JPS6317378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ternary acoustic transmission system that is particularly compatible with existing monophonic and biphonic receivers.

In response to increasing public awareness and interest in the reproduction of multichannel sound in the home, the process of selecting a standard transmission system for stereo sound for television is currently underway. Initially initiated by the broadcast and consumer electronics industries, this movement eventually encompassed the Federal Communications Commission (FCC) and the consumer market, and further improved multichannel services, especially for television broadcasting. This brings about the need for the provision of a ternary sound system for

For multichannel sound transmission, see JC
Steinberg and WBSnow's "Bell System"
Technical Journal, Volume 13, No. 2 (April 1934)
"Wired transmission of symphonic music, reproduction and physical factors in its acoustic perspective" published by
Bell in the early 1930s, published in a paper titled
It has its practical beginnings in experiments in Laboratories. National Stereophonic Radio, founded in 1959 by the Electronics Industries Association
Following the work of the Committee, the current system for FM stereo radio broadcasting was established by the FCC in 1961.
Approved by. Further research in the past decade has resulted in the development of many proposed systems for both AM stereo sound broadcasting and FM surround sound broadcasting.

Multichannel sound accompanied by visual imagery was first given a powerful boost by Walt Disney's first film, Fantasia, released in 1940. Today the specification for 35mm motion picture film provides four tracks for sound recording and the 70mm specification provides six tracks. Based on this well-established precedent in the film industry, and the routine transmission of filmed programs by television broadcasting companies, methods for transmitting one or more sound channels along with television images are now discussed. is being done. The acoustic requirements of film and television media are different, especially the size of the video screen, aspect ratio, audience seating, transmission bandwidth constraints, timeliness and manufacturing costs that are conceivable for today's television. Although it is argued that this would seem to suggest the use of the simplest sound system, large-screen home receivers are already becoming commonplace, and efforts are being made to establish wide-screen, high-resolution services. Serious research is being carried out in order to consider the acoustic demands of the near and distant future and to formulate the requirements to provide technological means to meet these future demands.

Since any transmission system for television stereo sound must be compatible with existing services, any system under consideration will require monophonic sum signals (M) for existing baseband channels and domestic A stereophonic difference signal (S) that allows the monophonic signal to be split into left and right components at the receiver.
start from. In existing two-channel stereo systems approved by the FCC, and in those systems being considered for the transmission of television stereo sound, a symmetric matrix is used, expressed by the following equation. That is, M = (L + 0.7C) + (0.7C + R) S = (L - R) In a home receiver, the signals applied to the left and right loudspeakers are the following combined signals: is obtained by addition and subtraction of the signals (and normalization of the gain). That is, Left channel = M + S = L + 0.7C Right channel = M - S = R + 0.7C Although it is not generally customary to indicate the front center term C in the above matrix formula, in this formula, multi-channel sound in television Included to illustrate some interesting characteristics that are important in broadcasting. No matter how many special sound effects or how wide projection screens are available, important dialogue and other salient sound signals have always been, and undoubtedly will continue to be, visible on the screen. It will be placed in the center of In conventional two-channel loudspeaker reproduction, the center signal is represented as a virtual or imaginary sound image produced by the sum of equal amplitude and phase sounds from each of the two loudspeakers.
If the left, center and right signals appeared with equal strength in the original program, such a normal condition would be maintained in a home stereo listening environment. However, in monophonic listening mode, the equal voltage components of the center signal in the left and right channels are arithmetically summed and the sum signal is expressed as (L+1.4C+R). This equation represents the well-known 3 dB imbalance in the center that is common to monophonic reproduction of all stereo systems using conventional amplitude panning control. Although an unavoidable consequence of the matrix method, the result is a desirable increase in the prominence of the central channel, especially in the presence of lateral stage effects. In the case of two-channel playback where the central sound image is at the normal level,
Listeners can easily make such discriminations even in the presence of competing sounds.

