[Audioarchivist]

I was referring to covering the other holes to get better frequency response, and warning not to record by accident. Let me explain further...

If there's no switch on the front of the deck to select tape type, there's a sensor looking for these other holes. Cover them to playback as normal tape. Playing back as normal bias gives a better high frequency response. Brighter and fuller.
Some decks use the other holes on top of CrO2 or metal tapes :
1) normal bias tapes have only a small hole (well, one for each side of tape) with tabs that you should pop out to prevent accidental recording. They are closest to the outer edges of the top of a tape. Don't cover them unless you want to accidentally erase your tape.
2) CrO2 tapes have an "extended" hole beside the record tab. Again, pop the tabs, but cover the second section of these holes towards the inside of the tape.
3) Metal type tapes have the extended hole beside the record tabs, and also another set of holes towards the center of the top of the tape. Again, if there's no switch for selecting bias for playback, cover the center holes and the inner portion hole next to the record tabs.

I would suggest this method for 99% of tapes, unless there's a huge high frequency response to some tinny sounding master that's too bright. Even then, there's still not much reason to dull down the tape response with these bias settings.

I hope I've cleared up my original meaning. If there's no bias switch, its got sensors looking for those holes. Cover them for better high end response. Don't playback with Dolby. Adjust the azimuth properly. Clean the heads and tape path. Clean the pinch roller rubber assembly with the right stuff. Try and find a tape head demagnetizer - eventually you might need to demagnetize the heads if you playback lots of tape.

Jeez, all this talk about holes, and no girlfriend for me right now. Sad state of affairs...haha