Patent Publication Number: US-9906876-B2

Title: Method for transmitting an audio signal, hearing device and hearing device system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. § 119, of German patent application DE 10 2016 206 985.3, filed Apr. 25, 2016; the prior application is herewith incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a method for transmitting an audio signal from a transmitter to a receiver. The invention also relates to a hearing device and to a hearing device system having two such hearing devices. The hearing device is preferably a hearing aid. 
     Persons who suffer from a reduction in their hearing power usually use a hearing aid. In this context, an environmental, ambient sound is in most cases detected by means of an electromechanical sound transducer. The detected electrical signals are processed by means of an amplifier circuit and fed into the auditory canal of the person by means of a further electromechanical transducer. Different types of hearing aids are known. The so-called “behind-the-ear devices” (BTE) are worn between the head and outer ear. The amplified sound signal is here fed into the auditory canal by means of an acoustic tube or sound tube. A further conventional embodiment of a hearing aid is an “in-ear device” (ITE) in which the hearing aid itself is introduced into the auditory canal. As consequence, the auditory canal is at least partially closed by means of this hearing aid so that apart from the sound signals generated by means of the hearing aid no further sound—or only greatly reduced sound—can penetrate into the auditory canal. 
     If the person suffers from an impairment of the hearing power of both ears, a hearing device system having two such hearing aids is utilized. In this arrangement, one of the hearing aids is in each case allocated to each of the ears. In order to provide spatial hearing for the person, it is required that the audio signals detected by one of the hearing aids are provided to the other hearing aid in each case. This requires, on the one hand, transmission with only a comparatively small offset in time. On the other hand, the head of the person acts as attenuation which is why the rate of transmission between the hearing aids is limited. In addition, a transmission power is limited because of the limited energy storage of the hearing aids and the burden on the person which is too strong otherwise. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a method for transmitting an audio signal which overcomes the above-mentioned and other disadvantages of the heretofore-known devices and methods of this general type and which is particularly suitable for transmitting an audio signal from a transmitter to a receiver and which is particularly suitable for hearing device and a hearing device system having two hearing devices. It is a primary object to provide for an audio quality to be improved and, preferably, a transmission rate to be reduced. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a method for transmitting an audio signal from a transmitter to a receiver, the method comprising: 
     at a transmitter end, dividing an input signal representing the audio signal into a plurality of channels for a particular time window; 
     at the transmitter end, allocating a current channel value to each channel of the plurality of channels; 
     at the transmitter end, generating a plurality of prognostic values by way of preceding channel values that are allocated to a time window preceding in time, and allocating one of the prognostic values to each current channel value; 
     at the transmitter end, determining a reference value; 
     at the transmitter end, determining a gain factor by way of the reference value and allocating the gain factor to one of the prognostic values, and modifying the current channel value associated with the one prognostic value by the gain factor to form an adapted channel value; 
     at the transmitter end, allocating the adapted channel value to an adapted data record; 
     transmitting a transmission value corresponding to the adapted data record from the transmitter to the receiver; 
     at a receiver end, generating a reconstructed adapted data record with a reconstructed adapted channel value which corresponds to the adapted channel value by way of the transmission value; 
     at the receiver end, generating a plurality of receiver-end prognostic values by way of reconstructed preceding channel values, one of the receiver-end prognostic values being allocated to the reconstructed adapted channel value; 
     at the receiver end, allocating a receiver-end gain factor to the reconstructed adapted channel value by way of the allocated receiver-end prognostic value; 
     at the receiver end, modifying the reconstructed adapted channel value by way of the receiver-end gain factor to form a reconstructed channel value; and 
     at the receiver end, adding the reconstructed value to a reconstructed output signal. 
     In other words, the method is used for transmitting an audio signal from a transmitter to a receiver, the transmitter or the receiver preferably being a component of a hearing device. The remaining element in each case, that is to say the transmitter or the receiver, respectively, is suitably a component of a further structural part of a hearing device system having the hearing device. 
     For example, the hearing device is a head set or includes a head set. Particularly preferably, however, the hearing device is a hearing aid. The hearing aid is used for supporting a person suffering from a reduction of their hearing power. In other words, the hearing aid is a medical device by means of which, for example, a partial loss of hearing is compensated for. The hearing aid is, for example, a “receiver-in-the-canal” hearing aid (RIC), an in-ear hearing aid such as an “in-the-ear” hearing aid, an “in-the-canal” hearing aid (ITC) or a “complete-in-canal” hearing aid (CIC), hearing-aid glasses, a pocket hearing aid, a bone conduction hearing aid or an implant. Particularly preferably, the hearing aid is a “behind-the-ear” (BTE) hearing aid which is worn behind an outer ear. 
     The method provides that, at the transmitter end an input signal corresponding to the audio signal is temporally subdivided into time windows, the length of the time windows being preferably identical. The length of the time windows is, for example, between 0.5 ms and 2 ms and particularly equal to 1 ms. The input signal is preferably the audio signal or a part thereof. For example, the audio signal is split into different input signals, each input signal being subdivided into different time windows in each case. The time windows, for example their length, differ in particular in the case of different input signals. For a particular time window, the input signal is divided at the transmitter end into a number of channels. The channels are here, for example, frequency channels. At the transmitter end, a current channel value is allocated to each frequency channel. The current channel value is, for example, an amplitude and/or a phase or a signal level. The current channel value is, in particular, a complex value and has a real and an imaginary part. 