The fact that the important central signal is displayed as a virtual image means that the sound image is reasonably well defined for a listener located exactly on the line of symmetry between the two loudspeakers, but for other listeners' locations. This is not preferable in that it becomes unclear and unstable. The movement of the listener's head brings about an obvious change. Even in the best case, the sound image position will be unclear, and in the worst case, the sound image position will seem to shift even with the slightest movement of the listener's head. Although this does not seem to be a significant hindrance in just listening to music,
This becomes an even bigger problem when the audio is accompanied by visual images. Even for a listener located along the line of symmetry of the loudspeaker, the sound image will appear to rise as it is panned from left through center to right. Although this rise in the central sound image has been recognized since it was first reported in 1959, this effect has not yet been fully explained. However, the degree of rise appears to be related to the angle from the listener to the loudspeaker, being least when this angle is small, but settling above the head when the listener is directly between the loudspeakers.

Even with the major advances in localization theory over the past roughly 20 years, and despite the fact that the traditional model requires careful positioning of the listener, this traditional model remains the only one in practice. It is something. One reason is that it allows for simple production techniques and relatively cheap equipment;
More importantly, a much more complex panning operation is required, which differs for each listener's position and orientation within the listening room. To summarize psychoacoustic positioning theory, the basic positioning model assumes that the geometry of the human head is symmetrical and that the hearing acuity in the two ears is equal. Thus, a central sound image is perceived when the outputs of the two loudspeakers heard in both ears are equal in amplitude and phase. Various other factors come into play when the head rotates. "J.
Acoustical Society of America, Volume 58, No. 3 (September 1975), the applicant and
The attached Figure 1, taken from the paper ``Diffraction of propagating sound waves produced by the human head and measurement of interacoustic delay'' published by Abbagnaro and Bauer, is shown at a 90° angle from the front of the listener. It shows the effect of the head on the wavefront of one sound wave arriving at . At low frequencies, the sound to the far ear is delayed by about 0.8 milliseconds, and the head also acts as a baffle, increasing the sound pressure at the near ear and increasing the sound pressure at the far ear. This causes a decrease in sound pressure. As the left and right difference curves in Figure 1 show, the overall amplitude difference between the sounds in the two ears in this case is
It varies from 0dB to about -15dB at 10KHz. The delay and sound pressure responses to other directions of the head are relatively small amounts but still significant.

It has long been recognized that listeners rely on the cue of the temporal difference between sounds for positioning.
In 1959, "Bell Laboratories Record"
In a November 1959 paper titled "Shared Stereo Sound System," FKBecker
A stereo acoustic matrix using arrival time information to change the apparent sound image position between two loudspeakers is proposed. Although temporal differences in the ear have been studied in detail by D.M.Leakey, resulting in a general localization theory based on phase differences at low frequencies and temporal differences between acoustic envelopes at relatively high frequencies, this The results of the study were published in the Journal of the Acoustical
Society of America” Volume 31, No. 7 (July 1959)
``Some measurements on the effects of intensity and temporal differences between channels in a two-channel acoustic system,'' published in 2013. Although panning effects based on the aforementioned criteria can be used in stereo sound mixing systems, it is clear that such effects can only be idealized for listeners on the line of symmetry between the loudspeakers.

Other researchers have studied the effects of virtual sound image positioning due to amplitude changes between stereo loudspeakers. “Journal of the Acoustical
Society of America” Volume 33, No. 11 (November 1961)
A paper by BBBauer entitled ``Phasor Analysis of Some Stereo Acoustic Phenomena'' in May) provided one of the first means of quantifying such panning. It describes the sine wave law.
Bauer obtained the following relational expression. That is, sinθ _I / sinθ _A = (S _L − S _R ) / (S _L + S _R ) However, θ _I is the azimuth angle of the virtual sound image, and θ _A
is the actual azimuth of the sound source, and S _L and R _S are the signal strengths provided to the left and right loudspeakers, respectively. Figure 2 shows the application of the "sine wave law" in the case of two loudspeakers at an angle of 90° to the listener. Bauer's law is not completely accurate because it only applies to frequencies below 500 Hz and is limited to the use of signals that are in phase. Although the slope of the curve shown in Figure 2 has been questioned by some researchers, most researchers have identified the required 20 dB separation end for a completely separated sound image. ing.

