SYSTEM FOR PRODUCING AN ARTIFICIAL SOUND ENVIRONMENT

Abstract: A method for simulating an artificial sound environment including sending an ultrasound reference signal to a headphone assembly worn by a user having two ears, the headphone assembly audibly providing at least one audio signal to each of the ears, processing arrival times of the ultrasound reference signal at each ear, so as to measure a phase difference of the signal as perceived by one ear in contrast to the other ear, modulating at least two audio signals, at least one signal for each ear, in accordance with the phase difference, and sending the at least two audio signals via the headphone assembly to each of the ears.

Description: SYSTEM FOR PRODUCING AN ARTIFICIAL SOUND ENVIRONMENT FIELD OF THE INVENTION The present invention relates to the field of headphones for the provision of surround sound in audio reproduction systems. BACKGROUND OF THE INVENTION The capabilities of the simple Hi-Fi stereo system have been extended recently to incorporate the surround sound effects required by home theater systems. Such systems include a large-screen television receiver or video cassette player, four additional speakers, and a surround amplifier. The new system dramatically improves the immersion of the viewer in the sound effects of the movie. A typical home theater system combines video capabilities with advanced audio systems, and it is based on the following major components: 1. A large screen TV receiver or video projector. 2. A laser disk player or a Hi-Fi video cassette player, which is the source of the audio and video signals. The audio track recorded on the film is not an ordinary stereo track. It encrypts additional information about the sound channels. The encryption protocols have evolved over the years. There are three major standards currently in use: a. Dolby ProLogic Surround, in which in addition to the standard left and right channels, a center channel and a rear channel are recorded on the sound track. All channels are analog. b. THX, manufactured by the Lucas film company, in which two separate rear channels are used instead of one. All channels are analog. c. AC-3, the latest development by Dolby lab, in which six channels of music are digitally recorded on the sound track - front right, front left, center, rear right, rear left and subwoofer. The latter is not a full spectrum channel, as only one octave is necessary. 3. A surround amplifier, for extracting the surround channels from the incoming signal. Surround amplifiers are typically based on the Dolby chip. Most amplifiers have DSP (Digital Signal Processor) capabilities, which can modify the sound of a non-surround music source to sound as if it originates from different artificial acoustic environments, such as a concert hall, a theater, a jazz club, etc. 4 Speakers A full surround system requires six different speakers, which must be of high quality to ensure realistic reproduction Their function is as follows a Two mam speakers, which reproduce most of the sound and music effect b One center speaker, located above or below the screen This speaker is dedicated to the actors' voices c Two rear speakers, responsible for the special effects generated by the surround sound system, and for the artificial echo effects generated m the different DSP modes of the surround amplifier d A subwoofer, for reproducmg all low frequency sounds, such as explosions Location of the subwoofer is not critical, as this channel contains little directional information Furthermore, such low frequency sound waves are felt by many parts of the body, and not specifically by the ears The subwoofer is usually placed in the front field The room itself has to be modified to fit the home theater requirements a Since there are six different sound sources m the room, any unwanted echo destroys the sound quality and directionality The room must therefore be covered with acoustically absorbing mateπals, such as carpets and drapes b Acoustical isolating mateπals must be used to avoid disturbing neighbors c Wiπng to the vaπous speakers must be installed in the room, preferably without being a visual eyesore Each of the system elements affects the overall sound quality The most important factor is the room acoustics If the room is big and the walls bare, the echo severely affects the sound The quality of the speakers is also a major element of the system High performance speakers are large and expensive, but essential for good sound Finally, the high power, low distortion amplifiers required for realistic surround sound are expensive These requirements make high quality surround sound systems very expensive both to purchase and to install the home In order to provide h gh quality audio reproduction at low cost and at a personal level of listening, conventional Hi Fi audio systems have for a long time made use of stereo headphones Attempts to utilize headphones to provide surround sound have been made by a number of manufacturers with limited success In order to appreciate the problems involved in achieving an effective implementation of surround sound headphone technology, it is J necessary to understand the physiological effects used by humans m experiencing three dimensional heaπng In order to recognize the direction of a sound, the bram combines information received by the two ears and uses several psycho-acoustic effects to achieve a 3-D sensation of the surrounding world, as follows 1 Phase difference The sound does not reach both ears in the same phase - the ear closer to the sound source hears the sound first By calculating the mmute differences m time of arrival of the sound at the two ears ( <1 msec ), the bram can detect the origin of the sound 2 Level difference The ear closer to the sound source hears a louder sound This information is converted by the bram into directional and range information 3 Head rotation If, for example, the sound source is directly in front of or directly behind the listener, the phase and level difference between the two ears is zero The body executes small, almost unnoticeable head movements in order to identify the origin of a sound Even the smallest movement creates phase differences significant enough for the bram to discern the orientation of the source 4 Doppler pitch difference During head rotation, the sound pitch changes due to the Doppler effect The ear which rotates towards the source hears a slightly higher pitch than the other one The bram is capable of detecting this slight change m pitch, and decoding the source direction from this information 5 Face blockage While rotating the head away from the sound