CA1202571A - Triphonic sound system - Google Patents
Triphonic sound systemInfo
- Publication number
- CA1202571A CA1202571A CA000441129A CA441129A CA1202571A CA 1202571 A CA1202571 A CA 1202571A CA 000441129 A CA000441129 A CA 000441129A CA 441129 A CA441129 A CA 441129A CA 1202571 A CA1202571 A CA 1202571A
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- CA
- Canada
- Prior art keywords
- frequency
- signals
- audio
- signal
- carrier
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04H—BROADCAST COMMUNICATION
- H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
- H04H20/86—Arrangements characterised by the broadcast information itself
- H04H20/88—Stereophonic broadcast systems
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04S—STEREOPHONIC SYSTEMS
- H04S3/00—Systems employing more than two channels, e.g. quadraphonic
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
- H04R2499/10—General applications
- H04R2499/15—Transducers incorporated in visual displaying devices, e.g. televisions, computer displays, laptops
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- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Stereophonic System (AREA)
- Stereo-Broadcasting Methods (AREA)
Abstract
ABSTRACT
A triphonic sound system in which three in-dependent stereophonically related audio frequency source signals L, R and C are combined to derive three other audio frequency signals M, S, and T which re-spectively comprise (L + 1.4C + R), (L-R) and (-1.4C). In a preferred transmitter embodiment, useful in television broadcasting, the audio signals S and T modulate two quadrature-related sub-carriers of the same frequency to develop two double-sideband, suppressed-carrier sig-nals, the frequency of the subcarriers being suffi-ciently high as to assure a frequency gap between the lower sidebands of the modulated subcarrier signals and the audio frequency signal (L + 1.4C + R). The afore-mentioned signals, and a pilot signal having a frequency which lies within the frequency gap, are combined and frequency-modulated onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers. The receiver is operative in response to reception of the high frequency carrier to reproduce each of the audio frequency source signals L, R and C, and includes means for reproducing conventional monophonic and two-channel stereophonic broadcasts. The described matrix equations are amenable to and useful with multi-channel television sound systems currently under con-siderarion for future broadcast service in the United States.
A triphonic sound system in which three in-dependent stereophonically related audio frequency source signals L, R and C are combined to derive three other audio frequency signals M, S, and T which re-spectively comprise (L + 1.4C + R), (L-R) and (-1.4C). In a preferred transmitter embodiment, useful in television broadcasting, the audio signals S and T modulate two quadrature-related sub-carriers of the same frequency to develop two double-sideband, suppressed-carrier sig-nals, the frequency of the subcarriers being suffi-ciently high as to assure a frequency gap between the lower sidebands of the modulated subcarrier signals and the audio frequency signal (L + 1.4C + R). The afore-mentioned signals, and a pilot signal having a frequency which lies within the frequency gap, are combined and frequency-modulated onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers. The receiver is operative in response to reception of the high frequency carrier to reproduce each of the audio frequency source signals L, R and C, and includes means for reproducing conventional monophonic and two-channel stereophonic broadcasts. The described matrix equations are amenable to and useful with multi-channel television sound systems currently under con-siderarion for future broadcast service in the United States.
Description
- ~ -TRIPHONIC SOUND SYSTEM
BACKGROUND OF THE INVENTION
~ This invention relates to a triphonic sound 5 transmission system that ;s particularly compatible with existing monophonic and biphon;c reeeivers.
To accommodate the increasing public awareness and interest in home reproduction o multi-channel sound, the process of selecting a standard transmission system for stereophonic sound for television is currently under-way. This activity, intially undertaken by the broadcast and consumer electronics industries~ will eventually in-clude the Federal Communicaticns Commission (FCC) and the consumer marketplace, and, in turn, creates 8 need for improving mul~i-channel service, in particular, the pro-vision of a triphonic sound system for television broad-casting.
Multi-channel sound transmisslon had its prac-tical beginning with the experiments at Bell Laboratories in the early 1~3Q's described by JO C. Steinberg and W. B.
Snow in an article entitled "Symposium on Wire Tr~ns-mission of Symphonic Music and its Reproduction in Audi-~5 tory Perspective: Physical Factors" publi~hed in the Bell System Technical Journal, Vol. XIIIa No. 2, April 1934~
Following the work of the National StereophGnie Radio Com-mittee established by ~he Electronics Indus~ries Asso-ciation in 1959, the present-day system for FM stereo-phonic radio bro~dcasting was authorized by the FCC in 1961. Further research in the past decade has led to the development of a number of proposed systems both for AM
stereophonic broadcasting and FM surround-sound broad-casting.
. . .
57~
Interest in multi channel sound with visual smageS was given strong impetus by Walt Disney's pioneer-ing movie 'IFantasia", first released in 1940. Today the specification for 35 millimeter cinematic film provides for four tra~ks of audio recording, and the 70 millimeter standard provides for six. With such well-established precedents in the film industry, and the routine trans-mission of filmed programs by television broadcasters, consideration is now being given to methods for ~rans-mitting more than a single audio channel with a televisionpicture. While it may be argued that the audio needs of the cinema and the televis~on media are different, and, in partic~l~r, that the viewing s~reen size9 aspect ratio, . ~udience seating, transmission band width limitations, timeliness, and production cos~s seem to suggest the use of the simplest possiblè audio system for today's tele-vision, larger-screen home receivers are already gaining in popularity, and serious studies are underway toward the ~stablishment of wide-screen high definition service, thereby creating the requirement to consider the audio needs in the near- and longer-term future and to provide the technical means to meet such fu~ure needs.
Since any transmission system for s~ereophonic ~S television sound must be compatible with existing ser-vice, all systems being considered begin with a mono~hon;c æum signal (M) on the existing baseband channel, and a s~ereophonic difference signal (S) to enable ~eparation of the monophonic signal into its lef~ and right com-ponents at ~he home receivPr. In the existing two-channel stereophonic system approved by the FCC, and also in those systems being considered for transmission of television stereophonic so~nd, a symmetrical matrix7 expressed by 7~
tbe following equations, is employed:
M=(L~0.7C)~(0.7C~) S=(L-R) In the home receiver, the signals applied to the left and right loudspeakers are derived by the addition and sub-straction (and normalization of gain3 of these combined signals:
Left Channel = M -~ S = L + 0.7C
Right Channel = M - S = R ~ 0.7C
1~ .
While it is generally not customary to show the center front term C in the matrix equation, i~ is included here to demonstrate some interesting properties important to multi-channel sound broadcasting wi~h televisicn. Re-gardless of how many special audio effects may be employedor how wide a viewing screen may be used, the important dialogue and other prominent audio signals conventionally have been, and undoubt~dly will continue to be, placed at the center of ~be picture. For traditional two-channel loudspeaker playback, the center signal is presented as a virtual, or phantom, image created by the acous~ic power summation of sound of equal amplitude and phase from each of the two loudspeakers. If the left, center~ and right signals appeared at equal intensity in the original pro-2S gram, such balance will be maintained in the stereophon$chome listening home environment. In the monophonic lis tening mode, however, the equal voltage components of the center signal in the left and right channels will add ~rithmetically~ causing the sum signal to be presented as L ~ 1.4C + R. This equation illustrates the well-known 3dB
center imbalance common to monophonic playback of all stereophonic systems which use traditional amplitude pan-ning controls. Although an inevitable consequence of the matrix process, the result is a desirable increase in the prominance of the center channel, especially in pres-ence of side stage effects. With two channel repro-~ C 1~76 ~D257 duction, where the center image is at normal level, a listener can perform such discrimination easily7 even in - the pre~ence of competing soundsO
That the important center signal is d;splayed as a phantom image is unfortunate in that while the image ls reasonably well defined for a lis~ener rigidly positioned on the line of symmetry between the two loudspeakers, its location for other listener pos~t~ons is vague and un-stable. Any motion of the listener~s head causes apparen~
~hangesr At best, image location will be vague; at worst, i~ will appear to move with the slightest motlon of the head. While-this appears not to significan~ly detract from the enjoyment of music alone, it presents a more 15 serious problem when the sound is accompani~d by visual images. Even for a lis~cener positioned along the line of loudspeaker symmetry, the image w;ll appear to rise as it is panned from left through center to righ~. Although this elevatlon of the center image has been recognized since first reported in 1959, the effect has not yet been ade-quately explained. However, the degree of elevation appears to be related to the angles subtended from the listener ~o the speakers, being least prominent when the angle is small, but settlin& overhead when the listener is ~5 directly between the loudspeakers.
Even with the significant body o locali-zation theory ~hat has been advanced in the las~ 20 years or so; and despite the fact that the traditional model requires careful seating of the listener, the traditional model still remains the only one in practical use. One reason may be that it permits the use of simple production techniques and relativ21y inexpensive equipment, but more importantly, is that different and far more complex pan-ning functions would be required for each listener posi-tion and orientation in the lis~ening room. Briefly summarizing psychoacoustics localiæation principles~ the
BACKGROUND OF THE INVENTION
~ This invention relates to a triphonic sound 5 transmission system that ;s particularly compatible with existing monophonic and biphon;c reeeivers.
To accommodate the increasing public awareness and interest in home reproduction o multi-channel sound, the process of selecting a standard transmission system for stereophonic sound for television is currently under-way. This activity, intially undertaken by the broadcast and consumer electronics industries~ will eventually in-clude the Federal Communicaticns Commission (FCC) and the consumer marketplace, and, in turn, creates 8 need for improving mul~i-channel service, in particular, the pro-vision of a triphonic sound system for television broad-casting.