Given that the perceptual requirements for a listener at any position in a room cannot be clearly met, it is no surprise that early practitioners of stereophonic sound characterized the central image problem as a ``hole in the center.'' Not surprising. Most early attempts to solve this problem were to derive the sum signal (L+R) and feed it to a centrally located third loudspeaker. An attempt like this (with a third frontal sound)
Especially Volume 7 of “IRETrans.Audio” 1959 3
As recommended by Klipsch in the paper ``Two-track three-channel stereo reproduction from three microphones'' in the April-April issue, if the gain of the center channel is If it can be increased by 3 dB, it certainly stabilizes the central sound image. However, as shown in Figure 3, this attempt
Bauer's "sine wave law" results in a dramatic reduction in the apparent width of the stereo sound field, with the original 90° width reduced to 45° when the signal levels at all loudspeakers are equal. become. If the center channel gain is reduced by 3 dB, the maximum sound field width increases to 73°, but of course this is at the expense of reduced center image stability.
More recent experiments using four-dimensional matrices often encode the frontal sound image by separating the left and right components of this signal by 90°, perhaps making the sound image itself too large to accept important music or dialogue. In order to give a sense of spaciousness, in this type of display, the front sound image does not move much.

One solution, which appears to be quite satisfactory from the listener's point of view (auditory), is regularly used in movies, where the key lines are usually separated by a separate loudspeaker energizing the central screen loudspeaker. Assigned to the central channel. Although this method requires slightly more complex mixing and recording equipment, it is straightforward in its endeavor and provides satisfactory reproduction of the important signals.
The addition of a new loudspeaker placed between the left and right loudspeakers creates the opportunity to pan separate virtual sound images near the left and right, especially for non-dialogue effects, where rapid movement and separation It seems particularly satisfying for non-target effects to produce a simple pan from left to right. This three-channel method provides a practical solution that allows each theater audience member to experience the sound image in its proper position, and allows for the incorporation of a separate central sound channel in television playback. It suggests something desirable.

Among the various proposals that have been made so far in the 3-channel FM stereo transmission system,
The method described in Halpern US Pat. No. 3,679,832 is illustrative. In this system, three independent sources of stereophonically related acoustic frequencies are summed together to obtain a sum signal.
The sound waves at each frequency are also used for amplitude modulation of each subcarrier signal, which has the same frequency but is shifted by 120° in phase. Using a suppressed carrier double sideband modulation method for each subcarrier, the frequency of the subcarrier signal is high enough to ensure a frequency gap between the lower sideband of the modulated subcarrier signal and the sum signal. Monophonic and two-channel stereo sound
To achieve the required interoperability with FM receivers,
The amplitude of each double sideband suppressed carrier signal is multiplied by the coefficient 2/√3. A conventional low level phase reference pilot signal existing within the frequency gap is used for receiver detection purposes. A second pilot signal of one-third amplitude, which is the third harmonic of this phase reference pilot, is used to achieve compatibility with monophonic or two-channel stereo sound broadcasts and three-channel receivers. The sum signal, three double sideband suppressed carrier signals and two pilot signals are used for transmission at high frequencies.
Frequency modulates the FM carrier.

The composite frequency modulated carrier signal is provided in either a conventional monophonic or two channel stereo sound format, or preferably in a three channel stereo receiver, for receiving and reproducing three channel broadcasts according to each mode of operation. transmitted to one or more good receivers. Compatibility with one or two channel broadcast and three channel stereo sound receivers is achieved through the use of the second pilot signal described above. In the absence of this pilot, the three channel receiver operates in a manner well known in the art to reproduce monophonic or two channel stereo broadcasts. The second pilot signal is used as an indicator for a three-channel broadcast and, when received by a three-channel receiver, acts to switch the receiver to a three-channel stereo sound reception mode. in this way,
A three-channel broadcast can have interoperability with one, two, or three channel receivers, while a three-channel receiver can also be interoperable with one, two, or three channel broadcasts.

