Abstract:
Sound and the spatial location of the sound relative to a microphone array are sensed and derived respectively and transmitted to a sound reproducing system that uses the sound as a monaural stream and shapes the monaural stream according to channels using time delays, attenuation, reverberation, and filters that represent head-related transfer functions (HRTFs) where each HRTF has coefficients that are functions of spatial location, particularly one or both angles of incidence. This invention in some embodiments provides for acoustical images of a speaker moving relative to the microphone array and in other embodiments provides for adjustments in a listener&#39;s HRTF database derived from sounds from the listener.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to spatial audio systems and in particular relates to systems and methods of producing, adjusting and maintaining natural sounds, e.g., speaking voices, in a telecommunication environment.  
       BACKGROUND  
       [0002]     Computer Telephone Integrated (CTI) audio terminals typically have multiple speakers or a stereo headset. The existence of multiple audio sources, and the flexibility in placing them, particularly in the case of computer audio speakers, creates the means to recreate a proper perspective for the brain to resolve the body&#39;s relationship to an artificial or remote speaking partner. Telephone handsets and hands-free audio conferencing terminals do not take into account the relative position between the one or more speaking persons and their audience. Present devices simulate a single point source of an audio signal that emanates typically from a fixed position, whether it is sensed via compression diaphragm of the handset or the speaker of a teleconferencing system.  
         [0003]     The relationship between this point source to the rest of the listener&#39;s body, specifically, his/her head, ears, shoulders, and chest, is drastically different compared how the relationship will be if the two participants were to speak face to face. The inaccurate portrayal of this relationship creates a pyschoacoustical phenomenon termed “listener&#39;s fatigue,” produced when the brain cannot reconcile the auditory signal to a proper audio source, and over time this incongruity results in varying degrees of psychosomatic discomfort when the brain is confronted with this situation for a period of time.  
         [0004]      FIG. 1  illustrates a system  100  where a listener  126  exchanges audio signals with a remote human speaker  102 . While both listener  126  and human speaker  102  may have similar interposed signal processing devices, only those elements necessary for illustrating the prior are illustrated. The user or listener  126 , perceiving his or her counterpart, the human speaker  102  or source, as a flat sound wall  128  emanating from a left audio speaker  122  and a right audio speaker  124 , for example. The flat sound wall  128  is not a realistic representation of an actual human audio source. In this example, a human speaker  102  is within pickup range of a microphone  104 . The microphone  104  connects to a computer  106  wherein the audio signals are converted into a format compatible with being transmitted to the listener. For transmission via a Public Switched Telephone Network (PSTN) or other circuit switched system, the microphone interface  108  may perform analog anti-aliasing filtering before sending the analog signal to a coder-decoder for sampling, quantizing, and compressing the digital stream to be expanded and converted to analog signals on the receiving end. Alternatively, the digitized audio signals, particularly compressed and encoded voice signals, may be transmitted as data packets over a network such as the Internet. The Voice-over Internet Protocol (VoIP) is an example of such an Internet protocol that may use a Session Initiation Protocol (SIP) to define the VoIP switching fabric. From a communication processing interface like a VoIP interface  110 , the voice data packets leave the human speaker&#39;s computer  106  and travel via the Internet  110  to the listener&#39;s computer  112 . The listener&#39;s communication processing interface like the VoIP interface  114  of the listener&#39;s computer reconstructs the media stream into the monaural signal  117  similar to the signal recorded at the speaker&#39;s microphone  104 . The destination processing  112  applies forms of spatial audio filtering  116  to shape the monaural signal  117  to then be sent to two or more audio speaker drivers  118 . With equalization filtering alone, the pair of audio speakers  122 , 124  are perceived by the listener as being a flat source  128  that is equidistant between the two audio speakers  122 ,  124 . Techniques are available for processing monaural signals to laterally translate the perceived source location  132  to the left or right of center by varying a transport delay between the two channels of a set of headphone, e.g., binaural processing. The left audio speaker  122  and right audio speaker  124  of the example illustrated in  FIG. 1  may be spaced, for computer-based telephony interface layouts, at +5 degrees and −5 degrees respectively from an axis having an origin at the listener and extending to and perpendicular with the audio speaker array. For teleconferencing environments, that spacing may be increased to +30 and −30 degrees. This audio speaker spacing produces crosstalk at the left and right ears of the listener. With transaural processing applied to cancel or substantially reduce crosstalk between audio speakers channels, the perceived audio effect can be enhanced. The perceived effect audio source translation is adjustable by the listener.  
