Phase Four ??

[fizzywiggs41]

I can easily see why the quadies in the seventies got this process mixed up with matrix quad.

They record in 4 track Reel from a 10 channel source , then mix down to 2.

 

[fizzywiggs41]

The process was invented sometime in early 1961, fwiw. This according to the lp liner notes.

And was not deliberately intended for surround sound .