On February 9, 1932, Duke Ellington and his Orchestra were in a studio in New York to make some records. For some reason lost to history, two separate recording setups were used beginning with the microphone continuing through to the disc-cutting lathe. No one thought about it until the 1980’s.
According to a 1985 article in the Chicago Times, Steve Lasker had a test pressing he had just received from a collector in Belgium. Lasker’s friend, Brad Kay, noticed that the master number on that disc was different than the number on the released performance owned by Kay. They thought perhaps that the test disc may have been an alternate take.
The two met again at a later date and listened to both the test disc and Kay’s disc of the released performance. As they listened closely, they noticed that the performances sounded the same. The same phrasing, the same mistakes, and so on. Knowing that no two jazz performances were the same they realized that the two discs were recordings of the same performance. They did notice, though, that there were acoustical differences between the two. They synchronized the two recordings on the two channels of a stereo tape recorder and discovered that they had a stereo recording, albeit an accidental one.
This led to further research on the part of Brad Kay and he discovered other “accidental stereo” recordings going back to as early as 1929 such as this recording of Igor Stravinsky’s Right of Spring as conducted by Leopold Stokowski.
It took until 1934 before progress was made on a disc that carried both channels on a single disc. Experiments by the Bell Telephone labs used vertical modulation of the grove for one channel and lateral modulation for the other. I find the lateral modulation seemed to give better separation than did the vertical. One channel almost seems mono whereas the other was only on one side.
Inasmuch as “accidental” stereo would not even be noticed for almost fifty years and the depression probably was not the time for anyone to pursue such a novel concept as stereo discs, stereo was to go nowhere for several years until until the industry that made the silver screen flicker thought they would give it a try..