         [0005]     Psychoacoustic characteristics of the sound may be exploited in whole or part to create a perceived change in distance. Psychoacoustic characteristics of the sound of a source increasing in distance from the listener include: quieter due to the extra distance traveled, less high frequency content principally due to air absorption; more reverberant particularly in a reflective environment; less difference between time of direct sound and first floor reflection creating a straight wave front: and attenuated ground reflection. An additional spatial filter effect that follows is to lower the intensity, or volume, attenuate the higher frequencies, and add some forms of reverberation, for example, whereby the listener perceives the audio source increasing in distance from the listener. Again, this perceived effect is adjustable by the listener. Thus, the perceived audio source can be translated to the left for example  132 , translated in added distance  130  or a combination of left translation and added distance  134 . For each ear of the listener, the Head-Related Impulse Response (HRIR) characterizes the impulse response, h(t), from the audio source to the ear drum, that is, the normalized sound pressure that an arbitrary source, x(t), produces at the listener&#39;s ear drum. The Fourier transform of h(t) is called the Head-Related Transfer Function (HRTF). The HRTF captures all of the physical cues to source localization. For a known HRTF for the left ear and the right ear, headphones aid in synthesizing accurate binaural signals from a monaural source. In the application of classical time and frequency domain analysis, the HRTF can be described as a function of four variables, i.e., three space coordinates and frequency. In spherical coordinates where distances are greater than about one meter, the source is said to be in the far or free field, and the HRTF falls off inversely with range. Accordingly, most HRTF measurements are free field measurements. Such a free field HRTF database of filter coefficients essentially reduces the HRTF to a function of azimuth, elevation and frequency. For a readily implementable system, the HRTF matrix of filter coefficients is further reduced to a function of azimuth and frequency.  
         [0006]     For audio frequency, ω, an angle in azimuth, φ, in the horizontal plane, and an angle in the vertical plane, δ, the Fourier transform of the sound pressure measured in the listener&#39;s left ear can be written as P PROBE, LEFT (jω, φ, δ) and the Fourier transform for the free field, independent of sound incidence, can be written as P REFERENCE (jω, φ, δ), where j represents the imaginary number, {square root}{square root over (−1)}. Accordingly, the free-field (ff) head-relative transfer function for the listener&#39;s left ear can be written as 
 
 H   FF, LEFT ( j ω, φ, δ)=[ P   PROBE, LEFT ( j ω, φ, δ)]/[ P   REFERENCE ( j ω, φ, δ)]
 
 The HRTF then accounts for the sound diffraction caused by the listener&#39;s head, torso and, given manner in which measurement data are taken, outer ear effects as well. For example, the left and right HRTF for a particular azimuth and elevation angle of incidence can evidence a 20 dB difference due to interaural effects as well a 600 micro second delay (where the speed of sound, c, is approximately 340 meters/second). 
 
         [0007]     In the case of a listener with headphones, the typically binaural spatial filtering may include an array of HRTFs that when implemented as impulse response filters, are convolved with the monaural signal to produce a perceived effect of hearing a natural audio source, that is one having interacted with the head, torso and outer ear of the listener.  FIG. 2  illustrates the case of audio speakers, particularly an array having a left audio speaker  122  and a right audio speaker  124  where, as part of the listener&#39;s processing interface  112 , the spatial filtering includes the convolution of filters representing HRTFs as well as transaural processing to cancel the crosstalk. HRTF databases, most commonly for a free field plane, are available and are mechanized as filters with tunable or otherwise adjustable coefficients. The listener can select nominal filters for the left and right ear as listener inputs  121 . The HRTF adjustments  216  may be for left and right translation where channel-to-channel delay may be employed, or may be for increased distance where intensity decrease, high frequency attenuation and reverberation may be introduced or may be for enhancing the natural sound of the audio speakers  122 ,  124  where coefficients of the filters representing the HRTF database  214  may be adjusted, or any combination thereof. The resulting filters, amplitudes and delays are convolved with the reconstructed monaural source  117  with the two channels being equalized, and transaurally corrected  212  before the signals are sent to the audio speakers  122 ,  124 .  
