US2273866A

US2273866A - Stereophonic sound recording and reproduction

Info

Publication number: US2273866A
Application number: US231997A
Authority: US
Inventors: Holst Gilles; Boer Kornelis De
Original assignee: Hartford National Bank and Trust Co
Current assignee: Hartford National Bank and Trust Co
Priority date: 1937-10-04
Filing date: 1938-09-27
Publication date: 1942-02-24
Anticipated expiration: 1959-02-24

Description

Feb. 24, 1942. G. HOLST ETAL I 2,273,866

STEREOPHONIC SOUND RECORDING AND REPRODUCTION Filed Sept. 27, 1958 AMPLIFIER POW!!! AHPLIFIEI A NPLIF/ER l POWER. l

AIPLIFIER 6'! 49.1. 5s 6: AM. Pawn W ll L.. J AMPLIFIER 55 AMPLIFIER 5 5: 4

4 W as Patented Feb. 24, 1942 UNITED STATES PATENT OFFICE STEREOPHONIC SOUND RECORDING AND REPRODUCTION Application September 27, 1938, Serial No. 231,997

In Germany October 4, 1937 9 Claims.

The present invention relates to a method and apparatus for the stereophonic recording and reproduction of sound and to a sound record for use in such reproduction.

The term stereophonic reproduction of sound as used herein and in the claims is to be understood to mean that type of reproduction in which the sound is reproduced by a plurality of reproducing devices in such a manner that a space efiect is obtained, i. e. so that it is possible to locate a sound source in space even in j: the artificial reproduction. Thus the term stereophonic reproduction includes not only the wellknown reverberation effect, but also the directional effect which allows one upon hearing a sound to localize its source and/or ascertain the movement thereof.

In sound recording it is well known to use for the above purpose, a plurality of specially-separated receiving devices whose vibrations are transmitted through separate channels which are subsequently reproduced separately by means of spacially-separated reproducing devices. It is also well known to divide the frequency range of the sound vibrations to be recorded and reproduced, into a plurality of frequency ranges to avoid distortion. However, when combining this measure with stereophonic recording and reproduction, the apparatus becomes very complicated. More particularly, if the frequency range is divided into n-parts and there is stereophonic transmission in m-channels, it will be necessary to use 12 times m transmitting and reproducing devices.

The object of our invention is to overcome the above difficulties and to simplify such methods of recording and reproduction as well as the apparatus used.

A further object of our invention is to provide a new type of sound record for use in such types of reproduction.

We have found that the sound vibrations in the lowest-frequency range are not essential for the stereophonic effect. More particularly these sound vibrations have a low frequency and large wave length, and thus have only a very slight directional effect and are not essential for 10- cating the sound source.

In accordance with the invention, we supply the sound vibrations in the higher frequency range of each recording device, to separate channels, and supply the vibrations in the lower frequency range of these devices to a single channel. The higher frequency ranges, are reproduced by reproducing devices which are separated both acoustically and spacially, whereas the vibrations of the lowest frequency range are reproduced by a common reproducing device.

The term "channel" as used herein and in the claims is to be understood to include both a recording of the sound vibrations such as a sound track on a carrier, and a path in which the electrical current variations corresponding to the sound vibrations can flow, for instance, a carrier wave or a transmission line.

In one form of the invention in which the vibrations are recorded, we record the high-frequency ranges in separate sound tracks on a carrier and separately reproduce these tracks with specially-separated reproducing devices, whereas we record the lowest frequency range in a common sound track and reproduce this latter track by a common reproducing device.

The upper limit of the lowest frequency range, which is consequently common to all recording and reproducing devices, generally lies between 200 and 300 vibrations per second. Below these frequencies the sound waves have substantially no directional effect.

In order that the invention can be more clearly understood and readily carried into effect, we shall describe the same in more detail with reference to the accompanying drawing in which:

Figure 1 is a schematic diagram of a stereophonic reproducing system embodying the invention,

Fig. 2 is a schematic diagram of a stereophonic recording system embodying the invention,

Fig. 3 is a schematic diagram of a stereophonic 1eproducing system for reproducing the record made-in system of Fig. 2, and

Fig. 4 is a perspective view on an enlarged scale of a stereophonic sound record according to the invention.

In the reproducing system shown in Figure 1 a sound carrier I 0 provided with two stereophonically-recorded sound tracks H and I2 is reproduced by two similar reproducing devices, one including an objective l3 and a photo-electric cell I5 and the other including an objective I 4 and a photo-electric cell IS. The tracks H and I2 are produced in the usual manner by the use of receivers which are spaced apart, and each track includes all the frequencies recorded.