     At the transmitter end, a number of prognostic values is generated for the current channel values by means of preceding channel values, one of the prognostic values being allocated to each of the current channel values. For example, the generation occurs in such a manner that a difference between the respective prognostic value and the current channel value allocated is as small as possible. At least, however, one of the current channel values is allocated one-to-one to each of the prognostic values. In other words, precisely the same number of prognostic values are created as there are current channel values. The preceding channel values have been allocated to a time window preceding in time, for example the time window preceding directly in time. In other words, a time window preceding in time has already been divided into the number of channels and to each of these channels a preceding channel value has just in time been allocated. If the method is carried out, for example, for the first time, the value zero (0), for example, is used for all preceding channel values for initialization. As soon as a second time window is present for the first time, the preceding channel values, for example, are allocated to the first time window in time and the current channel values are allocated to the subsequent time window. For example, a number of channel values preceding in time are used for creating the prognostic values, a number of preceding channel values which are allocated to the same time windows preceding in time being used, for example, for each of the prognostic values. Alternatively or in combination therewith, a number of preceding channel values which are allocated to different time windows preceding in time is used for each of the prognostic values. 
     At the transmitter end, a reference value is determined, the reference value having a particular characteristic and, for example, not deviating from a particular predetermined value, or deviating only to a slight extent. Alternatively, the reference value deviates from the particular predetermined value by the slightest amount. Furthermore, a gain factor which is determined by means of the reference value is allocated to a prognostic value at the transmitter end. The current channel value allocated to this prognostic value is modified by means of the gain factor to form an adapted channel value. In summary, a gain factor is allocated in consequence to one of the prognostic values and the gain factor is used for modifying the current channel value which is allocated to the same prognostic value to form the adapted channel value. For example, the current channel value is multiplied by the gain factor or the gain factor is added to the allocated current channel value for generating the adapted channel value. If the current channel value is, for example, a complex value, the gain factor is preferably applied both to the real component and to the imaginary component, thus both parts are modified by means of the same gain factor. In summary, the current channel value is used as argument of a function which has the gain factor at least as a parameter. The result of the function is the adapted channel value. 
     At the transmitter end, the adapted channel value is allocated to an adapted data record. In consequence, the adapted data record has the adapted channel value. For example, the adapted data record has other values, the adapted data record preferably exhibiting exactly the same number of values as there are current channel values present. A transmission value corresponding to the adapted data record is transmitted from the transmitter to the receiver, the transmission value suitably being generated firstly at the transmitter end by means of the adapted data record. The transmission value preferably has a lesser dimensionality or at the most the same dimensionality as the adapted data record and is, for example, a unidimensional value. 
     At the receiver end, a reconstructed adapted data record is generated by means of the transmission value, which corresponds to the adapted data record present at the transmitter end. For this purpose, the inverse function, in particular, is designed for generating the transmission value by means of the adapted data record. The reconstructed adapted data record generated in this way thus essentially corresponds to the adapted data record present at the transmitter end, there being differences preferably only due to the generation of the transmission value. In particular, if the function for generating the transmission value were to be applied to the reconstructed adapted data record, the transmission value would be obtained again. The reconstructed data record thus has a reconstructed adapted channel value which corresponds to the adapted channel value and, in particular, is equal to the adapted channel value. 
     Furthermore, at the receiver end, a number of receiver-end prognostic values is generated by means of reconstructed preceding channel values, the reconstructed preceding channel values corresponding particularly to the preceding channel values present at the transmitter end and suitably conform to these. For example, the receiver-end prognostic values are generated by means of the same calculating rule as the prognostic values which are present at the transmitter end. The reconstructed preceding channel values have suitably been reconstructed during a preceding execution of the method and, in particular, are allocated to a window preceding in time, preferably to the same time, window preceding in time to which the channel values preceding at the transmitter end are allocated. For example, zero (0) is allocated to the reconstructed preceding channel values when the method is executed for the first time. 
     In particular, the number of receiver-end prognostic values corresponds to the number of prognostic values which are present at the transmitter end. One of the receiver-end prognostic values is allocated to the reconstructed adapted channel value. In particular, that receiver-end prognostic value which was generated by means of the same data as the prognostic value which is allocated to the adapted channel value present at the transmitter end is allocated to the reconstructed adapted channel value. Furthermore, a receiver-end reference value is determined at the receiver end, the same procedure as that for determining the reference value present at the transmitter being selected for determining the receiver-end reference value. 
     Furthermore, at the receiver end, a receiver-end gain factor is allocated to the reconstructed adapted channel value. For this purpose, the receiver-end gain factor is firstly allocated to the receiver-end prognostic value which is allocated to the reconstructed adapted channel value, and via this gain factor, the receiver-end gain factor is just allocated to the adapted channel value. In addition, at the receiver end, the reconstructed adapted channel value is modified by means of the receiver-end gain factor to form a reconstructed channel value. In this context, in particular, an inverse function to the function is performed by means of which the current channel value present at the transmitter end is modified to form the adapted channel value. In other words, the adapted channel value is divided by the receiver-end gain factor or the receiver-end gain factor is subtracted from the reconstructed adapted channel value. In other words, the inverse operation is used. As an alternative to this, the same calculating rule is used but the receiver-end gain factor is the inverse element. In summary, the reconstructed channel value corresponds to the current channel value to which the gain factor is allocated at the transmitter end and, in particular, the two channel values correspond to each other, any differences preferably being present only due to the generation of the transmission value. 