This system is relatively complex in the sense that it requires two pilot signals and a phase shift network to ensure a 120° phase relationship between the subcarrier signals, with all three independent source signals Some of this information becomes the output of the two-channel receiver, although it has the disadvantage that it is modulated to enable reproduction of the third channel information.

The main object of the invention is to provide a ternary sound transmission system that is fully compatible with existing monophonic receivers and new television receivers that use only two loudspeakers.

A related object of the present invention is to provide an equivalent system with respect to all characteristics of the left and right channels without significantly impairing or compromising the service and coverage of current monophonic or future biphonic devices. The present invention provides a ternary acoustic transmission system that provides central channel characteristics.

According to the invention, three independent sources of stereoacoustically related acoustic frequency waves with characteristics L (left), R (right) and C (center) form three signals representing the following matrix equation: is matrixed to obtain That is, (1) M=L+1.4C+R (2) S=L-R and (3) T=-1.4C Each of the acoustic frequency waves S and T is used to amplitude modulate each subcarrier signal, and these subcarrier signals The signals are at the same frequency and in phase
It has a 90° deviation. Using suppressed carrier double sideband modulation of each subcarrier, the frequency of the subcarrier signal is high enough to ensure a frequency gap between the M signal and the lower sideband of the modulated subcarrier signal. A conventional low level phase reference pilot signal existing within the aforementioned frequency gap is used at the receiver for detection purposes. The above M
The two sideband suppressed carrier signals and the pilot signal frequency modulate the higher frequency FM carrier for transmission.

This composite frequency modulated carrier signal can be used in conventional monophonic or two-channel stereo format.
or to one or more remote receivers, preferably ternary acoustic receivers constructed in accordance with the present invention. Typically, multiple receivers of each type will receive and reproduce the three signals according to their respective modes of operation.
Traditional monophonic receivers decode only the sum signal (M), while two-channel receivers regenerate the M signal transmitted in both loudspeakers for monophonic reception and for biphonic and ternary acoustic modes. It reproduces conventional stereo sound signals. A playback option is available for a third receiver type with a large screen and three widely spaced loudspeakers. For the reproduction of monophonic transmissions, the sound image must be "off" from its desired central position.
The sum signal M can be used in all three loudspeakers, although at a lower level in the loudspeakers on both sides to avoid this. For biphonic broadcasting, an M signal can be used for the center loudspeaker and conventional left and right signals for the side loudspeakers. Finally, playback of a ternary sound broadcast will result in the display of left, center and right signals by each loudspeaker, with signal T being sent directly to the center loudspeaker and left and right By electrically subtracting the center signal component from the channel,
As a result, it can also be used to provide completely separate performance.

The present invention will be better understood upon reference to the following detailed description in conjunction with the drawings.

Prior to describing the present invention, we briefly introduce the basic principles of existing two-channel stereo systems approved by the FCC, as well as multichannel television sound systems currently under consideration for future broadcast services in the United States. That would be beneficial. In current radio broadcasting systems, stereophonically related signals are summed to
It constitutes a "monophonic channel" consisting of 15000Hz (L + R) signals, but the L and R
represent left and right independent acoustic signals or channels, and as mentioned above, each of the L and R signals can include a 0.7C component. standard monaural FM
It is this combined signal that is reproduced by the receiver, and therefore the descriptive term "monophonic channel" and the use of the letter M in the text refer to this channel. In contrast, the 38KHz subcarrier signal with both sidebands suppressed
S sin ω _s t is added with a pilot of 19 KHz, where S = (LR). The composite modulated signal can be expressed as follows. That is, e _n =M+Ssinω _s t+psin(ω _s t/2) However, ω _s =2π _s and _s = 38KHz, and p is
This is the amplitude of the 19KHz pilot. If we look at the fundamental band spectrum, we will find a monophonic channel M from about 50 Hz to 15 KHz, a pilot at 19 KHz, and a stereo sound channel S sin _{ω st} signal from 23 to 53 KHz. If SCA
(Subsidiary Communication Authorization)
is also being sent, 59.5 to 74.5K
There is an SCA frequency modulation subcarrier band of Hz.

