video signals testing

[relicmarks]

1.) What should the video levels be? be at clipping?

2.) What kind of video signals would i be testing?
(what are good video signals voltages/phase be?)
(what are bad video signals voltages/phase be?)
(What should they measure?)
3.) What would i use Assemble and Insert editing for? (i thought the video/film editor did this before i got the tapes)

4.) How to change lines of VITC? why would i need to change the lines of VITC?

[relicmarks]

1.) Set-Up levels Whites, Blacks, Hue Balances or Hue Amounts?

Yes how do i set the levels for whites,blacks,hue,saturation,illumance,hue balance?
What measurements are good and what measurements are bad?



2.) Good signals and voltages are best read using the waveform & Vectorscope.

Yea i know about using the waveform monitor and vectorscope but the problem i don't know is i need a QC spot check list so i know how to QC spot check the video signals. Most QC test the video signals using waveform monitors and vectorscope but in "general" what would be good testing video signals VS bad testing video signals?

Mostly QC or tape operators i guess FREEZE the frame by frame and measure the video signals for each frame? and right down the phase angle using the vectorscope and the voltages for the Black,white,hue video signals?

[RFBurns]

1.) What should the video levels be? be at clipping?

2.) What kind of video signals would i be testing?
(what are good video signals voltages/phase be?)
(what are bad video signals voltages/phase be?)
(What should they measure?)
3.) What would i use Assemble and Insert editing for? (i thought the video/film editor did this before i got the tapes)

4.) How to change lines of VITC? why would i need to change the lines of VITC?

Howdy!

There are a number of ways to test video signals. The best way is to use a very expensive test set such as a Techtronics 1910 pattern generator. Or you can use a DVD test disc that contains the most common test signals. These can be found at any high end electronic/home theatre store. The levels on these discs conform to the standards so the levels should be on the dot. But you might have some level variances between one DVD player vs another. But the variances would be miniscule.

1. Video max white level should be 100 IRE from baseline 0.
2. Video white clipping should begin at 105 IRE from baseline 0.
3. Black reference should be 7.5 IRE from baseline 0.
4. Maximum sync/blanking should be -40 IRE from baseline 0.
5. Color burst should be +20 and -20 IRE from center baseline of 0.

VITS is an area within the vertical blanking interval to allow for insertion of data such as closed caption or various other data like program information or test signals. Closed caption data occurs at line 21. In order to re-arrange VITS information, you need a VITS generator/inserter to re-allocate which line and in which field you want the information to appear. These devices are used in broadcast facilities and production houses, they are rather expensive to boot. Broadcaststore.com is one place to find these items.

Here is a link to some information on video signals and how they should appear when properly adjusted on the waveform and vectorscopes.

http://www.seanet.com/~bradford/ntscvideo.html

http://www.maxim-ic.com/appnotes.cfm/appnote_number/734

http://www.videouniversity.com/engineer.htm

Typical test pattern generator..

http://www.tek.com/site/ps/0,,20-14227-INTRO_EN,00.html

http://www.panoramadtv.com/overviews/PENPAL-sdi.html

Close up of waveform monitor w/color bars NTSC 525 2 field

http://en.wikipedia.org/wiki/Image:Waveform_monitor.jpg

Hope this helps.

[anonymez]

Fantastic response, as always RFBurns.

@relicmarks: Are these homework questions?

[relicmarks]

how do u check/test the vertical blanking interval? what should the voltage be? is it -40IRE?

how do u check/test the Horizontal blanking interval? what should the voltage be? is it -40IRE?

How do you measure/test the control track signal?
(control tracks was used for assemble/insert editing)

A Waveform monitor is used to check all the "pulses" and "scans" of the signal

How do you check/test the pulses and scan lines?

[RFBurns]

how do u check/test the vertical blanking interval? what should the voltage be? is it -40IRE?

Take a typical waveform monitor and set it to scan the vertical fields. Then take the multiplier switch and set it for 2x, this will "zoom" in on the pulses so you can see them individually. You can also scroll across the pulses to view each line if necessary. Vertical blanking is at -40IRE.

how do u check/test the Horizontal blanking interval? what should the voltage be? is it -40IRE?