     At the receiver end, the reconstructed channel value is added/combined to/with a reconstructed output signal. In particular, yet more values of the reconstructed adapted data record or values generated by means of the reconstructed adapted data record are combined/added with/to the reconstructed output signal. In particular, the reconstructed output signal corresponds to the input signal distributed to the channels/the totality of the current channel values. For example, the reconstructed output signal is processed further at the receiver end and the individual channels are combined and, for example, transferred into the time domain, if the channels correspond to individual frequencies. For example, the channel values of the reconstructed output signal are used as reconstructed preceding channel values when the method is executed again and by means of these, at least the receiver-end prognostic values are generated. In particular, the method is carried out again after the particular time window has elapsed. 
     Due to the adaptation of the current channel value, by means of the gain factor, a noise which is introduced due to the generation of the transmission value can be suitably distributed to the current channel values or reconstructed channel values so that an audio quality is increased. Due to the use of the transmission value, a data set to be transmitted is reduced. Since the gain factors are determined both at the receiver end and at the transmitter end, transmitting this value is not required which reduces a required transmission rate during the transmission. 
     For example, the reference value is allocated to a particular current channel value and/or one of the prognostic values, there being no adaptation of this current channel value by means of a gain factor, in particular, if this current channel value is allocated to the adapted data record. 
     The receiver-end reference value is suitably allocated to one of the receiver-end prognostic values. For example, a fixed value (e.g. 0 dB), the minimum of the prognostic values or the prognostic value allocated to a particular channel is utilized as reference value. Particularly preferably, however, the maximum of the prognostic values is utilized as reference value. In other words, the largest of the prognostic values is determined both at the transmitter and particularly at the receiver. Suitably, in this context, at the transmitter end, the current channel value, to which the maximum of the prognostic values is allocated, is also allocated to the adapted data record, and, at the receiver end, the reconstructed adapted data record is generated using the transmission value with the reconstructed adapted channel value which corresponds to the adapted channel value and with a reconstructed unadapted channel value which corresponds to the current channel value allocated to the maximum of the prognostic values. At the receiver end, the reconstructed channel value and the reconstructed unadapted channel value are combined to form the reconstructed output signal. Due to the use of the maximum, the current channel value which is allocated to the largest of the prognostic values and most probably is also the largest of the current channel values is not changed, whereas at least one of the remaining current channel values is changed. In particular, the gain factor is selected here in such a manner that the deviation between the allocated prognostic value and the reference value would be greater than a deviation between the reference value and the prognostic value modified by means of the gain factor. In consequence, a deviation between the adapted channel value and the current channel value allocated to the reference value is also most probably reduced which is why any noise introduced during the generation of the transmission value is only present to a reduced extent in the reconstructed channel value. The reconstructed unadapted channel value present at the receiver end is suitably not changed. 
     The gain factor is preferably chosen in such a manner that a deviation between the prognostic value allocated to these and the reference value would be greater than a deviation between the reference value and the prognostic value modified by means of the gain factor. In other words, the deviation between the reference value and the prognostic value just modified would be reduced with an application of the gain factor to the prognostic value to which the gain factor is allocated. In as much as, in consequence, a deviation between the prognostic values and the current channel values is comparatively low, a deviation between the adapted channel value and the current value, to which the maximum of the prognostic values is allocated, is, therefore, also reduced. In as much as, due to the generation of the transmission value noise is introduced which is in dependence on the current channel value to which the reference value is allocated, the noise which the reconstructed channel value exhibits is thus reduced due to the use of the receiver-end gain factor and of the gain factor. 
     The reconstructed unadapted channel value is suitably allocated to the same channel as the current channel value to which the reference value is allocated. For example, the reconstructed channel value is allocated to the same channel which is allocated to the current channel value at the transmitter end, to which the gain factor is allocated. Preferably, the preceding channel value allocated to the same channel is utilized as prognostic value. In other words, the respective preceding channel value is utilized as prognostic value for each of the current channel values. In this manner, an effort for generating the prognostic values is reduced. If the input signal thus has comparatively low fluctuations, a deviation between the prognostic value and the respective allocated current channel value is comparatively low. In particular, the reconstructed preceding channel values are also used as receiver-end prognostic values, the allocation to the respective channels also being taken into consideration in this respect. 
     In an alternative to this, a linear projection is utilized for generating the prognostic values or the receiver-end prognostic values, respectively, using, for example, a number of channel values preceding in time. In other words, each of the prognostic values is generated by means of a linear combination, using, for example, a number of channel values preceding in time. 
     It is suitably determined by means of the receiver-end reference value which of the values of the adapted data record is the reconstructed unadapted channel value. In this context, firstly the receiver-end prognostic values are generated and to each of the values of the reconstructed adapted data record one of the receiver-end prognostic values is allocated. The value of the reconstructed adapted data record to which the receiver-end reference value is allocated is utilized as reconstructed unadapted channel value. Alternatively, an index or the like is allocated to each value of the reconstructed adapted data record, on the basis of which an allocation to the respective channels is effected. 
     Particularly preferably, the gain factor is generated by means of the prognostic value to which the gain factor is allocated. The receiver-end gain factor is suitably generated by means of the receiver-end prognostic value to which the reconstructed adapted channel value is allocated. In this way, it is not required to transmit the gain factors or values corresponding thereto between the receiver and the transmitter which further reduces a data set to be transmitted. In particular, the same computing rule is used for generating the gain factor or the receiver-end gain factor, respectively. 
