US2421424A - Reverberation method and system - Google Patents

Description

June 3, 1947 B. vKREUzr-:R

REVERBERATION METHOD AND SYSTEM Filed Feb` 8, 1945 @N MHQN NSK@ SQQ Patented June 3, 1947 UNITED REVERBERATION METHOD AND SYSTEM Barton Kreuzer, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application February 8, 1945, Serial No. 576,812

Claims.

This invention relates to sound recording methods and systems, and particularly to a sound rerecording system wherein the original sound record is modied with respect to amplitude or frequency, or both.

It is Well-known that sound records, especially those which accompany motion pictures are generally rerecorded, while records made for radio broadcasts or home reproduction in phonographs may also be rerecorded before release. In motion picture work, rerecording is employed to combine dialogue, background effects, and/or music into a composite record for the picture, the various components being modified either with respect to amplitude or frequency, or both. Amplitude and frequency modiiications are also made during the rerocording of a single prerecorded record, particularly to simulate the sound as it would occur at the place of the scene. The sound may be recorded in a studio or on a set, which is actually only a portion of the entire scene, and thus, the quality of the sound is not appropriate to the scene being depicted in the picture. For instance, only two or three sides of a large hall or cave may be used, and the sound detected from the actors therein does not have the characteristic it would have had if produced in the actual hall or cave. However, by rerecording, the sound may be characterized by varying the amplitude and frequency relationship of its components, and by introducing reverberation, to give it the quality it would have had if actually recorded at the scene of action.

As disclosed in my copending application, Ser. No. 576,811, filed Feb. 8, 1945, reverberation is also used to improve or restore noisy records. In accomplishing sound wave modification, reverberation chambers are employed, and have been ernployed for some time. Reverberation chambers are simply enclosed spaces into which sound is projected by a speaker and detected by a microphone spacially disposed with respect to the speaker. To simulate large halls, railroad stations, caves, and the like, it is desirable to have a reverberation chamber of large size in order to get a true and accurate sound modification to simulate the scene, and such space is usually not readily available. The present invention is directed to a system which permits the use of the unused spaces in a studio or building not otherwise suitable for this purpose, such as a basement area, the plenum space in a building, or the actual recording stage itself While in use. Reverberation may, of course, be added to and during the original recording from a recording stage, the present invention permitting the stage to be used simultaneously for both the original sound source and the reverberation chamber.

One of the important features of the invention is the use of an ultra or supersonic frequency, which, of course, is not only inaudible to the performers, but also is inaudible to the audio detecting elements or microphones. Since the ultrasonic carrier modulated by an audio signal occupies only a relatively narrow band in its spectrum, a very high quality result is obtainable, while the use of an ultrasonic frequency as a carrier permits the reverberation chambers to be tanks or pipes filled with a liquid,

The principal object of the invention, therefore, is to facilitate the modification of a sound wave as recorded.

Another object of the invention is to provide an improved method of and system for obtaining reverberation in a signal being transmitted or recorded.

A further object of the invention is to provide an improved method of reverberating an audio signal.

A further object of the invention is to obtain reverberation in space not normally suitable therefor.

A still further object of the invention is to obtain reverberation of an audio signal by modulating an ultrasonic signal, which is reverberated and thereafter detected to obtain a reverberated audio signal.

Although the novel features which are believed to -be characteristic of this invention Will be pointed out with particularity in the appended claims, the manner of its organization and the mode of its operation will be better Vunderstood by referring to the following description read in conjunction with the accompanying drawings forming a part hereof, in which the single figure is a diagrammatic arrangement of a recording or rerecording sytem embodying the invention.

Referring now to the drawing, a source of signal currents to be reverberated is shown at 5 as a reproducer, which may be either film or disc, although it is to be understood that this source could be a microphone directly detecting the original sound source or sources. The output of the reproducer is fed into an amplier 6, the output of which is divided, one portion going to an amplifier 8 feeding a recorder il and a monitoring speaker l2 through a mixer 9. This channel contains the essential elements of a normal recording system, the mixer operator varying the amplitude of the currents in the proper amounts within the limits of the recorder II.

