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Old July 9th, 2003, 11:10 AM   #1
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Oscilloscope's - why do we use them?

Does anyone have any information or links on using an oscilloscope. Does anyone have a breif explaination on what it is used for? Should everyone use it?
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Old July 9th, 2003, 11:12 AM   #2
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I believe Tektronix, the king of scopes, has some tutorials on its site.
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Old July 9th, 2003, 11:23 AM   #3
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Scopes plot the amplitudes of periodic electrical signals with respect to time, or with respect to each other in Lissajous patterns, or in a variety of other ways. So oscilloscopes permit for a visualization of something that you can't see--electrical voltage differences.

With regards to video production, a video engineer will use a waveform monitor to look at the video signal being recorded to ensure that the levels fall within certain tolerances. One can "see" the electrical video equivalent of light exposure by looking at a waveform monitor.
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Old July 9th, 2003, 12:31 PM   #4
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Mark,
I'm willing to bet a blank tape that you are actually thinking of waveform monitors and vector scopes rather than oscilloscopes. If so, these displays are used for color correction and are available in software form from within editors such as Final Cut Pro and Avids.

See the book "Color Correction for Digital Video" for more detailed information.
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Old July 9th, 2003, 04:56 PM   #5
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waveform monitor = oscilloscope
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Old July 9th, 2003, 10:20 PM   #6
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Well, as an ex-Tektronix salesman and repairman, I'll just mention that an standard oscilloscope isn't a waveform monitor. A waveform monitor is a specialized oscilloscope and is quite different in function from a waveform monitor or vectorscope.

It takes special circuitry to decode the NTSC waveform and allow one to make a full spectrum of measurements. It even takes a special trigger circuit to get the normal oscilloscope to display a full-field or line trace properly.

Do you need this measuring equpment? Depends on where your finished output will be shown. If it is destined for cable or broadcast, you almost certainly need to monitor the video as it leaves your editing system.

I do use a portable Leader waveform monitor in the field when I really care about the proper setup of the camera system. I also have a Tektronix 520A in the studio so I can take a look at the video I deliver to the dupe rack.

I find that the Canopus software waveform and vectorscope measurements are very accurate (they are digital, they should be. It's just some mathematics to generate the display.) But one has to have faith that the output will be no different than the digital data.

I found, for example, on the old Canopus DVRexM1 composite video output, that it is only 75% of normal amplitude as measured on a waveform monitor using color bars. Canopus has admitted that that spigot does not perform correctly. Fortunately the S-Video and DV outputs are spot-on.

Without checking the video, I would have difficulty getting television commercials accepted by the local Comcast tech center without having first set the levels by refering to the waveform monitor and vectorscope. And bumping the DV to BetaSP would be more difficult if the video were not to spec.

DV will generate some very out-of-spec signals. Especially, as I've found, if one generates artwork in Photoshop or Illustrator. You cannot depend on the built-in NTSC filters in Photoshop or Illustrator or After Effects to keep you out of trouble.
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Old July 10th, 2003, 01:13 AM   #7
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Thanks guys, this helps a lot. I will read that book!
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Old July 10th, 2003, 01:17 AM   #8
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Mike,

Can you tell me what Canopus software you are talking about?
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Old July 10th, 2003, 12:30 PM   #9
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Mark, I think Mike's referring to the built-in software vectorscope and waveform monitor in the realtime Canopus editing aps, e.g., the latest Rex Edit, Storm Edit, EDIUS...

Great post, Mike, BTW. Thanks.
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Old July 15th, 2003, 02:18 AM   #10
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you can use the oscilloscope (o-scope) to measure voltage levels (from DC to microwave), phase differences, signal presence (or absence) logic highs and lows, frequency response, distortion, and complex waveform analysis, to name a few.
And as all you are arguing a basic o-scope is not going to enable you to view any video signal. You would need more specific equipment if you will.
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