     The gain factor is suitably generated by means of the difference between the reference value and the prognostic value. In other words, the difference between the reference value and the prognostic value, to which the gain factor is to be allocated, is first generated. By means of this difference, the gain factor is determined. In particular, the gain factor is the difference which, for example, is multiplied by means of a factor, the factor suitably being chosen to be constant. In particular, the difference between the receiver-end prognostic value to which the reconstructed adapted channel value is to be allocated and the receiver-end reference value is also determined at the receiver end and the receiver-end gain factor is determined by means of this difference. In particular, the receiver-end gain factor is the difference which, for example, is multiplied by a factor. In this way, the determination of the gain factor is comparatively simple. In addition, an adaptation of the adapted channel value is in this way such that a deviation with respect to the current channel value allocated to the reference value is reduced. In this context, current changes of the input signal are also taken into consideration which, for example, would not be the case with a fixed specification of the gain factors. 
     In particular, to each of the remaining prognostic values, a gain factor is allocated in each case and these are preferably adapted in each case by means of the allocated gain factor and allocated to the adapted data record. At the receiver end, a number of reconstructed adapted channel values is thus present, a receiver-end gain factor being allocated to each of these by means of which in each case reconstructed channel values are generated which are combined to form the reconstructed output signal. In other words, all current channel values with the exception of that current channel value to which the reference value is allocated are modified by means of the respective gain factor and the channel values adapted in this way are transmitted by means of the transmission value. At the receiver, the reconstructed output signal is generated by means of the reconstructed adapted channel values and the gain factors present at the receiver end, which output signal thus corresponds particularly to the input signal. The adapted data record here has only a single current channel value, namely the one to which the reference value is allocated. In particular, the receiver-end reference value is determined at the receiver end so that it can be determined comparatively simply which of the values of the reconstructed adapted data record is not to be changed with a gain factor. 
     Preferably, the receiver-end prognostic values and the prognostic values which are present at the transmitter and also the gain factor and the receiver-end gain factor are essentially generated simultaneously. This reduces a period of time which is used for transmitting the audio signal. In particular, a period of time between detection of the input signal and generation of the reconstructed output signal is shortened in this way. 
     The individual gain factors and the individual receiver-end gain factors preferably differ. These are suitably determined in each case by means of the respective prognostic value and the reference value or the receiver-end prognostic value and the receiver-end reference value, suitably by means of their difference. The gain factor is suitably
 
 G   i   =wΔL   i  
 
where w is a constant factor and ΔL i  designates the difference between the reference value and the i th  prognostic value or the receiver-end reference value and the i th  receiver-end prognostic value, respectively, i identifying the respective channel to which the respective prognostic value or receiver-end prognostic value is allocated. In this way, essentially all current channel values are adapted to an almost equal level with the current channel value to which the reference value is allocated. Thus, all values of the adapted data record essentially have the same magnitude which is why any noise is essentially uniformly distributed to all reconstructed adapted channel values and the reconstructed unadapted channel value. After application of the receiver-end gain factors, the noise is thus less in the case of the reconstructed channel values than in the case of the reconstructed unadapted channel value. In particular, if the maximum is utilized as reference value, a noise is therefore reduced with comparatively low current channel values which improves an audio quality.
 
     For example, the input signal is divided into the frequency channels by means of a Fourier transform. Particularly preferably, however, band-pass filters are used which are preferably combined to form a filter bank. Alternatively or in combination therewith, a difference between a predicted audio signal and the actual audio signal is used as input signal, the audio signal firstly being divided into the channels or channels deviating therefrom and the predicted audio signal being generated by means of a linear projection. 
     In summary, the predicted audio signal is determined by way of the formula 
                 x   ^     ⁡     (   n   )       =       ∑     i   =   1     N     ⁢           ⁢       a   i     ⁢     y   ⁡     (     n   -   i     )                     or                 x   ^     ⁡     (   n   )       =       ∑     i   =   1     N     ⁢           ⁢     Ay   ⁡     (     n   -   i     )               
where {circumflex over (x)}(n) designates the channels of the predicted audio signal, a i  designates a coefficient, A is a coefficient matrix and y represents the totality of the values which are utilized for the generation, in particular the value preceding in time of the audio signal divided into the channels. The time of generation is here n−i and the number used is N. A type of linear projection is, for example, disclosed in “Benesty, J., Chen, J. &amp; Huang, Y. (Arden). (2008), Linear Prediction. In J. Benesty, M. M. Sondhi &amp; Y. (Arden) Huang (Editors), Springer Handbook of Speech Processing (pages 111-125) Springer Verlag”, particularly in chapter 7.2 (page 112-113), particularly formula 7.6 and particularly in chapter 7.9 (page 120-124), particularly formula 7.108. The input signal used is, for example, the totality of the difference between the respective {circumflex over (x)}(n) and the corresponding y(n).
 
     For example, the transmission value is generated by means of quantization of the adapted data record. In this context, the transmission value which suitably can assume only a discrete number of different values is allocated to the adapted data record. In other words, the transmission value is a discrete value. 
     By means of the transmission value and by means of the gain factor, a transmitter-end reconstructed channel value and a transmitter-end reconstructed unadapted channel value are preferably generated at the transmitter end. The transmitter-end reconstructed channel value corresponds to the reconstructed channel value which is present at the receiver and the transmitter-end reconstructed unadapted channel value corresponds to the reconstructed unadapted channel value which is present at the receiver. The transmitter-end reconstructed channel value and the transmitter-end reconstructed unadapted channel value are present at the transmitter. 
