Abstract:
Input sound signals are accepted for presentation to a plurality of speakers where the number of physically present speakers is less than the number of input sound signals. The accepted signals are expanded and summed in a manner such that a listener perceives sounds as coming from the same number of speakers as there are input signals while having less speakers actually operational. In one embodiment there is shown a five input system having only two speakers. The system is functional when the inputs are stereo or monaural and when there are all five speakers available.

Description:
RELATED APPLICATIONS 
     Reference is hereby made to commonly assigned and U.S. patent application METHOD AND SYSTEM FOR SOUND EXPANSION, Ser. No. 08/858,594, now issued as U.S. Pat. No. 5,974,153 filed concurrently herewith, and U.S. patent application STEREO ENHANCEMENT SYSTEM INCLUDING SOUND LOCALIZATION FILTERS Ser. No. 08/511,788, filed Aug. 7, 1995, now issued as U.S. Pat. No. 5,774,556 which applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates to a sound enhancing system and more particularly to a system and method for providing full sound image coverage when a listener has less than the full compliment of speakers required to hear all of the available sound. 
     BACKGROUND OF THE INVENTION 
     There are sound systems available which provide a listener with a full sound experience such that the reproduced sound appears to come to the listener as though it were being played “live” in the presence of the listener. 
     The DOLBY (a trademark of Dolby Labs) surround systems are typical of such systems where a listener can enjoy a full range of sound spread out in a three dimensional pattern around the listener. One major drawback to such systems is that they require more than the traditional two (left and right) speakers. Typically, these systems require at least three (the third being a center speaker for speech and other “centered” sounds) and usually also require two rear speakers. For maximum enjoyment at least one sub-woofer is also required so that the listener can hear and perhaps even feel sounds in the range from 100 Hz and below. In addition, most existing surround systems provide the same sound to both rear speakers. An example of a system in which the rear speakers have the same sound signals is Dolby ProLogic. 
     New systems are coming on the market whereby an improvement has been made in that the rear speakers actually receive different sound signals thereby creating a left and right effect to the rear of the listener. An example of a prior art system in which the rear speakers have different sound signals is Dolby Digital (AC3). 
     The above-described systems assume a very import parameter that simply is not true in most situations. The assumption is that listeners of the sound system will have the five (or more) speakers necessary to take advantage of the full range of the sound systems. Most people simply can not afford to, or choose not to, install in their listening area the number (and quality) of speakers necessary for enjoyment of these full sound systems. Also, most people have more than one location from which they wish to listen to music, the TV, etc., and the need for five (or more) speakers limits their listening options considerably. 
     Furthermore, computer enthusiasts are precluded from taking advantage of the surround sound systems described above where use of more than two speakers is awkward. 
     Accordingly, a need exists in the art for a system which can accept the five sound signal inputs (left front, right front, center front, left rear and right rear) for a surround sound system and to convert those signal inputs for presentation to left and right front speakers while still maintaining the full sound experience for the listener. 
     A further need exists in the art for such a system in which the sound signal inputs for the rear speakers can be either the same or different for each speaker. 
     SUMMARY OF THE INVENTION 
     These and other objects and features of our invention are achieved by a system and method whereby in a first embodiment the five sound signal inputs from a full sound system (left front, right front, center, left rear, right rear) are converted to sound signals for presentation to left and right front speakers while preserving for the listener the perception that the sound is coming from fully around the listener. The system is designed such that speech and other front center speaker sounds still are perceived as coming from the center front while sounds which would be directed to the left and right rear speakers appear to the listener as coming from the same area as the “missing” rear speakers. 
     In an alternate embodiment, we have designed a system and method which will accept five sound signal inputs where the rear sound signals can be identical for both rear speakers or can be different for the two rear speakers. 
     In a second alternate embodiment, we have designed a system and method which will accept the five sound signal inputs and expand the sound from the front and rear pairs of speakers so that the sound appears to a listener to be coming from locations beyond the physical boundaries of the rive speakers. 
