i do not know the answer to this question.

but i always just assumed it was from the tape getting chewed up, if only slightly, and as a result not running smoothly over the playback head. this could be entirely wrong. just a guess.

BadComrade wrote:I think you're thinking of when a tape has lots of drop-outs in a row.

naw, i'm thinking of when a tape, generally both sides but sometimes only one entire side, has an almost flanger-like swooshing going on with the high frequency content. seems like tapes that have that effect pretty much always have a physical marring of the tape that's very slight but noticeable if you look at it.

I've noticed that when that flange-y type sound happens that little piece of felt on the tape itself is usually off center.

Everytime I've tried fixing it (removing and reglueing) I've embarrassed myself and ruined the tape. It can be done though.

Cassettes are weird.

Ooooh, I hate that! I had a cassette deck that did that to all cassettes I put into it. I don't know why it happens to certain tapes in an otherwise working deck, though.

That cassette deck was my enemy!

BadComrade wrote:So I've always wondered... What is it that causes /can cause certain old cassette tapes to get that weird swishing "rollercoaster" up and down effect on the high end. I'm guessing you know what I mean... it sounds like someone is turning the treble knob on your stereo up and down and up and down over and over at a steady rate...

Is it due to a capstan the tape was once played over having been magnetized, etc?

Cassette decks need to kept scrupulously clean - a little crud on the pinch roller will cause this effect and also damage the tape.

Another cause could be a distorted cassette shell. The easiest solution to this would be to transfer the tape to a new shell.

If you are going to be recording from the cassette onto another format then you need to check the head alignment carefully on each side of the tape (and possibly more often if this is a critical transfer). It is much easier to hear the effect of changing the head alignment if you sum both channels to mono.

Cheers.

James.