source, at a certain angle, the listener s head causes one ear to move into the "acoustical shade area " ' from the sound source, and the sound level m this ear becomes lower than in the other one The bram uses this effect to locate the sound origin point The first three effects are the most important, but in order to get a perfect illusion, all five have to be reproduced correctly When surround sound is produced by an array of speakers, the sound field produced is very similar to that present m real life, and the human brain is able to make use of all five of the above effects to appreciate the sound The use of headphones, however, effectively eliminates all five of the above effects present in free space propagation, since the sound ongmates from highly localized transducers close to the listener ' s ears As the listener moves or turns his head, the headphones move together with the listener's head The use of simple binaural audio signals do not therefore give a perception of realism, since the sound field moves with the listener's head In order to create a true surround sound effect, the audio signal supplied to the headphones must be coded -m a sophisticated manner m order to simulate all five of the above psycho-acoustic effects as the listener moves while listening to the performance or the film Japanese Unexammed Patent Publication No Sho 42-227 and Japanese Examined Patent Publication No 54-19242 descπbe a surround sound headphone system including a gyro compass or a magnetic needle compass installed on the headphones to measure head movement and to transmit information about head position to a microprocessor This microprocessor modifies the sound track signal according to the head angle, and transmits the modified signal back to the headphones, so that the listener expeπences a surround sound effect Such a system, using a gyroscope mounted in the headphones, has been marketed by the Sony Corporation In USA Patent Nos 5,181,248, 5,452.359 and 5.495,534, a further development of this system is descπbed m which the gyroscope is replaced by an ultrasomc ranging system The angular location of the head is obtained from relative time-of-arπval measurements of an ultrasomc reference signal emitted by a transmitter located m front of the listener, by means of ultrasomc detectors located in the left and πght arms of the headphone set As previously, a microprocessor modifies the sound track signal according to the measured head angle, and transmits the modified signal back to the headphones, so that the listener expeπences a surround sound effect In a further system, developed by Virtual Listemng Systems Inc and descπbed in Stereo Review, Apπl 97, p 38, head movements are ignored completely The surround sound effects from typical audio situations are pre-programmed by algoπthms which provide the phase shifts and volume changes corresponding to vaπous situations This system therefore simulates the surround sound effect by digital processmg means All of the above-mentioned pπor art systems use advanced real-time signal processmg to modify the audio signal information But the speed of available processors is such that they are unable to process the signals effectively, and the subjective results are unsatisfactory for a number of reasons a The systems deal only with the main psycho-acoustic parameters affecting 3-D recognition, namely the first two, or at best three, in the list above They all ignore the other usuallv neglected, yet important effects of Doppler pitch change effect and face blockage b The relatively slow signal sampling rate results in an unnatural "metallic sound" c The currently available real time computing used is not fast enough If the listener turns his head too fast, the computing delay is clearly discerned and disturbing d In both the above mentioned commercially marketed systems, RF is used for communication between the headphones and the processor RF is prone to interference from external sources such as cellular phones, radio transmitters or even a second headphone system nearby Conversely, RF can interfere with other such systems e The processor can only deal with one set of headphones In order for a second listener to enjoy the movie, a complete second system needs to be purchased f Because of the complexity of the systems, they are expensive Therefore, it would be desirable to provide a headphone surround sound system which overcomes the disadvantages of the pπor art technology, m that a It takes into consideration all five physiological aspects of 3-D sound appreciation, to provide perfect surround illusion, b It provides excellent sound quality, without any hesitation or metallic-soundmg effects, c It is useable by several listeners, each listener requiπng only a separate parr of headphones, all being controlled by one processmg unit, d It is reasonably pπced, and e It does not use mterference-prone RF commumcation channels SUMMARY OF THE INVENTION The present invention seeks to provide an improved headphone surround sound system There is thus provided m accordance with a preferred embodiment of the present invention a set of headphones, having earpieces each of which is equipped with an ultrasound detector for picking up the modulated audio signal information on an ultrasound wave transmitted into the listemng area from an ultrasound transmitter, above-mentioned information being deπved from the processmg and modulating of an audio signal, so as to simulate the effects of surround sound The processing and modulating of the audio signal is executed by an array of delay lines and modulators, connected and constructed such as to code the audio signal inputted to the earpieces with a simulation of the physiological effects that would be felt when listemng to the audio signal propagated m free space It is noted that throughout the specification and claims, the term "headphone" encompasses not only headphones, but also any other apparatus for listemng via the ears, such as a virtual reality helmet, for example There is also provided in accordance with another preferred embodiment of the present invention, a wireless headphone assembly including at least one ultrasound receiver for receiving at least one ultrasound signal along at least one ultrasound channel, and at least one transducer for converting each of the at least one ultrasound signal along the at least one ultrasound channel to a human audible signal Additionally, there is provided in accordance with yet another preferred embodiment of the present invention, a wireless headphone assembly wherem said at least one ultrasound receiver includes two ultrasound receivers, each of which