     In other words, the reconstructed output signal is generated at the transmitter end also by means of the transmission value and the gain factor, this output signal being able to deviate slightly from the input signal due to the quantization and the resultant introduced noise. In the case of a transmission following in time, the transmitter-end reconstructed channel value and the transmitter-end reconstructed unadapted channel value are utilized as the channel values preceding in time or at least as a part thereof. In this way, deviations between the output signal and the input signal, resulting from the quantization, are taken into consideration during the generation of the prognostic values which is why a maximum deviation between the input signal and the reconstructed output signal remains slight even with a repeated carrying out of the method, and thus a high quality is present when the audio signal is transmitted. 
     Suitably, a scalar quantization is utilized. Especially preferably, the quantization is a vector quantization. A so-called gain-shape vector quantization is suitably utilized. The quantized signal is then divided into the signal form/vector form (shape) and a scaling factor (gain). A particularly suitable form of the gain-shape vector quantization is represented by the logarithmic vector quantization, particularly the (spherical) logarithmic vector quantization. In this context, possible signal forms/vector forms are points on a (potentially) high-dimensional unit sphere (i.e. with a radius of 1). The scaling factor is here quantized logarithmically, for example with the familiar A law. As signal forms/vector forms, other forms also come into consideration such as, for example, (high-dimensional) pyramids or cubes. A spherical/logarithmic vector quantization is known, for example, from “B. Matschkal and J. B. Huber, “Spherical logarithmic quantization”, IEEE Trans. Audio, Speech, and Language Processing, vol. 18, pp. 126-140, January 2010”, particularly from chapter III, an example being disclosed in chapter IV, particularly in  FIGS. 8 and 9 . 
     The hearing device has a communication facility for transmitting and/or receiving an audio signal. For this purpose, the communication facility comprises a transmitter and a receiver, respectively. The communication facility is suitable and provided and configured to perform a method for transmitting an audio signal from the transmitter and to the receiver, respectively. In this context, the method provides that, at the transmitter end, an input signal corresponding to the audio signal is divided into a number of channels for a particular time window and that, at the transmitter end, a current channel value is allocated to each channel. Furthermore, at the transmitter end, a number of prognostic values is generated by means of preceding channel values which are allocated to a time window preceding in time, one of the prognostic values being allocated to each current channel value and, at the transmitter end, a reference value is determined. At the transmitter end, a gain factor determined by means of the reference value is allocated to one of the prognostic values and the current channel value allocated to this prognostic value is modified by means of the gain factor to form an adapted channel value. In a further operating step, at the transmitter end, the adapted channel value is allocated to an adapted data record. A transmission value corresponding to the adapted data record is transmitted from the transmitter to the receiver. 
     At the receiver end, a reconstructed adapted data record with a reconstructed adapted channel value which corresponds to the adapted channel value is generated by means of the transmission value. At the receiver end, a number of receiver-end prognostic values is generated by means of reconstructed preceding channel values which, in particular, are allocated to the time window preceding in time, one of the receiver-end prognostic values being allocated to the reconstructed adapted channel value. Furthermore, a receiver-end reference value, especially of the receiver-end prognostic values, is determined especially at the receiver end and, at the receiver end, a receiver-end gain factor, which is preferably determined by means of the receiver-end reference value, is allocated to the reconstructed adapted channel value by means of the allocated receiver-end prognostic value. At the receiver end, the reconstructed adapted channel value is modified by means of the receiver-end gain factor to form a reconstructed channel value. In a further operating step, the reconstructed channel value is combined to form a reconstructed output signal at the receiver end. 
     If the communication facility only comprises the transmitter, only the transmitter-end operating steps and an operating step for transmitting the deviations are then performed, in particular. If the communication facility only has the receiver, only the receiver-end operating steps and an operating step for receiving the deviations are performed, in particular. The transmission is suitably wireless, for example inductive or by radio. 
     The hearing device preferably comprises a sensor by means of which an audio signal is detected during operation. The sensor is preferably an electromechanical sound transducer such as a microphone. For example, the input signal is the audio signal or the input signal is generated by means of the audio signal. For example, the input signal is a part of the audio signal or corresponds to a particular frequency range of the audio signal. To generate the input signal from the audio signal, the hearing device comprises, for example, a signal processing unit and/or filter. The hearing device preferably comprises an amplifier circuit by means of which the audio signal/output signal/reconstructed output signal can be amplified. The hearing device preferably comprises an actuator by means of which a sound signal is generated, like a loudspeaker, and which is suitable, and, for example, is provided and suitable for outputting the output signal or the reconstructed output signal, respectively. 
     For example, the hearing device is a headset or comprises a headset. Particularly preferably, the hearing device is a hearing aid, however. The hearing aid is used for supporting a person suffering from a reduction of the hearing power. In other words, the hearing aid is a medical device by means of which, for example, a partial loss of hearing is compensated for. The hearing aid is, for example, a “receiver-in-the-canal” hearing aid (RIC), an in-ear hearing aid such as an “in-the-ear” hearing aid, an “in-the-canal” hearing aid (ITC) or a “complete-in-canal” hearing aid (CIC), hearing-aid glasses, a pocket hearing aid, a bone conduction hearing aid or an implant. Particularly preferably, the hearing aid is a “behind-the-ear” hearing aid which is worn behind an outer ear. 