Multi-channel sound transmisslon had its prac-tical beginning with the experiments at Bell Laboratories in the early 1~3Q's described by JO C. Steinberg and W. B.
Snow in an article entitled "Symposium on Wire Tr~ns-mission of Symphonic Music and its Reproduction in Audi-~5 tory Perspective: Physical Factors" publi~hed in the Bell System Technical Journal, Vol. XIIIa No. 2, April 1934~
Following the work of the National StereophGnie Radio Com-mittee established by ~he Electronics Indus~ries Asso-ciation in 1959, the present-day system for FM stereo-phonic radio bro~dcasting was authorized by the FCC in 1961. Further research in the past decade has led to the development of a number of proposed systems both for AM
stereophonic broadcasting and FM surround-sound broad-casting.
. . .
57~
Interest in multi channel sound with visual smageS was given strong impetus by Walt Disney's pioneer-ing movie 'IFantasia", first released in 1940. Today the specification for 35 millimeter cinematic film provides for four tra~ks of audio recording, and the 70 millimeter standard provides for six. With such well-established precedents in the film industry, and the routine trans-mission of filmed programs by television broadcasters, consideration is now being given to methods for ~rans-mitting more than a single audio channel with a televisionpicture. While it may be argued that the audio needs of the cinema and the televis~on media are different, and, in partic~l~r, that the viewing s~reen size9 aspect ratio, . ~udience seating, transmission band width limitations, timeliness, and production cos~s seem to suggest the use of the simplest possiblè audio system for today's tele-vision, larger-screen home receivers are already gaining in popularity, and serious studies are underway toward the ~stablishment of wide-screen high definition service, thereby creating the requirement to consider the audio needs in the near- and longer-term future and to provide the technical means to meet such fu~ure needs.
Since any transmission system for s~ereophonic ~S television sound must be compatible with existing ser-vice, all systems being considered begin with a mono~hon;c æum signal (M) on the existing baseband channel, and a s~ereophonic difference signal (S) to enable ~eparation of the monophonic signal into its lef~ and right com-ponents at ~he home receivPr. In the existing two-channel stereophonic system approved by the FCC, and also in those systems being considered for transmission of television stereophonic so~nd, a symmetrical matrix7 expressed by 7~
tbe following equations, is employed:
M=(L~0.7C)~(0.7C~) S=(L-R) In the home receiver, the signals applied to the left and right loudspeakers are derived by the addition and sub-straction (and normalization of gain3 of these combined signals:
Left Channel = M -~ S = L + 0.7C
Right Channel = M - S = R ~ 0.7C
1~ .
While it is generally not customary to show the center front term C in the matrix equation, i~ is included here to demonstrate some interesting properties important to multi-channel sound broadcasting wi~h televisicn. Re-gardless of how many special audio effects may be employedor how wide a viewing screen may be used, the important dialogue and other prominent audio signals conventionally have been, and undoubt~dly will continue to be, placed at the center of ~be picture. For traditional two-channel loudspeaker playback, the center signal is presented as a virtual, or phantom, image created by the acous~ic power summation of sound of equal amplitude and phase from each of the two loudspeakers. If the left, center~ and right signals appeared at equal intensity in the original pro-2S gram, such balance will be maintained in the stereophon$chome listening home environment. In the monophonic lis tening mode, however, the equal voltage components of the center signal in the left and right channels will add ~rithmetically~ causing the sum signal to be presented as L ~ 1.4C + R. This equation illustrates the well-known 3dB
center imbalance common to monophonic playback of all stereophonic systems which use traditional amplitude pan-ning controls. Although an inevitable consequence of the matrix process, the result is a desirable increase in the prominance of the center channel, especially in pres-ence of side stage effects. With two channel repro-~ C 1~76 ~D257 duction, where the center image is at normal level, a listener can perform such discrimination easily7 even in - the pre~ence of competing soundsO
That the important center signal is d;splayed as a phantom image is unfortunate in that while the image ls reasonably well defined for a lis~ener rigidly positioned on the line of symmetry between the two loudspeakers, its location for other listener pos~t~ons is vague and un-stable. Any motion of the listener~s head causes apparen~
~hangesr At best, image location will be vague; at worst, i~ will appear to move with the slightest motlon of the head. While-this appears not to significan~ly detract from the enjoyment of music alone, it presents a more 15 serious problem when the sound is accompani~d by visual images. Even for a lis~cener positioned along the line of loudspeaker symmetry, the image w;ll appear to rise as it is panned from left through center to righ~. Although this elevatlon of the center image has been recognized since first reported in 1959, the effect has not yet been ade-quately explained. However, the degree of elevation appears to be related to the angles subtended from the listener ~o the speakers, being least prominent when the angle is small, but settlin& overhead when the listener is ~5 directly between the loudspeakers.
Even with the significant body o locali-zation theory ~hat has been advanced in the las~ 20 years or so; and despite the fact that the traditional model requires careful seating of the listener, the traditional model still remains the only one in practical use. One reason may be that it permits the use of simple production techniques and relativ21y inexpensive equipment, but more importantly, is that different and far more complex pan-ning functions would be required for each listener posi-tion and orientation in the lis~ening room. Briefly summarizing psychoacoustics localiæation principles~ the
2 5 basic model of localization assumes tbat ~he geometry of the humsn head is sy~metrical from left to right, and that - the he~ring acui~y in the two ears is equa]. Thus, a center image will be perceived when the outputs of the two loudspeakeIs as ~eceived at the ~ars are equal in ampli-tude and phase. When the head is turned, various other factors come into account. FIG. 1 of the accompanying drawings, taken from an articlP entitled "Measurement of Diffraction and Interaural Delay of a Progressive Sound Wave Caused by the Human Head" published by applicant and Messrs. Abbagnaro and Bauer in J. Acoustical Society of America, Vol. 58, No. 3, September 1975, illustrates the effect of the head on a single-sound wave front arriving at an angl~ of 90 from the front of the listener. At low frequencies, the sound to the far ear is delayed by approximately 0.8 milliseconds, and, furthermore, the head acting as a baffle, causes a rise in sound pressure at the near ear and a decrease in sound pressure at the far ear. As the left-right difference curve in FIG. 1 illus-trates, the overall amplitude difference between thesound at the two ears in this case differs from OdB at low frequencies to approximately -15dB at lOkHz. Delays and pressure responses for other head orientations are of lesser magnitude, b~t st;ll significan~.
That listeners rely on interaural time differ-ence cues in localization has long been recognized. In 1959, in an article en~itled "A Compatible Stereophonic Sound System", Bell La~oratories Record, November 1959, F~ K. Becker proposed a stereophonic matrix which u~ed tim~-of-arrival information to vary the apparent location of images between two loudspeakers. Time differences at the ears were studied in detail by D. Mo Leakey, resulting în a general localization theory based on phase differ~
ences at low frequencies and time differences between sound envelopes a~ higher frequencies; the results of this study are described in an article entitled "Some Measure ' C-1476 ::~2~Z~
ments on the ~ffects of Interchannel Intensity and Time Differences in Two~Shannel Sound Systems", Journal of the Acoustical Society of AmeTica, Vol. 31, No. 7, July 1959.While a panning function based on the ~ ~ve-mentioned criteria could be employed in a stereophonicmixing system, it is elear that such a function could be idealized only for listeners on the line of symmetry between the loudspeakers.
lOOther researcbers ~ave studied the effect of varying the amplitude between stereophonic loudspeakers to position phantom images. An article entitled "Phasor Analysis of Some Stereophonic Phenomena" published by B. B. Bauer in the Journal of the Acoustical Society of i5~merica, Vol. 333 No. 11, November 1961, describes the now famous "Stereophonic Law of Sin~s" which provided one of the first means to quantify such panning. Bauer derived the following relationship:
Si~ sin ~A = (SL ~ SR~/(SL + SR), approximately~ where ~I is the azmith angle of the virtual image, and A is the azmith angle of the real sources, and SL and SR are the strengths of the signals applied ~o the left and right loudspeakers, respec~ively. FIG. 2 illustrates the use o~
the "Law of Sines" for the case o~ two loudspeakers at an angle of 90 ~o the listener. Bauer's law is not com-pletely accurate, since it applies only to low frequencies below 500 Hz and is constrained to the use of in-phase signals. While the slope of the curve shown in FIG. 2 has been questioned by some researchers, most confirm the end-point of 20 dB separation required for a fully discreteimage.
Given the apparent impossibility of satisfying the perceptual requirement for listeners at arbitrary locations in a room, it is not surprising that early practioners of stereophony characterized the center image problem as the "hole in ~he middle." Most early attempts at solving the problem involved t~e derivation of a sum C~ 76 ~7--signal ~L~R) and spplying it ~o a third loudspeaker loca~ed at ~he center. S~ch a "tri~rontal" approach does lndeed stabilize the center image, especially if ~he gain of the center channel is increased by 3dB with respect to the left or right channels as recommended by Klipsch in his article "Three-Channel Stereo Playback of Two Tracks Derived From Three Microphones", I.R E. TransO Audio, Vol. 7, March-April 1959. However, this approach causes a drama~ic shrinkage of ~he apparent width of the stereo-phonic stage; following Bauer's "Law of Sines" as illus-trated in FIG. 3, the original 90 width would be reduced to 45 when the signal level in all loudspeakers is equal.
If the center channel gain is reduced by 3dB, the maximum stage width will be increased to 73, but of course at the expensP of reduced stabili~y of the center image. Later experimen~ation with quadraphonic matrices some~imes en-coded the center-front ;mage by separating the left and rîght components of this signal by 9V; less shifting of the center-front image occurs in such a display, probably because the image itself appears so wide as to be un-acceptable for important music or dialogue.