receives an ultrasound signal along two ultrasound channels There is further provided in accordance with still another preferred embodiment of the present invention, a wireless headphone assembly wherem the at least one ultrasound receiver includes four ultrasound receivers, each of which receives an ultrasound signal along one ultrasound channel There is also provided m accordance with yet another preferred embodiment of the present invention, a wireless headphone assembly and wherein the at least one transducer includes at least one first transducer which converts the at least one ultrasound signal to at least one modulated electrical signal and at least one second transducer which converts the at least one modulated electrical signal to a human audible signal In addition, there is provided in accordance with another preferred embodiment of the present invention, a wireless headphone assembly and wherem at least one transducer compπses at least one multichannel transducer There is also provided in accordance with yet another preferred embodiment of the present invention, a wireless headphone assembly including at least one band pass filter associated with each ultrasound channel There is further provided m accordance with still another preferred embodiment of the present invention, a wireless headphone assembly including at least one demodulator associated with each ultrasound channel In addition, there is provided m accordance with a further preferred embodiment of the present invention, a wireless headphone assembly and wherem the at least one first transducer operative to convert the at least one ultrasound signal to at least one modulated electπcal signal, includes at least two first transducers, each arranged to be located adjacent to a different ear of a user There is fuπher provided m accordance with yet another preferred embodiment of the present invention, a wireless headphone assembly wherem the at least one second transducer includes at least two transducers, each providing a human audible output to a different ear of a user In addition there is provided in accordance with another preferred embodiment of the present invention, a wireless headphone assembly wherem a human audible signal deπved from ultrasound signals received at each of the at least two ultrasound receivers is supplied to each ear of a user There is also provided m accordance with yet another preferred embodiment of the present invention, a wireless headphone assembly and wherem the at least two ultrasound receivers each receive ultrasound signals along at least two ultrasomc channels, the at least two transducers convert ultrasound signals along at least two human audible channels to human audible signals, and information received along each one of the at least two channels of each of the at least two ultrasound receivers is supplied to each of two different ears of the user along a separate one of the human audible channels There is further provided accordance with still another preferred embodiment of the present invention, a wireless headphone assembly including delay lines operative to simulate the acoustic delay occurπng between the arπval of sound from at least one signal source at different ears of the user In addition, there is provided in accordance with yet another preferred embodiment of the present invention, a headphone system providing a simulated multi-source sound environment including at least one wireless headphone assembly which may be worn by a user and which includes at least one ultrasound receiver for receivmg at least one ultrasound signal along at least one ultrasound channel and at least one transducer for converting each of the at least one ultrasound signal along the at least one ultrasound channel to a human audible signal, and at least one processor receiving a multi-source signal and modulating the sound earner along the plurality of channels m accordance with the multi-source signal, and at least one transmitter for transmitting the modulated sound earner to the pair of headphones along a plurality of channels In addition, there is provided in accordance with yet another preferred embodiment of the present invention, a headphone system wherem the use of ultrasound for transmitting the modulated earner to the at least one headphone is operative to cause a listener using the headphone to expenence the psycho-acoustic effects that he would expeπence if the multi source signals were transmitted m free space as audible sound waves from suitably located sound sources There is further provided in accordance with yet another preferred embodiment of the present invention, a method for simulating an artificial sound environment including converting an audible signal to an ultrasound wave, receivmg the ultrasound wave by means of a wireless headphone assembly, and converting the ultrasound wave to an audible signal by means of the wireless headphone assembly There is also provided in accordance with a preferred embodiment of the present invention a method for simulating an artificial sound environment including sendmg an ultrasound reference signal to a headphone assembly worn by a user having two ears, the headphone assembly audibly providmg at least one audio signal to each of the ears, processmg arπval times of the ultrasound reference signal at each the ear. so as to measure a phase difference of the signal as perceived by one the ear m contrast to the other ear, modulating at least two audio signals, at least one signal for each the ear, m accordance with the phase difference, and sending the at least two audio signals via the headphone assembly to each of the ears In accordance with a preferred embodiment of the present invention the method also includes sending the at least two audio signals and the ultrasound reference signal via an ultrasound earner Further in accordance with a prefened embodiment of the present invention the step of sending the at least two audio signals includes sending the signals to the headphone assembly by wired communication Still further in accordance with a preferred embodiment of the present invention the step of sending the at least two audio signals includes sendmg the signals to the headphone assembly by wireless communication BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed descπption, taken m conjunction with the drawings in which Fig 1 is a pictoπal representation of a pπor art conventional speaker-based surround sound system, showing the component parts and their mutual location, Figs 2A and 2B illustrate how, m the pnor art conventional speaker-based surround sound system, the listener detects the direction