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-   -   Reference tapes for pre-capture calibration / regression test (http://www.digitalfaq.com/forum/video-workflows/11147-reference-tapes-pre.html)

swiego 11-01-2020 03:40 PM

Reference tapes for pre-capture calibration / regression test
 
I've long used calibration target media as pre-capture references in my workflow and this generally is the accepted norm in institutions that perform bulk media digitization. Doing so periodically is a good way for me to detect whether my capture hardware is degrading or if my workflow changed in some way that I missed--be it user error or SW updates. Examples for me are professionally mastered calibrated cassette and reel to reel audio tapes (the calibration run verifies speed, W&F and frequency response) and reference film slides to verify effective resolution and DR. Over the years it has definitely helped me detect failing hardware or some mistake I made in my capture setup that I might otherwise have missed.

I've really struggled with a methodology I'm satisfied with for magnetic video media like VHS and SVHS though. I'm not aware of any reference or calibration tapes - bench calibration is typically handled via signal generators feeding signals, which I suppose makes sense given the frequencies involved? But it does leave me without options. What I've done the last few years is use a couple of tapes I created myself... fresh off receiving a pair of AG-1980P players serviced by Tom Grant, I recorded 10 minutes of video (Snell & Wilcox targets, short clips from movies, clips I recorded myself) all from 1080p/4k down to s-video using the absolute best converter I could get my hands on. I recorded two identical SVHS tapes, one with each deck, then captured each tape with each recorder (4 captures) and compared them and couldn't really see a difference. This gave me some comfort that I have a couple of identical tapes made on two recorders that if not perfect are at least consistent. I typically recapture from one of these tapes every few months or when I'm using a deck I haven't used in a long time.

I suppose I'm happy with this method--the recording really does look good, much better than anything I've seen on VHS/SVHS--but I'm not sure if it really could be considered a 'reference' recording by any means. And as far as I can tell I have no way to know, which bothers me a little bit. So I was wondering if anyone else has thought about this and what if anything you've done.

By the way, the only other source I have are pre-recorded SVHS tapes--I've bought a few over the years thinking they might provide a better source of resolution, definition, etc. but my fresh recordings to new tape consistently looks better than the old pre-recorded tapes so they're just sitting.

dpalomaki 11-03-2020 05:31 PM

Alignment tapes were offered by VCR makers. The part number from the AG-1980 service manual is: VFM8080HQFP. However, finding one can be problematic at this date.
The https://www.unlimitedpurchasing.com/aviation/rfq/collins-avionics/vfm8080hqfp/
Web site claims to stock it, but I have not tried them.

NJRoadfan 11-03-2020 06:52 PM

The philosophy in the video world was to record calibrated SMPTE color bars and tone thru the equipment chain being used before any recording sessions. That way whoever plays back the tape has a reference to adjust their playback equipment to. That standard tools used for calibrating analog video levels is a waveform monitor (for luma/brightness/contrast) and a vectorscope (for chroma). There are software tools that can do this as well.


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