Abstract:
The invention relates to a method and a device for reproducing a binaural output signal generated from a monaural input signal and comprising a first output signal and a second output signal via at least a first and a second speaker of a binaural headset particularly for VoIP applications.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to the German application No. 10345167.6, filed Sep. 29, 2003 and which is incorporated by reference herein in its entirety. 
     FIELD OF INVENTION 
     The invention relates to a method for reproducing a binaural output signal generated from a monaural input signal and comprising a first output signal and a second output signal and a device adapted for implementing the method. 
     BACKGROUND OF INVENTION 
     Intelligent data terminals, e.g. PCs and PDAs, are increasingly used for voice communication in modern communication systems, with said data terminals being linked by means of VoIP for example. 
     Packet-based communication using VoIP and the associated deployment of what are known as VoIP Codecs has undesirable effects on voice quality. For example average to fairly long transit times can be expected during signal transmission, resulting in audible echoes. Also with packet-based communication, it is necessary to take into account reflections, the transit times of which are often longer and the attenuation of which is lower than that found in a natural environment. Therefore measures have to be implemented to suppress disruptive echoes, preferably by using echo cancellers in the data terminals. 
     Echo cancellers are based on current standards, e.g. ITU-T G.168 (2002), where for example gateway interfaces to the conventional telephone network are discussed. Alternatively ITU-T G.165 (1993) can be used for VoIP terminals, whereby this specifies significantly less stringent parameters relating to echo dispersion and required suppression than is the case with conventional telephony standards. 
     If the data terminals themselves are configured as VoIP terminals, they have the disadvantages of longer transit times during signal transmission and lack of echo cancellers compared with dedicated VoIP terminals. The lack of canceller in particular means that headsets have to be used for packet-based communication of this nature. 
     However conventional binaural headphones result in a rather un-natural hearing event, as the sound is no longer influenced by the head and the outer ear. In the case of natural hearing both ears receive the signals from all sound sources, so that time delays, level differences and tone differences create a spatial hearing experience. Tests on directional perception of incoming sound show that interaural transit time and level differences are only relevant in relation to a horizontal plane of symmetry of the head, so the direction of the incoming sound can be determined here. No time delays or level differences occur in respect of a vertical plane of symmetry of the head but the direction of the incoming sound is perceived here by means of tone differences. Three-dimensional hearing is important for spatial orientation, the differentiation of different sound sources (see Blauert, Jens (June 1997): Spatial Hearing, MIT Press, ch. 5.3) and the suppression of reflection perception (ibid, ch. 5.4). As the sound sources are located directly at the ears when headphones are used, three-dimensional hearing is prevented. The right ear only receives the signals from the right speaker, while the left ear only receives the signals from the left speaker. 
     SUMMARY OF INVENTION 
     The object of the invention is therefore to develop a method and a device for reproducing an output signal generated from a monaural input signal so that the quality of monaural VoIP voice connections using headsets is improved. 
     This object is achieved by the claims. 
     According to the invention the object is achieved by a method, with which a binaural output signal generated from a monaural input signal and comprising a first output signal and a second output signal is reproduced via at least a first and a second speaker of a binaural headset, particularly for VoIP applications. The first output signal and/or the second output signal is hereby generated for binaural simulation from the monaural input signal by phase displacement and/or amplitude amplification, to obtain a hearing event that represents a subjectively experienced static or dynamic positioning of a sound event. 
     The object is also achieved by a device, with which a binaural headset, particularly for VoIP applications, has at least a first and a second speaker to output a binaural output signal generated from a monaural input signal and comprising a first output signal and a second output signal and a connection to a receiver-side data terminal. A signal processing device generates the first output signal and/or the second output signal for binaural simulation from the monaural input signal by phase displacement and/or amplitude amplification, to obtain a hearing event that represents a subjectively experienced static or dynamic positioning of a sound event. 
     One important aspect of the invention is that the binaural simulation means that spatial hearing, largely experienced as natural, is achieved despite the use of headphones. 