One solution which appears to be quite sat;s-factory from ~he listener's poin~ of view (hearing) is employed routinely in the cinema, in which important dia~ogue is usually assigned to a discrete center channel feeding a center~screen loudspeaker. While the method requires slightly more complex mixing and recording a-cilities, it is direct in its approach and provides satisfactory reproduction of impor~ant signals. Although ~he addition of a new loudspeaker in~erposed between the left and right loudspeakers provides the opportunity to pan additional virtual images at the near left and near right locations, for non-dialogue ef fects it appears ~uite satisfactory ~o simply pan from lef~ to right~
especially for rapidly moving or non-discrete effects.
The three-channel technique provides a sensible solution which allows every member in a theatre audience to ex-perience sound images at the proper location, and suggests the desirability of incorporating a discrete cen~er-sound channel in telev;sion reproduction.
Among YarioUS pruposals ~hat have heretofore been advanced for three-c~annel FM stereo transmission systems, the one described in Halpern U.S. Pat. No.
That listeners rely on interaural time differ-ence cues in localization has long been recognized. In 1959, in an article en~itled "A Compatible Stereophonic Sound System", Bell La~oratories Record, November 1959, F~ K. Becker proposed a stereophonic matrix which u~ed tim~-of-arrival information to vary the apparent location of images between two loudspeakers. Time differences at the ears were studied in detail by D. Mo Leakey, resulting în a general localization theory based on phase differ~
ences at low frequencies and time differences between sound envelopes a~ higher frequencies; the results of this study are described in an article entitled "Some Measure ' C-1476 ::~2~Z~
ments on the ~ffects of Interchannel Intensity and Time Differences in Two~Shannel Sound Systems", Journal of the Acoustical Society of AmeTica, Vol. 31, No. 7, July 1959.While a panning function based on the ~ ~ve-mentioned criteria could be employed in a stereophonicmixing system, it is elear that such a function could be idealized only for listeners on the line of symmetry between the loudspeakers.
lOOther researcbers ~ave studied the effect of varying the amplitude between stereophonic loudspeakers to position phantom images. An article entitled "Phasor Analysis of Some Stereophonic Phenomena" published by B. B. Bauer in the Journal of the Acoustical Society of i5~merica, Vol. 333 No. 11, November 1961, describes the now famous "Stereophonic Law of Sin~s" which provided one of the first means to quantify such panning. Bauer derived the following relationship:
Si~ sin ~A = (SL ~ SR~/(SL + SR), approximately~ where ~I is the azmith angle of the virtual image, and A is the azmith angle of the real sources, and SL and SR are the strengths of the signals applied ~o the left and right loudspeakers, respec~ively. FIG. 2 illustrates the use o~
the "Law of Sines" for the case o~ two loudspeakers at an angle of 90 ~o the listener. Bauer's law is not com-pletely accurate, since it applies only to low frequencies below 500 Hz and is constrained to the use of in-phase signals. While the slope of the curve shown in FIG. 2 has been questioned by some researchers, most confirm the end-point of 20 dB separation required for a fully discreteimage.
Given the apparent impossibility of satisfying the perceptual requirement for listeners at arbitrary locations in a room, it is not surprising that early practioners of stereophony characterized the center image problem as the "hole in ~he middle." Most early attempts at solving the problem involved t~e derivation of a sum C~ 76 ~7--signal ~L~R) and spplying it ~o a third loudspeaker loca~ed at ~he center. S~ch a "tri~rontal" approach does lndeed stabilize the center image, especially if ~he gain of the center channel is increased by 3dB with respect to the left or right channels as recommended by Klipsch in his article "Three-Channel Stereo Playback of Two Tracks Derived From Three Microphones", I.R E. TransO Audio, Vol. 7, March-April 1959. However, this approach causes a drama~ic shrinkage of ~he apparent width of the stereo-phonic stage; following Bauer's "Law of Sines" as illus-trated in FIG. 3, the original 90 width would be reduced to 45 when the signal level in all loudspeakers is equal.
If the center channel gain is reduced by 3dB, the maximum stage width will be increased to 73, but of course at the expensP of reduced stabili~y of the center image. Later experimen~ation with quadraphonic matrices some~imes en-coded the center-front ;mage by separating the left and rîght components of this signal by 9V; less shifting of the center-front image occurs in such a display, probably because the image itself appears so wide as to be un-acceptable for important music or dialogue.
One solution which appears to be quite sat;s-factory from ~he listener's poin~ of view (hearing) is employed routinely in the cinema, in which important dia~ogue is usually assigned to a discrete center channel feeding a center~screen loudspeaker. While the method requires slightly more complex mixing and recording a-cilities, it is direct in its approach and provides satisfactory reproduction of impor~ant signals. Although ~he addition of a new loudspeaker in~erposed between the left and right loudspeakers provides the opportunity to pan additional virtual images at the near left and near right locations, for non-dialogue ef fects it appears ~uite satisfactory ~o simply pan from lef~ to right~
especially for rapidly moving or non-discrete effects.
The three-channel technique provides a sensible solution which allows every member in a theatre audience to ex-perience sound images at the proper location, and suggests the desirability of incorporating a discrete cen~er-sound channel in telev;sion reproduction.
Among YarioUS pruposals ~hat have heretofore been advanced for three-c~annel FM stereo transmission systems, the one described in Halpern U.S. Pat. No.
3,679,832 is illustrative. In this system, three in-dependent sources o stereophonically related audio fre-quency waves are added together to obtain a sum signalO
Each audio ~requency wave is also used to amplitude-modulate a respective subcarrier signal, the subcarrier signals being of the same frequency and spaced 120 apart in phase. A suppresse~-carrier, double~sideband modu-lation of each subcarrier is employed, with the frequency of the subcarrier signals being sufficiently high as to assure a frequency gap between the lower sidebands of the modulated subcarrier signals and the sum signal. To achieve the desired compatibility with monophonic and two-channel stereophonic FM receivers, the amplitude of each double-sideband suppressed-carrier signal is mul-tiplied by a factor of 2/ ~ . A conventional low-level phase reference pilot signal, lying within the frequency gap, ;s employed for receiver detection purposes. A
second pilot signal, of one-third the ampl;tude oE the third ~armonic of the phase reference pilo~, is utilized to achieve three-channel receiver compatibility with a monophonic or two-channel stereophonic broadcast. The sum signal, the three double-sideband suppressed-carrier signals, and the two pilot signals are frequency modu-lated onto a high frequency FM carrier for transmiss;on purposes.
~ C-1476 5~7~
The composite, f~equency modulated, carrier signal i~ t~ansmit~ed to one or more receivers, which may be either of ~he conventional monophonic or two-channel stereophoni~ type or preferably a ~hree-channel stereo receiver, each adapted to receive and reproduce the three-channel broadcast in accordance with its respec-tive mode of operation. Compatibility of the three-channel stereophonic receiver with one-channel or two-channel broadcast is achieved by the use of the second pilot signal. In the absence of this pilot, the three-channel receiver operates in a conventional manner to reproduce a monophonic or ~wo-channel stereophonic broadcast. The second pilot signal is used as an indi-cator for a three-channel broadeast and when the same îs received by a three-channel receiver it serves to switch the latter into a three channel stereophonic reception mode. Thus, a three-channel broadcast is compatible with a one, two, or three-channel receiver, while the three-channel receiver is compatib~e with a one, two, or three-channel broadcast.
This system ;s relatively complex in that ;trequires two pilot signals and a phase-shift network for establishing the 120 phase relationship between the subcarrier signals, and has the disadvantage that all three of the independent source signals are modulated to enable recovery of third-channel information, some of which information gets into the output of a two-channel receiver.
:~'25~S7~
- 1 o -SUMMARY OF TffE INVENTION
_ - It is a primary object of the present inven~ion ~o provide a triphonic transmission sys~em that is fully compatible with existing monophonic receivers and with new television receivers that may employ only two loud-speakers.
A related object of the invention is to provide a triphonic transmission system that will provide center-channel quality equivalent in all respects to that of the left 2nd right channels without significant degradation or compromise.of existing monophonic or future biphonic ~ervice and coverage~
In accordance with the present invention, three independent sources of stereophonically related audio frequency ~aves characterized as L(left) 3 R(right) and C(center), are matrixed to obtain three signals exhibit-~O ing the matrix equations:(l)M = L ~ 1.4C ~ R; (2)S=L-R; and (3)T - -1.4C. Each of audio frequency waves S and T is used to amplitude~modulate a respective subcarrier signal~
the subcarrier signals being of the same frequency and spaced 90 apart in phase. Suppressed-carrier, double-sideband modulation of each subcarrier is employed, withthe frequency of the subcarrier signals being suffi-ciently high as to assure a frequency gap below the lower sidebands of the modulated subcarrier signals and the M
signal. A conventional low-level phase reerence pilot signal, lying within the aforementioned frequency gap, is employed for receiver detection purposesO The afore-mentioned M signal, the two double-sideband suppressed-carrier signals, and the pilot signal are frequency modu-lated onto a high frequency FM carrier for transmission purposes.
