Dropout count on unused videotape?
 

Hello,

I have a question for Lordsmurf and to all the kind forum members who are willing to help.

Do you have any info on how many dropouts per minute you could find on "virgin" videotape? Did companies who used to make videotapes release any info to clients on how many dropouts per minute one could expect before beginning to record/play a tape?

Thank you in advance for your help,

Gaetano, Udine, Italy

Yes, manufacturers know the dropout performance of their products, but finding meaningful numbers applicable to consumer formats is harder. They were touted in general terms . Some tape test reports published in trade press have gave figures but finding then means visiting an library archive.

In one online publication on 1/2" video tape it states "Tape will accumulate dropouts with use, age and abuse. Sony videotape specifications indicate that up to 25 dropouts-perminute can be expected throughout a reel of 1/2- inch tape. If the dropouts really become constant and annoying the tape should be discarded or used for expendable programs. " Not quite the answer you were seeking but it gives an idea. Professional users were certainly concerned with this and tape manufacturers monitored it. While important for analog video tape it is vital information for data storage tape.

Of course the number will depend on how a dropout is defined. One definition I have seen is a 6 dB reduction in playback signal of a 1 mHz recording for 5 micro seconds or longer. Other factors are the threshold of visual detection abd performance of individual tape transports. Can you see a brief 6 dB dimming of a portion of a single scan line? A practical factor is the effectiveness of the dropout compensation (error correction) in the playback device.

https://www.digiommel.fi/images/Vide...log%20VCRs.pdf provides more reading on the subject.

The dropouts issue was an issue with the original 2" Quad pro videotape format in the mid 50's. Initially the dropout compensator system hadnt been invented in time for the early model Quad machines and I remember as a child watching the family TV set and seeing the familiar short white dashes flickering across some earlier videotape playbacks.

I think it was a young Ray Dolby, an original R & D team member who discovered that after some record and playback cycles, the dropouts seemed to decrease rather than increase. This led to them discovering the problem was related to unevenness in the magnetic oxide coating on the tape. They fed this info back to I think 3M who made the tapes, and it led to the development of a tape 'calendaring' process where towards the end of manufacture, the new tape was made to rub against itself via a looping system, which polished the oxide side tape to a higher standard of smoothness and consistency, decreasing dropouts.

Then the electronic dropout compensator came along and eventually was incorporated into even small consumer camcorders. It's interesting to once in a while do a test by switching off the VCR's DOC to see how many dropouts the DOC has been concealing. But a DOC can only conceal so much. At some point the DOC becomes overwhelmed.

Dropouts are also caused by tape damage and plain dust and dirt. Specs Bros recommend that before archival tape transfers, tapes be first professionally cleaned. With the cleaning, the proper playback on excellent machines and the DOC, great results can be had transferring even almost 70 year old video tapes.