Abstract:
A digital wireless audio transmission system having a wireless receiving unit for wirelessly receiving a high-frequency signal. An HF analysis unit analyzes the received high-frequency data, detects errors in the transmission within a time window, and outputs the received data and first items of information in respect of the detected errors. A decoding unit converts/decodes the received high-frequency data into audio data. An error detection unit checks errors in the conversion of the decoding unit within a previously established time window and outputs second items of information in respect of errors during decoding of the received high-frequency data. An error rate is determined based on the first and second items of information. If the error rate exceeds a first threshold value then no audio signal is outputted. Only if the error rate falls below a second value, lower than the first value, is an audio output is then again effected.

Description:
[0001]    The present application claims priority from German Patent Application No. 10 2015 201 087.2 filed on Jan. 22, 2015, the disclosure of which is incorporated herein by reference in its entirety. 
       FIELD OF THE INVENTION 
       [0002]    It is noted that citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention. 
         [0003]    The present invention concerns a digital wireless audio transmission system, in particular a wireless microphone system or a wireless pocket transmitter system for the wireless transmission of digital audio data. 
         [0004]    Digital wireless audio transmission systems of that kind have a wireless transmitter and a wireless receiver which digitally and wirelessly transmit audio data, for example as real time streaming. In that case audio artefacts can occur, more specifically both during the wireless transmission by way of a high frequency path and also in processing of the transmitted audio data. Such audio artefacts can represent audible artefacts which are to be avoided. 
         [0005]    In the German patent application from which priority is claimed the following documents were cited as state of the art: US 2004/0083110 A1, US 2014/0220904 A1 and WO 2014/001605 A1. 
       SUMMARY OF THE INVENTION 
       [0006]    An object of the present invention is to provide a digital wireless audio transmission system which substantially avoids audible audio artefacts. 
         [0007]    Thus there is provided a digital wireless audio transmission system, in particular a wireless microphone system or a wireless pocket transmitter system for the wireless transmission of digital audio data. The audio transmission system has a wireless receiving unit for wirelessly receiving a high frequency signal. The wireless receiving unit has an HF analysis unit for analyzing the wirelessly received high frequency data, for detecting errors in the wireless transmission within a previously established time window and for outputting the received data and first items of information in respect of the detected errors. The receiving unit further has a decoding unit for converting or decoding the received high frequency data into audio data. The audio transmission system further has an error detection unit for checking errors in the conversion of the decoding unit within a previously established time window and for outputting second items of information in respect of errors during decoding of the received high frequency data. An error rate can be determined based on the first and second items of information. If the error rate exceeds a first threshold value then no output of an audio signal takes place. It is only if the error rate falls below a second value which is lower than the first value that an audio output is then again effected. 
         [0008]    According to the invention therefore a hysteresis is achieved when switching on again, wherein switching-on again is effected only if the error rate falls below a second lower threshold value. It is thus possible to ensure that repeated muting and unmuting of the audio signal are avoided. 
         [0009]    According to an aspect of the present invention the wireless transmission is a wireless audio streaming with low latency. 
         [0010]    According to an aspect of the present invention the decoder can perform error concealment. 
         [0011]    According to the invention muting and unmuting of an audio output signal can be provided in dependence on the link quality of the wireless transmission path and/or the decoder quality. 
         [0012]    According to a further aspect of the present invention the first and second threshold values are adjustable by a user, for example externally adjustable. 
         [0013]    According to a further aspect of the present invention the first and second threshold values can be adjusted in dependence on the position of the audio transmission system and/or in regard to information about the installation location like for example the size of the hall and so forth. 
         [0014]    According to the invention therefore it is possible to achieve an audio watchdog functionality, wherein the watchdog takes account of the error rate of the wireless audio transmission and/or decoding. In addition the audio watchdog functionality can also take account of the link quality of the wireless transmission. 