~ 5~
The composite, requency modulated, carrier s;gnal is transmitted to one or more remote receivers, which may be of the conven~ional monophonic or two-channel stereophonic type, or preferably a triphonic receiver constructed in accordance with 4he :invention. Typically, a plurality of receivers of each type will receive and reproduce the three signals, each in accordance with its respective mode of operation. A conven~ional monophonic receiver decodes only ~he sum signal (M~, and a two-channel receiver reproduces the transmitted M signal inboth loudspeakers for mon ophonic reception, and the tra-ditional stereophonic signals for the biphonic and tri-phonic modes. For a third category of receiver having a large screen and three widely-spaced lo~dspeakers, a choice of reproduction is available. For reproduction of monophonic transmissions, the sum signal ~M) can be util ized in all three lolidspeakers, although at reduced level in the flanking loudspeakers so as to avoid "pulling" the sound image away from its desirable cen~er location. For biphonic broadcasts, the M signal may be used for the center loudspeaker, and the conveDtional left and right signals for the ~lanking loudspeakers. Finallg, the reproduction of triphonic broadcasts resul~s in the dis~
play of left, center, and right signals by respective loudspeakers; in this case, the signal T is fed directly to the center loudspeaker, and is also used to electri-cally subtract the center signal components from the leEt and right channels, resulting in fully discrete per-formance.
.
C-1~76 ~lZ~ZS~7~L
BRIE- o~S _I~TION OF THE DRAWINGS
The invention will be more fully appreciated . from the following de~ailed description when consid~red in connection with the accompanying drawings in which: , FIG. 1, to which reference has already been made, is a plot illustrating the effect of the head on a single-sound wave front arriving at an angle of 90 from the front of the listener;
FIG. 2, to which previous reference has been made, is a plot showing the use of the "Law of Sines" for the case of two lo~dspeakers at an angle of 90 to the listener;
FIG. 3, previously referrred to, illustrates an application of the "Law of Sines";
FIG. 4 is a requency diagram of the composite baseband signal developed in accordance with the prin-ciples of the present invention;
FIG. 5 is a simplified block diagram of a trans-mitting terminal for generating the composite signal of FI~. 4;
FIG. 6 is a simplified block diagram of a re-ceivîng terminal in accordance with the inventionS and FIG. 7 is a pictorial diagram illustrating the reception mode hierarchy in accordance wi~h ~he prin-ciples of the invention.
DETAILED DESCRIPTION
_ .
Before describing the present invan~ion, it maybe useful ~a briefly r~view the basic principles of the existing two-channel s~ereo system approved by the FCC, as well as multi-channel television sound systems presently under consideratîon for future broadcast service in the United States. In the current radio system, the stereo-phonically rela~ed signals ~hat are added together con-stitute a "monophonic channel" which consists of a (~+R)signal of 50 to 15,000 Hz, where L and R represent the left and right independent audio signals or channels9 as noted earlier, each of the L and R signals may also include a 0.7C component. It is this combined signal that is reproduced by a standard monaural FM receiver, hence the descriptive term "monophonic channel" and the use herein of the letter M to identify this channel. To this is added a double-sideband suppressed 38 kHz subcarrier signal Ssin~st, where S=(L-R), ~long with a pilot of l9kHz. The0 composite modulation signal can be written as:
em = M ~ Ssin~st + psin(~t/2) where ~S=2~fS and s=38kHz, and p is the amplitude of the l9k~lz pilot. Looking at the baseband sp2ctrum, one would find a monophonic channel M from about 50 H~ to 15kHz, a 19kHz pilot, and a stereophonic channel Ssin~st signal from 23 to 53kHz. If SCA tSubsidiary Communication Authorization) is also being transmitted, there is an SCA
frequency modulated subcarrier band rom 59.5 to 74.5kHz.
Three multi-channel television sound sytems are presently under consideration for future broadcast ser-vice in the United States. These three sy~tems are described in some detail in a July 1982 Electronics Industries Association report entitled "Multi-channel Television Sound: The Basis for Selection of a Single C-1~76 ~LZ~7:~
Stand~rd", but ~uffice lt eO s~y for ~p~e~ent p~rpose~ ~ba~
hree propose the tTan~mi6sion of a ~ter~oph~nic ~u~c~rrier for ~Do-channel sud~o progr~ g, ~ ~econd aLIdio prog~ SAP) f9r ~ddltional l~ngu~ge or other 5 ~ervice, ~nd a third ~ubcarrier for non-publie t~l@metry or el~ctronic new~ g~hering ~ENG3 u8~ ubc~rrler~
~re loc~ed ~t requ~ncies wh~ch are ~nteger OT frdCeiOnal multiple~ of the NTSC televi~ion lhorizont~l ~ync~ro~i-æa~iorl fr~quency (f~-15,743Hz). A syscem propo~ed by che 10 Electron~c Indu~er~e~ As~ociation of Japan u1:ilize~ fre~
quency modula~ion of the ~tereophonic 6ubcArrier, ~hale the other tlJO, ~ropose~ by Telesoni~s, Inc. and Zenith Radio Corporation, respectively, utilize double-sideband suppres~ed carrier amplitude modulation, similar to that employed in standard FM stereophonic radio broadcasts.
A6 has been noted earlier, io the pre~ent sy~tem ~n independent third or triphonic ~ignal ~ ~ provided for reproduction by ~ center loudspe~ker ~nd al~o to be used to electrically sub~ract the center ~i~nal component5 from the left &nd righe channel8 to give ~ fully di~crete perormance. There are ewo choiees9 ln ~he three propo~ed ~ulti-channel televi~ion sound ~y~ems, for the potential loc~tion of this new ~rip~onic ~ign~lg T~ Any of ~h~ ebree ~ystems could ~ccommoda~e the ~ignal T ~n the SAP channel, 25 ~lthough wiel: varying degrees of audio fidelityu The two sy~tems which u~e an amplitude modulated ~ter~ophonic ~ubcarrier provide an al~ernate means for transmi~sion of the T ~ignal, in that in ei~her one the new ~ignal T c~n be incorporated as quadrature D~odul~tion of the ~m~ ~up-30 pr~ssed carrier that c~rri~ ~he stereophonic diffe~encesig~aal S~tL-R3J The ~iphor~ic sy~tem of the pre~ent invention will be desc~ib~d irl the context of the Tele~
sonics and ~enith m-~lti-ch~nnel televi6ion ~ound sy~tems which diffes, for pre~ent purposes~ only in the Tequeney 35 o it~ ~tereophonic pilot tone9 wh~ch ~ fg~ or the Zenith ~ystem ~nd 5/4f~ for the Tele~nic~ i9yl3te!m~
b~ ~
'~'' :ILZ6~25~7~
In the triphonic ~ound system of the present invention, to the monophonic channel are added two double- -sideband kfH kHz signals (where k is 2.0 or 2.5~, one corresponding to a difference signal consisting of ~L-R~
and the other consisting of a signal (T=-1.4C) and spaced 90 apart in phase, along with a pilot signal having a frequency of either f~ or 5/4fH (for the Zenith and Telesonics systems, respectively) all as shown in FIG. 4.
In accordance with the ~enith and Telesonics design specifications, the amplitude o each o the doubl~-sideband signals is twice the amplitude of the monophonic channel signal, and tbe pilot, in turn, has a somewhat smaller amplitude. Thus, the composite baseband signal of this triphonic sound system can be written as follows:
em=(L~1.4C+R) ~ psin~t ~ (L-R~sin 2~t + (-1.4C)cos 2~t (Equation 1) where L, R and C are independent audio channels,w= ~ kfH
(~H - 15,734kHz and k = 2.0 or 2.5) and p is the amplitude of the pilot signal.
The transmitter for ~enera~ing this composite signal is illustrated in the block diagram of FIG. 5~ For purposes of simplicity, some of the more conventional transmitter circuits (e.g., pre emphasis networks, car-rier frequency source, and carrier frequency modulator~have not been shown and will be mentioned only briefly, ~here necessary, in the following description. The three audio frequency s;gnals L, C, and R, derived from three independent sources ~not shown~, are applied by pre-30 emphasis networks (not shown) to the inputs of a conven-tional matrix netwo~k 10 consisting, for examplet of a network of summing amplifiers arranged to produee at the output of tbe mat~ix three audio signals as follows: (1) (L+1.4C+R), (L-R), and (-1~4C). The monophonic signal (M) 35 is appl ied as one input to an adder 12 t and the stereo-phonic difference ~ignal (L-R~ and the triphon;c signal -16- .
(-1.4~ are applied to the inputs of respective modulators 14 and 169 the outputs of which sre also delivered to adder 12 where they are linearly combined with ~he monophonic signal.
The subcarrier and pilot signal are derived from a carrier generator 18, which is synchronized with and clocked by a signal fH (the television horizontal syn-chronization frequency) derived from the video signal to be transmitted along with the audio signals, and which is designed to provide an output sinewave signal S having a frequency of kfH kHz, where, again, k i5 either 2.0 or 2.5, depending upon whether the Zenith or Telesonics system is used. The carrier ~enerator includes any one of the known arrangements for providing a 90 phase displacement be-tween the subcarrier output signals applied to the re-spective modulators, as indicated in FlGo 5. The modu-lators 14 and 16 comprise suppressed-carrier ~mplitude modul~tors of known construction which serve to ampli-tude-modulate the two subcarriers with respective audio requency signals so as to produce the two double-side-band, suppressed-carrier, amplitude-modulated subcarrier signals (L-R)sin 2~t and (-1.4Cjcos 2~t. These latter signals are then combined in adder 12 with the monophonic signal M and a sinewave pilot signal of frequency k/2 fH
derived from carrier generator 18. The composite signal produced at the output o~ adder 12, set orth in Equation 1 above, is then applied to the FM exciter of the trans-mitter (not shown) and frequency modula~ed onto a high 3n frequency FM carrier for transmission purposes.