Three multichannel television sound systems are currently under consideration for future broadcast services in the United States. These three systems were described in a July 1982 document titled ``Multichannel Television Acoustics: Selection Criteria for a Single Standard.''
Although described in some detail in the Electronics Industries Association report, for purposes of this text, a stereo subcarrier for two-channel audio programming and a second audio program for another language or other service ( Suffice it to say, the three proposals are for transmitting non-public telemetry or electronic news gathering (ENG) applications. All subcarriers are placed at frequencies that are integer multiples or fractions of the horizontal sync frequency of NTSC television ( _H = 15743 Hz). The system proposed by the Japan Electronics Industry Association uses frequency modulation of a stereo acoustic subcarrier, while the other two proposed by Telesonics and Zenith are respectively used in standard stereo radio broadcasting. A similar double sideband suppressed carrier amplitude modulation is used.

As previously mentioned, in the present system an independent third or ternary acoustic signal T is provided for reproduction by the central loudspeaker, and the central signal components are electronically subtracted from the left and right channels. It is also provided for use in order to obtain sufficient separation performance. For potential positioning of this new ternary acoustic signal T, there are two options in the three proposed multichannel television acoustic systems. All three systems can use the signal T in the SAP channel, with varying fidelity of acoustic performance. Two systems using amplitude modulated stereo sound subcarriers provide different means for the transmission of this T signal, but in each case the new signal T is a stereo sound difference signal S=(L− R)
can be included as quadrature modulated components of the same suppression carrier carrying the . The ternary sound system of the present invention differs only in the frequency of its stereo sound pilot tone, which for present purposes is _H in the Zenith system and 5/4H in the Telesonics system.
It is described in the context of Telesonics and Zenith multichannel television sound systems.

In the ternary sound system of the present invention, for a monophonic channel, one (L-
The other corresponds to the difference signal consisting of the signal (T=-
14.C), two double sideband k _H KHz signals (k is 2.0 or 2.5) with a phase shift of 90° are:
Both are applied with a pilot signal having a frequency of either H or 5/4H (Zenith and Telesonics systems, respectively) as shown in FIG. In accordance with Zenith and Telesonics design specifications, the amplitude of each double-sideband signal is twice the amplitude of the monophonic channel signal;
The pilot signal also has a slightly smaller amplitude.
Therefore, the composite baseband signal of this ternary acoustic system can be written as: That is, e _n =(L+1.4C+R)+psinωt+(L−R) _sin2ωt
+(-1.4C)cos2ωt (Equation 1) However, L, R and C are independent acoustic channels,
ω=2πk _H ( _H =15734KHz and k=2.0 or
2.5), where p is the amplitude of the pilot signal.

The transmitter for generating this composite signal is the fifth
This is shown in the block diagram of the figure. For purposes of brevity, some conventional transmit circuitry (e.g., pre-emphasis circuitry, carrier frequency sources, and carrier frequency modulators) has not been shown and is only briefly discussed in the following description where appropriate. I decided to do it. The three acoustic frequency signals L, C and R obtained from three independent sources (not shown) produce at the output three matrix acoustic signals, e.g. is applied to the input side of a conventional matrix network 10 consisting of a network of summing amplifiers constructed as follows. That is, (1) (L+1.4C+R), (L-R)
and (−1.4C). Monophonic signal M
is given as a -input to the adder 12, and a stereo acoustic difference signal (L-R) and a ternary acoustic signal (-1.4C) are given to the input side of each modulator 14 and 16, but these modulations The output of the amplifier is also sent to adder 12 where it is linearly combined with the monophonic signal.