         [0015]    According to an aspect of the present invention an audio signal to be output is muted or deactivated if the decoder in the receiving unit is no longer capable of concealing the errors present. In that way it is possible to avoid audible audio artefacts and the hysteresis effect by means of the first and second threshold values also makes it possible to avoid the audio output signal being rapidly and uncontrolledly switched on and off. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a block circuit diagram of a receiving unit in a digital wireless audio transmission system according to a first embodiment. 
           [0017]      FIG. 2A  shows a graph view of the variation in respect of time of an error rate in the wireless transmission in the digital wireless audio transmission system according to the invention in a first embodiment. 
           [0018]      FIG. 2B  shows a graph view of the variation in respect of time of an error rate in the wireless transmission in the digital wireless audio transmission system according to the invention in a second embodiment. 
           [0019]      FIG. 3  shows a flow chart for a digital wireless audio transmission system according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0020]    It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements which are conventional in this art. Those of ordinary skill in the art will recognize that other elements are desirable for implementing the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. 
         [0021]    The present invention will now be described in detail on the basis of exemplary embodiments. 
         [0022]      FIG. 1  shows a block circuit diagram of a receiving unit in a digital wireless audio transmission system according to the invention. The wireless receiving unit  100  has a high frequency analysis unit  110 , a decoder  120 , an audio processing unit  130 , an error detection unit  140  and optionally an error detection adjusting unit  150 . A receiving unit  100  receives a high frequency signal RF by means of a high frequency analysis unit  110 . The high frequency analysis unit  110  detects errors in the wireless transmission and outputs corresponding first items of error information  112  to the error detection unit  140 . In addition the high frequency analysis unit  110  outputs the received data  111  to the decoder  120 . The decoder  120  output decoded data  121  to the audio processing unit  130  and second items of error information  122  to the error detection unit  140 . In that case the second items of error information  122  represent errors in decoding of the received data  111 . In the error detection  140  the first and second items of error information  112 ,  122  are detected and optionally brought together to give an error rate. The ascertained error rate is compared to parameters  151  like for example a first and a second threshold value  151   a,    151   b.  In that case the first threshold value  151   a  represents that threshold value, as from which the error rate is too high, so that the audio output by the audio processing unit  130  must be stopped or muted. In that case the second threshold value  151   b  represents that threshold value as from which the audio output by the audio processing unit  130  can be activated again. In that case the second threshold value  151   b  is lower than the first threshold value  151   a.  That provides a hysteresis effect when the audio data is output again by the audio processing unit  130 . In that way it is possible to prevent the audio output from being rapidly and uncontrolledly switched on and off or activated or deactivated if the error rate in the wireless receiving unit  100  assumes values which represent the limit range of an acceptable audio transmission and in particular if the error rate remains in that limit range over a period of several seconds. 
         [0023]    The invention is based on the idea that the receiving unit  100 , even in the case of error-affected transmission up to a given limit on the error rate, is capable of producing an audio output of acceptable quality by estimation and possibly error concealment. If however the error rate exceeds a limit value then the quality of the audio output produced in that way is no longer acceptable and it is better then not to output any audio signal at all, and therefore to “mute” the audio output signal. As soon as the error rate falls again an acceptable audio signal can again be output. If however the error rate is in the limit range between acceptable and unacceptable audio quality over some seconds the comparison with only one limit value would lead to an uncontrolled rapid succession of activation and deactivation of the audio output and would thus produce a completely unusable audio output signal. To avoid that according to the invention there is provided a hysteresis effect for the mute function in conjunction with estimation and error concealment. In addition, for ascertaining the error rate, a respective time window is analyzed, in which there is a relatively large number of for example more than 100 sample values in order to prevent an unnecessary reaction on the part of the system with very short disturbances in transmission. 