A triphonic receiver, in accordance with the invention, is shown in the ~lock diagram of FIG. 6 and, a~ain, for purposes of simplicity, some of tbe ~ore ~ 2 5 7 conventional FM receiver circuits ~e.g., RF and IF stages, discrimina~or~ and de-emphasîs netwo~ks~ have not been shown and will be only briefly mentioned as necessary. In ~ddition to reproducing a triphonic broadcast, in the manner to be descri~ed, the receiver is fully compatible with conventional monophonic and two-channel ~biphonic) ~tereophonic broadcasts. A received FM signal is ampli-f;ed in the RF and IF stages ~not shown) of a receiver/-demultiplexer 20, and demodulated in any of the known FM
detection circuits (not shown) and demultiplexed to de-rive the audio signals contained in the received FM
signal.
When a monaural broadcast is being received 7 the 15 output of the demultiplexer comprises the monaural signal M consisting of (L+1.4C~R). This signal i6 applied as a first input to both an adder 22 and a subtrac~or 249 the outputs of which are applied to a first input of an adder 26 and an adder 28, respectively. In the absence of signals applied to the second inputs o~ subtractor 24 and adders 22? 267 and 28, the monophonic M signal (i.e., [L+1.4C~R]) appear~ at the output of each of adders 26 ~nd 28~ one of which may be selected by suitable switching (not shown) for reproduction.
For a received two-channel stereo signal, the M
and S signals will be derived at the output of the demultiplexer; as before, the M signal is applied to one input of each of adder ~2 and subtractor 24, and the S
signal (L-R) is applied as a second input to adder 22 and is subtracted from the ~ignal M in sub~ractor 24. As a result, the output of adder 22 comprises the signal (2L+1.4C~, and absent a signal at the second input of adder 26, the output of adder 26 will be (2L~1.4C), the amplitude of which is then reduced by one-half to obtain a signal tL~0.7C~ for application to the left loudspeaker. Simi-larly, subtraction of the difference signal (L-R) from the C-147~
monophonic signal yields a signal (2R~1.4C), and since this signal likewise is not modified by adder 28, it appears at the output of 2dder 28; again, reducing the . amplitude of this signal by one-half ~ields ~he signal (R+0.7C~ fo~ reproduction by the right loudspeaker of the two-channel system. All of the above is typical of the mode of operation of a conventional ~wo-channel FM ~e-ceiver.
For a received triphonic signal, that is, a composite signal including the new T signal (-1.4C), the M, S, and T signals all appear at the output of demulti-plexer 20; the M and S signals are applied to adder 22 and subtractor 24 as before, and the T signal is applied to a splitter circuit 30, a known matrix ne~work designed ~o pass the (-1.4C) signal through to two separate outputs for application to the s~cond input of each of adders 26 and 28, and to alter the amplitude of the T signal and deliver to a third output terminal the signal 2C which, after suitable reduction in amplitude, is fed directly to the center loudspeaker of a triphonic reproduction sys-tem. The linear addition in adder 26 of the signals (2L+1.4C) and (-1.4C) yields a signal 2L and, similarly, the addition in adder 28 of the signals (2R+1.4C) and ~5 (-1.4C) yields the discrete signal 2R; thus, after suit-a~le reduction in amplitude, discrete L and R signals are available or application to the left and right loud-speakers9 respectively, of the triphonic sound repro-duction system.
3~
The reception mode hierarchy described above is seen in FIG. 7 which shows the three types of television receivers in which the three different transmit modes would be encountered 7 namely, a current conventional television set 30 having a single loudspeaker, a biphonic receiver 32 equipped with two loudspeakers for stereo-phonic reproduction of television sound, and a system ~ S'7~
likely to ~ave future p~ominance having a large screen display 34, a pair of outboard left and right loudspeakers 36 and 38, and a center loudspeaker 40 pdsitioned cen-trally of and below the viewing screen In the first case, as explained above, regardless of whether the trans-mission is monophonic7 biphonic, or triphonic in accord-ance with the present invention, the monaural M signal is reproduced by the single loudspeaker. The two-channel reproduction capability of receiver 32 displays the mon-aural signal M on each of its loudspeakers when thetransmiss;on is monophonic, and for both biphonic and triphonic transmissions displays the signal (L+0.7C~ on its left loudspeaker and the signal (R+0.7C) on its right loudspeaker. Finally, for the receiver having a large screen and three loudspeakers, the audio designer has a number of choices. For r~production of monophonic trans-missions, it is possible ~o utilize the M signal in all three loudspeakers, although at reduced level in the flanking loud speakers 36 and 28 so as to avoid "pulling"
the sound image away from its desirable center location.
Employing these flanking loudspeakers in the illusrated out;of-phase condition, may add somewhat to a feeling of increased ambience. For biphonic broadcasts, the M signal may be used for the center loudspeaker, and the con-~5 ~entional left and right signals for the flanking loudspeakers; here, too, an out~of-phase presentation may minimize slightly the impression of a shrunken stage wid~h. Fina~ly, for triphonic broadcasts, the discrete L
and R signals are applied to a respective flanking loud-~0 speaker snd the discrete C signal is fed directly to thecenter loudspeaker to provide accurate display of the three signals, comparable to that obtained in cinema sound systems.
Desirably the system according to the invention includes an identification signal to permit automatic switching of receivers to the triphonic reception mode.
~ 2 ~ ~ ~'7 Such a signal can be incorporated in the video signal or within the audio baseband spectrum. One oiE ac least ~wo - possibilities is to use a second pilot signal utilizing one-tbird am~litude of ~che third harmonic of the main 5 pilot as suggested by Halpern in the aforementioned U.S.
Pat. No. 3 9 679,832, which does not increase the instan-taneous frequency deviation of the FM carrier. Alter-natively, depending on the baseband configuration se-lected~ it may be preferable to employ amplitude modula-tion of the first pilot; a subharmonic frequency of the pilot should be selected to provide sidebands far enough beyond the eapture range of receiver pilot detec~ors, yet low enough in.frequency that the resultant sidebands about the pilot do not fall within the main or stereophonic channels.
It wîll have become apparent from the foregoing that the distinctive requirements for satisfactory multi channel sound reproduction in television make it de-sirable to extend the scope of the sound systems currently being considered for broadcast service. Although the un-stable center sound image does not present a severe handicap în the reproduction of sound without pictures, this is not the case in telev;sion, particularly those with wide-screen displays and widely spaced loudspeakers;
such systems demand a stable center sound, clearly sug-gesting that new television audio service must follow the example of the cinema rather than that of audio recording or FM r~dio broadcasting. The described triphonic system according to the present invention addresses and sat-isfies this need in that it is easily transmitted, with little or no penalty in station modulation capability or area of broadcast coverage. The system offers the potential for minimizing program production and editing costs, since the major portion of sound-track program will undoubtedly continue to be eenter-channel dialogue. Fin-ally, since the triphonic system is hierarchical, it offers broadcasters and receiver manufacturers alike an - unusual opportunity for flexibility in selection ~f op-erational modes.
S
The foregoing disclosure is intended to be merely illustra~ive of the principles of ~he present inven~ion and numerous modifications or alterati~ns might be made therein without departing from the spirit and scope of the invention. For example, although the T signal is described as having a value of -1.4C, it is obvious that the value may be ~1.4C, which would require that adders 26 and 28 instead be subtra~ting circuits to obtain the same results.
Each audio ~requency wave is also used to amplitude-modulate a respective subcarrier signal, the subcarrier signals being of the same frequency and spaced 120 apart in phase. A suppresse~-carrier, double~sideband modu-lation of each subcarrier is employed, with the frequency of the subcarrier signals being sufficiently high as to assure a frequency gap between the lower sidebands of the modulated subcarrier signals and the sum signal. To achieve the desired compatibility with monophonic and two-channel stereophonic FM receivers, the amplitude of each double-sideband suppressed-carrier signal is mul-tiplied by a factor of 2/ ~ . A conventional low-level phase reference pilot signal, lying within the frequency gap, ;s employed for receiver detection purposes. A
second pilot signal, of one-third the ampl;tude oE the third ~armonic of the phase reference pilo~, is utilized to achieve three-channel receiver compatibility with a monophonic or two-channel stereophonic broadcast. The sum signal, the three double-sideband suppressed-carrier signals, and the two pilot signals are frequency modu-lated onto a high frequency FM carrier for transmiss;on purposes.
~ C-1476 5~7~
The composite, f~equency modulated, carrier signal i~ t~ansmit~ed to one or more receivers, which may be either of ~he conventional monophonic or two-channel stereophoni~ type or preferably a ~hree-channel stereo receiver, each adapted to receive and reproduce the three-channel broadcast in accordance with its respec-tive mode of operation. Compatibility of the three-channel stereophonic receiver with one-channel or two-channel broadcast is achieved by the use of the second pilot signal. In the absence of this pilot, the three-channel receiver operates in a conventional manner to reproduce a monophonic or ~wo-channel stereophonic broadcast. The second pilot signal is used as an indi-cator for a three-channel broadeast and when the same îs received by a three-channel receiver it serves to switch the latter into a three channel stereophonic reception mode. Thus, a three-channel broadcast is compatible with a one, two, or three-channel receiver, while the three-channel receiver is compatib~e with a one, two, or three-channel broadcast.
This system ;s relatively complex in that ;trequires two pilot signals and a phase-shift network for establishing the 120 phase relationship between the subcarrier signals, and has the disadvantage that all three of the independent source signals are modulated to enable recovery of third-channel information, some of which information gets into the output of a two-channel receiver.
:~'25~S7~
- 1 o -SUMMARY OF TffE INVENTION
_ - It is a primary object of the present inven~ion ~o provide a triphonic transmission sys~em that is fully compatible with existing monophonic receivers and with new television receivers that may employ only two loud-speakers.