The othe1` portion of the output from the amplier 6 is fed into a modulator I5 which is supplied with an ultrasonic carrier frequency, such as 30,000 cycles, from a generator I6, the output of the modulator being fed to an ultrasonic reproducing speaker I8 in a reverberation chamber 20. The ultrasonic frequency sidebands produced by modulation are reverberated in the chamber 20 and picked up by an ultrasonic microphone 2 I, amplilied in amplier 22, and detected in a demodulator 24 to obtain the original audio frequencies. rihe reverberated audio signal is then ampliiied in amplifier 25, impressed on a mixer 26, and then on the recorder II and monitor I2. By the proper adjustments of the mixers 9 and 26, as indicated in the monitor I2, the normal and reverberated currents are mixed together in the desired proportions for recording into the final record.

Although a split channel has been illustrated wherein only a portion of the signal is reverberated, it will be understood that the entire signal may be passed through the reverberation chamber or the operator may use only that portion passing through the reverberation chamber. Alsoy since the ultrasonic frequency spectrum is very large compared with the audio frequency range which determines the Widths of the sidebands (one of which may be suppressed), it is feasible to utilize the reverberation chamber for reverberating more than one audio signal simultaneously. That is, by the use of a second reproducer, shown at 30, and another detector, shown at 3I, two or more audio signals could be reverberated simultaneously by using a different carrier frequency for each audio signal. Furthermore, the same ultrasonic wave translator and detector could be used for a plurality of carriers, the carriers being separated by electrical band pass lters, as is well-known in the art.

As mentioned above, the unused spaces of a building may now serve as reverberation chambers, such as the basement or attic, or the actual recording stage during the original sound Droduction. In the latter instance, the audio frequency elements are insensitive to the ultrasonic frequencies, and the ultrasonic elements are not sensitive to the audio frequencies, so there is no interference therebetween. Also, since the range of the ultrasonic reproducer and detector is large and only a Very narrow range is employed, a uniform response is obtained.

By the use of ultrasonic frequencies as the reverberation medium, tanks or pipes lled with liquid can be used with under water sound propagators and detectors. By varying the tuning of the carrier generator, various reverberation characteristics are obtainable, thus avoiding changing the size of the chamber as is now necessary with audio frequency chambers. The system thus is particularly flexible to provide a wide range of sound characteristics covering spaces having a wide range in size, while permitting the same chamber to be used for reverberating several signals simultaneously.

I claim as my invention:

l. A reverberation system comprising a plurality of generators of super audible electrical currents, each current having a different frequency, a plurality of signals in the audio spectrurn, a reverberation chamber, means for modulating each of said super audible currents with a respective audio signal, means for simultaneously generating ultrasonic waves from said products of modulation Within said chamber, means for translating said reverberated Waves into corre sponding electrical currents, and a demodulator for each of said electrical currents of different frequency,

2. The method of generating and detecting a signal in a certain area and simultaneously regenerating and again detecting said signal in said area comprising detecting sound waves from the original source of said Waves in a certain area, modulating a supersonic carrier frequency with the products of detection, reproducing the products of modulation in said certain area, and detecting said reproduced products of modulation.

3. The method in accordance with claim 2, in which said detected products of modulation are combined with said origina-l products of detection.

4. A method of producing artiiicial reverberations on a sound stage without interfering with the normal recording operations being conducted thereon comprising producing an audible sound signal on said stage, detecting said signal during the production thereof, generating a super-audible carrier frequency, modulating said carrier with said detected signal, translating said products of modulation into ultrasonic waves Within the space of said sound stage, detecting said ultrasonic waves within said space, and demodulating said detected currents to obtain a reverberated original signal.

5. The method of obtaining varying reverberation characteristics of an audio signal without modifying the reverberation chamber, itself, comprising generating a super-audible carrier of predetermined frequency, varying the frequency of said carrier to obtain desired changes in reverberation characteristics, modulating said carrier with said audible signal, generating ultrasonic waves with the products of modulation, reverberating said waves, translating said waves into electrical currents, and demodulating said last mentioned currents.

BARTON KREUZER REFERENCES CITED rThe following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,318,417 Phelps May 4, 1943 1,853,286 Round Apr. 12, 1932

Images