Human Factor in Piano Tone Production
William Braid White · The Journal of the Acoustical Society of America · 1929
A special form of portable Westinghouse oscillograph, using a Western Electric double-carbon-button 387-W microphone, and one stage of radio amplification, was used to obtain a large number of sound-wave photographs representing the sounds produced at the piano by various eminent artists, particularly Rudolf Ganz, John Powell, Ernest Schelling, and Olga Samaroff. The object was to discover how variations in attack upon the piano keys, transmitted to the strings through the hammers, affect (a) the intensity, (b) the quality of the sounds produced. The following conclusions were arrived at as a result of many experiments. (1) The number of possible variations in key speed and in the control thereof is indefinitely great, much greater than is commonly appreciated by ordinary hearers, or by ordinary players, of the piano. (2) An indefinitely great number of variations in the velocity of the hammer during its travel to the string is likewise possible. (3) Every velocity value of the hammer, in a manner dependent among other things upon the physical make-up of hammer and string, produces a corresponding intensity value, and a parallel color value, in the sound. (4) Faint sounds on the piano tend to converge in color value until at the minimum of intensity all sounds from bass to treble have the same sine wave form, that is, are perfectly simple sounds. Contrariwise, as intensity increases, the number of audible harmonics increases accordingly. (5) It may therefore be concluded that every change in loudness involves a change in color, and every change in color requires a change in loudness; that is to say, tone color control on the piano is dependent upon control of intensity, that is, upon control of hammer velocity, and that again, on control of the speed and acceleration of the key. The paper is illustrated with numerous sound-wave photographs, the evidence of which confirms the conclusions arrived at. The interpretation of these photographs is guided by the general rule that amplitude measures loudness, and shape of vibration-pattern measures quantity.