All the other answers are wrong! Joking, of course, but... It was from a student radio station? In the 70s it is likely they had dual pole patch bays and plugged one in upside down, or something like that. Or they had instructors who were less detail oriented...
I would assume that you are playing back on a familiar tape deck, so no need to test its polarity.
KPFA had those dual patch bays in the 70s...
Sent from Lou Judson's iPad 2
On Feb 6, 2013, at 6:55 AM, Henry Borchers <[log in to unmask]> wrote:
> Hi all,
> I've got a question for you that has been a real head scratcher for me and I hope there is someone here who might be able to shed some light on it.
> I've been digitizing a number of amateur recordings from a student radio station from the 1970s recorded on 1/4" reel tape and a number of these recordings from this collection seems to be mono and have no stereo field but the left and right channels have opposing polarity. It is easy to just digitize both channels and play them on stereo headphones but since they are 180 degrees out of phase, they cancel each other out when summed together with a mono speaker.
> I understand the physics of canceling waves (and I know how deal with this) but my question is this. Does anybody know how an amateur reel-to-reel recording could have gotten this way?
> Henry Borchers
> Broadcast Media Digitization Librarian
> University of Maryland
> B0221D McKeldin Library
> College Park, MD 20742
> (301) 405-0725