Quantcast Good s-video calibration source? - digitalFAQ Forum
  #1  
04-02-2018, 10:20 PM
swiego swiego is offline
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I am looking for a good s-video calibration pattern source that I can use to feed into a deck to verify recording and playback quality. Color bars, resolution targets and the like. (Comparative measurement from deck to deck.) Iím thinking any old DVD player with svideo output and a calibration disc would do the job but wanted to double check. Do all DVD players maximize output quality over svideo or are there differences from model to model? Is there another option I should look into?
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  #2  
04-03-2018, 08:00 AM
dpalomaki dpalomaki is offline
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A couple questions that will help focus answers to your specific needs.

Are you concern about both the record and playback accuracy of the VCR, or mainly playback for purposes of converting VHS and S-VHS tapes to digital format?

Do you have a budget in mind?
What do you plan to use to evaluate the output of the VCR (e.g., a TV set, professional video monitor, etc.)?
Do you have any electronics test equipment now, such as an oscilloscope?
Are you intending to so some VCR maintenance/repair?
That is your technician skill level?

VCR manufacturers generally offered alignment tapes for use in maintaining and adjusting their products, but availability may be problematic at this late date.

Video test pattern generators are available that can be used to generate standard test patters including color bars, multiburst, sweep, ramps, etc. to evaluate linearity, frequency response, etc.
www.gekco.com offers some moderate priced kits as a starting point.

"Any old DVD player" may not be the solution, some were better than others. You would need to evaluate the output of the DVD player against the known disk content to determine how accurate it is, and then against the output of the VCR to determine what losses were added by the VCR under test.
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  #3  
04-03-2018, 11:23 PM
swiego swiego is offline
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Quote:
Originally Posted by dpalomaki View Post
A couple questions that will help focus answers to your specific needs.

Are you concern about both the record and playback accuracy of the VCR, or mainly playback for purposes of converting VHS and S-VHS tapes to digital format?

Do you have a budget in mind?
What do you plan to use to evaluate the output of the VCR (e.g., a TV set, professional video monitor, etc.)?
Do you have any electronics test equipment now, such as an oscilloscope?
Are you intending to so some VCR maintenance/repair?
That is your technician skill level?

Video test pattern generators are available that can be used to generate standard test patters including color bars, multiburst, sweep, ramps, etc. to evaluate linearity, frequency response, etc.
www.gekco.com offers some moderate priced kits as a starting point.

"Any old DVD player" may not be the solution, some were better than others. You would need to evaluate the output of the DVD player against the known disk content to determine how accurate it is, and then against the output of the VCR to determine what losses were added by the VCR under test.
Thank you for the detailed response and excellent questions. They get one thinking! In short, my interest is in verifying recording and playback accuracy, and developing in the absence of calibration tapes, some methods to quickly health check and comparatively benchmark personal decks against each other. Skill set wise, fairly experienced insofar as I can work with scopes and repair equipment. However, deeply inexperienced with video from an equipment perspective.

Iíll look at Gekco, thank you for the suggestion. Iíll also set aside the dvd topic for the moment, I donít want to accumulate another set of devices just for data collection purposes. Would rather do it right if I can manage in a roughly ~$400-500 budget.
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04-04-2018, 09:59 AM
dpalomaki dpalomaki is offline
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Of course the GEKCO gear would require having an oscilloscope to be fully effective.

In you quest it is probably better to focus on S-VHS gear for highest quality record-playback potential. (Actual performance will depend on the current state of the machine in question.)

The following is one quick check approach to determine is a candidate VCR is worth further consideration. Have on hand a few known good prerecorded commercial video tapes with typical material of interest; e.g., favorite movies, a few "throw-away" tapes to use for initial checks, some blank tapes for record/playback checks, and a camcorder with analog outputs to use as a source for record tests. ( Some other threads have mentioned tapes others have used for their testing.)

