DVD=D1=LD<>VCD (Well maybe not all. Also can't cross between 4:3 and 16:9) :)

One interesting note on kell is that It may apply across the width of the picture for CCD cameras. I'm not sure about how CCDs work, but this would be an interesting twist.

PS: I'm impressed about the DVD thing. So many projects ...

Edit
Here (http://www.maxim-ic.com/appnotes10.cfm/ac_pk/26/ln/en) are a bunch of good techincal articles. In 1 they say DVD bandwidth is limited to about 6.2MHz. (490 TVL, or 650 13.5 pixels) I guess it depends on how you measure.

Here (http://www.maxim-ic.com/appnotes.cfm/appnote_number/750/ln/en) is an excellent one from that list.

It gives a direct calculation between TVL, Pixels, and Bandwidth. TVL == BW :D

TVL = (2 tHA BW)/AR
or
BW = TVL * AR / (2 * tHA)
and
TVL * AR = Pixels

Where:
2 = our magic nyquist number
tHA = the active picture in microsec
BW = bandwidth in MHz
AR = aspect ratio
TVL = TV Lines of Horizontal Resolution (vertical lines)

IE:
540 = 2 * 53.333 * 6.75 / 1.333
or
6.75 = 540 * 1.333 / (2* 53.333)
and
540 * 1.333 = 720

It may be all circular, but someone at a company that describes themselves as "Maxim Integrated Products is a worldwide leader in design, development, and manufacture of linear and mixed-signal integrated circuits ", thinks it's ok.

Arachnotron

22nd December 2003, 21:00

Hi trev,

I finished a crude version of the DVD emulator. Give it a whirl if you have some time to spare.

You can find it here (http://www.arachnotron.nl/videocap/site/dvdemu/)

Its a 40 sample line. You can give luminance values between 0 and 1 and see what the resulting analogue signal looks like when only using sinc(x) functions. Only works in IE for now, and the plotting is very basic.

There probably is more to it than this ( or I made a mistake somewhere) since the result oscillates a bit more than a DVD player does.

numlock

5th February 2004, 03:20

Arachnotron:

I used the guide from your Web site to capture video form a DVD player and then calculate the actual capture area.

However I have discovered another problem. I used two different players and the same card and the same drivers. The captured results are different. It looks like each DVD player crops video signal differently. So how can I calibrate my capture card when I don't even know whar exactly is coming in.

There are 2 pictrues of the 2 captures I have done:

http://www.wtlzone.com/pictures/cap1.jpg

http://www.wtlzone.com/pictures/cap2.jpg

The first one has 6 black lines on the bottom the second has only 4. Why are there any black lines there to begin with ?

Also look on the left and right side and compare the 2 pictures. They are both visibly different.

SO as far as I can tell thre is no way I can calibrate my captrure card with this. Any ideas ?

Arachnotron

5th February 2004, 13:29

Almost no DVD player will display all 720 pixels. Most will crop some of, sometimes going even as far as displaying only 704 pixels. If your card caps a wider area than that, the difference will be made up in black pixels.

A second point is what horizontal offset is used to play back the pic. Or in other words, where the player puts the center of the picture. This is your problem: the centers are at different positions for your players

Last, most DVD players will crop a varying number of lines off at the top and the bottom, and where the first line of the DVD pic ends up in the final video signal can vary too.

But there is one constant factor: one DVD pixels takes exactly 1/13.5 µs to be played back. This MUST be the same for all DVD players, otherwise the aspect ratio will be wrong.

It is this effect that makes my method work, if you foloow the instructions to the letter.

The picture from one DVD player may have shifted to the right compared to the other, but the width of the capture area is the same for both pics. And that is the number we are after.

Have you done the math as described on my page?