         [0008]      FIG. 3  illustrates a monaural microphone and an example of its spherical coordinate system  300 . From a first reference axis  302 , x, one subtends an azimuth angle  304 , φ, one next subtends an elevation angle  306 , δ. Along this directional vector, the audio source  102  lies a distance, ρ, from the microphone origin  301 , O. Other microphones have left and right microphones integral to a single device, i.e., coincident, providing directionality principally from the pressure differences.  FIG. 4  illustrates a coincident microphone  402  having two principal sensing elements in a horizontal plane  400 . In the horizontal plane, the audio source  102  subtends an azimuth angle  304 , φ, from the reference axis  302 , x, and lies a distance  407 , ρ 0 , from coincident microphone  402 . By differencing the pressure sensed by the two elements for example, the azimuth angle  304 , φ, can be measured.  
         [0009]      FIG. 5  illustrates an example of a two-dimensional microphone array that has microphones in an array  502  distributed linearly, each at an equal distance, d  504 , from one another. For an azimuthal angle of incidence  304 , φ from an audio source  102  distant enough from the microphone array  502  to produce a substantially linear wave front  506 , the wave front  506  time of arrival delay between each microphone is characterized as an inverse z-transform: 
   z   −1   =e   −(jdω/c)costφ   
         [0010]     The frequency response for an array of n such equally spaced microphones is expressed as:  
         H   ⁡     (     j   ⁢           ⁢   ω     )       =       ∑     n   =   0       n   -   1       ⁢           ⁢       a   n     ⁢     ⅇ         -     j   ⁡     (     ω   /   c     )         ⁢   nd   ⁢           ⁢   cos   ⁢           ⁢   ϕ     ⁢                       
 
         [0011]     Because the response functions as a spatial filter, a n  may be adjusted and/or shaped with finite impulse response filtering to steer the array to an angle φ 0  by inputting a time delay.  
         [0012]     With the speed of sound, c, a nominal time delay, t 0 , is set with 
 
 t   0   ≧nd/c  
 
 a   n   =e   jωtt     0     e   +j(ω/c)ndcosφ     0    
 
         [0013]     With the adjustment of a n  within the effective steerable array spatial filter, the 2D array of microphones are steerable to φ 0 . In addition, conditioning the output of each microphone with a finite impulse response filer, the n−1 nulls are available to be placed at n−1 frequencies to notch out and otherwise mitigate discrete, undesired, noise sources.  
         [0014]     The steerable array may employ passive sweeps, or infrared optics to augment source locations.  
         [0015]     Stereophonic microphones are separated by distances that often precluding steerability, but providing time delay information nonetheless. For example, with two coincident microphones separated by a known distance, d 1,2 , as illustrated in  FIG. 6 , the angle incidence to each, φ 1    632  and φ 2    630  is measured from which both ρ 1    606  and ρ 2    608  may be determined as well as the distance, s 1    614 , from the array. For example, applying the Law of Sines: 
 
ρ 1   =[d   1,2  sin φ 1 ]/[sin(π−φ 1 −φ 2 )]; 
 
ρ 2   =[d   1,2  sin φ 2 ]/[sin(π−φ 1 −φ 2 )]; and 
 
 s   1 =ρ 1  sin φ 2 =ρ 2  sin φ 1 . 