     The natural path of the sound, namely free-field, outer ear and auditory canal transmission or natural hearing achieved through phase differences, time delays, level differences and tone differences, is thereby simulated using phase, transit time, attenuation and/or HRTF (Head Related Transfer Function) processing elements. Such simulation allows the perception of reflections, for example tone loss or echoes, to be suppressed to the maximum, as the occurrence of echoes is to a certain degree controlled mentally and is a function for example of experience and awareness. This is due particularly to the fact that sound events occurring at the same time but originating from different sound sources can be more easily differentiated. This improves the ability of the hearer to concentrate on one sound source and pinpoint its sound events perceptively in relation to the sound events of the other sources. Moreover the simulation of three-dimensional hearing means that the precedence effect, i.e. the law of the first wave front, can be used, once the sound from a plurality of coherent sources reaches the listener from different directions. The sound event then seems to come only from one direction, whereby echoes are not perceived. 
     In a first preferred embodiment therefore the monaural input signal is supplied to the VoIP application by a transmitter-side and/or receiver-side data terminal. This has the advantage particularly that the sound event generated by the receiver-side terminal is included in the binaural simulation as well as the sound event generated by the transmitter-side data terminal. With natural hearing a person&#39;s own voice can also be heard as a three-dimensional sound event, so a clear delimitation is possible in respect of a further sound source, e.g. a further speaker. 
     The static positioning of the sound event caused by the transmitter-side data terminal is advantageously simulated by phase displacement in a first sub-function. For this the first output signal is generated by a delay to the input signal supplied by the transmitter-side data terminal or the sign is reversed and said signal is fed to the first speaker. The second output signal is also generated by unmodified reproduction of the input signal and this is fed to the second speaker. The static positioning of the sound event caused by the transmitter-side data terminal is hereby preferably achieved “closer” to the second speaker. A first component for generating a three-dimensional hearing event is implemented here based on phase displacement and the associated different transit times of the two output signals. 
     In one advantageous embodiment the dynamic positioning of the sound event caused by the transmitter-side data terminal is simulated in a second sub-function. For this a mean level comparison is effected between the input signal supplied by the transmitter-side data terminal and the monaural input signal supplied by the receiver-side data terminal. The input signal supplied by the transmitter-side data terminal is then delayed, to generate the first output signal via this first delay. A second delay to the input signal provides the second output signal. The first output signal reaches the first speaker, the second output signal is fed to the second speaker. This means that the dynamic positioning of the sound event caused by the transmitter-side data terminal is achieved “closer” to the respective speaker, which the corresponding output signal reaches first due to a different transit time. With regard to the dynamic positioning of sound events, a further component for generating a three-dimensional hearing event is advantageously implemented based on phase displacement and the associated different transit times of the two output signals. 
     Static and dynamic positioning here describe simulation of the directional perception of the incoming sound from the point of view of the receiver-side data terminal or the receiver-side user. In other words the arrival of the generated sound event from a specific direction is simulated. If static positioning is simulated, the sound supplied is processed such that the hearing event generated by it gives rise to the assumption that the transmitter-side user is not moving. Simulation of a moving transmitter-side user on the other hand is described by the dynamic positioning of said user. The sound is processed such that a change of location by the transmitter-side user is simulated. Simulation of both the static and dynamic positioning of the sound event therefore allow a hearing experience experienced as natural hearing in the event of audio transmission. 
     Static positioning of the sound event caused by the receiver-side data terminal is preferably simulated in a third sub-function. For this a delay is effected to the monaural input signal supplied by the receiver-side data terminal to reproduce this as the first output signal. At the same time the input signal is reproduced unmodified to supply it as the second output signal. The first output signal then reaches the second speaker while the second output signal is fed to the first speaker. Static positioning is therefore achieved in that the sound event caused by the receiver-side data terminal appears “closer” to the first speaker. 
     Inherent reflections with short delay, as proposed here, are desirable and are described in detail in conventional telephony. See also for example ITU-T G.131 (1996) or ITU-T G.111 (1993) Annex A, keyword STMR (Side Tone Masking Rating, Talkers&#39;s Sidetone). 
     Static positioning of the sound event caused by the transmitter-side data terminal and static positioning of the sound event caused by the receiver-side terminal are advantageously simulated at the same time. This essentially corresponds to a combination of the first and third sub-functions. The incoming sound at both terminals involved in the voice transmission can therefore be perceived from different directions, including the echo of the receiver-side terminal. The precedence effect of the sound generated by the receiver-side data terminal is amplified at the same time. What is known as the echo threshold according to Blauert is shown in  FIG. 1  based on this. See also FIG. 3.13 of ITU-T G.131 for typical amplification in the terminal. The TELR (Talker Echo Loudness Rating) “gain” can be clearly identified. 