Cap 1:

720-13-15=692 capture pixels contain 700-20+1 = 681 DVD pixels
681/692=0.9841
0.9841 * 720 pixels = 708.6 DVD pixels in your cap window
that equals 708.6 /13.5 µs = 52.49 µs

Cap 2:
720-6-22=692 capture pixels contain 700-20+1 = 681 DVD pixels
681/692=0.9841
0.9841 * 720 pixels = 708.6 DVD pixels in your cap window
that equals 708.6 /13.5 µs = 52.49 µs

Hey presto, it is the same number!!!

The picture from the DVD player shifted, but the width of the capture window is the same!!

With your card, if you want to make DVD's, cap at 708x480 or if not possible (some codecs need a multiple of 8 pixels to work), resize to that afterwards. Pad with black pixels untill you reach 720x480 and you have a DVD with correct aspect ratio.

I never got around to making a page about what a DVD player does to your pictures. If I have the time I will add it.

Arachnotron

5th February 2004, 14:29

@numlock

I just found a mistake in my testpic! I shifted the numbers under the righ side marks one mark to the left!!

For your card, the calculation becomes:

680-20+1 = 661 DVD pixels
720-13-15 = 692 captured pixels
(661/692) * 720 = 687.8 DVD pixels
687.8 / 13.5 = 50.94 µs

So, for DVD cap at 688x480 and pad with black pixels untimm 720x480

Is it a CX23881 based card by the way? Or perhaps BT878, but not with the BTwincap drivers?

[edit] I'll try to download corrected testpics tonight

numlock

5th February 2004, 16:33

Thanks for the great info. Yes, this is CX23881 based card.

Also I have 2 more questions: I undestand based on the calculations that the active capture area is 688 pixels. However how do I find out how many black pixels do I need to add on both sides to make it 720 ? Is it 16 -16 on both sides. Or more on 1 side nad less on the opther ? Problem is both DVD players shift the picture differently so I'm not sure there is a way to figure this out.

The other question is do I need to calibrate my capture card vertically also ? Or do all cards capture full 480 NTSC (576 PAL) lines ?

TIA

Arachnotron

5th February 2004, 16:57

Since you never know what a DVD player is going to do (you might get a new one some day after all) it is best to stick to the standards and simply put the center in the center of the 720x480 DVD frame.

The problem is not that drastic anyway. If you hadn't run this test, you probably never would have noticed the difference between the players anyway.... :)
The error will never be more than about 8 pixels. Not that much on a TV screen..

So, 16 pixels on either side is fine.

Vertically calibrating is not neccesary, as all cards do 480/576. Other vertical resolutions are resizes of that, sometimes by dropping lines, sometimes by really resizing. (don't do this! It really messes up interlacing)

The exception are VCD resolutions (240 lines) Here, most cards simply drop every second field.

There are some differences in what the first line is that gets captured by a card, but since again what line is the first one to get played back varies per player there is not much you can test on that using a DVD player.

So, for letterboxing out crap lines and black lines at the top and bottom (devidable by 2 of course) again simply keep whatever good video you have centered in the frame, and let the DVD player chips fall where they may on playback. :)

Nice clean cap by the way.

numlock

6th February 2004, 05:26

Great, thanks for your help.

Also a little bit off topic.
I did a capture of the same DVD using BT878 card.

Thes are the results for both CX23881 & BT878

CX23881
http://www.wtlzone.com/pictures/cap1.jpg

BT878
http://www.wtlzone.com/pictures/bt878.jpg

If you look closely at both pictues you will notice that CX23881
capture has visible 'ghost' lines and BT878 capture doesn't.

Also CX23881 is sharper then BT878. (this is understanable)

Any idea why are there ghost lines in CX23881 capture ? Can it be that the drivers are not good ?

Also, both of them have kind of like rainbox colors around the white letters. Any idea why ?

TIA

Arachnotron

6th February 2004, 12:18

If you look closely at both pictues you will notice that CX23881 capture has visible 'ghost' lines and BT878 capture doesn't.

It is not so clear because of the jpeg compression artefacts, but I see ghost lines in both caps. This is normal, and has to do with the way a DVD player generates an analogue signal from a single pixel.

So it is not an artefact; both cards are capping something that is actually there in the analogue signal

Look on my page for an explanation, under "Why are the white lines in my capture so blurred?"

The pic shown there shows the DVD pixels, a graph of the resulting analogue signal and under it the row of pixels generated from it by a BT878.

If you want to know more about this stuff, look for terms like
"reconstruction filter" and "sinc function"

The rainbows around the letters are also a normal capping artefact. They are more pronounced if you cap a composite source, but even from a s-video source you will see some, especially with bad cabling.

From the cap guide:Rainbows are caused by imperfect separation of the luma and chroma components of a composite video signal. This effect is called color crosstalk, and is a special case of signal aliasing. It is most noticeable on computer generated images like subtitles, weather maps, and stationary logos. Whenever you have an edge (= high frequencies) in luma, you have rainbows, even faint.

[edit] I think it can also be caused impresisions in the chroma scaler. Perhaps Trevlac would care to comment on that?

trevlac

6th February 2004, 14:40

@Arach & Num,

I think a couple things, and there are also a few things I wonder about myself. :)

1) I see lines in both of the caps. The settings (like brightness, contrast, etc) don't seem to be right for the BT. The picture is too bright vs the CX pic. Here (http://trevlac.us/pics/712Full.png) is a resolution chart picture from my (Aver)BT using BTwincap. I think the lines could be 2 things. 1st, what Arachno is talking about which is the fact that an analog signal is a curve, so when sampled it may not produce a nice pixel box. 2nd, may be the effect of the luma horiz resize filters on the cards. Resize always happens and it may make the 1st issue worse. A resize averages across a number of pixels, so maybe that is why the ghost. 3rd, may be what they call ringing. Basically, when you filter (resize), you specify a cutoff point where any detail higher than that point should be removed. You can do a sharp cutoff or a gradual cutoff where a range of detail is gradually removed. If you use a sharp cutoff, you get an effect where detail just under the cutoff point gets ghost. You can produce this with a bicubic resizer.

You should be able to tell from my guesses, that I don't know myself, but I am still learning. :)

2) The Rainbows are also a special area of interest for me. I'm surprized that you get them so pronounced. Try a better s-video cable. (or s-video if you are not using that). If you use composite, it is certainly y/c seperation. If you use s-video, the driver is not doing what you would like. It may be trying to seperate y/c and adding some c to y. Can't say. It may also be due to how the chroma is resized, but this effect does not always happen no all source (so I am suspecious that it is the root problem). So to be 'unclear', it could be the source, the cable, the driver, or the chip's resizer. I'm still trying to figure this out myself. On the BTwincap, you can pick a B&W option. This effectively removes all color regardless of how it gets in the signal. That's a good way to test without getting messy color artifacts. I think this option is also on my CX card, but it doesn't work. The driver is probably wrong.

So.... In the end Good Questions ! :D

Arachnotron

6th February 2004, 15:15

I should perhaps add I have seen similar rainbows in the caps made with other cards (including my own Terratec), so I don't think you have to run to the shop to get a refund. (But do check your cables, it might help)

When I made these testpics I turned off the anti-aliassing for the fonts in painshop pro, which means you now have sharply defined curves with a hard white to 50% gray edge in the letters.

vhelp

7th February 2004, 16:59

@ trevlac,

where can I D/L this test pattern that has ben floating around this
thread ??

I'd like to test it out on my advc-100 and DC10+ card.

@ Arachnotron,

I noticed how you mentioned the issue w/ the "cableling" (w/ respect
to the quality of the pic's noise)
I have not used really good cabling (normal s-video black cords) in
my prev testings, though I do have a pare of Monster Cables (blue)
My question to you is..

* What are you thoughts on cabling ??
* Do they really make any improvement in quality, OR just to
...help eliminate any outside/external noise ??

Thanks guys for your help and all :P

-vhelp

Arachnotron

8th February 2004, 18:53

Originally posted by vhelp
@ Arachnotron,

I noticed how you mentioned the issue w/ the "cableling" (w/ respect
to the quality of the pic's noise)
I have not used really good cabling (normal s-video black cords) in
my prev testings, though I do have a pare of Monster Cables (blue)
My question to you is..

* What are you thoughts on cabling ??
* Do they really make any improvement in quality, OR just to
...help eliminate any outside/external noise ??

Thanks guys for your help and all :P
-vhelp [/B]

Crap in crap out is still valid :)

The main problem with bad cabling is outside interference I think. But cable noise and color cross talk can also be a problem, thogh you need truly crap cables for that to be a big problem. And signal loss with long cables..

Make sure a cable is short, each wire in the cable has it's own shielding (in cheap cables to wires are often shielded as a pair, which kina defeats the purpose of s-video cables) and the connectors are metal too.

trevlac

9th February 2004, 02:00

@V

I re-arranged my web space. Below is a list to all old pics I posted. I think you want resolution1.png.

http://trevlac.us/pics/

vhelp

9th February 2004, 02:25

@ trev,

I just D/L'ed a few pics, and one thing I noticed, was how clean your
captures are.

My short story ..

After waiking up to a dead pc, I went out and purchased a new mobo.
It's the K7 Triton 400 (KT 400 series) and I tell you, this Noise is
still plauging me to death. I thought for sure, if I got another mobo
(different brand) I be rid of it. But, although my DVD captures seems
to be very clean, I still can not get my VHS captures to follow this
same clean captured output. I used my ATI-TV Wonder. My quick 704 x 480
capture of "The Fifth Element" off my AD-1500 was very clean. But when
I capture "Mission to Mars" from my JVC S-VHS HR-S3910U - very noisey.
Just what could it be ?? - rats.

Sorry for going off topic. But, I thought maybe it's still ok.

Thanks for the pics :)
-vhelp

Arachnotron

9th February 2004, 12:13

@vhelp

If you don't mind my butting in...

The only thing I can think of is that JVC's are very much plastic (mine is) and that, in combination with most of the internal electronics being analogue (a DVD player is digital up to the last DAC) makes them much more susceptible to catching external interference. (provided you are using properly shielded s-video cables that is)

Also, from other threads in this forum, I got the impression Athlon boards in general tend to produce more of it.

I never got around to it, but I still have two old half PC desktop cases lying around I wanted to use to create a shielded metal box around my VCR to see if that would get rid of some of the last noise.

So many things to try, so little time..... :D

trevlac

9th February 2004, 14:24

@VHelp,

I have 4 basic sources I can capture from.
- CATV 1%
- VHS 1%
- Satellite 98%
- DVD (Just for testing) 1%

I hardly ever do anything but satellite. This is an extreamly clean source. Added noise may infact improve the picture. (Dither)

I also tend to use my BT card which is in a P3 machine. For CATV, the philips tuner really cleans up the signal (and softens a bit). If I use my CX card which is in an XP1800, I get more noise only from noisey source. I've concluded that for CATV, the tuner makes the difference. For VHS, a short monster (svideo) cable seems to be better. Also, the deck itself has noise reduction. Finally, I think the CX has a slightly sharper capture, which means it grabs the noise the BT would not. (The BT does grab all the real signal, its resolution is well above VHS).

... In short, I find little difference between my XP1800 and my P3. I do try to use a good short cable and keep a metal case side between my source and the machine. But mainly, I start with clean source.

PS: Both machines are smp. ;)

Arachnotron

9th February 2004, 14:29

Sorry, Trevlac is of-course right. Even without dragging interference into it, DVD or anything digital simply is a cleaner source than analogue VCR.

trevlac

9th February 2004, 15:27

Originally posted by Arachnotron
Sorry, Trevlac is of-course right. Even without dragging interference into it, DVD or anything digital simply is a cleaner source than analogue VCR.

Hey....

I just took the easy way out of the problem. If you do VHS, you do have to be real careful. I can definately see noise if I have the VCR too close to (not shielded from) the machine.

All of this also depends upon what the noise is. Ground hum or FM interference can be fixed with a grounded pulg or a cheap in line filter. I believe in my pics, cap6 and cap7 show channels 6 and 7 for my CATV. 6 has terrible FM interference. Also, for cable, I found getting your pc as close as possible to the feed from the company was very important.

Arachnotron

9th February 2004, 16:03

Also, for cable, I found getting your pc as close as possible to the feed from the company was very important.

In my case, I had to use a RF amplifier. The CATV signal was a bit weak. My TV didn't mind, but my TV cards didn't like that at all.

vhelp

10th February 2004, 02:08

Hi guys.

One of the reasons why I posted this slight out-of-topic about the noise
issue from my new MOBO was becuase I felt it was somewhere's in the
vicinity of the thread topic. K.. I was thinking that perhaps, if all the
resolutions were tried (as an experiment) that, the one that showed no
Noise was the ulimate resolution to use in capturing. See my point ?
Anyways.., I haven't actually tried this experiment though, cause this
is a new MOBO KT-400 and I'm using the same CPU chip XP 1700
.
.
I'm thinking that the resolution may play a part of all this too.. somehow.
Perhaps during the sharpining or contrast, else during the pixel color
spacing algorithem or something to that effect.
.
.
So, given the above, perhaps this wasn't such a bad idea in posting my
Noise issue then ?
.
.
If anything, this would hint toward how various cards produce their final
quality during capturing, and that it also depends upon the source type
as well :roll:

On another note..

I have to wonder why I seem to suffer from noise in my analog captures :roll:
.
.
In my DC10+ card (an analog capture card, and a great one at that) it produces
excellent quality, and w/ ZERO noise. You just can't find any. But, any
other analog capture card, and I have noise gallore. Also, my advc-100
gives me ZERO noise as well. These are the only two cards that provide
zero noise.. one being external (ie, advc) and the other, a pci internal
card. As you know, the DC10+ does not have a tuner., and uses the Zoran
chip. This card I purchased some 3 or 4+ years ago, if memory serves me :roll:

Another note on Noise..
When looking at the noise, it seems to look like it's MV related. The
reason why I say so, is because the noise color seems to look almost gray
ish, except when looking at a blue-screen, it looks black.. like when you
turn on your VCR and the screen goes blue on you. I'll have to post a
small untoutched sample of this noise, so that you can understand what
I'm on about ??

I do have a set of blue monster cables, but they prove the same effect -
noise.

But, what I don't understand is this. If I connect my pc and monitor (LCD)
and vcr all to a power battery, w/ no hint of house-hold current or any
grounding to worry about, and all I have for AC power is my 12 volt
battery and AC converter, I STILL GET LINE NOISE :roll:
So, I'm stumped.

But, about the resolutions. Do you think that in some capture cards, that
noise level is (or can be) reduced depeding upon the resolution setting,
ie, a tweaked resolution ??

-vhelp

Arachnotron

10th February 2004, 12:50

Going down in cap resolution has the same effect as filtering out higher resolutions. You can even script a crude noisefilter in avisynth that way. So capping low is a noise filter.

Also, a DC10 is a MJPEG card, so lossy. Again, some filtering I suppose.

Also, different cards may have different noise filters. So, assuming a standard VHS source goes no higher than 3 MHz, If card 1 filters out anything above 4 MHz and card 2 filters out anything above 6 MHz the second one will show more noise for the same amount of detail from a VHS source.

The interesting thing would be to cap a DVD pic with patterns with known frequencies up to 6.75 MHz, and to determine what exactly the frequency range is these cards capture. There are some problems with getting a DVD player to reliably output higher frequencies between ca. 4 and 6.75, but 6.75 itself is simply to do (a dvd with alternating black and white vertical stripes) and easy to spot if it is filtered out in the cap by the card (you get a solid 50% gray field)