What specific technology did British engineer Alan Blumlein develop in the 1930s?

Stereophonic sound utilizing two audio channels.

Alan Blumlein, a British engineer, made a substantial contribution to spatial audio development in the 1930s by focusing on stereophonic sound. This development represented a major advance over the prior standard of mono sound reproduction. Blumlein's work utilized two distinct audio channels specifically engineered to create a sense of directionality for the listener. Although stereo is now considered foundational rather than purely spatial audio in the modern sense, Blumlein’s established technique laid essential groundwork that would subsequently support the development and understanding of more complex multi-channel and spatialization techniques that followed later.