You can view the video on a TV set, but keep in mind that many TV's include image correction processing circuitry that can do a lot to clean up a marginal output from a VCR. A good video monitor designed for analog TV signals would be better because it will show the actual image, warts and all. (Some computer monitors offered analog video inputs, but may not provide accurate color representation of video because they were designed for computer color space.)

The process:
1. Check the VCR visually for obvious abuse, damage, broken or missing parts, belts, cleanliness, PBJ sandwiches inserted in the cassette compartment, etc. Does it power up, control panel light, want you to set the time? Forget any with obvious problems. Cleaning heads and tape path would probably be a good idea at thsi point.
2. Connect the VCR to the monitor.
3. Use a throw-away tape to check basic functions including tape loading/unloading, Play, FFW, REW, Slo/Fast play, Pause, and erase protection. If the VCR eats the tape, little is lost.
4. If so-far-so-good, try play your prerecorded test tapes to evaluate the image quality including color, and image stability. Check both composite and s-video outputs (if present).
5. If so-far-so-good, connect the camcorder to the analog input, insert a blank tape, and record the live camcorder output. Try various subjects such as still life (bowls of colorful fruit), resolution targets, Macbeth color charts, and some moving subjects. Play the recording and see if it is a good match to the camcorder's analog output fed directly to the monitor.
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  #5  
04-04-2018, 11:17 PM
swiego swiego is offline
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Thank you, your suggestions have been helpful. Perhaps a bit more detail. I’d like to see how high quality a signal I can get onto tape. I can permute the tape type as well as the recording deck. What I don’t have is the excellent source tape... I think. I have a few pre-recorded SVHS tapes I’ve accumulated over the years. All are mixed quality to my eyes; recording from a cheap DVD player directly to high quality tape on a 1980p or similar seems to match or exceed the pre-recorded tapes I own. What I’m unsure of is whether said cheap DVD player represents the best s-video output I can send to a deck. In the way of possible alternatives, I’m considering:
- use an older PC video card with s-video output.
- use an older PC with RGB output and look for some kind of conversion box to get me y/c
- output off TBD DVD player or similar with high quality output
- use a dedicated signal generator similar to what you pointed out (those are fairly inexpensive btw...)
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  #6  
04-05-2018, 08:10 AM
dpalomaki dpalomaki is offline
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I guess what I am unsure of is your ultimate goal in this project. Recording to VHS, S-VHS, or other consumer analog tape format this day and age is a bit unusual. It is much more common to want to convert material from existing legacy tapes to a currently supported digital format. The old analog formats suffer from limited bandwidth (especially the color portion of the image), high noise floor, no way to make a copy without significant generation loss, and a plethora of machine dependent image issues on both record and playback. Is it the act of recording to VHS/S-VHS itself (the pleasure of working with old technologies - kind of like doing antique cars) rather than the extraction of information from a legacy tape inventory for restoration and use with current technology that you have in mind?

I would probably prefer to use a calibrated video signal generator for static test images. The objective is to have quality, stable, repeatable, known legal SD signals for test purposes. The output from other sources you mention would have to be evaluated individually to determine if they are suitable for the task at hand.

Last edited by dpalomaki; 04-05-2018 at 08:22 AM.
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  #7  
04-07-2018, 06:56 PM
swiego swiego is offline
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Yes itís the pleasure of recording to an old format to see what itís capable of. Iíve gotten as far as I can with the tapes I have. This is the next step.

Anyhow I am going to look for a good test pattern generator and go from there. I did some test recordings using different cables and premium svhs tapes and no significant difference was observed so Iíll focus my attention on quality svhs sources.
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  #8  
04-07-2018, 08:01 PM
dpalomaki dpalomaki is offline
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As you have observed, different cables, once you get above a minimum quality standard, and if relatively short and used in an electro-magnetically clean environment, will have minimal effect on the image. Similarly the issues with individual VCRs can often dominate variations among premium tapes, at least until you get into a high quality, well aligned machine with good source material.

A important key to your success will be restoring and aligning the VCRs you test. This involves both the mechanisms and the electronics, and may involve piece parts replacement on circuit boards as well as adjustments.

Good luck in you quest.
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