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THE PHONOGRAPHIC METHOD
43
imately equidistant from the two bearings of the shaft, and whatever addition to the friction at these points is due to it may be supposed equally distributed between them. At the close of an inscription the needle is very near, almost over the right-hand bearing, and whatever friction it causes may be conceived as mainly concentrated at this point. Let it be admitted that this gradually increasing disparity between the amount of friction at the two bearings would cause a gradual slowing of the cylinder as the needle went on in its course; this supposed change in conditions of friction, and consequently this slowing, would take place both in inscription and reproduction: but if it were any less in amount in the latter case, the note would tend to rise in pitch as the reproduc­tion went on. For a source of constant pitch imparts to the phonograph dia­phragm equal numbers of impulses in equal times; if now the cylinder takes a longer time to move through an equal arc, as the needle advances over it the indentations it makes will be closer together in later than in earlier positions of its path. In the reproduction, on the supposition that the change of place of the needle caused no slowing at all, — that is, that a given arc of the cylin­der passed under it in exactly the same time wherever it was, — since later in­dentations are closer together than earlier ones, the impulses they communicate to the diaphragm would be more and more rapid as the reproduction advanced. What went in a constant tone would emerge a gradually rising one. But a similar effect would be produced even supposing the reproducing needle re­tarded the cylinder somewhat, so long as this retardation were less in amount than that of record, the sharping being less conspicuous as the friction of the reproducing needle were greater. Now the inscribing needle is a plough (that is, cuts a furrow through the wax) and the reproducing needle is a harrow (that is, is dragged through this furrow), and the amount of resistance made by the former to the turning of the cylinder must be much greater than that made by the latter. Hence we may assume that the amount of slowing which takes place as the needle advances on the cylinder is much greater in inscrip­tion than in reproduction. It is the difference, we may therefore conclude, be­tween these two retardations that appears as the minute upward movement several times observed in the note of Cylinder B.
The fact that this progressive change disappeared in the last trial of Cylin­der B is perhaps not incompatible with this hypothesis of its origin. For we can interpret the preponderance of noise in this reproduction as a sign of an increase of friction between the reproducing needle and the cylinder. The needle then possessed a greater power than at first to retard the movement of the cylinder; and, as we have seen, if it possesses the same as that of the needle
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E-Book - An Annotated Compendium of Old Time American Songs by James Alverson III