The Dynamics of Pianoforte "Touch."
G. H. Bryan · Proceedings of the Physical Society of London · 1912
The author discussed Helmholtz's and Kaufmann's theories of the vibrations of a pianoforte wire excited by impact, with special reference to the effects obtainable with the modern pneumatical piano-players and player-pianos, and the common widespread belief that these can never reproduce the touch of the human fingers. While the rendering of many commercial piano-players in the hands of an average performer bears little resemblance to the performance of a professional pianist, the author finds that there is generally believed to be a certain element missing even in music played by a skilled performer on a first-class modern piano-player, this missing element being commonly associated with what is described as touch. In view of the great value of piano-players to lovers of music, it thus becomes interesting to examine more closely what is meant by touch, and whether it is capable of being reproduced to a greater extent than hitherto upon pneumatically controlled pianos. The question turns very largely on the extent, if any, to which the quality of individual notes can be varied by striking the notes in different ways. Such a possibility involves the inferences that (a) the intensities of the fundamental tone and its several harmonics are capable of independent variation; (b) these variations can only be produced by varying the behaviour of the pianoforte hammer while it is in contact with the string, for example, by lengthening or shortening the duration of contact; (c) such an effect can only be produced by rapid time variations of the pressure applied to the keys while they are being depressed - e.g., by a fairly rapid decrease or increase of pressure produced by smartly striking or heavily pressing on the key. The author finds that Kaufmann's investigation fails to account for any such effects, and that difficulties arise even when the equations are modified so as to take account of impressed forces on the hammer comparable with those due to gravity. On the other hand, he describes experiments which appear to indicate beyond all reasonable doubt the existence of such effects of touch, and which certainly demonstrate the possibility of reproducing them by means of the modern instrument. For this purpose the author's piano-player, which is a first-class instrument of the Standard type, but with the whole keyboard under one common control, was fitted with an for which a patent application has been filed. This lever operates directly on the face of the auxiliary regulating bellows, and the air-tension in the bellows can be regulated by means of a sliding weight placed on the lever, or by applying hand pressure to the lever itself. In this way the touch of the human hand can be transmitted directly to the keys of the piano. So far as the experiments go, they indicate that even if the lever is worked in conjunction with suitable expression marks, as could be done by a person of moderate experience, increased breadth of contrast is obtained. While by varying the position of the load independently of the pedalling a variety of dynamical effects can be produced, which can further be increased by hand control. A short, sharp pressure produces a bright ringing treble with a light bass, a sustained pressure produces a rich bass with a soft treble; the general character of the tone being suitably described as metallic in the first case and woody in the second. A very conspicuous feature of these experiments is the marked differentiation which they show between notes in different parts of the scale, especially in chords, the notes of which are accurately ranged (as is unfortunately often not the case in music rolls). The duration of the pressure required to produce the maximum effect on a particular note of the piano varies continuously from the treble to the bass end, being least in the treble and greatest in the bass, and by means of this natural or dynamical differentiation notes in a particular part of a chord at any part of the scale can be accented independently of the rest. Whether it is possible to vary the quality of individual notes is a point that can only be tested by playing single notes as opposed to chords. The differences that can be effected can only be noticed by a trained ear; in the author's experiments it has been found that some persons notice very marked differences, others notice very slight differences, others no differences at all. The differences are probably as conspicuous as those between a stopped string and a harmonic on the violin. It is not always easy to produce these differences for purposes of demonstration, though it is often easier to do so in the course of playing through a suitable composition. In any case the author finds that the effects can be obtained more easily with a pneumatic player fitted with auxiliary lever than in striking the keys with fingers. When the lever is disconnected the change observed affords some indication of the origin of the popular belief in the limitations of the pneumatically played piano. Unlike the gramophone, aeroplane, motor car and cinematograph, the modern piano-player has been conspicuous by the absence of reference to it in scientific and technical journals. The present Paper, which arises out of an attempt to obtain a closer degree of approximation to playing the piano with these instruments indicates that they open up some interesting problems in the study of acoustics.