The electric current variations produced by photo-electric cell I5 are amplified by a. preliminary amplifier IT and a power amplifier l9, and the high frequency variations pass through a high pass filter 2| to a reproducing device 25 and the lower frequencies pass through a low pass filter 22 to a reproducing device 21. Similarly the current variations produced by photo-electric cell l5 are amplified by a preliminary amplifier l8 and a power amplifier 20, and the high frequency variations pass through a high pass filter 24 to a reproducing device 26 which is spaced from reproducing device 25, whereas the low frequency variations pass through a low pass filter 23 to the reproducing device 21.

The high pass filters 2i and 24 allow the passage of only oscillations above about 200 to 300 cycles per sec. and preferably about 250 whereas the low pass filter 22 and 23 allow the passage of only oscillations whose frequencies lie below this value.

Thus, with a system such as shown in Fig. 1, the stereophonic sound record, as regards the high-frequency range, is separately supplied to the spacially-separated reproducing devices 25 and 26, whereas all the low frequency oscillations of both tracks II and 12 are supplied to the single reproducing device 21.

In the drawing each of the reproducing devices 25, 26, and 21 consist of only a single loudspeaker. However, it should be well understood that for each of these devices it is possible to substitute a plurality of loudspeakers which are connected in parallel acoustically. For instance reproducing device 21 may be replaced by a plurality of loudspeakers which are electrically interconnected to the feed conductor 15, or some of the speakers may be supplied directly from filter 22 and others supplied directly from filter 23. However, with the method according to the invention, one reproducing device, i. e. a loudspeaker or a plurality thereof connected acoustically, can be dispensed with. If in accordance with the prior art each frequency range were reproduced in a separate manner acoustically, it would be necessary to use two of the reproducing devices 21.

In the recording system illustrated in Fig. 2, the sound to be recorded is picked up by two specially-separated sound receiving devices 28 and 29 which together eifect the stereophonic recording. A shown each device consists of a single microphone, but each may comprise a plurality of electrically-connected microphones which are connected in parallel acoustically.

The electrical current variations produced by device 28 are amplified in a preliminary amplifier 30, whereupon the high frequency variations pass through a high pass filter 32, are amplified by a power amplifier 36, and applied to a recording device 39. The low frequency variations leaving amplifier 30 pass through a low pass filter 33, are amplified by a power amplifier 31, and transmitted to a recording device 40. In a similar manner, the current variations produced by device 29 are amplified by a preliminary amplifier 3|, filtered by low pass filter 34 and high pass filter 35, the high frequencies being amplified by a power amplifier 38 and transmitted to a third recording device 4|, and the low frequencies being amplified by amplifier 31 and passing to recording device 40.

The recording may be effected in any of the well known manner, but as indicated it is effected mechanically by the method described in the U. S. Patent #l,9l9,116 toJames A. Miller. In this case each of the

recording devices

39, 40 and 4! is provided with a cutting tool having a V shaped cutting edge which cuts a track in a carrier 45. As shown more clearly in Figure 4 the carrier 45 comprises a cutting layer 16 of transparent material and a thin covering layer 11 of opaque material, the

tracks

42, 43 and 44 being produced by removing portions of layer 11.

The filters 32 and 35 pass only frequencies above above 250 cycles per sec. so that the two

sound tracks

42 and 44 are stereophonic records of the high frequency range. However, the variations of the low frequency range are passed by the low pass filters 33 and 34, which have a cutoff at about 250 cycles per sec., and after bein amplified by the common amplifier 31, are recorded by the single recording device. Thus, it is seen that the apparatus is considerably simplified because only a single power amplifier 31 and recording device are used for the low frequency range.

As shown in Fig. 4 the resulting sound carrier has only a single track 43 for the low frequencies, and two

stereophonic tracks

42 and 44 for the high frequencies. In some cases, for instance for stereophonic transmission of sound in large rooms, it may be desirable to use a purality of recording groups. For instance, it may be desirable to use six tracks in the high range and two tracks in the low range. In any case, however, the invention makes it possible to reduce the number of tracks and thus to simplify the recording apparatus.

In the reproducing system of Fig. 3, the

sound tracks

42, 43 and 44 of the carrier 45 are optically scanned by three

objectives

52, 5| and respectively to produce current variations by means of photo-

electric cells

55, 54 and 53 respectively.

