US1855148A - Sound transmission - Google Patents

Description

April 19, 1932. w B JONES 1,855,148

' SOUND TRANSMISSION Filed Aug. 4, 1927 means are employed in Patented Apr. 19, 1932 W. BARTLETT JONES, OF CHICAGO, ILLINOIS SOUND TRANSMISSION Application filed August 4, 1927. Serial No. 210,629.

The present invention relates to the interception'and the transmission of sounds, and has particular reference to the production and the shifting of virtual sound sources.

In my copending application Ser. No. 183,414, filed April 13th, 1927, I have described in considerable detail means for the creating of virtual origins of sound by use of the binaural effect. Among the apparatus described there are shown various sound intercepting means and various presentation means. For the purpose of the above named application the intercepting or transmitting ear-locations, or in other words, are binaurally located, that is, the two sound intercepters are so located that they gather in surrounding sounds substantially as do the two ears of a human being. The corresponding right and left ear-eifects thus picked up are transmitted elsewhere, or are phonographically recorded for presentation at a different time or place, or both, according to the character of the link between the pick-up devices and the presentation means.

The presentation means described in the above named application are of two types,

generically referred to as receivers, one, the

head phones, and two, the loud speaker. The head phones are well known as being suitable for reproducing left and right ear-effects binaurally intercepted. The combination of binaural interception and the use of head phones permits thevlistener to sense the exact direction and mutual relations of the several sound sources transmitted.

The above-named application teaches that when a pair of head phones are replaced by a pair of loud speakers, the same space impressions may be obtained when the listener is midway between the two speakers in such a manner that sound paths of equal length prevail from each loud speaker to the nearer ear. The application also teaches that when there is motion from the mid-position, there is an arcuate shifting ofeach virtual source, depending upon its actual position. The degree of arcuate shifting is unequal for the several sources, so that there is created a distortion of the actual relation. Such distortion provides countless combinations of virtual sources changing considerably with changes of the listeners position amounting to only a few inches. .These changes provide a pleasing variant to the source of sound or music which is fully within the control of the listener, and it is a great improvement over the fixed and monotonous single location of sound reproduced by phonograph or radio.

The primary object of the present inven- 0 tion is to provide a system for the transmission and reception of sound of such a character that the listener has within his own control the power to vary through infinite combinations the apparent sounds and possibly to isolate one or more of the sources from the others for the concentration of his attention upon it.

Binaurally intercepted sound has been limited to presentation by ear phones. of loud speakers for the presentation of binaurally intercepted sound ermits retention of all the advantages of head phones and provides in addition the many pleasing variants above mentioned, without the dis- 76 advantage of the hysical connection of the body to the receivmg means.

The present invention aims pick-up devices in positions outside of binaural relation as one place the receivers or loud speakers in a similar extra-binaural relation.

The invention may be more readily understood from the following description of the to place the the digrammatic apparatus shown in the accompanying drawings, in whlch Fig. 1 represents two associated phone or sound channels with head phones at the receiving end and extra-binaurally located transmitters placed before several sound sources.

Fig. 2 represents an arrangement corresponding enerally to Fig. 1, with the head phones of ig. 1 replaced by extra-binaurally located receivers, between which a listener 1s located in mid-position.

Fig. 3. represents a receiving or audltory station similar to that of Fig. 2 with rthe listener in a position other than mid-position.

Fig. 4 shows the listener in still another locations of the 65 The use 7 feature and also to 80 position for illustrating the'shifting ofthe origins with such a change of position.

More particularly, Fig.1 shows a stage or platform from which issue a plurality of 5 sounds that are intercepted by two micrographic record, as described in respectively phones at extra-binaural locations. The effect at each microphone is transmitted or otherwise linked to the receiving means for presentation to a human being. The transmission or linking hereinafter referred to contemplates any suitablecarrier or channel for sound efiects or for sound. It may comprise a simple telephone system, a phonomy copending or it may be a single carrier application Ser. No. 183,414, duplex system employing a wave, either conducted over a single pair of wires, or radiated through the ether.