from which a sound emanates by discerning the small time difference between receipt of the sound by the ear closer to the oπgm, and by that further from the ongm, Figs 3A and 3B show how, in the pπor art conventional speaker-based surround sound system, the listener detects the direction from which a sound emanates, and by rotating his head towards the sound ongm, equalizes the phase of the sound heard by both ears, Fig 4A and Fig 4B present the timing sequence of the receipt of the sound by the left and πght ears of a listener seated m front of a conventional pπor art surround sound system, and how the timing sequence changes when he rotates his head towards the sound ongm and equalizes the phase of the sound heard by both ears, Fig 5 is a pictoπal representation of a headphone-based sunound sound system constructed and operative in accordance with a prefened embodiment of the present invention, Fig 6 is a block diagram of an encoder unit constructed and connected in accordance with a preferred embodiment of the present invention, showing how the five separate inputs from the sunound sound audio signals are inputted through delay lines and modulators to provide the correct mixture of signals for outputtmg to the ultrasound transmitter, Fig 7 is a schematic block diagram of a pair of headphones constructed and operative in accordance with a prefened embodiment of the present invention, showing the components and their interconnections required to receive, demodulate and convert the ultrasound signals emitted by the system transmitter, to audible signals to be perceived by the listener as smround sound, Figs 8A and 8B illustrate how a sunound sound headphone system constructed and operative m accordance with a prefened embodiment of the present invention simulates the phase difference psycho-acoustic effect in order to enable the listener to detect the direction from which a sound emanates, Figs 9A and 9B show how a sunound sound headphone system constructed and operative in accordance with a prefened embodiment of the present invention simulates how the listener detects the direction from which a sound emanates, and by rotating his head towards the sound ongm, equalizes the phase of the sound heard by both ears, Fig 10A and Fig 10B illustrate the timing sequence of the receipt of the sound by the left and nght ears of a listener using a sunound sound headphone system constructed and operative m accordance with a prefened embodiment of the present invention, and shows how the timing sequence changes when he rotates his head towards his perception of the sound ongm, and equalizes the phase of the sound heard by both his ears. Fig 11 illustrates how listeners seated over extensive areas of a room equipped with a sunound sound headphone system constructed and operative in accordance with a prefened embodiment of the present invention all have the conect spatial illusion of the sunound sound. Fig 12 is a schematic block diagram of a headphone-based sunound sound system constructed and operative m accordance w th another prefened embodiment of the present invention, wherein the ultrasound signal of the embodiments of Figs 5-11 is used as a reference signal and the audio signals are sent by wired or wireless communication to the headphones, and Fig 13 is a schematic block diagram of a headphone-based sunound sound system constructed and operative m accordance with yet another prefened embodiment of the present invention, this system being substantially the same as the system illustrated in Fig 12, except that wherem the system of Fig 12 is a stand-alone system, the system of Fig 13 is suitable for packaging as a printed circuit board m a personal computer DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A prefened embodiment of the present invention is descnbed in the field of surround sound systems However, it is appreciated that the present invention is readily applicable for use in other applications such as virtual reality systems, computer games, simulator systems, Reference is now made to Fig 1 which is a pictonal representation of a pπor an conventional speaker-based surround sound system, as descnbed in the "Background to the Invention", showing the component parts and their mutual location with respect to the listener The parts shown are a TV receiver or video screen 10, an audio signal source 12, such as a laser disk player or video cassette player, the sunound sound amplifier 14, the mam speakers, namely the front left speaker 16 and the front nght 17, the center speaker 18, the rear left speaker 20, and the rear nght speaker 21 In this representation, only the five speakers which provide the directional information are shown The sub-woofer is understood, and its location is not cntical The listener 22 is shown seated at the "sweet spot", the only area in the room where the sunound sound effect is felt rea sticallv Figs 2A and 2B show how a listener 22 seated m front of a pnor art speaker-based sunound sound system is able to detect the direction from which a sound emanates by discerning the small time difference between receipt of the sound by the ear closer to the ongin, and by that further from the ongm In Fig 2A, a sound wave 30 coming from the nght front speaker 17 is shown impinging first on the listener s nght ear 32 In Fig 2B, the sound is shown hitting his left ear 34 a short while later, typicallv 0 3 msec for a signal emanating Figs 3 A and 3B are illustrations of the method by which a listener 22 seated in front of a pnor art speaker-based sunound sound system detects the direction from which a sound emanates, and by rotating his head towards the sound ongm, equalizes the phase of the sound heard by both ears In Fig 3 A. a sound wave 30 commg from the nght front speaker 17 is shown impinging on the listener s ears, with a small time delay between the moment of impingement on the left ear as compared with the nght ear In Fig 3B, the listener 22 has turned his head m the direction of the sound ongm, and is able to detect this direction by mentally discerning when the sound is received by both ears at the same time Fig 4A shows a quantitative depiction of the timing sequences for Figs 2A and 2B, for the arπval of the sound at the left and nght ears of a listener seated in front of a pnor art sunound sound system The honzontal axis represents the time elapsed during the propagation of the sound waves Fig 4B shows the same timing sequences for the situation depicted in Figs 3A and 3B, where the listener turns his head towards the sound source In Fig 4 A, the sound wave is depicted leaving the speaker 17 at time t o and arnving at the listener