The subcarrier signal and the pilot signal are obtained from a carrier generator 18, which
clocked and synchronized with the signal _H (television horizontal sync frequency) derived from the video signal to be transmitted with the audio signal, and
Depending on which Telesonics system is used, it is configured to produce a sinusoidal output signal S with a frequency of k _H KHz, where k is 2.0 or 2.5. The carrier generator may include any known device for creating a 90° offset between the subcarrier output signals applied to each modulator, as shown in FIG. Modulators 14 and 16 provide amplitude modulated subcarrier signals (L-R) of the two sideband suppressed carriers.
A suppressed carrier amplitude modulator of known construction operates to amplitude modulate two subcarriers with each acoustic frequency signal to yield sin2ωt and (−1.4C)cos2ωt. These signals are then combined in adder 12 with the monophonic signal M and the sinusoidal pilot signal of frequency K/2 _H obtained from carrier generator 18. The composite signal produced at the output of the adder 12 as shown in Equation 1 above is then applied to an FM exciter of a transmitter (not shown) to provide a high frequency FM exciter for transmission purposes.
The carrier is frequency modulated.

A ternary acoustic receiver according to the invention is shown in the block diagram of FIG.
Some of the components (discriminator and de-emphasis circuitry) are not shown and will be briefly described where appropriate. In addition to reproducing ternary audio broadcasts, the receiver is fully compatible with conventional monophonic and two-channel (biphonic) stereo audio broadcasts in the manner described below. The received FM signal is sent to the RF and
It is amplified in an IF stage (not shown), demodulated in any known FM detection circuit (not shown), and demultiplexed to obtain the acoustic signal contained in the received FM signal.

While receiving a monaural broadcast, the output of the demultiplexer contains a monaural signal M consisting of (L+1.4C+R). This signal is applied as a first input to both adder 22 and subtracter 24;
Its output is added as the first input of adder 26 and adder 28, respectively. When there is no signal applied to the subtracter 24 and the second inputs of adders 22, 26 and 28, a monophonic M signal (i.e. "L+1.4C+R") is present at the output of each of adders 26 and 28. appears, one of which can be selected for reproduction by a suitable switching mechanism (not shown).

For the received 2-channel stereo signal,
The M and S signals are available at the output of the demultiplexer, but as before the M signal is applied to one input of each of adder 22 and subtractor 24;
The S signal (LR) is applied as a second input to adder 22 and is subtracted from signal M in subtractor 24. As a result, the output of adder 22 contains the signal (2L+1.4C), and since there is no signal at the second input of adder 26, the output of adder 26 contains (2L+1.4C).
1.4C) and its amplitude is then attenuated by half to obtain the signal (L+0.7C) for application to the left loudspeaker. Similarly, the subtraction of the difference signal (L-R) from the monophonic signal is the signal (2R
+1.4C) and this signal is likewise not modified by adder 28, so it appears as is at the output of adder 28, and again the amplitude of this signal is attenuated by half and reproduced by the right loudspeaker of the two-channel system. Therefore, a signal (R+0.7C) is generated. All of the above are typical of the operating mode of a conventional two-channel FM receiver.

The received ternary acoustic signal, i.e. the new T signal (-
1.4C), all of the M, S and T signals appear at the output of the demultiplexer 20, and the signals M and S are applied to the adder 22 and subtracter 24 as before. , T signal is divided circuit 3
Added to 0. This circuit 30 passes the signal (-1.4C) to two individual outputs for application to the second input side of each of adders 26 and 28, and varies the amplitude of the T signal to is a known matrix network configured to send to a third output terminal a signal 2C which is sent directly to the central loudspeaker of the ternary sound reproduction system after appropriate attenuation of the ternary sound reproduction system. Linear addition of signals (2L+1.4C) and (-1.4C) in adder 26 produces signal 2L, and similarly addition of signals (2R+1.4C) and (-1.4C) in adder 28 produces separated signal 2R. and thus, after appropriate attenuation of the amplitude, the separated signals L and R are available for application to the left and right loudspeakers, respectively, of the ternary sound reproduction system.

