Stereo sound was an invention patented by Alan Blumlein in 1931. The inspiration for it came from a cinema visit with him and his wife.
During the film he was frustrated with one of the character’s dialogue coming through monaural speakers on both sides of the room, ruining the immersion of the film for him and giving him the idea to use two speakers, left and right channel, not modelled after the human ears, but instead allowed for different signals to come through each channel.
For example, on mono speakers, a character speaking on the left side of the scene would be in the same aural space as sound effects or background music, which sounded like it came from the middle of the scene; however on stereo speakers it gives the chance for speech to be accurately represented in the aural periphery of the film’s viewers.
On the 14th of December 1933 the first ever stereo recording took place as a test to illustrate his idea. This stereo technique is still remarkably used to this day, with major labels and recording studios pioneering the technique in the mid 20th century with releases such as the Beatles’ Sgt. Pepper. I extensively utilise stereo in my personal work as I love to create soundscapes, giving the listener the chance to hear sounds from all different directions.
Thank you very much, Mr. Blumlein! : )