s nght ear after a time t o -^ DR/V, where V is the velocity of the sound, and DR is the distance from the speaker to the nght ear 32 The sound arnves at his left ear only after a time t 0 + DL V, where DL > DR The listener ' s bra discerns this slight delay to locate the ongm of the sound In Fig 4B, the listener is shown after rotating his head towards the sound ongm The timing sequence shows how the sound wave leaves the speaker 17 at time t t and arnves at both of the listener's ears after a time tA DR/V, which is identical to tι+ DL/V, smce the distance from the speaker to the two ears is equal A pictoπal representation of a sunound sound headphone system, constructed and operative m accordance with a prefened embodiment of the present invention, is shown in Fig 5 It is seen that the five speakers shown in the conventional pnor art system of Fig 1 have been eliminated In their place are three small-size components, which compπse the basic components of the headphone sunound sound system These components are a sunound sound encoder 24. an ultrasound transducer 26, and a set of sunound sound headphones 28 The sunound sound encoder 24 is provided with an input signal from the audio signal source 12 - a laser disk player, a VCR , or any other stereo source The unit can be connected to a sunound sound amplifier 14, such as an external Dolby processor, or it can be fitted with its own internal sunound processor The encoder 24 processes the five conventional separated sunound sound channels The modified signal is then modulated, by AM or FM for example, and amplified to bnng it to a sufficient level for transmission The simulation of different sound sources is made by using four different earner frequencies on one transmitted ultrasound beam Two are used to simulate the front sound sources and two for the rear sources It is appreciated that even though the descnbed embodiment of this invention is constructed and operative to handle signals coded according to the Dolby recording standard it can easily be adapted to any other 3-D sound recording standard The modulated and amplified signal is fed to the ultrasound transducer 26, mounted on top of the TV receiver, and transmitted into the listemng room in the form of coded ultrasound waves containing the sunound sound signals It is appreciated that even though the descnbed embodiment of this invention is constructed and operative to convey all of the audio information by one transmitter, it can easily be adapted to transmit via several transmitters such as one for rear channels and one for front channels The sunound sound headphones 28 worn by the listener contain two special microphones mounted on each ear-piece, which receive the ultrasound signals transmitted from on top of the TV monitor Four decoders convert the signal into audio surround sound, which is then amplified and reproduced by the headphones " speakers Each ear-piece is sensitive to two frequencies - one front and one rear The propagation effects of the above descnbed system are now explained Since ultrasound is a normal sound wave but of super-audible frequency, it propagates through air m exactly the same manner as any other sound wave It is therefore the specific use of an ultrasound reference signal sent from the transmitter to the listener ' s head, which enables the sunound sound effect produced by the present invention to behave exactly like the audio sound produced by a conventional free space sunound sound system (In the embodiment of Fig 5, the ultrasound signal is not only used as the reference signal but also as the earner signal for the audio information In another prefened embodiment of the present invention, descπbed herembelow with reference to Figs 12 and 13, the ultrasound signal acts only as the reference signal and the audio information is transmitted separately by wired or wireless communication ) In particular, all the parameters affecting normal heanng are applicable to ultrasound with respect to the five psycho-acoustic effects mentioned above 1 The velocity of the ultrasound earner generates an accurate phase difference between the listener ' s two ears 2 The level of the ultrasound earner causes the conect transduced sound volume differences between the two ears 3 No special consideration need be given to measuring head movements The ultrasound is affected by head movements exactly like audible sound signals 4 The Doppler effect changes the pitch with head rotation in exactly the same way as if real speakers were being used 5 Due to the location of the ultrasomc receivers on either side of the headphone arms, the face blockage effect is retained A further advantage of the use of ultrasound is that, unlike RF, the environment does not interfere with the transmission, giving nse to a noisy signal, nor does the transmission cause interference to the environment Fig 6 shows a schematic block diagram of the encoder unit This unit modifies the signals from each of the five conventional surround sound input channels 40 - front left, front nght, center, rear left and rear nght - by means of delay lines 42, operative on the signals according to their source channel and their destination channel The resulting signal information is routed into four output channels - front left, front nght, rear left and rear nght - which are, for example, AM or FM modulated 44 onto four different earner frequencies using a built-in local oscillator, and inputted to a mixer 46, whose output 48 is amplified for feeding to the ultrasound transducer The five different input channels are processed and connected in the following manner The center channel signal is fed directly to the C_ and C FR modulators for transmission by the two front channel earners - Cπ . and C FR The front nght channel signal is fed in parallel to two channels - directlv to the C FR channel modulator, and to the C FL modulator via a 0 3 msec delay line (calculated for a sound source located 30° off center) The front left channel, m a manner similar to the nght channel, is fed directly to the C FL channel modulator, and with a 0 3 msec delay to the C F modulator The rear nght channel signal is connected directly to the C RR modulator, and via a 0 3 msec delay line to C The rear left channel signal is connected directly to the C RL modulator, and via a 0 3 msec delay line to C R In order to see how this method of encoding produces effective surround sound, it is necessary to understand how the decoding process is executed m the sunound sound headphones The construction of these headphones is shown m Fig 7 The headphones are based on standard Hi-Fi headphones equipped with additional electronic components, as follows two ultrasound microphones 50 and 52, four filters 53, 54, 55 and 56, four demodulators 51. 