In the drawings 10 represents a stage upon which the dots represent sound sources. The source 11 and the source 12 are designated for the purpose of discussing their relation to the'sound transmissionsystem. The transmitters are two microphones l3 and 14 with their channels 15 and'16 linked by suitable means 17 to the auditory station having the receivers provided as head phones 18 and 19, associated withthe channels 15 and 16. The arrangement described is distinguished from the binaural systems by the fact that the micro bones are separated from each other by a distance which is greater than the distance between human ears. The are therefore considered to be outside the binaural relation. In the present instance they are represented as being three feet apart and are equidistant from the source .11. However, as to source 11, and any other equidistant source, they act as if they were in the binaural relation, for the sound paths from 11 are equal in length. Thus a person listening at the head phones will sense the source 11 directly ahead of him. source indicated in'the drawings, for example, source 12, the two sound paths are of different lengths and the differential length in sound paths is too great to fall'within the limits upon which the binaural efi'ect deends, which is substantially six inches.

ach one of the sources indicated will be heard either to the right or to the left of the listener, depending upon which microphone is nearer the source.

nated as X, Y and'Z.

The preferred form of the invention employs loud speakers as receiving means so that the listener may shift the mutual relations of himself and the loud speakers to shift the locations of the virtual origins. In Fig. 2 a stage 20 has three sound sources thereon which are herein shown in alinement for no important reason. They are desig- In a parallel line ten feet away there are two microphones 21 and 22, which are shown as-being four feet apart. The source Y islocated equidistant from the y this reason,

For every other two microphones. The sound channels a1 designated 23 and 24 and these respectivel connect loudspeakers 25 and 26 to the micrc phones 21 and 22.

The parts described are drawn to scal and permit an approximate graphical meas ure of the sound paths. H represents a per son positioned midway between the low speakers, and (1 represents the distance be tween each speaker and the nearer earof H The distance from the source Y to the micro phones is represented by A in both instances From Y to H the air paths of the sound trans mitted through both channels .23 and 24 an the same inlength, being A plus d. Accord ingly H will hear the source of Y directly aheadof him because each ear will hear thr same sound at the same time. This is indicated by the arrow 27 pointing to the encircled source Y. Because of the great distance between the two microphones the sources of X and Z will each have differential distances from themicrophones greater than the binaural limit, and each will be heard in the direction indicated by the arrows 28 and 29. It will be noted that there is one source on each side of the listener H, and that the source Y has been isolated from the others. When the two ears hear the same sounds in the same phase relation, as occurs when the source is faced directly, it is easier to concentrate the attention upon it. For H may better focus attention upon Y than he could if he was present before the stage 20. a By isolating Y from the alined .grouphe has placed X and Z as much in the background as is possible by this invention. i

Fig. 3 represents a different arrangement of the auditory station. The transmitting end of Fig. 2 is to be considered as the source of the two effects for the station of Fig. 3. Loud speakers 30 and 31 are here shown with the listener H located away from midposition. paths from the source X through the two transmission channels are equal, whereby to place the virtual of H. In order to show this relation it may be considered that the distance from X to 21 1s 11 feet and the distance from X to 22 is 14 feet. H is so located with reference to the loud speakers that from one ear to speaker 30 the distance is 4 feet and from the other speaker to the other ear the distance than the binaural llmit, and each will be is so located that the sound source of X directly in front heard in the direction indicated by the arrow 33.

In Fig. 4 an arrangement is shown which isolates the virtual source of Z. Loud speakers 34 and 35 are shown and are considered as the receiving station for the transmitting means of Fig. 2. The listener H" is so positioned between the speakers that the tWo sound paths from source Z are equal in length. From Z to 21 the distance may be considered to be 11 feet, and from Z to it is 10 feet. Accordingly, for any distance L which is added to the Z21 path there must be added to the Z-22 path a distance L plus 1 foot. In Fig. 4 the added distance L is shown as 2 feet between the speaker 34 and the nearer ear of H". The other car is therefore 3 feet from the speaker 35. This causes the virtual source of Z to lie directly ahead of H" in the direction indicated by the arrow 36. The natural consequence of the isolation of Z is the appearance of the sources of X and Y at the left of I .as indicated by the arrows 37.

In Fig. 4, it may be considered that if H" moves toward speaker 34, he will first hear Z with the ear on that side. By such a motion he may cause the virtual'source of Z to swing (counter clockwise in Fig. 4) so that it will also be at the left side and be indistinguishable in direction from the virtual sources of X and Y. Starting from such a position he may move from his left to right (to position of Fig. 4) swinging Z from the left to the center. As he continues to move and approaches mid-position Z will have passed on to the. right and Y will have been swung out from the left following Z (Fig. 2). As motion continues past mid-position, Y will move around to the right to join Z and X will swing about in its turn, as illustrated in Fig. 3. As motion continues he will be so near the right hand speaker that X will join Y and Z at the right. He will thus have selectively paraded the sources in an are from his extreme left to his extreme right, isolating each from the others.

