Abstract:
In a multi viewer environment where multiple viewers simultaneously experience an audio-visual production, with the visual production occurring on a display surface, a method of increasing the perceived reality of the audio stream of the production, the method comprising the steps of: (a) locating a series of speakers along a periphery of the viewing audience; (b) panning an audio stream between the series of speakers so as to provide for the sense of an audio sound moving along the side of the viewing audience. In preferred embodiments, the output of one of the speakers is delayed relative to another speaker.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the processing of audio for reproduction in a cinema type audience environment. 
   BACKGROUND OF THE INVENTION 
   The utilisation of audio reproduction in a cinema type environment is well known in the art. Examples of popular reproduction formats include the Dolby® Digital format and the DTS format. 
   In the Dolby® Digital format, the cinema track is recorded in a five channel format for reproduction over five speakers. The five channel format includes a front left, front centre and front right channel and a rear left and right channel. The input audio format is designed for reproduction in a cinema type environment where five speakers are placed around an audience. An example of the format is illustrated schematically in  FIG. 1  wherein, in a cinema environment  1 , two audience members  2 A and  2 B are placed with five speakers  3 – 7  being placed around the audience members. The audio track of the movie is then mixed in a five channel format for reproduction in such an environment. 
   The utilisation of a system such as that in  FIG. 1  is thought to provide for enhanced spatialization capabilities of an audio track. The five channel format allows a listener to experience a degree of spatialization due to the “mix” previously encoded. Hence, the audio format of  FIG. 1  has become quite popular. 
   Unfortunately, the arrangement of  FIG. 1  has a number of drawbacks. For example, where an audience member  2 C is located near to one of the speakers then the speaker source  7  is likely to drown out the other speaker sources. As a result, the spatialization effects will be substantially lost. Further, the degree of spatialization that can be provided to the audience is limited as a result of the limitations of the choice provided by a five track arrangement. 
   SUMMARY OF THE INVENTION 
   In accordance with a first aspect of the present invention, there is provided in a multi viewer environment where multiple viewers simultaneously experience an audio-visual production, with the visual production occurring on a display surface, a method of increasing the perceived reality of the audio stream of the production, the method comprising the steps of: (a) locating a series of speakers along a periphery of the viewing audience (b) panning an audio stream between the series of speakers so as to provide for the sense of an audio sound moving along the periphery of the viewing audience. 
   In a preferred embodiment, the series of speakers comprises an array of at least three speakers located along a side of the viewing audience substantially perpendicular to the viewing surface. 
   The step (b) further can comprise the step of panning the same audio stream to a series of speakers whilst simultaneously delaying the audio stream transmitted by each speaker by an amount that varies along with the panning gain. 
   In accordance with a further aspect of the present invention, there is provided in a multi viewer environment where multiple viewers simultaneously experience an audio-visual production, with the visual production occurring on a display surface, a method of increasing the perceived reality of the audio stream of the production, the method comprising the steps of: (a) panning an audio stream between at least two speakers so as to provide for the sense of an audio sound moving along the periphery of the viewing audience (b) whilst panning the audio stream, delaying the output of one of the speakers relative to another speaker. 
   Preferably, the delay of the output from one of the speakers varies along with the panning gain. 
   In accordance with a further aspect of the present invention, there is provided a system for increasing the perceived reality of an audio stream in a multi viewer environment where multiple viewers simultaneously experience an audio-visual production, with the visual production occurring on a display surface, the system comprising: a series of speakers located along a periphery of the viewing audience; panning means for panning a sound trajectory between the speakers so as to simulate the effect of a sound trajectory along the side of the audience. 