58, 59 and 60, a pair of amplifiers 61 and 62 These amplifiers feed the speakers 63 and 64 of the headphones The two ultrasound microphones 50, 52, are located one on each ear-piece, on either side of the earphone bndge 65. and act as receivers for the transmitted ultrasound signals The signals from each of these microphones are filtered and demodulated to extract the two channels, front and rear, associated with each ear The resulting signals are amplified and fed to each ear-piece ' s speaker, which transduce them to human audible signals Each microphone is connected to both ear-pieces as follows The front earner is connected directly to the ear-piece on the side on which the microphone is mounted, and the rear earner to the opposite ear-piece Specifically, for the front channels, the nght microphone transmits C FR to the nght ear and the left microphone transmits C FL to the left ear For the rear channels, the connections are crossed such that the nght microphone transmits C to the left ear and the left microphone transmits C RR to the nght ear Using this crossed-connection, any sound source m any direction can be simulated using only one ultrasomc transmission In particular, rear sound sources are conectly simulated using one transmitter located in the front Figs 8A and 8B illustrate how a sunound sound headphone system constructed and operative m accordance with a prefened embodiment of the present invention simulates the phase difference psycho-acoustic effect, enabling the listener 22 to detect the direction from which a sound seems to emanate In Fig 8 A, two front channel signals C FR and C F are sent out by the transmitter 26, but with a slight time delay between them The C FL signal is delayed by about 0 3 msec companng to C FR Because of the direct pickup and connection m the earphones, the listener 22 hears the sound first in his nght ear 32, and only 0 3 millisecond later, as shown m Fig 8B. m his left ear 34 It seems to the listener as if a virtual speaker 36 is located on his nght side at about 30° Figs 9A and 9B demonstrate how the sunound sound headphone system enables the listener to detect the direction from which a sound emanates by rotating his head towards the sound ongm m order to equalize the phase of the sound heard by both ears The figure nomenclature is the same as in Figs 8A and 8B If the listener rotates his head to the nght, the delay between the signals C F and C FR decrease until his head is turned 30° to the nght At this point, the delay is zero and the listener has the illusion of looking directly towards the ongm of the sound, as illustrated in Fig 9B Figs 10A shows a quantitative depiction of the timmg sequences for Figs 8A and 8B, for the arnval of the sound at the left and nght ears of a listener using a sunound sound headphone system The honzontal axis represents the time elapsed duπng the propagation of the sound signals Fig 10B shows the same timing sequences for the situation depicted in Figs 9A and 9B, where the listener turns his head towards the sound source In Fig 10 A, the front nght signal C FR leaves the transmitter 26, at time t-. and arnves at the listener's nght ear after a time t r - DR/V, where V is the velocity of the sound, and DR is the distance from the transmitter to the nght ear 32 The front left signal C FL leaves the transmitter 26, at time t] and arnves at the listener's left ear after a time ti - DLN Since DR = DL when the listener is looking forward, the sound arnves at his left ear a time t { - ^ later than at his nght ear, and the listener s bram discerns this slight delay to locate the ongm of the sound as if it were to the nght of him at about 30° In Fig 10B. the listener is shown after rotating his head towards the sound ongin m an attempt to localize its direction The timing sequence shows how, even though they were transmitted a time t, - t,. apart, the C FR and C FL signals both seem to arnve at the listener's ears at the same moment, after a time t r - 1 - DR/V, equal to tι+ DL/V, and give the listener the illusion as if they oπgmated from the direction towards which he turned his head, namely his front nght hand side at about 30° The reason for the crossed connection for the rear channels in the headphones is now clear If a real sound source is located m front of the listener, by turning his head to the nght for example, his nght ear moves further from the source, while his left ear moves closer to it If on the other hand, the source is located behind him, the effect is opposite, m that by turning his head to the nght, for example, his nght ear moves closer to the source, while his left ear moves further from it Thus, sources located behind the listener behave as if thev were left-to- nght reversed m companson to those m front of him The headphones implement this effect by crossing over the rear connections as shown in Fig 7 Several listeners 70, 71, 72, are shown m Fig 11, sitting in a room equipped with the headphone sunound sound transmission system 73 So long as they each have a headphone set, they all have the illusion of complete surround sound, as if a "center speaker" were located m the direction of the TV receiver, and four additional speakers located around each of them m perfect locations The front virtual speakers are located 30° left and 30° nght of the TV set, and the rear speakers, 30° rear left and 30° rear nght In this respect, there are A prefened embodiment of the present invention includes a headphone sunound sound system having many advantages companng to pnor art speaker-based sunound sound systems These advantages are summanzed as follows 1 Surround headphones are considerably cheaper, since a There is no need to cover the room with acoustic absorbing and isolating mateπals b The need for expensive, space consuming speakers is eliminated c Expensive high power amplifiers are not needed 2 In most cases, sunound headphones provide the listener with improved sound quality and better immersion, since a The acoustic environment is perfect, since there are no unwanted echoes or external noises b Because of the low power levels involved, headphones have a considerably lower distortion level than speakers in the same quality class c Since headphones are very close to the listener's ear, they require only a low power amplifier to dnve them, and these too have a considerably lower distortion level than high power amplifiers d In standard home theater rooms, only a small listemng area in the middle of the room, called the "sweet point", is optimum