Temporary loss of tracking and sound...

[justin81]

Hi all,

Lately, I've experienced this problem on some old tapes. The tapes are mid-90s era Sonys and were recorded in EP mode. They actually play and track perfectly, but there are some points where the hi-fi sound starts to drop out, and the tracking goes haywire, causing bad jitter. I've also noticed that the counter on the VCR actually stops "counting" at these problem points, almost as if it is playing back a blank unrecorded section of tape. The problems usally are severe enough to throw off the tracking for the rest of the playback unless it is manually adjusted.

I've visually inspected the tapes at these problem points and detected no damage. Any ideas what this may be and any ideas on how to rectify it?

Thanks.

[sum_guy]

Try it in another player to determine if it's the tape or the player.

[Cornucopia]

Partial erasure? Has the tape been resting near speakers for some time?

Scott

[johnmeyer]

This is pretty common. It can be caused by slight tape stretching, which is something you'll probably not be able to see with visual inspection. It can also be caused by slight head misalignment between the deck/camera which recorded the tape, and the one you are using to transfer the tape to digital. It is very unlikely to be caused by erase because it is actually quite difficult to erase magnetic tape simply by placing it near a magnetic field.

Several possible ways to get around the problem.

The first is to set the VCR to manual tracking, and then adjust the manual tracking control to get a usable picture while you re-capture the "bad" portion of the tape. You may have to do this several times, but only for the bad portion of the tape. Even if this doesn't work completely, you may find that you will be able to capture video frames in the second capture that were blanked out on the first capture.

Second, set the VCR to not turn the screen to blue when it starts to lose tracking. If you do this, you will often be able to get some video (and audio) instead of having it totally blanked out. The video may contain quite a bit of noise and tearing, but the content may still be visible.

Third, set the VCR to output the linear audio track. This very often will still provide usable audio, even when the Hi-Fi track (which is embedded in the video) won't play. This works because the linear track is recorded on a separate, thin strip near the edge of the tape, and doesn't rely on tracking or on any sort of sync. When you play the linear track, it can provide some clues as to what is going on. You may find that it changes pitch which indicates that the tape is speeding up and slowing down as it tries to sync. If instead it sounds garbled, this may indicate tape stretch.

Using the linear track, if you can capture audio, even if you can't capture all the video, you can freeze the last good frame and play that while the audio continues, or can take the last segment of good video and, using your video editor, play it in slow motion over the top of the good video. For home movies, the audio is often as important as the video, so if you can get the audio, you can often make the client happy.

You then line up these various captures on the timeline in your video editor and switch between them.

[Cornucopia]

No it isn't. Full erasure is more difficult, but partial erasure, the kind I was referring to, is NOT that difficult to have happen and it can be demonstrated empirically quite easily.

In fact, most consumer blank tapes (Cassette, VHS, DV, etc), as well as many professional ones, come with a little label sheet + warning/instruction/disclaimer sheet that specifically states to avoid placing the tapes "near strong magnetic fields, such as speakers". I just looked at one...

Scott

[johnmeyer]

No it isn't. Full erasure is more difficult, but partial erasure, the kind I was referring to, is NOT that difficult to have happen and it can be demonstrated empirically quite easily.

I spend a lot of time on a professional video and audio editing forum. This topic has come up several times, and the pros there claim that it is nearly impossible to erase a videotape using just a magnet, much less merely having the tape near a speaker.

I don't have the time to search and then link to the posts in that forum, but here is a post by one person who tried to erase a tape doing exactly what you describe. He failed to erase the tape.

effects of magnets on video tape

[johns0]

A tape can be erased by a magnet as long as it has been sitting on it for a few hours,one persons experiment as you linked is usual as a reference.