     The hearing device is particularly provided and configured to be worn on the human body. In other words, the hearing device preferably comprises a holding device by means of which attachment to the human body is possible. If the hearing device is a hearing aid, the hearing device is provided and configured to be arranged, for example, behind the ear or inside an auditory canal. In particular, the hearing device is cableless, or cordless, and provided and configured to be introduced at least partially into an auditory canal. For example, the hearing device is a component of a hearing device system which comprises a further hearing device or a further device such as a directional microphone or another device having a microphone. In this context, the device preferably comprises the transmitter and the hearing device comprises the receiver and the transmission of the audio signal between the transmitter and the receiver occurs in accordance with the method. 
     The hearing device system preferably comprises two hearing devices which have in each case a communication facility which are provided and configured for transmitting and/or receiving an audio signal according to the above method. In this context, the hearing device system is suitable and provided and configured to transmit audio signals between the two hearing devices by means of their respective communication facilities, the above method being performed. In particular, each of the communication facilities has in each case a transmitter and a receiver and the audio signals are transmitted between the two communication facilities, at least from one of the hearing devices to the remaining one. The transmission is suitably wireless, for example inductive or by means of radio. 
     Particularly preferably, the hearing device system is a hearing aid system. The hearing aid system is used for supporting a person suffering from reduction of the hearing power. In other words, the hearing aid system is a medical device by means of which, for example, a partial loss of hearing is compensated for. The hearing aid system suitably comprises a “behind-the-ear” hearing aid which is worn behind an outer ear, a “receiver-in-the-canal” hearing aid (RIC), an in-ear hearing aid, such as an “in-the-ear” hearing aid, an “in-the-canal” hearing aid (ITC) or a “completely-in-canal” hearing aid (CIC), hearing-aid glasses, a pocket hearing aid, a bone conduction hearing aid or an implant. The hearing device system is particularly provided and configured to be worn on the human body. In other words, the hearing device system preferably comprises a holding device by means of which attachment to the human body is enabled. If the hearing device system is a hearing aid system, at least one of the hearing devices is provided and configured to be arranged, for example, behind the ear or inside an auditory canal. In particular, the hearing device system is cordless and provided and configured to be introduced at least partially into an auditory canal. Particularly preferably, the hearing device system comprises an energy store by means of which an energy supply is provided. 
     In summary, the invention provides, in particular, for the audio signal to be split into frequency channels. Following this, a vector is formed by a set of channel values and one of a reference value and application of a gain factor to all elements of the vector, the gain factors preferably differing. If the reference value is a current channel value, no gain factor is preferably applied to it. The gain factor is calculated as a function of preceding (past, “reconstructed”) channel values and, therefore, information which is present both at the transmitter and at the receiver end is used. A preceding channel value is here understood to be, for example, a quantized channel value or a reconstructed channel value in the sense of a predictive coding (i.e. as a sum of deviation and prognosis). The channel values adapted in this manner are vector quantized. Following this, the inverse gain factor is applied to the values that are now quantized. 
     The further developments and advantages described in conjunction with the method are analogously also to be transferred to the hearing device or the hearing device system, respectively, and conversely. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a method for transmitting an audio signal, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows diagrammatically a hearing device system with two hearing devices; 
         FIG. 2  is a flow diagram illustrating a method for transmitting an audio signal between the two hearing devices; 
         FIG. 3  shows an input signal corresponding to the audio signal; 
         FIG. 4  shows the input signal divided into a number of channels; 
         FIG. 5  shows current channel values; 
         FIG. 6  shows prognostic values; 
         FIG. 7  shows an adapted data record; 
         FIG. 8  diagrammatically shows sections of the hearing device system; and 
         FIG. 9  shows a reconstructed adapted data record and a reconstructed output signal. 
     
    
    
     Parts and elements that correspond to one another are identified with the same reference symbols in all figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a hearing device system  2  having two structurally identical hearing aids  4 , which are provided and configured to be worn behind an ear of a user. In other words, they are in each case a “behind-the-ear” hearing aid which has a non-illustrated sound tube, or acoustic tube, which is introduced into the ear to connect a receiver in the ear canal. Each hearing aid  4  comprises a housing  6  which is manufactured from a plastic material. Within the housing  6 , a microphone  8  having two electromechanical sound transducers  10  is arranged. By means of the two electromechanical sound transducers  10 , a directional characteristic of the microphone  8  can be changed in that a temporal offset between the acoustic signals detected by way of the respective electromechanical sound transducer  10  is changed. The two electromechanical sound transducers  10  are coupled with respect to signals to a signal processing unit  12  which comprises an amplifier circuit. The signal processing unit  12  is formed by means of circuit elements such as, for example, electrical and/or electronic components. 
     Furthermore, the signal processing unit  12  is connected to a loudspeaker  14  by means of which the audio signals  16  recorded by the microphones  8  and/or processed by the signal processing unit  12  are output as sound signals. These sound signals are conducted into the ear of a user of the hearing device system  2  by way of the acoustic tube. 
     Each of the hearing aids  4  also has a transmitter  18  and a receiver  20 , also referred to as a transceiver, by means of which data signals  22  are exchanged between the two hearing aids  4 . The exchange is wireless, for example by means of radio or inductive transmission. The signal processing unit  12 , the transmitter  18  and the receiver  20  here together in each case form a communication facility  24 . The exchange of the data signals  22  enables a spatial hearing sensation to be conveyed to the wearer of the hearing device system  2 . In summary, the hearing device system  2  is a binaural system. 