 
         [0016]     Where omnidirectional or coincident microphones  402  may provide inadequate resolution of their respective angles of incident, a steerable array of microphones  602  can be exchanged for each to enhance coincident microphones resolution. Also illustrated in  FIG. 6  is the arrangement where an audio source  102  is directly aligned with one microphone position. In such an arrangement, any other microphone positions along a 2D array line will sense the audio source signals with delay relative to the first microphone position. This delay and known microphone positions are used to resolve the distance, s 2    612 , which should be substantially the same as ρ 3    610 , of the audio source  102  from the array  602  and can be used to refine the angle of incidence, φ 1    632  and φ 2    630 , for those microphones not directly in line, with the audio source  102 .  
       SUMMARY  
       [0017]     The present invention in its several embodiments includes a method of and system for processing sound data received at a microphone. The method includes the steps of: receiving a transmission having sound data and an audio source spatial data set relative to the microphone; using a sound conditioning filter database having filters characterized by a stored set of coefficients wherein each stored set of filter coefficients is a function of at least one element of the audio source spatial data set, to determine two or more stored sets of coefficients proximate to the at least one element of the audio source spatial data set; interpolating between the determined two or more stored sets of coefficients; convolving the sound data with a shaping filter having the interpolated filter coefficients; and then transmitting the resulting signal to a sound-producing device. A preferred embodiment accommodates a spatial data set having a first angle of incidence relative to the microphone, a second angle of incidence relative to the microphone substantially orthogonal to the first angle of incidence, or a distance setting relative to the microphone, or any combination thereof. A second embodiment of the method of for processing sound data received at a microphone includes steps of: transmitting sound waves toward a subject having a torso and a head via an audio speaker array; receiving the reflected sound waves via a microphone array; processing the received sound waves to determine time-relative changes in subject head orientation and subject torso orientation; translating the determined time-relative changes in subject orientation into changes in an audio source spatial data set using a sound conditioning filter database having filters characterized by a stored set of coefficients wherein each stored set of filter coefficients is a function of at least one element of the audio source spatial data set, to determine two or more stored sets of coefficients proximate to the at least one element of the audio source spatial data set; interpolating between the determined two or more stored sets of coefficients; convolving the sound data with a shaping filter having the interpolated filter coefficients; and transmitting the resulting signal to a sound-producing device. Example sound-producing devices that support effective three dimensional (3D) audio imaging includes headphones and audio speaker arrays.  
         [0018]     The several system embodiments of the present invention for spatial audio source tracking and representation include one or more microphones; a microphone processing interface for providing a sound data stream and an audio source spatial data set; a processor for modifying spatial filters based on the audio source spatial data set and for shaping the sound data stream with modified spatial filters; and a sound-producing array, e.g., headphones or an array of audio speakers. As with the method embodiments, the spatial data set include an audio source distance setting relative to the one or more microphones and a first audio source angle of incidence relative to the one or more microphones either separately or in combination and may include a second audio source angle of incidence relative to the one or more microphones, the second audio source angle of incidence being substantially orthogonal to the first audio source angle of incidence. In some embodiments, the system also includes a first communication processing interface for encapsulating the sound data and an audio source spatial data set relative to the one or more microphones into packets; and transmitting via a network the packets; and a second communication processing interface for receiving the packets and de-encapsulating sound data and the audio source spatial data set. In some embodiments, the system also includes a first communication processing interface for encoding the sound data and an audio source spatial data set relative to the one or more microphones into telephone signals; and transmitting via a circuit switched network; and a second communication processing interface for receiving the telephone signal and de-encoding the sound data and the audio source spatial data set. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, and in which:  
         [0020]      FIG. 1  illustrates a speaker-listener session of the prior art;  
         [0021]      FIG. 2  illustrates the incorporation of HRTFs of the prior art;  
         [0022]      FIG. 3  illustrates a microphone-centered spherical reference frame of the prior art;  
         [0023]      FIG. 4  illustrates a microphone-centered polar reference frame of the prior art;  
         [0024]      FIG. 5  illustrates a steerable microphone array of the prior art;  
         [0025]      FIG. 6  illustrates a coincident microphone array for determining relative angle of incidence and relative distance of the present invention of the prior art;  
         [0026]      FIG. 7  illustrates a speaker-listener session embodiment of the present invention;  