     The embodiments discussed above take advantage of sound expansion techniques known in the art and on techniques based on copending patent application entitled METHOD AND SYSTEM FOR SOUND EXPANSION. The prior art techniques for sound positioning are disclosed in U.S. Pat. Nos. 5,105,462 and 5,208,860 issued to Lowe et al. on Apr. 14, 1992, and May 4, 1993, respectively, which are hereby incorporated by reference herein, and which are illustrations of systems for positioning sound images at any desired location around a listener. The Lowe patents take a monaural sound image input and position that sound image at a selected location. The systems discussed in the above-identified patents is herein referred to as the Q1 system. 
     Techniques for stereo expansion are disclosed in U.S. Pat. No. 5,440,638 issued to Lowe et al. on Aug. 8, 1995 and incorporated by reference herein. The system discussed in the above identified patent is herein referred to as the QX system. 
     Thus, it is one technical advantage of our system and method that a five input sound signal system can be processed in a manner that will allow the sound to be expanded so that it will appear to a listener as though it emanates from five speakers while only two speakers are used. 
     It is a further technical advantage that the system will operate properly in situations where the sound signal inputs which would be directed to the two rear speakers have the same content and when they have different content. 
     It is a still further technical advantage of our system that it can be used in situations where the listener has five speakers placed around a listening area or when the listener has only two speakers and the sound input for the rear speakers is monaural or stereo. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
     FIGS. 1A,  1 B and  1 C show embodiments of our invention for operation where the rear speaker inputs are different, together with a pictorial of the speaker placement and a diagram of the enhanced sound image as perceived by a listener; 
     FIGS. 2A,  2 B and  2 C show other embodiments of our invention where the rear speaker inputs are the same, together with a pictorial of the speaker placement and a diagram of the enhanced sound image as perceived by a listener; 
     FIGS. 3A,  3 B and  3 C show still other embodiments of our invention for providing enhanced sound imaging for use in situations where the listener has five speakers and the sound signals for the rear speaker are monaural, together with a pictorial of the speaker placement and a diagram of the enhanced sound images as perceived by a listener; 
     FIGS. 4A,  4 B and  4 C show still other embodiments of our invention for providing enhanced sound imaging for use in situations where the listener has five speakers and the sound signals for the rear speaker are stereo, together with a pictorial of the speaker placement and a diagram of the enhanced sound images as perceived by a listener; and 
     FIG. 5 shows a monaural to stereo conversion circuit, also referred to as a 1 2 3D circuit; 
     FIG. 6 shows an omni to stereo conversion circuit, also referred to as an OMNI 2 3D circuit; 
     FIG. 7 shows the prior art Q1 circuit for producing a left virtual image; and 
     FIGS. 8A and 8B show different versions of the QX circuit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before beginning a detailed discussion of the operation of the various embodiments of our invention it should be noted that the detailed operation of the 1 2 3D, OMNI 2 3D, Q1, single and dual QX circuits, various embodiments of which are shown in FIGS. 5,  6 ,  7 ,  8 A and  8 B, respectively, together with sound enhancement diagrams, can be found in the above-discussed copending patent application and patents. These details will not be repeated herein. 
     Turning now to FIG. 1A, there is shown circuit  10  which is designed to accept five sound signal inputs,  11 ,  12 ,  13 ,  14  and  15  and to combine the rear sound signals with the front sound images to provide an enhanced full dimensional sound output image to listener  100  via only left speaker  16  and right speaker  17 . To date, prior art systems have only been able to combine five input signals to produce the left  16 , right  17  and center  110  sound images as shown in FIG.  1 B. FIG. 1C shows sound images  120 ,  121  and  122  perceived by listener  100  when the sound input signals are processed by circuit  10 . 
