Mixed mode SP/EP tape?

[Mack]

I know it is possible to change modes (SP, LP, EP, etc) on the same tape, but I've run into a tape that seems to change at random times. The recording was made on what I assume is a consumer/prosumer grade recorder in 1984. These were recordings of concerts and I am fairly certain that the mode was not changed purposely this many times and certainly not during the middle of a performance piece. Could have been someone hitting a button randomly I guess.

Any ideas why this is happening? It's making capture difficult as there as you can see the quality difference every time it shifts. Probably half a dozen times during the same recorded concert.

Tried different machines....1980, 7600, 9900, and a cheapie JVC.

Curious.

[latreche34]

Probably the control track is corrupted, Is the tape curly or dirty at the bottom edge when the switch happens? If not it is possible the tape was lost that signal due to an exposure to a magnetic field such as magnets, close enough to only affect the bottom side of the tape spool.

[timtape]

Quote:

Originally Posted by Mack

It's making capture difficult as there as you can see the quality difference every time it shifts. Probably half a dozen times during the same recorded concert...

If the only problem is the obvious quality difference (picture and sound?), you're probably doing well. The quality difference is baked into the recording.
Maybe it was as you suggest, someone changing the tape speed as it was recorded. Perhaps a child?

[latreche34]

Recording mode cannot be changed while recording, the recording has to be stopped and the setting changed and record again, That's how it works for at least for the vast majority of VCRs.

[dpalomaki]

These are changes in the middle of a number (not at breaks between numbers)?

If the change is in the middle of a number how much of teh number (time) is "lost" making the change

Does the playback VCR play the tape OK (especially linear track audio and video) and indicate the different speed with the only change being a glitch of sorts at the speed change and the change in quality associated with the speed?

[Tester]

Quote:

Originally Posted by latreche34

Probably the control track is corrupted, ...the tape curly or dirty at the bottom edge...

That would my guess as well, the most likely scenario too.