         [0027]      FIG. 8  illustrates a functional block diagram of an embodiment of the present invention;  
         [0028]      FIG. 9  illustrates a speaker-listener session embodiment of the present invention;  
         [0029]      FIG. 10  illustrates a functional system block diagram of an embodiment of the present invention;  
         [0030]      FIG. 11  illustrates a functional block diagram of an embodiment of the present invention;  
         [0031]      FIG. 12  illustrates a tuning embodiment of the present invention; and  
         [0032]      FIG. 13  illustrates a tuning embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0033]      FIG. 7  illustrates voice data transmission from a human speaker  102  to a human listener  126  via a first voice processing device  106  and a second voice-processing device  112  operably connected by a network such as the Internet  110 . In this example, a coincident microphone  402  captures the voice of the human speaker  102 . A steerable array of microphones  502  or a distributed array  602  of coincident microphones  402  or omnidirectional microphones are alternatives that may be preferred for teleconferencing. The microphone interface  108  may include filters necessary to shape the audio signals prior to digitization to minimizing aliasing effects, for example. The microphone interface  108  may include sampling and quantizing the signal to produce a digital stream. The microphone interface  108  may also include digital signal processing for deriving an angle of incidence of the audio source  102  in a measurable plane and may include nulling or notching filters to eliminate noise sources directionally.  
         [0034]     Conceptually, the voice data is transmitted via a data plane. In implementation, the captured voice for example is, in the preferred embodiment, converted into a format acceptable for transmission over the Internet such a VoIP thereby encapsulating the voice data with destination information for example. The second voice-processing device  112  de-encapsulates the voice data from the VoIP protocol  114  into a monaural digital signal  117 . The monaural signal  117  is convolved with spatial audio filtering  116 , converted via speaker drivers  118  to drive two channels in this example each having an audio speakers  122 ,  124 . The listener may have indicated  121  selections, via an interface  120  for the spatial audio filtering to draw from a bank of HRTFs that are either close to the listener in acoustical effect or tuned for the listener. In the preferred operation, the resulting effect is an audio source for the listener that is more natural and in this example, the audio “image” may be centered between the two audio speakers, moved left or right of center by the listener and given frequency response shaping, reverberation and amplitude reductions that may produce an effect of a more distant source. While the HRTF has in the past been described and analyzed according to classical time and frequency domain analysis, it is important to note that the same relationships can be alternatively modeled in the wavelet domain, i.e., instead of describing the model as a function of time, space, or frequency; the same model can be described as a function of basis functions of the one or more of the same variables. This technique, as well as other modern mathematical techniques, such as fractal analysis, a modeling technique based on self-similarity of multivariable functions, may be applied in some embodiments with intent of achieving greater processing and storage efficiencies with greater accuracy than that the classical methodologies.  
         [0035]     In an embodiment of the present invention illustrated in  FIG. 7 , the microphone interface  708  in addition to other signal processing functions, derives an angle of incidence, φ, for the voice of the human speaker  102  preferably relative to the microphone  402  or center of the microphone array  502 ,  602 , for example. Conceptually, this angle of incidence may be communicated on the signal plane. In a preferred implementation, this derived angle incidence, φ, as source-to-microphone relative spatial data  711  is encapsulated along with the voice data  709  with an extended VoIP  710 , accommodating this data, and the data is transmitted as packets  140 ,  150  via a network  110  to a second VoIP processing device  112  enabled to de-encapsulate the extended VoIP data packets at the communication processing interface  714  having angle of incidence, φ, data into a reconstructed monaural signal  117  and the reconstructed source-to-microphone relative spatial data  717 . The spatial filtering of the second VoIP processing device  112  includes the angle of incidence information by interpolating  716  the selected HRTFs to account for an angle of incidence if not already overridden by the listener via listener inputs  121  at the listener interface  120 . In this example, the human speaker  102  is left of center of a microphone assembly  402  or array  502 ,  602 . With the listener  126  having set the source preference to be that the human speaker acoustical image is nominally facing the listener when the listener is facing the audio speaker array  122 ,  124 , then the resulting “imaged” audio source  728  is perceived to be right of center of the audio speaker array  122 ,  124 . In addition, the listener may choose to add depth cues to push off the perceived distance of the translated human speaker  730  to be aft to the audio speaker array. Alternatively, the listener  126  may select to ignore the angle of incidence information in the processing of his spatial filtering of the monaural signals, leaving the “imaged” source to be in the center  128  of the speaker array  122 ,  124 . The user may add distance effects  130  if he so desires.  