   The panning means further preferably can include delay means for delaying the output of one speaker relative to another by an amount that varies with the panning gain. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
       FIG. 1  illustrates schematically a standard cinema speaker arrangement; 
       FIG. 2  illustrates one form of a speaker arrangement in accordance with the method of the present invention; 
       FIG. 3  illustrates the process of panning a sound from one speaker to another so as to simulate an audio trajectory; 
       FIG. 4  is a graph of panning magnitudes in panning a sound from a first speaker to a second speaker; 
       FIG. 5  illustrates the utilization of delay processing in panning signals; 
       FIG. 6  illustrates a portion of a speaker layout in a cinema environment; 
       FIGS. 7 to 9  illustrate, respectively, graphs of amplitude, delay and listener delay components in panning signals in the speaker arrangement of  FIG. 6 ; 
       FIG. 10  illustrates schematically a first signal processing embodiment; and 
       FIG. 11  illustrates schematically a second signal processing embodiment. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   In the preferred embodiment, an alternative audio arrangement is proposed. This alternative arrangement can be as illustrated in  FIG. 2  wherein a series of speakers  10  to  19  are placed down each side of the cinema audience. Additionally, a series of speakers  20  to  25  can optionally be placed at the back of the listening audience. The arrangement of  FIG. 2  allows for a larger degree of spatialization of audio tracks around a listener whilst maintaining a degree of “coherence” in the sound registering at the ears of each audience member. For example, in the arrangement of  FIG. 2 , it is possible to pan the sound along the right hand side speakers  15  to  19  to simulate the effect of, for example, an automobile or helicopter passing down the right hand side edge of the listeners. The panning effect can be enhanced through the utilization of delay in addition to amplitude panning. This is especially the case for the simulation of moving sound sources. 
   For example, turning to  FIG. 3 , three listeners  30 ,  31 ,  32  are seated next to one another. It is desired to simulate a virtual sound  35  which moves from a left speaker  33  to a right speaker  34  at a constant velocity through three intermediate positions  36 ,  37 ,  38 . A normal technique would be to pan the speaker signal between the two speakers  33  and  34 , with the panning being similar to that shown in  FIG. 4  with the relative amplitudes emitted by the left and right speakers at times  36 ,  37  and  38  indicated. However, whilst the panning arrangement of  FIG. 4  may work highly effectively for a person  31  located midway between the two speakers, it is often not the case that this arrangement will be as effective for someone  30  located closer to one of the speakers  33  in providing a spatialisation effect 
   Because of the listener&#39;s proximity to speaker  33 , the output of speaker  33  will sound louder than the output from  34  until later in the panning than for the centrally located listener  31 . Furthermore, the listener  30  will always hear the signal from speaker  33  slightly prior to the signal from speaker  34 . The resultant effect is that the listener  30  will not experience the same sensation as listener  31  that the virtual sound source has moved closer to speaker  34  or at least with the same smooth trajectory. Listener  32  of course experiences the opposite effect that the virtual source starts at the left speaker but too quickly moves to the right speaker rather than with a steady velocity. 
   In the preferred embodiment, not only are the speaker signals panned, but the two signals also undergo a varying delay shifting with respect to one another. One example of delay shifting is as illustrated in  FIG. 5  which depicts the degree of delay between the left and right channels as the sound source moves from the left to the right point. The degree of delay is created so that two sounds projected from each speaker  33 ,  34  can better give the effect of apparent movement of the virtual sound source  35  for all audience members, not just those located on centre. 
   Observing  FIGS. 4 and 5  in combination, at a time when the position of the virtual source is at location  36 , the sound from left speaker  33  is of greater amplitude and lower delay than for right speaker  34 , that is, the signal from speaker  33  is emitted slightly prior to the signal from speaker  34 . At this time, the relative delay between speakers  33 ,  34  may be up to approximately 10 ms. The effect is that each of the listeners  30 ,  31 ,  32  will experience the sound emanating predominantly from speaker  33 . As time progresses and the virtual source moves from left to right as in  FIG. 3 , the delay from speaker  33  increases and the amplitude decreases whilst the delay from speaker  34  decreases and the amplitude increases. At the point  37 , the amplitudes and delays from each of the speakers are equal. The central listener will thus experience the sensation that the virtual source is centrally located between the speakers. The listener  30  however, being situated closer to the speaker  33 , will still experience the sensation that the virtual source  35  is located more left than right whilst the listener  32  will experience the source having already moved through a centre position. As the source  35  progresses through to point  38 , the delays from speakers  33 ,  34  smoothly increase and decrease respectively to the point where the created delay overcomes the inherent delay experienced by listener  30  due to the difference in propagation distances from the speakers  33 , 34  to the listener  30 . Thus listener  30  not only perceives the sound from speaker  34  as louder, but the sound from speaker  34  also arrives simultaneously with or earlier than the sound from speaker  33 . The effect is that listener  30  perceives the sound source to have smoothly moved from left to right. 