To test the H blanking, just use the waveform monitor's 2x function. It will "zoom" in on the blanking pulse, and you can scroll across the signal just like the vertical signal. H blanking is also at -40IRE.

How do you measure/test the control track signal?
(control tracks was used for assemble/insert editing)

Best way is to use an oscilliscope and tap across the control track head, or if the machine has a control track output port, connect the scope to that. Control track signal levels are dependant on the machine being used. But typically the signal should be around 3 to 400mv peak to peak.

A Waveform monitor is used to check all the "pulses" and "scans" of the signal

How do you check/test the pulses and scan lines?

Again use the waveform and its zoom functions to view and verify the signals and pulses. Some waveform monitors can also zoom in on each scan line themselves so you can see each field and line of video. Quite neat if your trying to isolate a blanking timing problem, typical within frame syncs that have a bad memory bank somewhere.

[relicmarks]

Thanks alot RFBurns for your information and time

1.) what causes vertical blanking problems or timing problems?

2.) what causes Horizontal blanking problems or timing problems?

3.) what causes a color burst problem?

4.) Can a Time base correct fix/correct vertical/horizontal/color burst timing problems or sync problems and how please?

5.) What type of sync signals or sync waveforms is there please? and would a TBC fix sync signals/waveforms and how please?

[relicmarks]

6.) what causes bad frame syncs? and would a TBC fix frame sync?

7.) what should the IRE be for the frame sync?

8.) what should the IRE be for each scan line?

9.) What cause bad scan lines? and would a TBC fix bad scan lines?

[relicmarks]

10.) Whats the difference between Sync VS pulse VS blanking?

[relicmarks]

11.) When looking at the video signal color bars on the waveform monitor how do i test/check the ""linearity""?

12.) What causes the color videl signals to have BAD linearity? and would a TBC processor correct linearity and how please?

[RFBurns]

Thanks alot RFBurns for your information and time

1.) what causes vertical blanking problems or timing problems?

2.) what causes Horizontal blanking problems or timing problems?

3.) what causes a color burst problem?

4.) Can a Time base correct fix/correct vertical/horizontal/color burst timing problems or sync problems and how please?

5.) What type of sync signals or sync waveforms is there please? and would a TBC fix sync signals/waveforms and how please?

1 & 2. Usually timing problems are caused by loss of "GEN-LOCK" or more commonly refered to as "HOUSE SYNC", which is the primary reference for all devices within a facility. Problems can also be caused by adjustments drifting due to component tolorance changes and/or temperature changes. Correctable by re-adjusting the H-Sync to the reference so that the devices match the pulses from the house sync.

3. There are a variety of things that can cause a color burst problem. A lack of frequency response through the system due to bad cables or connectors, bad distribution amplifiers or processing amplifiers, or a fault within the device/s. Most commonly its due to frequency response, ie something along the signal path is degrading the upper frequency response (3.57Mhz) of the signal path.

4. Yes. As long as the "house-sync" is known to be correct, a TBC and/or Frame Sync can correct alot of source video problems. These perform their job by removing the source signal H and V timing pulses, stripping out the color burst signals and inserting new H and V and color burst signals generated by the TBC/Frame Sync based on the house sync signal. The TBC/Frame Sync, some of them anyway, can in effect correct these signals by generating the new H, V and color signals without a house sync reference, known as "free-running" time base correction.

5. Types of sync pulses are Horizontal (NTSC=15Khz), Vertical (NTSC=59hz) at frame rate of 29.92. Again a TBC/Frame Sync can correct errors of these pulses with or without house sync depending on the type and functionality of the TBC/Frame Sync.

It is common practice however to have a house reference for the TBC/Frame Sync so that the timing is standardized thru the entire video chain and eliminates variables and headaches in trying to maintain multiple time base corrections. Its like having 5 doors each with locks and they all take the same key instead of 5 different keys.

[relicmarks]

Thanks alot RFBurns for your information and time u are the man of video knowledge and to answer the questions

Did these other questions make sense? are u thinking about them?

6.) what causes bad frame syncs? and would a TBC fix frame sync?
7.) what should the IRE be for the frame sync?
8.) what should the IRE be for each scan line?
9.) What cause bad scan lines? and would a TBC fix bad scan lines?
10.) Whats the difference between Sync VS pulse VS blanking?