         [0036]     As illustrated in  FIG. 8 , the first transmitted angle of incidence, the second transmitted angle of incidence substantially orthogonal to the first transmitted angle of incidence, or a relative distance setting or any combination  717  is used to drive the interpolation  804  of the HRTF database to a solution of filter coefficients between previously quantified incident angles, i.e., those having filter coefficient arrays based on acoustical measurements, so that the convolution includes the spatial filters adjusted for one or both of the transmitted incidence angles. In embodiments having planar implementations, the HRTFs may be a function of frequency and azimuth angle. In a horizontal plane HRTF interpolation example, the interpolation can be a linear interpolation of the HRTF coefficients for the stored azimuth angles of incidence that bound the derived azimuth angle of incidence. While the above example is illustrated in a horizontal plane, the invention is readily extended to a three-dimensional array where the microphone array and audio speaker array is in a plane rather than linear. In the three-dimensional implementation, the HRTFs may be a function of frequency, azimuth and elevations angles of incidence where the range is removed in free field implementations. In a horizontal and vertical HRTF interpolation example, the interpolation can be a linear interpolation of the HRTF coefficients for the stored azimuth and elevation angles of incidence pairs that bound the derived azimuth angle of incidence and the derived elevation angle. Conceptually, this is interpolating to a point within a parallelogram region defined by the stored coefficients as functions of pairs of azimuth and elevation angles of incidence. Higher order and nonlinear interpolations may be applied where appropriate to properly scale the perceived effect. Where interpolation is inadequate to supply the shaping sought for the acoustical “image” for all expected angles of incidence, then increasing the resolution of the HRTF database may be required.  
         [0037]     In  FIG. 9 , the speaking human  102  moves from a first location to a second location during a session where the distance relative to the microphone  402  or microphone array  502 ,  602  is characterized as a vector  902  having time differences in measured angles of incidence and differences in perceived distance settings. The microphone interface processing  706  of the microphones  402  or microphone array  502 ,  602  in this example for the first location may yield an initial angle of incidence of sufficient quality to be included along with the voice data in data packets and transmitted over a network. The listener interface processor  112  processes  716  the angle of incidence and places the perceived audio source to the right of center of the two audio speakers  728 . This is an automatic nominal setting. The listener can override this effect and may adjust the filters to induce a distancing effect  730  for a listener-selected nominal position of the acoustical “image.” The new position of the human speaker is derived from the microphone processing  708  and via the VoIP communication processing interface  710 , whereby the new angle of incidence is transmitted to effect, in the signal processing  716 , the interpolation  804  in the signal processing  716  of the coefficients of the HRTFs. In this example, the microphone processing also derives a relative change in the distance of the human speaker  102  relative to a reference point of the microphones  402  or microphone array  502 ,  602 . As with the derived angle of incidence, the derived relative distance may be included as relative spatial data  711  along with the voice data  709  in data packets preferably the VoIP  710  and transmitted over a network  110 . The listener interface processing  112  may then account for the change in angle of incidence  910  from a nominal derived position  728  or may then account for the change in derived relative distance  730 , or account for both  912 . If the listener set a perceived distance  914  or angle or both for the human speaker, then the listener interface processing may account for the change in angle of incidence  920 , change in distance  916 , or both  918 .  