A related object of the invention is to provide a triphonic transmission system that will provide center-channel quality equivalent in all respects to that of the left 2nd right channels without significant degradation or compromise.of existing monophonic or future biphonic ~ervice and coverage~
In accordance with the present invention, three independent sources of stereophonically related audio frequency ~aves characterized as L(left) 3 R(right) and C(center), are matrixed to obtain three signals exhibit-~O ing the matrix equations:(l)M = L ~ 1.4C ~ R; (2)S=L-R; and (3)T - -1.4C. Each of audio frequency waves S and T is used to amplitude~modulate a respective subcarrier signal~
the subcarrier signals being of the same frequency and spaced 90 apart in phase. Suppressed-carrier, double-sideband modulation of each subcarrier is employed, withthe frequency of the subcarrier signals being suffi-ciently high as to assure a frequency gap below the lower sidebands of the modulated subcarrier signals and the M
signal. A conventional low-level phase reerence pilot signal, lying within the aforementioned frequency gap, is employed for receiver detection purposesO The afore-mentioned M signal, the two double-sideband suppressed-carrier signals, and the pilot signal are frequency modu-lated onto a high frequency FM carrier for transmission purposes.
~ 5~
The composite, requency modulated, carrier s;gnal is transmitted to one or more remote receivers, which may be of the conven~ional monophonic or two-channel stereophonic type, or preferably a triphonic receiver constructed in accordance with 4he :invention. Typically, a plurality of receivers of each type will receive and reproduce the three signals, each in accordance with its respective mode of operation. A conven~ional monophonic receiver decodes only ~he sum signal (M~, and a two-channel receiver reproduces the transmitted M signal inboth loudspeakers for mon ophonic reception, and the tra-ditional stereophonic signals for the biphonic and tri-phonic modes. For a third category of receiver having a large screen and three widely-spaced lo~dspeakers, a choice of reproduction is available. For reproduction of monophonic transmissions, the sum signal ~M) can be util ized in all three lolidspeakers, although at reduced level in the flanking loudspeakers so as to avoid "pulling" the sound image away from its desirable cen~er location. For biphonic broadcasts, the M signal may be used for the center loudspeaker, and the conveDtional left and right signals for the ~lanking loudspeakers. Finallg, the reproduction of triphonic broadcasts resul~s in the dis~
play of left, center, and right signals by respective loudspeakers; in this case, the signal T is fed directly to the center loudspeaker, and is also used to electri-cally subtract the center signal components from the leEt and right channels, resulting in fully discrete per-formance.
.
C-1~76 ~lZ~ZS~7~L
BRIE- o~S _I~TION OF THE DRAWINGS
The invention will be more fully appreciated . from the following de~ailed description when consid~red in connection with the accompanying drawings in which: , FIG. 1, to which reference has already been made, is a plot illustrating the effect of the head on a single-sound wave front arriving at an angle of 90 from the front of the listener;
FIG. 2, to which previous reference has been made, is a plot showing the use of the "Law of Sines" for the case of two lo~dspeakers at an angle of 90 to the listener;
FIG. 3, previously referrred to, illustrates an application of the "Law of Sines";
FIG. 4 is a requency diagram of the composite baseband signal developed in accordance with the prin-ciples of the present invention;
FIG. 5 is a simplified block diagram of a trans-mitting terminal for generating the composite signal of FI~. 4;
FIG. 6 is a simplified block diagram of a re-ceivîng terminal in accordance with the inventionS and FIG. 7 is a pictorial diagram illustrating the reception mode hierarchy in accordance wi~h ~he prin-ciples of the invention.
DETAILED DESCRIPTION
_ .
Before describing the present invan~ion, it maybe useful ~a briefly r~view the basic principles of the existing two-channel s~ereo system approved by the FCC, as well as multi-channel television sound systems presently under consideratîon for future broadcast service in the United States. In the current radio system, the stereo-phonically rela~ed signals ~hat are added together con-stitute a "monophonic channel" which consists of a (~+R)signal of 50 to 15,000 Hz, where L and R represent the left and right independent audio signals or channels9 as noted earlier, each of the L and R signals may also include a 0.7C component. It is this combined signal that is reproduced by a standard monaural FM receiver, hence the descriptive term "monophonic channel" and the use herein of the letter M to identify this channel. To this is added a double-sideband suppressed 38 kHz subcarrier signal Ssin~st, where S=(L-R), ~long with a pilot of l9kHz. The0 composite modulation signal can be written as:
em = M ~ Ssin~st + psin(~t/2) where ~S=2~fS and s=38kHz, and p is the amplitude of the l9k~lz pilot. Looking at the baseband sp2ctrum, one would find a monophonic channel M from about 50 H~ to 15kHz, a 19kHz pilot, and a stereophonic channel Ssin~st signal from 23 to 53kHz. If SCA tSubsidiary Communication Authorization) is also being transmitted, there is an SCA
frequency modulated subcarrier band rom 59.5 to 74.5kHz.
Three multi-channel television sound sytems are presently under consideration for future broadcast ser-vice in the United States. These three sy~tems are described in some detail in a July 1982 Electronics Industries Association report entitled "Multi-channel Television Sound: The Basis for Selection of a Single C-1~76 ~LZ~7:~
Stand~rd", but ~uffice lt eO s~y for ~p~e~ent p~rpose~ ~ba~
hree propose the tTan~mi6sion of a ~ter~oph~nic ~u~c~rrier for ~Do-channel sud~o progr~ g, ~ ~econd aLIdio prog~ SAP) f9r ~ddltional l~ngu~ge or other 5 ~ervice, ~nd a third ~ubcarrier for non-publie t~l@metry or el~ctronic new~ g~hering ~ENG3 u8~ ubc~rrler~
~re loc~ed ~t requ~ncies wh~ch are ~nteger OT frdCeiOnal multiple~ of the NTSC televi~ion lhorizont~l ~ync~ro~i-æa~iorl fr~quency (f~-15,743Hz). A syscem propo~ed by che 10 Electron~c Indu~er~e~ As~ociation of Japan u1:ilize~ fre~
quency modula~ion of the ~tereophonic 6ubcArrier, ~hale the other tlJO, ~ropose~ by Telesoni~s, Inc. and Zenith Radio Corporation, respectively, utilize double-sideband suppres~ed carrier amplitude modulation, similar to that employed in standard FM stereophonic radio broadcasts.
A6 has been noted earlier, io the pre~ent sy~tem ~n independent third or triphonic ~ignal ~ ~ provided for reproduction by ~ center loudspe~ker ~nd al~o to be used to electrically sub~ract the center ~i~nal component5 from the left &nd righe channel8 to give ~ fully di~crete perormance. There are ewo choiees9 ln ~he three propo~ed ~ulti-channel televi~ion sound ~y~ems, for the potential loc~tion of this new ~rip~onic ~ign~lg T~ Any of ~h~ ebree ~ystems could ~ccommoda~e the ~ignal T ~n the SAP channel, 25 ~lthough wiel: varying degrees of audio fidelityu The two sy~tems which u~e an amplitude modulated ~ter~ophonic ~ubcarrier provide an al~ernate means for transmi~sion of the T ~ignal, in that in ei~her one the new ~ignal T c~n be incorporated as quadrature D~odul~tion of the ~m~ ~up-30 pr~ssed carrier that c~rri~ ~he stereophonic diffe~encesig~aal S~tL-R3J The ~iphor~ic sy~tem of the pre~ent invention will be desc~ib~d irl the context of the Tele~
sonics and ~enith m-~lti-ch~nnel televi6ion ~ound sy~tems which diffes, for pre~ent purposes~ only in the Tequeney 35 o it~ ~tereophonic pilot tone9 wh~ch ~ fg~ or the Zenith ~ystem ~nd 5/4f~ for the Tele~nic~ i9yl3te!m~
b~ ~
'~'' :ILZ6~25~7~
In the triphonic ~ound system of the present invention, to the monophonic channel are added two double- -sideband kfH kHz signals (where k is 2.0 or 2.5~, one corresponding to a difference signal consisting of ~L-R~
and the other consisting of a signal (T=-1.4C) and spaced 90 apart in phase, along with a pilot signal having a frequency of either f~ or 5/4fH (for the Zenith and Telesonics systems, respectively) all as shown in FIG. 4.
In accordance with the ~enith and Telesonics design specifications, the amplitude o each o the doubl~-sideband signals is twice the amplitude of the monophonic channel signal, and tbe pilot, in turn, has a somewhat smaller amplitude. Thus, the composite baseband signal of this triphonic sound system can be written as follows:
em=(L~1.4C+R) ~ psin~t ~ (L-R~sin 2~t + (-1.4C)cos 2~t (Equation 1) where L, R and C are independent audio channels,w= ~ kfH
(~H - 15,734kHz and k = 2.0 or 2.5) and p is the amplitude of the pilot signal.
The transmitter for ~enera~ing this composite signal is illustrated in the block diagram of FIG. 5~ For purposes of simplicity, some of the more conventional transmitter circuits (e.g., pre emphasis networks, car-rier frequency source, and carrier frequency modulator~have not been shown and will be mentioned only briefly, ~here necessary, in the following description. The three audio frequency s;gnals L, C, and R, derived from three independent sources ~not shown~, are applied by pre-30 emphasis networks (not shown) to the inputs of a conven-tional matrix netwo~k 10 consisting, for examplet of a network of summing amplifiers arranged to produee at the output of tbe mat~ix three audio signals as follows: (1) (L+1.4C+R), (L-R), and (-1~4C). The monophonic signal (M) 35 is appl ied as one input to an adder 12 t and the stereo-phonic difference ~ignal (L-R~ and the triphon;c signal -16- .