11.) When looking at the video signal color bars on the waveform monitor how do i test/check the ""linearity""?
12.) What causes the color videl signals to have BAD linearity? and would a TBC processor correct linearity and how please?

[RFBurns]

6. Component failure within the frame sync/TBC. And depending on what is wrong, putting another frame sync or TBC in line with a bad one probably wont fix anything.

7. Same as video specs, 1 volt peak to peak.

8. IRE for each scan line is dependant on video content. Since video varies in amplitude and frequency per the content, it ranges from the 7.5 black reference to the 100 IRE white maximum point.

9. Bad scan lines can be caused by bad video source or something electronic in the source. Sometimes a TBC can correct it, sometimes not. It depends on the type of TBC used and if it does any serious AD to DA conversion.

10. Sync is matching the H and V pulses so you get a frame instead of a mess of scrambled looking video. Without syncronizing the H and V, the frame cannot exsist.

11. Testing linearity is best performed by sending a "sweep" or multi-burst signal through the video chain. You should have a nice flat top response on the signal...like this..../-----\. Any other shape of that sweep signal across the video path will cause loss.

12. Color loss can be caused by inadequate frequency response on the video path or some other failure within the source device. A TBC may be able to compensate for this loss, but that depends on how much loss there is. It is best to make sure your signal is as good as possible from the begining, or you end up with the "garbage in-garbage out" scenario.

Hope that helps.

[relicmarks]

Thanks so much for the information it helps me out alot to understand video testing more

1.) I thought "1 volt peak to peak" is BAD because its clipping and over 100 IRE which is bad/distortion

2.) How do u MATCH the H and V pulses? )Sync is matching the H and V pulses)

3.) Do i use the GEN-LOCK" or "HOUSE SYNC" or TBC H and V pulses as the REFENCES so i can compare them to the H and V pulses from the video signal? so they match?

4.) How do u find the "frequencys" for each color bar? and the sync,blanking,H and V pulses,color burst,control track?
(Why would i need to know about the frequencys about these? what would i use it for please knowing the frequencys of these) ?

[RFBurns]

Thanks so much for the information it helps me out alot to understand video testing more

1.) I thought "1 volt peak to peak" is BAD because its clipping and over 100 IRE which is bad/distortion

Your forgetting that the 1 volt peak to peak standard contains everything, including the 100 IRE white max level as well as the -40 IRE sync level. When properly adjusted, it all fits within the 1 volt peak to peak specification.

2.) How do u MATCH the H and V pulses? )Sync is matching the H and V pulses)

Matching, or "timing" as it is refered to is set by adjusting the blanking interval of the source to the reference....\_/... is a typical blanking waveform at the H rate. If you have two sources that need to "match" or "time" together, each signals \_/ (or blanking interval) must equal to the same time instant as the reference or the signals will not be able to join together through a video mixer.

3.) Do i use the GEN-LOCK" or "HOUSE SYNC" or TBC H and V pulses as the REFENCES so i can compare them to the H and V pulses from the video signal? so they match?

You want to use the house sync/gen-lock as the reference. House sync and gen-lock are the same thing, just two different terms. Remember that a TBC/Frame Sync stripps the source video's H and V and color pulses and puts in new signals with the video at the output.

4.) How do u find the "frequencys" for each color bar? and the sync,blanking,H and V pulses,color burst,control track?
(Why would i need to know about the frequencys about these? what would i use it for please knowing the frequencys of these) ?

The color frequencies are as follows: 0.5Mhz, 1.5Mhz, 2.0Mhz, 3.0Mhz, 3.58Mhz and finally 4.2Mhz. From start to end, this comprises the entire color bandwidth of a typical video signal. Each of these color frequency bands must be equalized, or at the same level, like this...../------\. Each of the horizontal lines, or dash lines in the example symbol above must be at the same level across the waveform. If it is not even and flat, you get poor color response. The same is true with luminance linearity, or video linearity. Remember there are several signals within a video signal. Luminance, chrominance, H pulse, V pulse, color burst, H blanking, V blanking and VITS signals. Lots going on there within two frames of video. To find these frequencies you can use a regular oscilliscope, or the prefered device to use is the waveform monitor that is capable of looking at each of these vital signals independantly.