for expenencing the sunound sound effect fully Using sunound sound headphones, this area is much more extensive 3 Headphones are more convenient to use. since a Every room is suitable for watching surround sound movies, and there is no need to dedicate a special room to this purpose b There is no need to extensively wire the listemng room c The listener can use high volume sound reproduction without bothenng others Reference is now made to Fig 12 which is a schematic block diagram of a headphone- based sunound sound system constructed and operative in accordance with another prefened embodiment of the present invention In the system of Fig 12, the ultrasound signal of the embodiments of Figs 5-11 is used as a reference signal and the audio signals are sent by wired or wireless communication to the headphones Accordingly, only the audio processmg portion of the system is illustrated and descnbed with reference to Fig 12, the ultrasound reference signal being as descπbed heremabove with reference to Figs 5-11 An analog-to-digital converter 102 receives analog audio signals, such as from 5 x PreAmp Sunound or any other kind of analog stereo input The audio signals contain, for example, the information conespondmg to front nght, front left, center, rear nght, rear left, as descπbed heremabove The signals are then sent for processmg, preferably via a data controller 104, to a signal processor 106 Signal processor 106 may be packaged as an FPGA (Optionally, data controller 104 may receive a digital audio input, such as digital AC-3 input via an AC-3 decoder 114 ) In order to process the signals, ultrasound transducer 26 (Fig 5) sends an ultrasound reference signal to ultrasound microphones 50 and 52 (Fig 7) A head angle calculator 120 processes arnval times of the ultrasound reference signal at each ear, so as to measure a phase difference of the reference signal as perceived by one ear m contrast to the other ear, as descnbed heremabove In this manner, head angle calculator 120 calculates the azimuthal angular movement and elevational angular movement β of the head The angular movements are sent by data controller 104 to signal processor 106 for modulating the audio input in accordance with the phase difference, in order to provide the user with the conectly directed sound, as descnbed heremabove Alternatively, a head sensor 116 may be provided, for example, mounted on surround sound headphones 28 worn by a user, which senses movement of the head of the user For example, head sensor 116 may sense azimuthal angular movement and elevational angular movement of the head, and send the sensed data to head angle calculator 120 via a head sensor interface 118, such as an amplifier An input switch 122 may be provided for selecting and switching between the kind of inputs available, ultrasound, or non-ultrasound The signal processmg may be earned out by any known method, such as, but not necessanly, FIR (finite impulse response) As seen in Fig 12, duπng the course of signal processing, signal processor 106 may cooperate with an input buffer 108 and a memory device 109 Input buffer 108 may be any land of suitable buffer, such as a fast RAM (20 ns, 5K x 16 bit) Signal processor 106 may compnse a decoder, such as a ProLogic Decoder, if it is required to decode the signals Preferably signal processor 106 cooperates with mput buffer 108 m the following way If, for example, an audio mput is coming from 0° with respect to the listener (l e , directly m front of the listener) or if it is desired to artificially mimic an audio input coming from 0°, then signal processor 106 takes the audio input for each ear at the same time from buffer 108 However, if an audio input is coming from 30° with respect to the listener, or if it is desired to artificially mimic an audio input coming from 30°, then signal processor 106 takes the audio input from buffer 108 for one ear, then waits a certain time delay conespondmg to the delay that the listener would in real life sense between both ears, and only then takes the input for the other ear from buffer 108 The processed signals are preferably output to a D-A converter 110 which sends the processed signals to headphones 28 via an LNA 112, or alternatively or additionally to a stereo speaker or subwoofer It is important to point out that the embodiment of Fig 12 is different from the pnor art mentioned above in the background, namely, USA Patent Nos 5,181,248, 5,452,359 and 5,495,534 In the pnor art, the angular location of the head is also obtained from relative time-of-arnval measurements of an ultrasomc reference signal emitted by a transmitter located in front of the listener, by means of ultrasonic detectors located in the left and nght arms of the headphone set However, the pnor art can only measure angular changes in azimuth conespondmg to sideways motion of the head In contrast, the present invention can measure and respond to any kind of angular motion, including elevation and roll and any combination of angular and linear movement of the head The pnor art cannot measure distance between ears of the listener This is a particularly important drawback because not every listener has the same size head and so the sound effects are different for each user In contrast, the present invention does indeed measure the distance between the two ears of the user and modifies the audio input to the two ears accordingly, as descnbed heremabove In addition, the pnor art does not use an input buffer as does the present invention (mput buffer 108) as descnbed heremabove Fig 13 is a schematic block diagram of a headphone-based sunound sound system constructed and operative in accordance with yet another prefened embodiment of the present invention, this system being substantially the same as the system illustrated in Fig 12, except that wherem the system of Fig 12 is a stand-alone system, the system of Fig. 13 is suitable for packaging as a pπnted circuit board m a personal computer It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and descnbed heremabove Rather the scope of the present invention mcludes both combinations and subcombmations of the vanous features descnbed heremabove as well as vanations and further developments thereof which would occur to persons skilled m the art upon reading the foregomg descnption and which are not m the pπor art