The hierarchy of the aforementioned reception modes is shown in FIG. 7, which shows three types of television receivers corresponding to three different transmission modes;
namely, a television set 30 common today with a single loudspeaker, a biphonic receiver 32 with two loudspeakers for stereophonic reproduction of the television sound, and a large screen display 34 and an outer pair. left and right loudspeakers 36, 38 and a central loudspeaker 4 located in the center and below the projection screen.
A possible future system with 0 and 0 is shown. In the first case, as mentioned above, the monophonic signal M
is played by a single loudspeaker. The two-channel reproduction capability of receiver 32 reproduces the mono signal M in each of its loudspeakers when the transmission is monophonic, and the signal (L+0.7C) in its left loudspeaker for biphonic and ternary acoustic broadcasts. and play the signal (R+0.7C) on the right loudspeaker. Finally, in the case of a receiver with a large screen and three loudspeakers, the audio designer has many choices. In the case of monophonic broadcast playback, the signal M is transmitted at all three loudspeakers, although at a low level at the side loudspeakers 36 and 28, to avoid "shifting" the sound image from its desired central position. It is possible to use. Using such side loudspeakers in out-of-phase conditions as shown slightly increases the sense of realism. In the case of biphonic broadcasting, it is possible to use signal M for the center loudspeaker and traditional left and right signals for the side loudspeakers, but again, the out-of-phase This state slightly suppresses the impression that the stage width is shortened. Finally, in the case of a ternary sound broadcast, separate left and right signals are provided to each of the side loudspeakers, a separate C signal is provided directly to the center loudspeaker, and It provides accurate reproduction of three signals that can be shared with those available in movie sound systems.

The system according to the invention includes an identification signal to enable automatic switching of the receiver to ternary acoustic reception mode. Such a signal may be included within a video signal or an audio fundamental band spectrum. One of at least two possibilities is
A second pilot utilizing the amplitude of one-third of the third harmonic of the main pilot signal as suggested in Halpern, supra, U.S. Pat. No. 3,679,832, without increasing the instantaneous frequency deviation of the FM carrier. By using signals. Alternatively, it may be desirable to use amplitude modulation of the first pilot signal according to the selected fundamental band configuration, the frequency of this pilot subharmonic being well beyond the acquisition range of the receiver's pilot detector, and The resulting sidebands for the pilot should be selected to provide sidebands that are sufficiently low in frequency that they do not fall within the main or stereo sound channel.

From the foregoing, it should be clear that the explicit requirements for satisfactory multichannel sound reproduction in television become desirable in order to widen the range of sound systems currently under consideration for broadcasting services. . Although an unstable central sound image is not a severe handicap in the reproduction of sound without images, it is not particularly true in television, especially with large screen displays and widely spaced loudspeakers. First, such systems require stable central sound, which clearly suggests that new television sound services must follow the cinematic example rather than sound recording or FM radio broadcasting. The ternary sound system according to the invention described herein is rooted in the need to be easily transmitted with little or no sacrifice to the modulation capacity of the station, i.e. the broadcast reach, and which It satisfies the following. This system offers the possibility of minimizing program production and editing costs, since most of the programs on the acoustic track will undoubtedly continue the lines of the central channel. Finally, the hierarchical nature of the present ternary sound system provides broadcasters and manufacturers alike with extraordinary flexibility in the selection of modes of operation.

The present disclosure is merely illustrative of the principles of the invention, and many modifications may be made without departing from the spirit and scope of the invention. For example, although the T signal was described as having a value of -1.4C, this value would require the aforementioned adders 26 and 28 instead of the subtraction circuit to obtain the same result.
It is clear that 1.4C would be sufficient.