         [0038]      FIG. 10  illustrates an example of an embodiment of the system in one direction of transmission with the understanding that the bi-directional transmission is intended as well with each participant in the voice exchange having the necessary devices and functionality. The microphones or microphone array  1010  is connected with the computer  106  of the human speaker  102 . The microphone signal processing  708  may include analog filters to mitigate aliasing for example and digital filters for setting nulls or notches and for reducing cross-talk for example. If available, the microphone signal processing  708  determines one or both of the angles of incidence and the nominal distance setting of the human speaker  102  relative to the microphone array  1010 , i.e., the voice origin data  711 . The determined relative angle of incidence and relative distance settings are prepared  1012  to be added to packets according to the VoIP and then the voice data  109  are encapsulated along with the voice origin data  711  according to the enhanced VoIP communication processing interface  1014 . With a session established  1018 ,  1019 , the voice and voice origin data are sent to the listener via the Internet  110 . The computer of the listener  112  receives the data packets  150  and de-encapsulates the voice data packets according to the enhanced VoIP communication processing interface  1016 . The voice data provides the monaural signal  117  and the voice origin data  717  may be used, depending upon the settings  1040  input by the listener  126  via the HR filter interface  120 , in the HRTF interpolation  804  of spatial filter coefficients  214  for the conditioning  1020  of the monaural signals  117 . Also illustrated is a pathway via the listener microphone or microphone array  1030  whereby the listener  126  may, in some embodiments, effect by his voice characteristics  1031 , changes in the interpolation by the microphone or microphone array processing  1008  determining changes the listener’ state  1042 , particularly changes in the listener&#39;s relative angle of incidence to, and changes in the listener&#39;s relative distance from, the microphone or microphone array. This same pathway may be exploited passively in some embodiments to process acoustical waves originally emanating from the acoustical speaker array  1032  and diffusing  1034  from the listener&#39;s body and body parts particularly including the head and torso.  
         [0039]      FIG. 11  illustrates in an expanded view the functional block diagram of the passive pathway process where acoustical waves are reflected  1034  by the listener&#39;s head or torso, or both  1102 , and registered by the listener&#39;s microphone or microphone array  1030 . The frequency content of the acoustical waves are preferably selected to provide the most probative effect of the changes in the listener&#39;s orientation where interpolation may readily effect improvements and corrections to the perceived source. Filters downstream from the microphone or microphone array may be employed to eliminate or otherwise ameliorate unwanted sound sources proximate to the listener. The corrective potential of this passive path is enhanced with additional audio speakers, with additional microphones and with an anechoic environment.  
         [0040]      FIG. 12  illustrates an example array of microphones and an example array of acoustical speakers where the listener  126  originally sets  120 ,  121  the HR filters to a desirable acoustical “image” of the human speaker source. The listener moves away from the front microphone and turns to the place head and torso at an angle relative to the front line of audio speakers  1202 . To the extent these changes in listener orientation are discernable by the microphones and microphone signal processing, there is then an automatic adjustment, via the interpolation of HRTF bank, with the resulting acoustical image being corrected for the listener&#39;s change in orientation. The acoustical measurements may also be augmented with passive optical sensing and by manual adjustments of the listener.  FIG. 13  illustrates, together with  FIG. 12 , a translation only example of exploiting the listener microphone or microphone array  1030  pathway where the acoustical speaker array includes, for example, left and right audio speakers  122 ,  124 , and additional left and right audio speakers  1222 ,  1224  that are responsive to the relative changes in the listener&#39;s relative translational position and rotational position  1202 . If done actively, the microphone processing  1008  is principally dependent upon the voice of the listener  126 . If done passively, the process is similar to the passive process as described and illustrated in  FIG. 12 .  
         [0041]     Where headphones are used by the listener, true binaural effect achieved without the need for the much transaural processing, if any, of the audio speaker embodiments. But, preferably head-tracking is employed to accommodate the listener rotation in the interpolation process to “stabilize” the perceived location of the audio source.  
         [0042]     While the above examples have been with data packets typical of Internet-based communications, the invention in other embodiments is readily implementable via encoding on switched circuits, for example in a Integrated Services Digital Network (ISDN) preferably with users having computer telephony interfaces.  
         [0043]     The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself.  
         [0044]     Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention and its several embodiments disclosed herein. Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims.