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The fundamentals of stereo theory and microphone placement (specifically the "crossed mikes" technique) were established in England in 1931 by A. D. Blemlein of the Columbia Gramophone Company (now a part of EMI). Some experimental two-channel discs were made in 1933 as a part of that research. These recordings, which have never been released, were conducted by Sir Thomas Beecham and include a Mozart "Jupiter".
Also in the early 1930's Bell Laboratories conducted some stereophonic experiments in the United States culminating in a direct-line live transmission in collaboration with Leopold Stokowski. Though this was not recorded, it may have planted the seed which later resulted in Stokowski's 1939 nine-channel "Fantasia" recording on optical film.
In several countries research had been slowly progressing on methods of recording an audio signal magnetically on lengths of paper tape coated with iron oxide. But it was in Germany in the late 1930's and early 1940's that this goal was finally realized and brought to a measure of perfection. The development of dual-channel recording followed immediately and it was on one of the Magnetophon recorders then developed that the present recording was made.
Rumors of stereo tapes of Furtwangler's wartime performances have never been confirmed by their issuance on records, but it seems likely that those - and possibly dual-channel tapes by Richard Strauss - did or do exist, possibly in East Germany or the Soviet Union.
One other 1944 stereo is known: one movement only of the Bruckner "Eighth Symphony" (the "Finale"), conducted by Herbert von Karajan. It has been issued by the Bruno Walter Society.
In the United States strong interest in stereophonic and binaural recording techniques firstly began to emerge about 1952. Tapes with the National Philharmonic Orchestra of Washington, D.C. were reportedly made by the Berlant Concertone Tape Recorder Company, but they have never appeared commercially. Stereo tapes sponsored by another recorder manufacturer - Webcor - did, however, appear briefly about 1954 and some of these are now available on disc from Everest Records.