Sound Recording System Research Articles

What the clinician should know about electromyography.

Electromyography is a recognized clinical procedure that supplies laboratory information to assist the physician in making a diagnosis, outlining a treatment program, and formulating a prognosis for the various disorders of the neuromuscular system.1The instrument used is called an electromyograph.2It is designed specifically for the detection of electrical potentials associated with the activity of skeletal muscle fibers. It is imperative that the proper selection of equipment and techniques should be made in order to obtain reliable information regarding any electrical disturbance of the lower motor neuron or muscular system. This requires the use of needle electrodes, a cathode ray oscillograph, an optical and sound recording system, and a loud-speaker audio system. The curves exhibited or recorded by the electromyograph represent electrical potentials associated with motor activity of skeletal muscles. As a rule the monopolar technique is employed, consisting of a dispersive electrode (percutaneous) that is affixed

A German Magnetic Sound Recording System in Motion Pictures

A German Magnetic Sound Recording System in Motion Pictures

35-Mm and 16-Mm Portable Sound-Recording System<!--<xref ref-type="other" rid="fn1-10.5594_J16515">*</xref>-->

A new low-cost portable sound-recording system suitable for recording a standard variable-density sound track on 35-mm or 16-mm film in synchronism with a motion picture film is described. The basic system includes a two-channel mixer, a main amplifier including associated noise-reduction circuits, a compact recorder, and a power unit for operating the entire system from a 115-volt, alternating-current supply. An optional inverter providing for operation from 96-volt batteries and an alternating-and direct-current multiduty motor-control unit are also available. The various circuit facilities and the performance of the components and system with respect to sensitivity, signal-to-noise ratio, harmonic distortion, and flutter are discussed in detail. The mechanical and electrical design of the equipment make possible a high-quality sound product for both speech and music recordings, the performance specifications being consistent with the requirements and standards of major Hollywood studios.

Magnetic Recording for Motion Picture Studios<!--<xref ref-type="other" rid="fn1-10.5594_J12734">*</xref>-->

Magnetic sound recording systems are being investigated for possible application by the motion picture industry. With limited current literature and the general nature of present industry discussions, certain peculiar requirements for studio use have not been taken into account, but are outlined here. The discussion represents the opinion of one studio's sound department based on the present state of developments and the information at hand, but is, of course, subject to modification as experience and additional information are acquired.

The ABC of Photographic Sound Recording<!--<xref ref-type="other" rid="fn1-10.5594_J07978">*</xref>-->

Suggestion has been made that a paper be prepared outlining the broad principles of photographic sound recording as practiced for motion pictures. If it is attempted to make such a paper deal with anything like adequacy with the many phases of this complex art, it would be nothing short of a book. However, it appears possible to present in reasonably brief space the essential principles of photographic sound recording systems and to supplement this with a bibliography which will at least give the reader a start in studying any special phases of the question. — It is hoped that a paper of this type may serve a useful purpose in helping those who are suddenly confronted with the necessity of working in this field to gain a preliminary picture of what is involved in photographic sound recording, so that they can with less difficulty read the papers which discuss the various special problems.

A Comparison of Variable-Density and Variable-Width Systems<!--<xref ref-type="other" rid="fn1-10.5594_J07413">*</xref>-->

In the earlier stages of the development of the sound recording system of RCA Photophone, the balance seemed to swing at times in favor of variable-density and at times in favor of variable-width recording. The close tolerances for exposure and development which the variable-density system requires made the variable-width system seem preferable. Difficulties in obtaining, with narrow recording slits, sufficient exposure for variable-width recording on high-resolution films were overcome by various improvements in the optical recording system and galvanometers. A slit image 0.00025 inch wide is standard for the newest recording equipment. — While for variable-density recording a number of combinations of exposure and development of both negative and positive have been worked out which give a linear relation between exposing light and print transmission, practical considerations, especially that of obtaining reasonably high outputs, have led to departures from the ideal conditions. Measurements have been published which show the wave-form distortion found in actual recordings of both types, made under representative conditions. The measurements indicate considerably greater distortion in the variable-density records for amplitudes in excess of 50 per cent modulation. For smaller modulations the distortion in both systems is of the order of 5 per cent or less. Variable-width records are subject to a wave-shape distortion which becomes appreciable at very high frequencies. Printing to a suitable density largely neutralizes this type of distortion. — The output from variable-width records is higher by 3 to 8 db. With respect to ground-noise due to scratches and dirt on the positive, the variable-density system may be expected to show a better ratio; while the hiss due to film graininess, and noise due to imperfections of the negative, is less in variable-width records. The fact that extension of the frequency range makes the latter type of noise a more serious factor, plus the fact that the prints will be relatively new, puts the variable-width system at advantage for first-run theaters and for master records for re-recording. — The system of monitoring by observing the moving light spot in variable-width recorders and the ability to judge a recording by inspection of the negative are of considerable practical importance. The full benefits of the recently developed “push-pull” sound-track are obtained only with variable-width recordings.

Vacuum Tube and Photoelectric Tube Developments for Sound Picture Systems

This paper reviews some recent vacuum tube and photoelectric cell developments which are of interest in sound recording and reproduction systems. An indirectly heated cathode triode is described, in the output circuit of which the current components due to the a-c. power supply of the heater have been reduced approximately 20 decibels below previously obtained levels. This tube makes it possible to use an a-c. supply in amplifiers having flat frequency characteristics with over-all gains of the order of 100 decibels. The microphonic disturbances in vacuum tubes are discussed. A measuring system for evaluating the microphonic noise currents is described, and the characteristics of a filamentary cathode tube of low microphonic noise level are given. The characteristics of a double anode, thermionic, gas-filled, rectifier tube for use in a d-c. power supply unit for the sound lamp and vacuum tube filaments of reproducing systems are given. A photoelectric cell of high sensitivity for use in sound reproduction work is described.

Some Aspects of a Western Electric Sound Recording System

This is intended to give a general picture of the part played by the Western Electric sound recording system in connection with the production of talking motion pictures. It is not proposed to introduce any new material but an attempt is made to trace the sound, with particular emphasis on sound recorded on films, from the time it originates in the studio until it is finally ready for theater projection. Some of the many details which are necessary and which must be properly correlated in order to produce a satisfactory product are discussed.

The Optics of Sound Recording Systems

The Optics of Sound Recording Systems