Don Lewis

Devices for Studying Interference in Psychomotor Performance: III. the Doubledisk Pursuit Apparatus

Abstract : Three attempts were made with rotary pursuit apparatus to induce decrements in performance subsequent to interpolated practice. An ordinary Koerth-type rotor was first employed with mirror-vision practice preceding direct-vision practice. Mirror-vision performance during relearning was not adversely affected by the interpolated practive. With the Double-Disk Pursuit Apparatus, subjects learned to trace a kind of figure-eight pattern. Original practice with the disks rotating in one way was followed by practice with the directions of rotation reversed. The decrements that appeared at the outset of relearning were small and could not confidently be attributed to interference effects. A second model of the Double-Disk Pursuit Apparatus provided for a variable pursuit pattern. The change in the tasks, as between original and interpolated learning, depended upon a reversal of the directions of rotation of the disks. Here again, a decrement appeared at the outset of relearning, but it was too small to be clearly identifiable as a product of interference. (Author)

The Measurement of Timbre

Research designed to measure timbre as a function of harmonic structure, frequency level, and intensity level is in progress. This paper, the first of a series of projected reports, includes a description of apparatus, a brief discussion of problems of measurement, and a summary of some of the data already secured.The apparatus consists mainly of an electrostatic generator, described in part elsewhere. This instrument produces complex tones constituted of desired combinations of any or all of sixteen consecutive harmonics, the frequencies, intensities, and phase relationships of which are subject to control. Each harmonic is reasonably free from stray components. A calibrated Western Electric 555 receiver is used with the generator. The current flowing through the receiver (current being proportional to the r.m.s. value of pressure developed in the ear canal) is measured with a vacuum tube voltmeter. As many as five different test tones, each to be paired a required number of times with a suitable standar...

FM synthesis in musical instruments

The objective of the presentation will be to explain the development and implementation of FM synthesis in musical instruments. Topics to be covered include: (1) development of FM synthesis; (2) introduction of FM synthesis in musical instruments; (3) explanation and demonstration of principles of FM synthesis; (4) implementation of FM synthesis in current Yamaha instruments: the DX7; (5) demonstration of the musical capabilities of FM synthesis.

Method of Measuring Audiofrequencies

We have recently developed a method of measuring audiofrequencies which has proved to be quite accurate as well as fairly rapid. The apparatus consists of a vacuum‐tube oscillator which controls a multivibrator whose fundamental frequency is 100 c.p.s.; a beat‐frequency oscillator equipped with an incremental‐frequency control calibrated in cycles per second over a 100‐cycle range: a G.R. Type 636‐A wave analyzer; and a cathode‐ray oscilloscope. The measurement of frequency is made in the following manner: (1) With the incremental‐frequency condenser set at zero, the beat‐frequency oscillator is adjusted to the unknown frequency through the use of Lissajous figures on the oscilloscope. (2) The wave analyzer is then set to the multiple of 100 cycles which is nearest to the frequency being measured, as shown by the main dial of the oscillator, and adjusted exactly by tuning it to one of the harmonics of the multi‐vibrator. (3) The analyzer is then switched to the oscillator and the incremental‐frequency dia...

Pitch and the Missing Fundamental

Jeffress recently reported a study of the pitch of organ‐pipe tones from which the fundamental component had been eliminated. His results, contrary to those of Fletcher, indicate that the average observer does not judge pitch to remain unchanged when the fundamental is eliminated. We have been making a further study of the problem as a part of a general investigation of subjective tones. Complex stimulus tones, produced with an electrostatic type multi‐harmonic generator, have typically consisted of harmonics 2, 3 and 4 in combination, with values of Δf as follows: 268, 402 and 536 cycles. Intensity levels of 50, 70 and 90 db have been employed. Eight observers, seven of whom have had advanced musical training, were instructed to adjust the frequency of an oscillator tone until its pitch was judged to be the same as the pitch of the complex tone. On the whole, the results indicate that Fletcher was probably somewhat too optimistic in his original report. Far more often than not, the adjusted frequencies w...

Masking and the Perception of a Series of Successively Prominent Partials in a Vocal Sound

At the last meeting of the Society, we presented a paper dealing with a vocal sound of short duration and of essentially constant pitch and loudness whose upper partials (three to seven, inclusive) became successively and individually prominent during the course of the sound. There was no way of knowing, at the time of the previous report, whether or not masking effects were of any importance in determining how the sound was heard. Data have recently been secured on the masked absolute thresholds of each of the five crucial partials for the periods immediately preceding and immediately succeeding the period during which it was heard as prominent. Although the threshold measurements were made indirectly (that is, in relation to similar complex sounds produced with a multi‐harmonic generator), the obtained values are believed to be approximate measures of the masking introduced by the vocal sound. Masking was by no means negligible; but only the fifth partial was found to be below its masked absolute thresh...

On the Phase and Magnitude of Subjective Tones

It has been shown by Lewis and Larsen that the phase and the magnitude of a subjective tone heard monaurally may differ significantly for two different observers with normal hearing. This paper deals with a study of the two ears of the same observer. Differences as well as similarities in both phase and magnitude are indicated, differences in magnitude being more common than differences in phase. Further investigation seems necessary before a satisfactory explanation of the findings can be offered.

Resonant Frequencies and Damping Constants of Vocal Resonators

In a recent paper by Lewis, a method was developed for determining the resonance frequencies and damping constants of the principal resonators typically involved in the production of sustained vocal tones. The method has been used in further research; and the present report deals with data secured on the vowels “O” and “AH”. Generalized values are presented. In addition, some of the effects on vowel structure of variations in pitch and loudness level are shown. It is evident, for example, that the magnitude of high frequency components, relative to the magnitude of low frequency components, varies with loudness level. The effects of pitch variation are, on the whole, neither clear‐cut nor consistent.

An Analysis of Perceptible Overtones in the Voice

Both oscillographic and phonographic recordings were made of a vocal sound in which five successively prominent partials were produced, in a few seconds, by a singer who meanwhile maintained the sound at a specified pitch level. Representative waves from the period of prominence of each partial were subjected to harmonic analysis, the results showing the physical bases for corresponding auditory experiences. Detailed investigation of the periods of transition from a given perceptibly prominent partial to the succeeding one revealed significant changes in energy distribution. For example, during the transition from the 4th to the 5th partial, there was found to be a 5 db decrease in the intensity level of the 4th, a 20 db increase in the level of the 5th, and a 10 db increase in the level of the 6th, with all other partials remaining essentially constant. The changes were gradual but rapid, and were apparently dependent upon resonance factors. The crucial importance of a given transition in attracting atte...

Pitch Variations Arising from Certain Types of Frequency Modulation

This report deals with an investigation of the pitch of sounds characterized by frequency modulation. It has to do mainly with the perceived extent of pitch glides. By means of a specially‐designed variable condenser the frequency of an oscillator could be modulated, intensity of output remaining essentially constant. Either sinusoidal or linear modulation could be obtained, and the amount and rate of modulation were both subject to control. It was possible to secure, among others, the following types of variation: (a) isolated frequency sweeps, either upward or downward in direction; (b) upward‐downward or downward‐upward sweeps; (c) sweeps, either upward or downward, at the beginning or end of a steady‐state sound; (d) periodic modulation, that is, frequency vibrato. Sounds with vibrato were studied only casually. The experimental data, which reveal the relationship between perceived extent of glide and both the amount and the rate of frequency modulation, are interpreted to indicate their bearing on pr...