The reproducing is effected by two spaciallyseparated reproducing

devices

62 and 63. Device 62 comprises a high-frequency loudspeaker 64 and a low-frequency loudspeaker 66, and device 63 comprise a high-frequency loudspeaker 65 and a low-frequency loudspeaker 61. The current variations produced by cell 55 are amplified by a preliminary amplifier 58 and a power amplifier GI, and supplied to speaker 64, and

similarly the current variations produced by cell; 53 are amplified by a preliminary amplifier 55- and a power amplifier 59 and supplied to speaker 65. The low-frequency current variations produced by cell 54 are amplified by a preliminary amplifier 51 and a power amplifier 60, and the amplified current variations are supplied to both the

speakers

66 and 61.

Instead of reproducing the low frequency range by means of the speakers and 61, which are acoustically combined with the high-frequency speakers, it is of course possible to use a separate reproducing device for this purpose, as shown in Figure 1. In this case it is possible to use for the low frequencies a single speaker or a plurality of speakers which are separated acoustically from the high-frequency speakers.

Although Figures 2 and 3 illustrate recording and reproduction in which the sound is recorded in a carrier and then reproduced, it should be understood that our invention is not limited thereto. The invention also extends to a completely electrical system in which the vibrations are transmitted completely by electric transmission, i. e. by wire or carrier wave, from the recording point to the reproducing point. Furthermore, it is possible to divide the high frequencies into a plurality of bands and reproduce these by additional speakers.

While we have described the invention in connection with specific examples and applications, we do not wish to be limited thereto but desire the appended claims to be construed as broadly as is permissible in view of the prior art.

That we claim is:

1. A method of sterophonically recording sound vibrations by means of a plurality of recording devices, comprising the steps of dividing the vibrations into a plurality of frequency ranges, transmitting in separate channels the vibrations in the higher frequency ranges of each recording device, and transmitting in a single channel the vibrations in the lowest frequency range of said devices.

2. A method of stereophonically recording sound vibrations by means of a plurality of recording devices comprising the steps of dividing the vibrations into a plurality of frequency ranges including a low frequency range whose upper limit lies between about 200 to 300 cycles per sec., transmitting in separate channels the vibrations in the higher frequency ranges of each recording device, and transmitting in a single channel the vibrations in the low frequency range.

3. A method of stereophonically reproducing sound vibrations by means of separate reproducing devices, comprising the steps of separating the vibrations into a plurality of frequency ranges, transmitting the vibrations of the higher frequency ranges to a plurality of said devices which are separated acoustically and spaclally, and transmitting the vibrations of the lowest frequency to only one of said reproducing devices.

4. A method of stereophonically reproducing sound vibrations by means of a. plurality of separate reproducing devices, comprising the steps of transmitting the vibrations by separate channels, separating the vibrations of each channel into a plurality of frequency ranges including a low frequency range having ,an upper limit between 200 to 300 cycles per sec., transmitting the vibrations of the high frequency range to a plurality of said devices which are separated spacially and acoustically, and transmitting the vibrations of the low-frequency range to only one of said reproducing devices.

5. A method of stereophonically recording sound vibrations on a carrier comprising the steps of separating the vibrations into a plurality of frequency ranges including a low frequency range, recording the vibrations of the low frequency range in a single sound track, and recording the remaining vibrations in a plurality of sound tracks.

6. A method of reproducing sound vibrations from a stereophonic sound record having a plurality of sound tracks, comprising the steps of scanning the sound tracks, separating the current variations produced by the scanning into a plurality of frequency ranges including a low frequency range, transmitting the low-frequency variations to a single reproducing device, and transmitting the remaining frequencies to a plurality of acoustically-separated reproducing devices.

'7. A stereophonic sound record comprising a carrier provided with a plurality of highfrequency sound tracks and low-frequency sound tracks, the number of the low-frequency sound tracks being substantially less than the number of high-frequency sound tracks.

8. A stereophonic sound record comprising a carrier provided with a plurality of high-frequency sound tracks and a single low-frequency sound track.

9. A sterephonic sound recording system comprising a plurality of sound receiving devices, filtering means for separating the current variations of each device into a low-frequency range and a high-frequency range, means to apply the high-frequency variations produced by each device to individual recording devices, and means to apply the low-frequency variations produced by all the devices to a single recording device.

GILLES HOLST. KORNELIS DE BOER.