     In  FIG. 2 , a method  26  is shown according to which the audio signals  16  are transmitted between the two hearing devices  4  by means of their respective communication facility  24 . In a first operating step  28 , the audio signal  16  is received by means of one of the hearing aids  4 . In a subsequent second operating step  30 , an input signal  32  is generated from this which, in consequence, corresponds to the audio signal  16  and which is shown in  FIG. 3  by way of example. For this purpose, the audio signal  16  is especially filtered. Furthermore, the input signal  32  is subdivided into time windows  34  which have the same length in time and which, for example, is equal to one millisecond. As soon as the last time window  34  in time is ended, this time window  34  is divided into a number of channels  36  as shown, for example, in  FIG. 4 . The channels  36  are frequency channels and for dividing the input signal  32  into the individual frequency channels  36 , frequency-pass filters  38  are utilized which are present within the signal processing unit  16 . Furthermore, the input signal  32  only comprises the channels  36  whereas the audio signal  16  has the channels  36  and yet further frequency channels. To each of the frequency channels  36 , a particular current channel value  40  is allocated. In summary, the input signal  32  is divided into the individual frequency channels  36  in the second operating step  30  and discretized by means of the allocation of the current channel value  40 . 
     Furthermore, after execution of the first operating step  16  at the transmitter  18 , a third operating step  42  is carried out in which channel values  44  preceding in time are filled. These have been determined, for example, in a preceding run of the method  26  or, if the method  26  has not yet been carried out, standard values are utilized for this purpose such as zero (0). As well, a fourth operating step  46  is carried out at the receiver  20  in which reconstructed preceding channel values  48  are determined. These correspond to the channel values  44  preceding in time and are determined in the same way as the channel values  44  preceding in time. 
     In  FIG. 5 , the current channel values  40  are shown, each of which is in each case allocated to a channel  36 . One of the current values  40  is comparatively large in this case. In an application of a spherically logarithmic quantization to the input signal  32 , a first noise level  50  would be introduced due to the increased current channel value  40  which is greater than the remaining actual channel values  40  in wide parts such that these values would be excessively corrupted. 
     In a fifth operating step  52 , therefore, a number of prognostic values  54  is therefore generated at the transmitter end by means of the preceding channel values  44 , each of the prognostic values  54  being allocated to one of the channels  36  and thus also to one of the current channel values  40 , as shown in  FIG. 6 . The channel value  44  preceding in time allocated to the same channel  36  is utilized as prognostic value  54 . 
     In a subsequent sixth operating step  56 , a reference value  58  of the prognostic values  54  is determined, the maximum of the prognostic values  54  being utilized as reference value  58 . In other words, the largest of the prognostic values  54  and thus the largest of the preceding channel values  44  is determined. 
     To the remaining prognostic values  54  is allocated a gain factor  62  in each case in a seventh operating step  60 , the gain factors  62  differing. Thus, gain factors  62  are allocated to the channels  36  for the time window  34 , each of the gain factors  62  being allocated to precisely one of the current channel values  40 —with the exception of the current channel value  40  to which the reference value  68  is allocated. Each of the gain factors  62  is determined with the formula
 
 G   i   =wΔL   i  
 
where w is an arbitrary factor between zero (0) and one (1), for example 0.5. G i  is the gain factor  62  which is allocated to channel  36  having the index i. ΔL i  designates the difference  64  between the reference value  58  and the prognostic value  54  which is allocated to the channel  36  having the index i. In consequence, all of the gain factors  62  differ and the respective gain factor  62  is generated by means of the respectively allocated prognostic value  54  to which the gain factor  62  is allocated.
 
     In a subsequent eighth operating step  68 , each of the current channel values  40  is modified by means of that gain factor  54  which is allocated to the respectively allocated prognostic value  54  and generated by means of the latter. Thus, each of the current channel values  40 , with the exception of that current channel value  40  to which the reference value  58  is allocated and to which, in consequence, none of the gain factors  52  is allocated, is modified to form an adapted channel value  70 . The respective current channel value  40  is multiplied by the gain factor  62  allocated in each case as, for example, shown diagrammatically in  FIG. 8 . Thus, the respective gain factor  54  is chosen in such a manner that a deviation between the allocated prognostic value  54  and the reference value  58  would be greater than a deviation between the reference value  58  and the prognostic value modified by means of the gain factor  54 . Since the current channel values  40  in most cases deviate only comparatively little from the respective channel value  44  preceding in time, the deviation between the current channel value  40  to which the reference value  58  is allocated and the adapted channel values  70  is thus also reduced. 
     The adapted channel values  70  and the current channel value  40  to which the reference value  58  is allocated are allocated to an adapted data record  72  which is thus a vector which has precisely the same number of elements as there are current channel values  40 . In a ninth operating step  74 , the adapted data record  72  is quantized by means of a spherically logarithmic quantization and a transmission value  76  is formed which is unidimensional in consequence. In other words, the transmission value  76  is generated by means of quantization of the adapted data record  72 , the spherically logarithmic quantization being utilized as quantization. Due to the quantization, a second noise level  78  is introduced into the adapted data record  72 . The transmission value  76  is transmitted to the remaining hearing device  4  as component of the data signal  22 . 
     The transmission value  76  is received by means of the receiver  20  and a tenth operating step  80  is carried out in which a reconstructed adapted data record  82 , which is shown in  FIG. 9 , is generated by means of the transmission value  76  at the receiver end. This corresponds to the adapted data record  72  with the exception of any noise which has been introduced due to the quantization. In other words, the reconstructed adapted data record  82  has a number of reconstructed adapted channel values  84  corresponding to the number of adapted channel values  70 , each of the reconstructed adapted channel values  84  corresponding to one of the adapted channel values  70  and, in particular, conforming to this one. Furthermore, the reconstructed adapted data record  82  has a reconstructed unadapted channel value  86  which corresponds to the current channel value  40  allocated to the reference value  58  of the prognostic values  54  and thus is essentially the only current channel value  40  which, with the exception of the quantization, has been transmitted essentially unchanged from the transmitter  18  to the receiver  20 . 