   Whilst each listener has received a different apparent audio stream experience due to their different positions relative to the speakers, each listener has nonetheless experienced the sensation of the virtual sound source moving from left to right with a smoother trajectory than if a time delay were not employed. 
   The shaping of the time delay signals can determine to what extent the spatialisation effects of the audio stream are experienced by the listeners and will depend on case specific factors such as speaker separation, the number of speakers in the array, the speed of the virtual sound source, the proximity of the speakers to audience members and the size of the audience. 
   In this manner, an improved sound rendering is provided which allows for an improved listening experience for those located off centre of the arrangement of  FIG. 3 , thereby providing for a more linear response to moving sound sources. The arrangement discussed in respect of  FIG. 3  can be extended to an audience environment and, for example, projecting virtual sounds travelling down the side of the audience. Such an arrangement is illustrated schematically in  FIG. 6  wherein a listener  40  listens to a virtual sound source  41  which travels at a constant velocity down their right hand side so that moments later it is at the point  42 . The sound source is played over speakers A to E. 
   In order to simulate the effect of the moving sound source, the sound is first panned along the speakers as is illustrated in  FIG. 7 , with the signal to each speaker A–E in turn having its amplitude rise to a maximum and then decay. Similarly, as shown in  FIG. 8 , the signal to each speaker is delayed depending on a current location of the virtual sound source. The delay can be in accordance with the discussion as mentioned in respect of  FIG. 3 . In this case, however, it is extended to a multi-speaker arrangement. For the particular listener  40 , the approximate overall delay will be similar to that shown in  FIG. 9  with the sound appearing to move along the right hand side of the speakers. Speaker A which is located furthest from the listener  40  will have the greatest delay while speaker D which is located adjacent the listener will have the least delay. Importantly, a second listener  45  also hears the sound moving along the series of speakers however with a slightly different delay pattern and timing sequence. A number of different systems incorporating the method of the preferred embodiment are possible. 
   In a first arrangement, where the speaker arrangement in a cinema is known, the audio track can be totally pre-rendered with custom sets of speaker feeds being created. 
   In alternative environments, the usual Dolby Digital type speaker feeds might be provided and separate mono channels provided with associated spatial information locating the sound source. The system can then utilise the associated spatial information to render the audio trajectory in the audio output environment. In this embodiment, the spatial information is utilised to pan its corresponding separate mono channel in a sequence across multiple speakers, providing greater spatial resolution than would have been possible if the audio channels had all been pre-mixed into the 5 channel Dolby Digital data (see  FIG. 10 ). 
   In an alternative environment, where a cinema is not equipped with a separate channel of amplification for each side or rear surround speaker, the system may take the separate mono channels and their associated spatial information, and simply mix the mono channels into the standard speaker signals that connect to the standard cinema sound system. This provides backward compatibility so that this new digital sound format may be employed in cinemas that are not equipped to make use of the added channels. 
   In a further improved system with backward compatibility, the original multichannel digital surround audio may already be provided in a form suitable for a standard cinema playback environment, and cinemas with an enhanced playback environment may employ a process whereby the additional separate mono channels and associated spatial information is used to (i) render these separate mono channels to the available speaker system using the panning techniques already described above, and (ii) computing the equivalent panned result of these mono channels in a standard surround configuration, and subtracting said equivalent panned mono channels from the standard surround channels. See  FIG. 11 . 
   In a further example system, the ability to manipulate the input Dolby® Digital signals or the like might also be provided. In this example system, the original Dolby® Digital sound track may be analysed to determine when panning sequences are occurring. The panning sequences can then be subtracted out of the Dolby® Digital signal and the system of the invention can be utilised to pan audio around a cinema environment whilst maintaining the Dolby® Digital environment. In this manner, the preferred embodiment provides for an enhanced audio rendering capability. 
   It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.