     As shown in FIG. 1A left and right front inputs  11  and  12  are provided as respective inputs to QX filter  101 . This QX filter can be either that shown in FIG. 8A or in FIG.  8 B. The left and right outputs of filter  101  then form one input to each of summers  104  and  106 , the other input to each of these summers is the output of attenuator  102 . Attenuator  102  provides an attenuation of center input  13  in the range of −6 dB to zero with −3 dB in a preferred embodiment. The output of summers  104  and  106  are input to the input of summers  105  and  107 , respectively. The other input to each of summers  105  and  107  come from the left and right outputs of expansion circuit  103 . Note, that in situations where a center speaker is available, the input for the center speaker would be presented to the center speaker without attenuation and without being summed with the other speaker signals. 
     Expansion circuit  103  receives rear left and right stereo sound signal inputs  14  and  15  and converts that input to an expanded sound image by using a pair of the circuits shown in FIG. 7 or preferably the circuit shown in FIG.  6 . 
     In another embodiment, expansion circuit  103  may be comprised of either of the circuits shown in FIGS. 8A and 8B if attenuators  1615  and  1619  effectuate an attenuation in the range of approximately −20 dB to approximately −80 dB. 
     The output of summers  105  and  107  form the inputs to speakers  16  and  17  to create the sound enhanced image shown in FIG.  1 C. 
     Turning now to FIG. 2A there is shown circuit  20  which is designed to accept four different sound signal inputs,  11 ,  12 ,  13 , and  21 , where input  21  is a monaural signal for presentation to the rear two speakers of a five-speaker system. Circuit  20  combines the rear sound signal inputs with the front sound signal inputs to provide an enhanced full dimensional sound output image to listener  100  via left speaker  16  and right speaker  17 . To date, prior art systems have only been able to combine five input signals to produce the left  16 , right  17 , and center  210  sound images as shown in FIG.  2 B. FIG. 2C shows sound images  220 ,  221  and  222  perceived by listener  100  when the sound input signals are processed by circuit  20 . 
     As shown in FIG. 2A left and right front inputs  11  and  12  are provided as respective inputs to QX filter  101 . As discussed above, this QX filter can be either that shown in FIG. 8A or in FIG.  8 B. The left and right outputs of filter  101  then form one input to each of summers  104  and  106 , the other input to each of these summers comes from a 3 dB attenuation, via box  102 , of center input  13 . The output of summers  104  and  106  are input to summers  105  and  107 , respectively The other inputs to summers  105  and  107  come from the left and right outputs of expansion circuit  201 . 
     Expansion circuit  201  receives a monaural sound signal  21 , which can come from various sources such as, by way of example, from the rear “surround” outputs of the above-mentioned Dolby ProLogic system. Circuit  201  operates to convert that monaural input to an expanded sound image by using the circuit shown in FIG. 5 or preferably the circuit shown in FIG.  6 . 
     The output of summers  105  and  107  form the inputs to speakers  16  and  17 , respectively, to create the sound enhanced image shown in FIG.  2 C. 
     Turning now to FIG. 3A there is shown circuit  30  which is designed to accept four different sound signal inputs,  11 ,  12 ,  13 , and  21 , where input  21  is a monaural signal for presentation to the rear two speakers of a five-speaker system. Circuit  30  operates in situations where all five speakers are present to provide an enhanced full dimensional sound output image to listener  100  via left speaker  16 , right speaker  17 , center speaker  31 , rear left speaker  32 , and rear right speaker  33 . FIG. 3B illustrates the sound images which are produced by prior art systems in which there are five input sound signals in which the input to the rear speakers is monaural. FIG. 3C shows sound images  320  and  321  perceived by listener  100  when the sound input signals are processed by circuit  30 . 
     As shown in FIG. 3A left and right front inputs  11  and  12  are provided as respective inputs to QX filter  101 . As discussed above, this QX filter can be either that shown in FIG. 8A or in FIG.  8 B. The left and right outputs of filter  101  then form the input to the front left and right speakers  16  and  17  in a five-speaker system. 
     Center input  13  goes directly to center speaker  31  without modification. 
