Harvey Fletcher (1884-1981): Acclaimed physicist, professor, researcher, inventor.

During his time at Bell Laboratories, between 1916-1949, Harvey Fletcher learned everything he could about speech and hearing that could help match the telephone system more closely, and more economically, with human needs and abilities. The techniques that he and his associates devised for their studies led directly to high-fidelity recording, sound motion pictures, the first accurate clinical audiometers to measure hearing, and the first electronic hearing aids. He made landmark contributions to the theory of speech perception, equal-loudness contours, and the critical band (the frequencies in which a second sound will interfere with a first tone). 

Harvey Fletcher

Fletcher’s early work at Bell Laboratories focused on aspects of speech and hearing required to improve speech transmissions. Fletcher made precise measurements to determine the threshold of hearing and its relation to pitch (frequency), observing that small imperfections in speech sounds impact the listener’s ability to recognize what was said. He identified the minimal pitch and loudness differences that a normal ear can perceive, and measured our ability to interpret speech sounds correctly under varying conditions of loudness, from the minimum perceptible to the loudest that could be tolerated.

Analyzing speech and music, Fletcher determined the parts of complex sounds that are essential to complete perception, and what parts are not. He discovered that certain components of speech sounds, or of musical notes, could be omitted without impairing their intelligibility or quality. In Fletcher's time at Bell Laboratories, this knowledge was of great value in guiding the development of telephone transmission. What he accomplished, in essence, was to specify physically what is in the voice and what the ears get out of it.

One outgrowth of his acoustic research was the development of recording devices that reproduce sound and could accurately transmit the entire audible frequency range. These devices made it possible to synchronize sound with a motion picture and produce talking pictures. Fletcher went on to lead teams tasked with developing cinema sound systems.

In the 1930s Fletcher was the first to demonstrate the spatial effect of sound which he referred as “auditory perspective” and later “stereo”. At the 1932 World's Fair in Chicago, Bell Laboratories presented a demonstration where headsets were placed in a semicircle around a glassed-in stage. In the center of the stage was a dummy called Oscar. Microphones were placed in each ear of the dummy and were connected to receivers in each of the headsets. A person walked around the dummy on stage and spoke. The glass prevented the audience from hearing the person through the air, but the people who had the headsets were startled. To them it seemed that someone was walking around them and speaking to them. They would turn and look over their shoulders to see who it was.

1933 Oscar the Dummy demonstration of stereo sound

In the 1920s and 1930s Bell Laboratories was working on improvements to microphone designs, electronic recording equipment, carbon microphones, radio transmitters, and amplification systems. In 1932 the Laboratories developed stereophonic recording equipment. Fletcher’s profound interest in music led him to partner with conductor Leopold Stokowski and the Philadelphia Orchestra to create the first demonstrations of stereophonic sound, both by direct transmission (from Philadelphia to Washington in 1933) and by recording (in New York in 1940). This collaboration produced more than 100 electronic stereo recordings. Equipment developed under Fletcher's direction enabled a conductor or artist to create an original recording and on playback enhance or modify the sound to achieve variations.

1933: Bell Labs enables the first live transmission of stereo sound – a symphony concert broadcast over telephone lines from Philadelphia, Pa. to Washington D.C. Here, Leopold Stokowski, left, and Bell Labs' Harvey Fletcher are shown at Washington's Constitution Hall with Stokowski adjusting the controls on early stereo equipment.

After his retirement from Bell Laboratories in 1949, Fletcher became a professor of electrical engineering at Columbia University where he organized a department on acoustics.  After 3 years he returned to his undergraduate alma mater as Director of Research at Brigham Young University and eventually became chairman of the Department of Engineering Science. Harvey Fletcher remained active in acoustic research until his death in 1981.

During his lifetime, Fletcher was honored with numerous awards and titles, including first President of Acoustical Society of America, honorary member of the Acoustical Society, member of the Executive Committee of the American Institute of Physics, President of the American Physics Society, member of the National Academy of Sciences, President of the American Society for Hard of Hearing, President of the American Physical Society, and awarded Progress Medal Award by the American Academy of Motion Pictures.  

In 2016 the Recording Academy posthumously awarded a Technical GRAMMY® to Harvey Fletcher for recognition to his contribution to the recording arts.