In Fig. 2 the sources X, Y, and Z have been so related to each other and to the transmitting system shown, that no two sources may at the same time be heard binaurally by the listener between the two receivers. In order to secure this isolation there must be a difference in the differential distance of each source to the microphones. The differential distances should, and they do, vary by at least the binaural limit of about six inches. For the differential is 2.5 feet. For Y it is zero. For 2 it is 1 foot. Hence, least 'aboutsix inches, or an amount which is not less than the binaural limit.

It is of course to be understood'that possibilities and increasing as creases. The actual the and the combinations are many the number of sources inlocation of the sources,

X sound interceptcrs,

to the intercepters,

the distance of the microphones from the sources and from each other, relative motion of the microphones and the sources, the locations of the loud speakers relative to each other, the character and intensity of wall reflections in a room, all bear more or less upon the results achieved. Nevertheless, the variants are within the control of the listener to a sufiicient extent because of the use of loud speakers.

The greatest differential which may exist at the pick-up end is of course the distance between the transmitters, such as four feet in Fig. 2. In order to perceive a virtual image at the receiving end so that it appears isolated into a direct-ahead position, the same differential distance must obtain at the receiving end. The only possible way to secure this in open air paths is to have the two receivers separated by a distance at least equal to that maximum.

With reference to Fig. 1, it may now be seen that when the microphones are fixedly separated and used in combination with fhead the phones, there is no flexibility in use 0 combination. a If the sources move, or if the microphones move, some effect will be observed, but it is not within the control of the listener. The arrangement involving loud speakers imparts to the separated microphones a much greater and more practical utility than any combination using head phones. However, I do not hereby mean to exclude from the invention the combination of Fig. 1, nor any other combination or feature which is defined by the appended claims.

I claim: .7

1. A sound transmission system comprising in combination, two transmitters located outside the binaural location and directed generally toward a plurality of separated sound sources of original and distinctive characters, two receivers directed generally toward each other and separated by a distance at least about six inches greater than the distance between the transmitters, and two independent linking means respectively connecting said two transmitters and said two receivers, whereby a listener between said receivers may position his ears to receive two sounds in-a binaural phasing determining direction.

2. A sound transmission system comprising in combination, a plurality of separated sound sources of original and distinctive characters, two ext-ra-binaurally locate and two receivers linked said receivers being at least about six inches further apart than the intercepters, the sources and the interc'epters being so located that the difierential distance of each source from the inter'cepters difiers from the similar differential distance of every other source by an amount not less than the binaural limit, whereby to permit a listener to isolate the virtual position of each source from the other sources,

3. A sound transmission system compr1s ing in combination, a plurality of separated 5 sound sources of original and distinctive characters, two extra-binaurally located sound intercepters, and two receivers linked to the intercepters, said receivers being at least about six inches further apart than the intercepters, the sources and the intercepters being so located that the differential distance of one of the sources from the intercepters differs from the similar difierent-ial distance of the other sources by' an amount not less than the binaural limit, whereby to permit a listener to isolate the virtual position of said one source from the virtual positions of the remaining sources.

4. A sound transmission system comprising in combination, a plurality of separated sound sources of original and distinctive characters, two extra-binaurally located sound intercepters, and two receivers linked to the intercepters, said receivers being. at least about six inches further apart than the intercepters, the sources and the intercepters being so located that the differential distance of one of thesources from the intercepters diflers from the similar differential distance of the other sources by an amount which is sufliciently close to the binaural limit topermit a substantial isolation of the virtual position of said one source from the virtual positions of the remaining sources. 5. The method of transmitting sound for binaural reception and, for separation of the binaural images which consists of intercepting the same sound waves from separated sources of original'and distinctive characters, 40 said interception taking place at two points located outside the binaural location, separately reproducing the intercepted sounds, and presenting the reproduced sounds to the ears of a listener in such a way that the two sounds reach the ears over time-delay paths, and such that one ear hears one intercepted version and the other ear hears the other intercepted version, each-ear hearing its respective version before it hears any other version, whereby binaurally phased components determine a binaural image, and changing the differential in the time of delay in said paths, whereby to vary the time of arrival of the reproduced sounds, and to bring other a components into binaural phasing relative to the time of arrival at the ears.

In testimony whereof I hereunto aifix my signature.

W. BARTLETT JONES.

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