     Expansion circuit  201  receives a monaural sound signal  21 , which can come from various sources such as, by way of example, from the rear “surround” outputs of the above-mentioned Dolby ProLogic sound system. Circuit  201  operates to convert that monaural input to an expanded sound image by using the circuit shown in FIG. 5 or preferably the circuit shown in FIG.  6 . The output of circuit  201  forms the inputs to left rear and right rear speakers  32  and  33  to create the sound enhanced image shown in FIG.  3 C. 
     Turning now to FIG. 4A, there is shown circuit  40  which is designed to accept five different sound signal inputs,  11 ,  12 ,  13 ,  14  and  15 , where inputs  14  and  15  are full stereo inputs for presentation to the rear two speakers  32  and  33  of a five-speaker system. Circuit  40  operates in situations where all five speakers are present to provide an enhanced full dimensional sound output image to listener  100  via left speaker  16 , right speaker  17 , center speaker  31 , left rear speaker  32  and right rear speaker  33 . FIG. 4B illustrates the sound images which are produced by prior art systems in which there are five input sound signals in which the input to the rear speakers is monaural. FIG. 4C shows sound images  420  and  421  perceived by listener  100  when the sound input signals are processed by circuit  40 . 
     As shown in FIG. 4A, left and right front inputs  11  and  12  are provided as respective inputs to QX filter  101 . As discussed above, this QX filter can be either that shown in FIG. 8A or in FIG.  8 B. The left and right outputs of filter  101  then form the input to the front left and right speakers  16  and  17 , respectively, in a five-speaker system. 
     Center input  13  goes directly to center speaker  31  without modification. 
     Expansion circuit  401  receives a stereo input signal  14  and  15 , which can come from various sources such as, by way of example, from the rear speaker signals of the Dolby AC 3  outputs of the above-mentioned Dolby surround sound system. Circuit  401  operates to enhance the stereo rear speaker input to an expanded sound image by using the circuit shown in FIGS. 8A or  8 B or preferably the circuit shown in FIG.  6 . The circuit shown in FIG. 8B can be used as shown or in a modified form with attenuators  1615  and  1619  set to −80 dB or greater. This enables the circuit in FIG. 8B to operate more like a pair of Q1 filters such as those used in the circuit in FIG.  6 . The outputs of circuit  401  form the inputs to left rear and right rear speakers  32  and  33 , respectively, to create the sound enhanced image shown in FIG.  4 C. 
     It should be noted that the essential difference between FIGS. 1A,  2 A and FIGS. 3A,  4 A is the elimination of the summing circuits. The elimination of summing switches may be effectuated by a switch (not shown), thus permitting a single system to handle 2-, 3-, 4- or 5-speaker configurations. The use of subwoofers and other sound enhancement transducers is left out for convenience. The concepts discussed herein could work as well for such components. 
     Also note that as used herein, a two-speaker system is a system having right and left front sound transducers. A three-speaker system includes an additional center front speaker. A five-speaker system adds rear left and right (either stereo or monaural) speakers, while one four-speaker system eliminates the front center speaker. A second four-speaker configuration would have left front, center front, right front and a monaural surround sound speaker in the rear. 
     While the concepts of our invention are discussed in relation to Dolby sound systems they will work on any type of sound system having different front and rear sound input signals. One example of such other systems is the sound system for the DVD audio-visual format. The system can also be used with signals available from different sources such as from a telephone or computer system working in conjunction with a separate sound source. In addition, while a five input set of signals has been shown and discussed the number of input signals is not critical. Also, it is important to note that although it has been assumed that the front speaker input will be stereo the system will work with a monaural front speaker input by substituting the mono to expanded stereo process for the QX filter. 
     The invention can be arranged to work with various combinations of “n” input signals and “x” playback speakers. For example, a single input (“n=1”) can be expanded to stereo (“x=2”) or a set of left, center and right input signals (“n=3”) can be processed to produce an expanded stereo sound field for playback over a pair of stereo speakers (“x=2”). Thus, the invention is very flexible since the number of inputs can be greater than the number of speakers (“n&gt;x”), the number of inputs can be equal to the number of speakers (“n=x”) or the number of inputs can be less than the number of speakers (“n&lt;x”). 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.