The Sounds of Speech

AS professor of vocal physiology, Alexander Graham Bell did pioneer research in "devising methods of exhibiting the vibrations of sounds optically." In 1873, he became familiar with the phonautograph, developed by Scott and Koenig in 1859, and with the manometric capsule, developed by Koenig in 1862. Greatly impressed by the success of these instruments "to reproduce to the eye those details of sound vibration that, produce in our ears the sensation we term timbre, or quality of sound" Bell used an improved form of the phonautograph having a stylus of wood about a foot long. He obtained "large and very beautiful tracings of the vibrations of the air of vowel sounds" upon a smoked glass. In describing his early attempts to improve the methods and apparatus for making speech waves visible and to interpret wave form, Bell wrote: " I then sang the same vowels, in the same way, into the mouth-piece of the manometric capsule, and compared the tracings of the phonautograph with the flame-undulations visible in the mirror. The shapes of the vibrations obtained in the two ways were not exactly identical, and I came to the conclusion that the phonautograph would require considerable modification to be adapted to my purpose. The membrane was loaded by being attached to a long lever, and the bristle, too, at the end of the lever, seemed to have a definite rate of vibration of its own. These facts led me to imagine that the true form of vibration characteristic of the sounds of speech had been distorted in the phonautograph by the instrumentalities employed.