(-1.4~ are applied to the inputs of respective modulators 14 and 169 the outputs of which sre also delivered to adder 12 where they are linearly combined with ~he monophonic signal.
The subcarrier and pilot signal are derived from a carrier generator 18, which is synchronized with and clocked by a signal fH (the television horizontal syn-chronization frequency) derived from the video signal to be transmitted along with the audio signals, and which is designed to provide an output sinewave signal S having a frequency of kfH kHz, where, again, k i5 either 2.0 or 2.5, depending upon whether the Zenith or Telesonics system is used. The carrier ~enerator includes any one of the known arrangements for providing a 90 phase displacement be-tween the subcarrier output signals applied to the re-spective modulators, as indicated in FlGo 5. The modu-lators 14 and 16 comprise suppressed-carrier ~mplitude modul~tors of known construction which serve to ampli-tude-modulate the two subcarriers with respective audio requency signals so as to produce the two double-side-band, suppressed-carrier, amplitude-modulated subcarrier signals (L-R)sin 2~t and (-1.4Cjcos 2~t. These latter signals are then combined in adder 12 with the monophonic signal M and a sinewave pilot signal of frequency k/2 fH
derived from carrier generator 18. The composite signal produced at the output o~ adder 12, set orth in Equation 1 above, is then applied to the FM exciter of the trans-mitter (not shown) and frequency modula~ed onto a high 3n frequency FM carrier for transmission purposes.
A triphonic receiver, in accordance with the invention, is shown in the ~lock diagram of FIG. 6 and, a~ain, for purposes of simplicity, some of tbe ~ore ~ 2 5 7 conventional FM receiver circuits ~e.g., RF and IF stages, discrimina~or~ and de-emphasîs netwo~ks~ have not been shown and will be only briefly mentioned as necessary. In ~ddition to reproducing a triphonic broadcast, in the manner to be descri~ed, the receiver is fully compatible with conventional monophonic and two-channel ~biphonic) ~tereophonic broadcasts. A received FM signal is ampli-f;ed in the RF and IF stages ~not shown) of a receiver/-demultiplexer 20, and demodulated in any of the known FM
detection circuits (not shown) and demultiplexed to de-rive the audio signals contained in the received FM
signal.
When a monaural broadcast is being received 7 the 15 output of the demultiplexer comprises the monaural signal M consisting of (L+1.4C~R). This signal i6 applied as a first input to both an adder 22 and a subtrac~or 249 the outputs of which are applied to a first input of an adder 26 and an adder 28, respectively. In the absence of signals applied to the second inputs o~ subtractor 24 and adders 22? 267 and 28, the monophonic M signal (i.e., [L+1.4C~R]) appear~ at the output of each of adders 26 ~nd 28~ one of which may be selected by suitable switching (not shown) for reproduction.
For a received two-channel stereo signal, the M
and S signals will be derived at the output of the demultiplexer; as before, the M signal is applied to one input of each of adder ~2 and subtractor 24, and the S
signal (L-R) is applied as a second input to adder 22 and is subtracted from the ~ignal M in sub~ractor 24. As a result, the output of adder 22 comprises the signal (2L+1.4C~, and absent a signal at the second input of adder 26, the output of adder 26 will be (2L~1.4C), the amplitude of which is then reduced by one-half to obtain a signal tL~0.7C~ for application to the left loudspeaker. Simi-larly, subtraction of the difference signal (L-R) from the C-147~
monophonic signal yields a signal (2R~1.4C), and since this signal likewise is not modified by adder 28, it appears at the output of 2dder 28; again, reducing the . amplitude of this signal by one-half ~ields ~he signal (R+0.7C~ fo~ reproduction by the right loudspeaker of the two-channel system. All of the above is typical of the mode of operation of a conventional ~wo-channel FM ~e-ceiver.
For a received triphonic signal, that is, a composite signal including the new T signal (-1.4C), the M, S, and T signals all appear at the output of demulti-plexer 20; the M and S signals are applied to adder 22 and subtractor 24 as before, and the T signal is applied to a splitter circuit 30, a known matrix ne~work designed ~o pass the (-1.4C) signal through to two separate outputs for application to the s~cond input of each of adders 26 and 28, and to alter the amplitude of the T signal and deliver to a third output terminal the signal 2C which, after suitable reduction in amplitude, is fed directly to the center loudspeaker of a triphonic reproduction sys-tem. The linear addition in adder 26 of the signals (2L+1.4C) and (-1.4C) yields a signal 2L and, similarly, the addition in adder 28 of the signals (2R+1.4C) and ~5 (-1.4C) yields the discrete signal 2R; thus, after suit-a~le reduction in amplitude, discrete L and R signals are available or application to the left and right loud-speakers9 respectively, of the triphonic sound repro-duction system.
3~
The reception mode hierarchy described above is seen in FIG. 7 which shows the three types of television receivers in which the three different transmit modes would be encountered 7 namely, a current conventional television set 30 having a single loudspeaker, a biphonic receiver 32 equipped with two loudspeakers for stereo-phonic reproduction of television sound, and a system ~ S'7~
likely to ~ave future p~ominance having a large screen display 34, a pair of outboard left and right loudspeakers 36 and 38, and a center loudspeaker 40 pdsitioned cen-trally of and below the viewing screen In the first case, as explained above, regardless of whether the trans-mission is monophonic7 biphonic, or triphonic in accord-ance with the present invention, the monaural M signal is reproduced by the single loudspeaker. The two-channel reproduction capability of receiver 32 displays the mon-aural signal M on each of its loudspeakers when thetransmiss;on is monophonic, and for both biphonic and triphonic transmissions displays the signal (L+0.7C~ on its left loudspeaker and the signal (R+0.7C) on its right loudspeaker. Finally, for the receiver having a large screen and three loudspeakers, the audio designer has a number of choices. For r~production of monophonic trans-missions, it is possible ~o utilize the M signal in all three loudspeakers, although at reduced level in the flanking loud speakers 36 and 28 so as to avoid "pulling"
the sound image away from its desirable center location.
Employing these flanking loudspeakers in the illusrated out;of-phase condition, may add somewhat to a feeling of increased ambience. For biphonic broadcasts, the M signal may be used for the center loudspeaker, and the con-~5 ~entional left and right signals for the flanking loudspeakers; here, too, an out~of-phase presentation may minimize slightly the impression of a shrunken stage wid~h. Fina~ly, for triphonic broadcasts, the discrete L
and R signals are applied to a respective flanking loud-~0 speaker snd the discrete C signal is fed directly to thecenter loudspeaker to provide accurate display of the three signals, comparable to that obtained in cinema sound systems.
Desirably the system according to the invention includes an identification signal to permit automatic switching of receivers to the triphonic reception mode.
~ 2 ~ ~ ~'7 Such a signal can be incorporated in the video signal or within the audio baseband spectrum. One oiE ac least ~wo - possibilities is to use a second pilot signal utilizing one-tbird am~litude of ~che third harmonic of the main 5 pilot as suggested by Halpern in the aforementioned U.S.
Pat. No. 3 9 679,832, which does not increase the instan-taneous frequency deviation of the FM carrier. Alter-natively, depending on the baseband configuration se-lected~ it may be preferable to employ amplitude modula-tion of the first pilot; a subharmonic frequency of the pilot should be selected to provide sidebands far enough beyond the eapture range of receiver pilot detec~ors, yet low enough in.frequency that the resultant sidebands about the pilot do not fall within the main or stereophonic channels.
It wîll have become apparent from the foregoing that the distinctive requirements for satisfactory multi channel sound reproduction in television make it de-sirable to extend the scope of the sound systems currently being considered for broadcast service. Although the un-stable center sound image does not present a severe handicap în the reproduction of sound without pictures, this is not the case in telev;sion, particularly those with wide-screen displays and widely spaced loudspeakers;
such systems demand a stable center sound, clearly sug-gesting that new television audio service must follow the example of the cinema rather than that of audio recording or FM r~dio broadcasting. The described triphonic system according to the present invention addresses and sat-isfies this need in that it is easily transmitted, with little or no penalty in station modulation capability or area of broadcast coverage. The system offers the potential for minimizing program production and editing costs, since the major portion of sound-track program will undoubtedly continue to be eenter-channel dialogue. Fin-ally, since the triphonic system is hierarchical, it offers broadcasters and receiver manufacturers alike an - unusual opportunity for flexibility in selection ~f op-erational modes.
S
The foregoing disclosure is intended to be merely illustra~ive of the principles of ~he present inven~ion and numerous modifications or alterati~ns might be made therein without departing from the spirit and scope of the invention. For example, although the T signal is described as having a value of -1.4C, it is obvious that the value may be ~1.4C, which would require that adders 26 and 28 instead be subtra~ting circuits to obtain the same results.
Claims (17)
1. In a triphonic sound transmission system, a transmitter comprising:
means for combining three independent stereo-phonically related audio frequency source waves, L, R and C
to obtain three audio frequency signals M, S and T respectively comprising (L + 1.4 C + R), (L-R) and (-1.4C);
means for generating two subcarriers of the same frequency and spaced 90° apart in phase, means for amplitude-modulating each subcarrier with a respective one of said audio frequency signals S and T to develop two double-sideband suppressed-carrier signals, the frequency of said subcarriers being sufficiently high as to assure a frequency gap between the lower sidebands of the modulated sub-carrier signals and the said M signal;
means for generating a phase reference pilot signal having a frequency which is one-half the frequency of the subcarriers and lies within said frequency gap; and means for frequency modulating the aforementioned signals onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers.
means for combining three independent stereo-phonically related audio frequency source waves, L, R and C
to obtain three audio frequency signals M, S and T respectively comprising (L + 1.4 C + R), (L-R) and (-1.4C);
means for generating two subcarriers of the same frequency and spaced 90° apart in phase, means for amplitude-modulating each subcarrier with a respective one of said audio frequency signals S and T to develop two double-sideband suppressed-carrier signals, the frequency of said subcarriers being sufficiently high as to assure a frequency gap between the lower sidebands of the modulated sub-carrier signals and the said M signal;
means for generating a phase reference pilot signal having a frequency which is one-half the frequency of the subcarriers and lies within said frequency gap; and means for frequency modulating the aforementioned signals onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers.
