I read that same information in an article in Rolling Stone that was
contemporaneous with the release of the album, and this was a pretty concise
summary of the explanation it contained.
> Hi, all-
> Thought I would throw another wrench in the fire
> (probably replete with erroneous 70's memories, too).
> It seems I read once that 10cc used a large multitrack
> recorder to create a playable choir of their own
> voices on the song "I'm Not In Love". Once the vocal
> tracks were laid down on the same area of tape, the
> section was cut out, and spliced in a loop. It was
> loaded back on the machine (with appropriate tension),
> and played off a mixing console using the solo buttons
> as a keyboard. I don't know where I read this, but it
> stuck in my mind for years. Maybe a similar idea was
> used by those clever Germans.
>