[Brief explanation of the drawing]

Figure 1 is a graph showing the effect of a person's head on a single sound wave arriving at a 90° angle from the front of the listener; Figure 2 is a graph showing two loudspeakers at a 90° angle to the listener. FIG. 3 is a graph showing the application of the "sine wave law" in the case of FIG. 4 is a diagram showing the application of the "sine wave law"; FIG. 5 is a simplified block diagram showing a transmitting terminal for generating the composite signal of FIG. 4; FIG. 6 is a simplified block diagram showing a receiving terminal according to the invention; and FIG. 7 is a simplified block diagram showing a receiving terminal according to the invention. FIG. 2 is a schematic diagram showing a hierarchy of reception modes according to the principle of FIG. 10...Matrix circuit network, 12...Adder, 14, 16...Modulator, 18...Carrier generator, 20...Receiver/demultiplexer, 2
2, 26, 28...Adder, 24...Subtractor, 3
0... Television set, 32... Biphonic receiver, 34... Large screen display, 36, 38... Loudspeaker, 40...
...Central loudspeaker.

Claims (1)

[Claims] 1. In a three-way acoustic transmission system, three stereophonically related acoustic frequency waves L, R and C
with two independent sources, each (L+1.4C+
A device that combines the waveforms to obtain three acoustic frequency waves M, S and T consisting of R), (L-R) and (-1.4C) and two subcarriers of the same frequency but 90° out of phase. and apparatus for amplitude modulating each subcarrier with each of said acoustic frequency waves S and T to produce two double sideband suppressed carrier signals, the frequency of said subcarriers being equal to the modulated subcarrier signal and said signal M. is sufficiently high to ensure a frequency gap between the lower sidebands of the subcarrier, the phase reference pilot signal has a frequency that is half the frequency of the subcarrier and is within said frequency gap, and one carrier of the higher frequency. A three-way acoustic system characterized by comprising a device for frequency modulating said frequency carrier with each of said signals for transmission to said remote receiver. 2. A ternary acoustic system as claimed in claim 1, wherein a receiving device operates in response to reception of said high frequency carrier to reproduce said respective acoustic frequency source signals L, R and C. 3. The three-way audio system of claim 2, wherein said receiving device includes a device for reproducing conventional monophonic and two-channel stereo audio broadcasts. 4. Combining three independent stereo acoustically related acoustic frequency source signals L, C and R,
(L+1.4C+R), (L-R) and (-
1.4C) a transmitting device comprising a device for obtaining three acoustic frequency waves M, S and T consisting of 1.4C) and amplitude modulating each of two equal frequency quadrature subcarriers with each of said acoustic frequency signals S and T; apparatus; apparatus for frequency modulating a high frequency carrier with said respective signals for transmission to one or more remote receivers; and apparatus responsive to receiving said frequency modulated carrier; and a receiver operative to reproduce each of the acoustic frequency source signals. 5 said carrier is modulated according to a modulation function: e _n =M+psin(ω _s t/2) +Ssin ω _s t+Tcos ω _s t , where p is the amplitude of the phase reference pilot signal sin(ω _s t/2) , and the relationship ω _s 2π _s exists, where _s is the subcarrier signal
sinω _s t and cosω _s t fundamental frequencies, and each subcarrier signal is a double sideband signal of a suppressed carrier amplitude-modulated by each of the acoustic signals S and T. Three-way sound system as described in section. 6 _s = k _H , where k is a constant and _H is 15734
6. The ternary sound system according to claim 5, wherein the frequency is Hz, that is, the horizontal synchronization frequency in NTSC television. 7. Three-dimensional acoustic system according to claim 6, characterized in that the constant k is selected from the values 2.0 or 2.5. 8. The ternary sound system of claim 7, wherein said receiving device includes a device for selectively reproducing conventional monophonic and two-channel stereo sound broadcasts. 9 The receiving device combines the acoustic signals M and S to obtain an intermediate acoustic signal (2L+
1.4C) and (2R+1.4C), and combining the first and second intermediate acoustic signals, respectively, with the acoustic signal T to obtain the acoustic frequency source signal L; 9. The three-way acoustic system according to claim 8, further comprising third and fourth devices for obtaining R and R.