2. A triphonic system as defined in claim 1 including receiver means operative in response to the reception of said high frequency carrier to reproduce each of the audio fre-quency source signals L, R and C.
3, A triphonic system as defined in claim 2 wherein said receiver means includes means for reproducing conventional monophonic and two-channel stereophonic broadcasts.
4. A triphonic sound system comprising:
a transmitter including means for com-bining three independent stereophonically related audio frequency source signals L, C, and R to obtain three audio frequency signals M, S and T respectively comprising (L + 1.4C + R), (L-R) and (-1.4C), means for amplitude-modulating each of two equal frequency quadrature-phased subcarriers with a respective one of said audio frequency signals S and T, and means for frequency modulating the afore-mentioned signals onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers; and receiver means operative in response to the reception of said frequency-modulated carrier for reproducing each of said audio frequency source signals.
a transmitter including means for com-bining three independent stereophonically related audio frequency source signals L, C, and R to obtain three audio frequency signals M, S and T respectively comprising (L + 1.4C + R), (L-R) and (-1.4C), means for amplitude-modulating each of two equal frequency quadrature-phased subcarriers with a respective one of said audio frequency signals S and T, and means for frequency modulating the afore-mentioned signals onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers; and receiver means operative in response to the reception of said frequency-modulated carrier for reproducing each of said audio frequency source signals.
5. A triphonic sound system as defined in claim 4, wherein said carrier is modulated in accordance with the modulation function em = M + psin(.omega.st/2) + Ssin .omega.st + Tcos .omega.st where p is the amplitude of a phase reference pilot signal sin.omega.st/2), and .omega.s = 2.pi.fS, where fs is the fundamental frequency of the subcarrier signals sin .omega.st and cos .omega.st each subcarrier signal being suppressed-carrier double-sideband amplitude-modulated by a respective one of said audio frequency signals S and T.
6. A triphonic sound system as defined in claim 5, wherein fs = kfH, k is a constant, and fH = 15,734 Hz, the horizontal synchronization frequency for NTSC tele-vision.
7. A triphonic sound system as defined in claim 3, wherein the constant k is selected from 2.0 or 2.5.
8. A triphonic sound system as defined in claim 4, wherein said receiver means includes means for alter-natively reproducing conventional monophonic and two-channel stereophonic broadcasts.
9. A triphonic sound system as defined in claim 8, wherein said receiver means includes first and second means for combining said audio signals M and S to obtain first and second intermediate audio signal (2L + 1.4C) and (2R + 1.4C), respectively, and third and fourth means for combining said first and second intermediate audio signals, respectively, with said audio signal T to obtain said audio frequency source signals L and R.
10. In a triphonic sound transmission system, a transmitter comprising:
means for combining three independent stereophonically related audio frequency source signals L, C, and R to obtain three audio frequency signals M, S
and T respectively comprising (L + 1.4C + R), (L-R) and (-1.4C), means for modulating each of two sub-carriers with a respective one of said audio frequency signals S and T, and means for frequency modulating the afore-mentioned signals onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers.
means for combining three independent stereophonically related audio frequency source signals L, C, and R to obtain three audio frequency signals M, S
and T respectively comprising (L + 1.4C + R), (L-R) and (-1.4C), means for modulating each of two sub-carriers with a respective one of said audio frequency signals S and T, and means for frequency modulating the afore-mentioned signals onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers.
11. A transmitter as defined in claim 10, wherein a first of said subcarriers is modulated by said audio frequency signal S and has a frequency which assures a frequency gap between the lower sideband of the modulated subcarrier signal and the M signal, and wherein the second of said subcarriers is modulated by said audio frequency signal T and has a frequency higher than the frequency of said first sub-carrier.
12. A transmitter as defined in claim 10, wherein said subcarriers are quadrature-phased and of the same frequency, which frequency is sufficiently high as to assure a frequency gap between the lower sidebands of the modulated subcarrier signals and the said M
signal.
signal.
13. A receiver for use in a triphonic sound system having a transmitter including means for com-bining three independent stereophonically related audio frequency source signals L, C, and R to obtain three audio frequency signals M, S and T respectively comprising (L + 1.4C + R), (L-R) and (-1.4C), means for modulating each of two subcarriers with a respective one of said audio frequency signals S and T, and means for frequency modulating the aforementioned signals onto a high fre-quency carrier for the purpose of transmitting the same to one or more remote receivers, said receiver com-prising:
means operative in response to reception of said high frequency carrier for deriving said audio frequency signals M, S and T, and means for combining said M, S and T signals to reproduce each of the audio frequency source signals L, R and C.
means operative in response to reception of said high frequency carrier for deriving said audio frequency signals M, S and T, and means for combining said M, S and T signals to reproduce each of the audio frequency source signals L, R and C.
14. A receiver as defined in claim 13, wherein said combining means includes first and second means for combining said audio signals M and S to obtain first and second intermediate audio signals (2L + 1.4C) and (2R +
1.4C), respectively, and third and fourth means for combining said first and second intermediate audio sig-nals, respectively, with said audio signal T to obtain said audio frequency source signals L and R.
1.4C), respectively, and third and fourth means for combining said first and second intermediate audio sig-nals, respectively, with said audio signal T to obtain said audio frequency source signals L and R.
15. A receiver as defined in claim 13, wherein said receiver includes means for alternatively reproduc-ing conventional monophonic and two-channel stereophonic broadcasts.
16. A receiver as defined in claim 13, wherein said combining means is operative to alternatively re-produce received conventional monophonic and two-channel stereophonic broadcasts.
17. In a triphonic sound system, a receiver for demodulating a high frequency carrier signal frequency modulated by first and second subcarriers respectively modulated by audio frequency signals S and T and by an audio frequency signal M, where the signals M, S and T
comprise combinations o three independent stereophonically related audio frequency source signals L, C and R, said combinations comprising (L + 1.4C +R), (L-R) and (-1.4C), respectively, said receiver comprising:
means operative in response to said high frequency carrier for deriving said audio frequency sig-nals M, S and T, means for combining said audio signals M
and S to obtain first and second intermediate audio signals (2L + 1.4C) and (2R + 1.4C), respectively, means for deriving said audio signal T, and means for separately combining said audio signal T with each of said intermediate audio signals to obtain said audio frequency source signals L and R.
comprise combinations o three independent stereophonically related audio frequency source signals L, C and R, said combinations comprising (L + 1.4C +R), (L-R) and (-1.4C), respectively, said receiver comprising:
means operative in response to said high frequency carrier for deriving said audio frequency sig-nals M, S and T, means for combining said audio signals M
and S to obtain first and second intermediate audio signals (2L + 1.4C) and (2R + 1.4C), respectively, means for deriving said audio signal T, and means for separately combining said audio signal T with each of said intermediate audio signals to obtain said audio frequency source signals L and R.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US44157182A | 1982-11-15 | 1982-11-15 | |
| US441,571 | 1982-11-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1202571A true CA1202571A (en) | 1986-04-01 |
Family
ID=23753416
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000441129A Expired CA1202571A (en) | 1982-11-15 | 1983-11-14 | Triphonic sound system |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS59107655A (en) |
| CA (1) | CA1202571A (en) |
| FR (1) | FR2536234A1 (en) |
| GB (1) | GB2130056B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3442388C1 (en) * | 1984-11-20 | 1986-03-20 | Institut für Rundfunktechnik GmbH, 8000 München | Method for audio transmission in a high-resolution television system |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3812295A (en) * | 1970-10-19 | 1974-05-21 | Columbia Broadcasting Syst Inc | Quadraphonic reproducing system with gain riding logic |
| US3679832A (en) * | 1971-03-23 | 1972-07-25 | Bell Telephone Labor Inc | Three-channel fm stereo transmission |
| DE2220255A1 (en) * | 1972-04-25 | 1973-11-15 | Siemens Ag | METHOD OF TRANSMISSION OF THREE SIGNALS IN THE FREQUENCY BAND OF A STEREO SIGNAL FOR VHF BROADCASTING |
| GB1522135A (en) * | 1974-08-29 | 1978-08-23 | Dolby Laboratories Inc | Stereophonic sound system |
| US4339772A (en) * | 1980-10-14 | 1982-07-13 | Zenith Radio Corporation | TV Sound Transmission system |
-
1983
- 1983-11-14 CA CA000441129A patent/CA1202571A/en not_active Expired
- 1983-11-14 GB GB08330296A patent/GB2130056B/en not_active Expired
- 1983-11-15 JP JP58214930A patent/JPS59107655A/en active Granted
- 1983-11-15 FR FR8318138A patent/FR2536234A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| GB8330296D0 (en) | 1983-12-21 |
| JPS6317378B2 (en) | 1988-04-13 |
| JPS59107655A (en) | 1984-06-21 |
| GB2130056A (en) | 1984-05-23 |
| FR2536234A1 (en) | 1984-05-18 |
| GB2130056B (en) | 1986-06-25 |
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