     In an eleventh step  88 , a number of receiver-end prognostic values  90  is generated at the receiver end by means of the reconstructed preceding channel values  46 , one of the receiver-end prognostic values  90  being allocated in each case to the reconstructed adapted channel values  84  and the reconstructed unadapted channel value  86 . In a twelfth operating step  92 , a maximum of the receiver-end prognostic values  92  is determined and in this way the reconstructed unadapted channel value  86  is identified within all values of the reconstructed adapted data record  82 . In a subsequent thirteenth operating step  84 , receiver-end gain factors  96  are determined by means of the receiver-end prognostic values  90  and the receiver-end maximum of the receiver-end prognostic values  90 . Each of the receiver-end gain factors  96  is in each case allocated to one of the reconstructed adapted channel values  84  and the respective receiver-end prognostic values  90 . Since the reconstructed preceding channel values  48  substantially correspond to the preceding channel values  44 , the prognostic values  54  and the receiver-end prognostic values  90  correspond to one another. For the determination of the receiver-end gain factors  96 , the same calculating rule is used as for determining the gain factors  62  which is present at the transmitter  18 . The receiver-end gain factor  96  which corresponds to the transmitter-end gain factor  62  is here allocated to the same channel  36 . 
     In summary, the eleventh, twelfth and thirteenth operating step  88 ,  92 ,  94  essentially correspond to the fifth, sixth and seventh operating step  52 ,  56 ,  60 , wherein, however, different input data are utilized, namely one time the channel values  44  preceding in time and the other time the reconstructed preceding channel values  48  which, however, are equal due to the fourth operating step  46  and the third operating step  42 . Thus, each gain factor  62  is equal to the transmitter-end gain factor  96  which is allocated to the same channel  36  in each case. Transmission of the gain factor  96  from the transmitter  18  to the receiver  20  is not required. 
     In a fourteenth operating step  98 , each of the reconstructed adapted channel values  84  is modified at the receiver end by means of the receiver-end gain factor  96  allocated in each case to form a reconstructed channel value  100  and combined with the reconstructed unadapted channel value  86  to form a reconstructed output signal  102 , which thus, with exception of noise introduced due to quantization, corresponds to the current channel values  40  which are present at the transmitter  18 . In this context, a third noise level  104  is present due to the quantization which noise level is different with each of the channels  36 . Thus, the third noise level  104  is in each case below the reconstructed channel value  100  or the reconstructed unadapted channel value  86 , respectively, which is why an audio quality is improved. When the method  26  is carried out again, the reconstructed output signal  102  is utilized at least partially as the reconstructed preceding channel values  48 . In a subsequent fifteenth operating step  106 , the reconstructed output signal  102  is transferred into the time domain and output by means of the loudspeaker  14 . 
     Furthermore, a sixteenth operating step  108  is carried out at the transmitter  18  in which, by means of the transmission value  76  and the gain factors  62 , channel values  110  reconstructed at the transmitter end and an unadapted channel value  112  reconstructed at the transmitter end are generated which correspond to the reconstructed channel values  100  and the reconstructed unadapted channel value  86 , respectively. In other words, the reconstructed output signal  102  is also generated at the transmitter  18 . The channel values  110  reconstructed at the transmitter end and the unadapted channel value  112  reconstructed at the transmitter end are utilized as the channel values  44  preceding in time in the case of a transmission following in time. In this way, any deviation which is present due to the spherically logarithmic quantization in the reconstructed output signal  102  is also present at the receiver  18  which is why a deviation is reduced in the case of a subsequent transmission. 
     The invention is not restricted to the exemplary embodiment described above. Instead, other variants of the invention can also be derived therefrom by the expert without departing from the subject matter of the invention. In particular, all individual features described in conjunction with the exemplary embodiment can also be combined with one another in other ways without departing from the subject matter of the invention. 
     The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:
           2  Hearing device system     4  Hearing aid     6  Housing     8  Microphone     10  Sound transducer     12  Signal processing unit     14  Loudspeaker     16  Audio signal     18  Transmitter     20  Receiver     22  Data signal     24  Communication facility     26  Method     28  First operating step     30  Second operating step     32  Input signal     34  Time window     36  Frequency channel     38  Frequency-pass filter     40  Current channel value     42  Third operating step     44  Channel values preceding in time     46  Fourth operating step     48  Reconstructed preceding channel values     50  First noise level     52  Fifth operating step     54  Prognostic value     56  Sixth operating step     58  Reference value     60  Seventh operating step     62  Gain factor     64  Difference     68  Eighth operating step     70  Adapted channel value     72  Adapted data record     74  Ninth operating step     76  Transmission value     78  Second noise level     80  Tenth operating step     82  Reconstructed adapted data record     84  Reconstructed adapted channel value     86  Reconstructed unadapted channel value     88  Eleventh operating step     90  Receiver-end prognostic value     92  Twelfth operating step     94  Thirteenth operating step     96  Receiver-end gain factor     98  Fourteenth operating step     100  Reconstructed channel value     102  Reconstructed output signal     104  Third noise level     106  Fifteenth operating step     108  Sixteenth operating step     110  Transmitter-end reconstructed channel value     112  Transmitter-end reconstructed unadapted channel value