     In a different embodiment the inventive solution provides for simultaneous simulation of the dynamic positioning of the sound event caused by the transmitter-side data terminal and static positioning of the sound event caused by the receiver-side data terminal. This essentially corresponds to a combination of the second and third sub-functions. The sound event caused by the receiver-side data terminal, the echo of this sound event and the sound event caused by the transmitter-side data terminal are thereby advantageously perceived from different directions. This makes it possible to pinpoint the incoming sound from the transmitter-side data terminal or the incoming sound from the receiver-side data terminal perceptively in relation to the echo of the incoming sound from the receiver-side data terminal. 
     In a further preferred embodiment the binaural headset is configured with a signal processing device, which has at least one transit time element. The transit time element thereby generates the above-mentioned phase displacement of the respective output signals. Alternatively or additionally the signal processing device can provide at least one attenuation element and/or at least one HRTF (Head Related Transfer Function) processing element. Amplitude amplification and/or tone differences can then also be generated as well as phase displacements. With these elements, with the combination of elements and particularly with the combination of all the elements realistic three-dimensional hearing can advantageously be generated even when using binaural headphones, as natural hearing is characterized by time delays, intensity differences and tone loss. 
     Further features and advantages of an inventive device will emerge from the features and advantages of the inventive method. 
     The invention is described in more detail below with reference to an exemplary embodiment that is described with reference to the drawing, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows talker echo tolerance curves, 
         FIG. 2  shows an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  shows what are known as talker echo tolerance curves, which allow conclusions to be drawn about voice quality from the echoes occurring. The curves thereby allow the acceptability of the conversation to be judged. The abscissa shows the mean echo transmission time T and the ordinate the talker echo loudness rating TELR. The curve K 1  shows the masked threshold, the curve K 2  shows the acceptable. The acceptable is equivalent to the curve, in which a disruptive echo occurs with a probability of 1%. The curve K 3  shows the limiting case, the curve K 4  the binaural limiting case for an arrangement of stereophonic speakers at an angle of 80°). 
       FIG. 2  shows an exemplary embodiment of the inventive device as a functional block circuit diagram. Here a transmitter-side data terminal is shown with the reference character A and a receiver-side data terminal with the reference character B. The transmitter side data terminal B is ideally equipped with binaural headphones, which in turn have a first speaker L and a second speaker R. 
     To control the signal flow accordingly, there is a signal processing device  1  between the respective terminals A, B. In this embodiment the signal processing device  1  has three function blocks F 1 , F 2 , F 3  and a level processing element PVE. 
     The function blocks F 1 , F 2  and F 3  each have at least one transit time element (not shown). Alternatively or additionally the function blocks F 1 , F 2  and F 3  can also each be configured with at least one attenuation element and/or an HRTF (Head Related Transfer Function) processing element (not shown). 
     In this exemplary embodiment the function block F 1  and the function block F 2  are connected in series, while the function block F 2  is connected parallel to the function block F 1 . 
     A voice connection is set up from the receiver-side data terminal B to a transmitter-side data terminal A, whereby the link operates by means of a switching network using VoIP. 
     The receiver-side data terminal B transmits a monaural input signal in a step  100  to the first function block F 1 . At the same time the receiver-side data terminal B transmits the monaural input signal in a step  101  to the function block F 2  and in a step  102  to the level comparison element PVE. 
     The function block F 1  delays the received signal and transmits it in a step  200  to the function block F 3 . At the same time the function block F 1  allows the received signal to pass unmodified and transmits the unmodified signal similarly in a step  201  to the function block F 3 . The signal present at the function block F 2  from step  101  is subject to a first delay in the function block F 2  and is transmitted with this in a step  300  to the function block F 3 . At the same time the signal present at the function block F 2  from step  101  is subject to a second delay and is transmitted with this in a step  301  to the function block F 3 . 
     In a step  102  the level comparison element PVE also receives the signal supplied by the receiver-side data terminal B. At the same time a signal supplied by the transmitter-side data terminal A is present at the level comparison element PVE and this is forwarded in a step  502 . The first and second delays to the signal supplied by the receiver-side data terminal B implemented in the function block F 2  and described above are then effected as a function of a mean level comparison of the signals supplied by the data terminals A, B. 