Claims: CLAIMS What is claimed is 1 A wireless headphone assembly compπsmg at least one ultrasound receiver for receiving at least one ultrasound signal along at least one ultrasound channel, and at least one transducer for converting each of said at least one ultrasound signal along said at least one ultrasound channel to a human audible signal 2 The wireless headphone assembly according to claim 1 and wherem said at least one ultrasound receiver compnses two ultrasound receivers, each of which receives an ultrasound signal along two ultrasound channels 3 The wireless headphone assembly according to claim 2 and wherem said two ultrasound receivers, called a nght receiver and a left receiver, provide ultrasound signals to nght and left ears of a user, wherein the nght receiver provides a front nght signal to the nght ear and the left receiver provides a front left signal to the left ear, and wherein the nght receiver provides a rear left signal to the left ear and the left receiver provides a rear nght signal to the nght ear 4 The wireless headphone assembly according to claim 1 and wherein said at least one ultrasound receiver compnses four ultrasound receivers, each of which receives an ultrasound signal along one ultrasound channel 5 The wireless headphone assembly according to claim 1 and wherem said at least one transducer compnses at least one first transducer which converts said at least one ultrasound signal to at least one modulated electncal signal and at least one second transducer which converts said at least one modulated electncal signal to a human audible signal 6 The wireless headphone assembly according to claim 5 and wherem said at least one transducer compnses at least one multichannel transducer 7 The wireless headphone assembly according to claim 1 and also compnsmg at least one band pass filter associated with each ultrasound channel 8 The wireless headphone assembly according to claim 1 and also compnsmg at least one demodulator associated with each ultrasound channel 9 The wireless headphone assembly according to claim 1 and wherein said at least one first transducer is operative to convert said at least one ultrasound signal to at least one modulated electncal signal compnses at least two first transducers, each ananged to be located adjacent a different ear of a user 10 The wireless headphone assembly according to claim 1 and wherein said at least one second transducer compnses at least two second transducers, each providing a human audible output to a different ear of a user 11 The wireless headphone assembly according to claim 10 and wherem a human audible signal denved from ultrasound signals received at each of said at least two ultrasound receivers is supplied to each ear of a user 12 The wireless headphone assembly according to claim 11 and wherem said at least two ultrasound receivers each receive ultrasound signals along at least two ultrasomc channels, said at least two second transducers convert ultrasound signals along at least two human audible channels to human audible signals, and information received along each one of said at least two channels of each of said at least two ultrasound receivers is supplied to each of two different ears of the user along a separate one of said human audible channels 13 The wireless headphone assembly according to claim 12 and compnsmg delay lines operative to simulate the acoustic delay occurnng between the arnval of sound from a signal source at the two ears of the user 14 A headphone system providing a simulated multi-source sound environment compnsmg at least one headphone assembly which may be worn by a user, including at least one ultrasound receiver for receiving at least one ultrasound signal along at least one ultrasound channel, and at least one transducer for converting each of said at least one ultrasound signal along said at least one ultrasound channel to a human audible signal, at least one processor receiving a multi-source signal and modulatmg an ultrasound earner along a plurality of channels, in accordance with said multi-source signal, and at least one transmitter for transmitting said modulated ultrasound earner to the at least one headphone assembly along said plurality of channels 15 The headphone system according to claim 14, and wherein the use of ultrasound for transmitting said modulated earner to said at least one headphone assembly is operative to cause a listener using said headphone assembly to expenence psycho-acoustic effects that said listener would expenence if the multi-source signal were transmitted free space as audible sound waves from suitably located sound sources 16 A headphone system compnsmg a headphone assembly which may be worn by a user, and two audio receivers, called a nght receiver and a left receiver, mounted m said headphone assembly, said receivers providing received audio signals to nght and left ears of the user, wherein the nght receiver provides a front nght signal to the nght ear and the left receiver provides a front left signal to the left ear, and wherein the nght receiver provides a rear left signal to the left ear and the left receiver provides a rear nght signal to the nght ear 17 A method for simulating an artificial sound environment compnsmg converting an audible signal to an ultrasound wave, receiving said ultrasound wave by means of a wireless headphone assembly, and converting said ultrasound wave to an audible signal by means of said wireless headphone assembly 18 A method for simulating an artificial sound environment compnsmg sendmg an ultrasound reference signal to a headphone assembly worn by a user having two ears, said headphone assembly audibly providing at least one audio signal to each of the ears, processing arnval times of said ultrasound reference signal at each said ear, so as to measure a phase difference of said signal as perceived by one said ear m contrast to the other ear and to measure a distance between the two ears of the user, modulatmg at least two audio signals, at least one signal for each said ear, in accordance with said phase difference, and sendmg said at least two audio signals via said headphone assembly to each of the ears 19 The method according to claim 18 and compnsmg sending said at least two audio signals and said ultrasound reference signal via an ultrasound earner 20 The method accordmg to claim 18 and wherem the step of sending said at least two audio signals compnses sendmg the signals to said headphone assembly by wired communication 21 The method according to claim 18 and wherein the step of sending said at least two audio signals compnses sendmg the signals to said headphone assembly by wireless communication

Inventors: BAR ON AMIR, COHEN YUVAL, NAVEH GIORA, BAR ON, AMIR, COHEN, YUVAL, NAVEH, GIORA
Applicants: BAR ON AMIR, BE4 LTD, COHEN YUVAL, NAVEH GIORA, BAR ON, AMIR, BE4 LTD., COHEN, YUVAL, NAVEH, GIORA
Application year: 1998
Main classification: H04S1
IPC codes: H04R5