     The signals originating from steps  200  and  300  or from steps  201  and  301  are now present at the function block F 3 . At the same time the signal from the transmitter-side data terminal originating from a step  501  is present at the function block F 3 . In this exemplary embodiment the signals originating from steps  200  and  300  can pass function block F 3  without hindrance and are then fed in a step  400  to the first speaker L. The signals resulting from steps  201  and  301  and present at the function block F 3  can also pass the last function block F 3  without further processing but are fed in a step  401  to the second speaker R. The signal delays already implemented beforehand in the function blocks F 1  and F 2  mean that on the one hand static positioning of a sound event induced by the transmitter-side data terminal A takes place “closer” to the second speaker R, while on the other hand dynamic positioning of a sound event induced by the transmitter-side data terminal A is achieved “closer” to the respective speaker, which receives the signals with the shorter delays in each instance. 
     The function block F 3  delays the signal transmitted in step  501  and feeds this to the second speaker R. At the same time the signal transmitted in step  501  passes the function block F 3  without hindrance and is transmitted to the first speaker L. As a result, as mentioned above, static positioning of the sound event induced by the transmitter-side data terminal A is achieved “closer” to the first speaker L. 
     Finally in a step  500  the transmitter-side data terminal A sends a signal without further processing directly to the receiver-side data terminal B. 
     The splitting of a monaural input signal proposed here and its processing to achieve transit time differences allows three-dimensional hearing via binaural headphones, which is experienced as natural hearing. As natural hearing results from transit time differences, level differences and tone loss in the incoming sound from different sound sources, hearing experienced as three-dimensional can ideally be experienced by generating transit time differences along with level differences and tone loss. 
     The exemplary embodiment described above describes the function blocks as signal processing blocks, the purpose of which is to generate transit time differences and therefore phase differences from a monaural input signal by splitting it. Alternatively it is possible to replace the transit time elements with attenuation elements. A spatial hearing experience is thereby experienced, which is only achieved by means of amplitude amplification or attenuation. It is also possible to provide only HRTF (Head Related Transfer Function) processing elements, to simulate the nature of the head and ears and thereby the directional characteristics of the ear. The function blocks F 1  to F 3  can however hold all the signal processing elements at the same time, to achieve an optimum result in respect of simulation of natural hearing. 
     Alternatively (not shown) it is for example possible to combine the function blocks F 1  and F 3 . This essentially corresponds to the embodiment shown in  FIG. 2 , without however making the monaural input signal supplied by the receiver-side data terminal B available at the function block F 2 . The signals then pass through the function block F 3  at the same time as the input signal supplied by the transmitter-side data terminal A is being processed to be fed to the speaker L or R. 
     It is also possible (also not shown) for the function blocks F 2  and F 3  to be combined.  FIG. 2 , as already described, can be used as a basis here too but without function block F 1 . The monaural input signal supplied by the receiver-side data terminal B is supplied here exclusively to the function block F 2  or to the level comparison element PVE, to forward the resulting output signals via the function block F 3  to the speakers L and R. According to the sub-function F 3  processing of the monaural input signal from the receiver-side data terminal B takes place in the function block F 3 . 
     The combination of two function blocks represents a high-quality but nevertheless low-cost variant, whereby the quality of the three-dimensional simulation can be tailored in each instance to the area of use of the headset. 
     Changing the monaural signal using one of these processing elements also generates a hearing event, which reflects at least components of natural hearing. It is therefore possible using the proposed headset to locate different sound sources and particularly to suppress the perception of reflections. This is substantiated by the natural hearing experience, with which people have actually learned to suppress reflection perception. 
     The exclusive use of individual function blocks as transit time elements and/or attenuation elements and/or HRTF processing elements allows a spatial hearing experience, which is for example adequate, if little background noise occurs during communication. 
     It should be pointed out here that all the above elements described, taken alone and in any combination, particularly the detailed representations in the drawing, are claimed as essential to the invention. The person specialized in the art is accustomed to making modifications. Therefore means for reversing the sign of one of the processed signals can replace the transit time elements or delay elements mentioned above.