         [0024]      FIG. 2A  shows a graph view of the variation in respect of time of the error rate ER according to a first embodiment. As long as the error rate ER is below the first threshold value  151   a,  for example 40%, output of the audio signal to be reproduced takes place. If however as illustrated at time t 1  the error rate is greater than the first threshold value  151   a  then the audio output is deactivated and the system is thus muted. An audio output is activated again only when the error rate falls below a second threshold value  151   b,  for example 1%, for a given period of time. In  FIG. 2A  the error rate ER falls at the time t 2  below the second threshold value  151   b  and has to remain there for a period from t 2  to t 3  before the audio output is re-activated. Thus in the time interval tM, that is to say between t 1  and t 3 , the system is muted and no audio output takes place. 
         [0025]      FIG. 2B  shows a graph view illustrating the variation in respect of time of the error rate ER according to a second embodiment. This embodiment does not provide for ascertaining the error rate ER continuously in relation to time, but an error rate is respectively ascertained at a discrete moment in time, that rate relating to a respective time window which has just expired. The error rate  212  is accordingly ascertained by the errors being counted in the time window from the moment in time  201  to the moment in time  202  in an error counter and by the number of transmitted audio signals being counted for the same time window in a sample counter. With the number of errors both the errors  112  detected by the high frequency analysis  110  and also the errors  122  detected by the decoder  120  can be taken into consideration. The value of the error rate ER  212  at the moment in time  202  is then afforded by division of the state of the error counter by the state of the sample counter. In this case the time window is of the first duration  221  which has elapsed from the moment in time  201  to the moment in time  202 . The first duration  221  can be for example 100 ms. After calculation of the error rate both counters are set to zero so that the error rate ER respectively takes account of the time window which has elapsed since the previous calculation of the error rate. 
         [0026]    In the configuration shown by way of example in  FIG. 2B  output of the audio signal is firstly activated. At the moment in time  204  the error rate  214  is ascertained, relating to the time window from the moment in time  203  to the moment in time  204 . As that error rate  214  is above the first threshold value  151   a  output of the audio signal is deactivated at that time  204 . The receiving unit  100  therefore switches into the “muted” state. In that state a second duration  222  can optionally be used for the length of the time window, to which a calculated error rate ER respectively relates. The error rate  215  which is calculated at the moment in time  205  thus relates to a time window which is between the moment in time  204  and  205  and which is of a duration  222  of for example 200 ms. 
         [0027]    At the moment in time  207  the example in  FIG. 2B  involves calculating an error rate  217  which is below the second threshold value  151   b.  Because the error rate  217  relates to the time window from the moment in time  206  to the moment in time  207 , this means that the error rate has remained on average below the second threshold value  151   b  for the entire duration of that time window. This ensures that a corresponding improvement in transmission quality has actually occurred. At the moment in time  217  therefore the audio output is activated again and the receiving unit  100  thus goes into the “unmuted” state. 
         [0028]    The length of the time window used for analysis of the error rate ER is again set to the first duration  221  in the “unmuted” state. The first duration  221  (unmuted) is preferably shorter than the second duration  222  (muted) as a fast reaction on the part of the system is desired in the “unmuted” state in order to interrupt the audio output as quickly as possible when the audio quality is no longer acceptable while in the “muted” state it is possible to ensure by the longer duration  222  that the transmission functions in stable fashion again before the audio output is re-activated. Optionally a user of the system can adjust the two values for the first duration  221  and the second duration  222 . A typical value for the first duration  221  is 100 ms while a typical value for the second duration is 200 ms. A low limit for the selectable range of both values can preferably be established at 10 ms in order to ensure that a relatively large number of sample values is taken into consideration and thus an unnecessary reaction on the part of the system is prevented in the event of very short disturbances in the transmission. 
         [0029]    Optionally a user can also adjust the first threshold value  151   a  and the second threshold value  151   b.  A typical for the first threshold value  151   a  is 40% while a typical value for the second threshold value  151   b  is 1%. By the choice of the first threshold value  151   a  the user can establish the error rate up to which he considers acceptable the quality of the audio signal produced by estimation and possibly error concealment, in respect of his use. By the choice of the second threshold value  151   b  he can establish the limit as from which a sufficiently stable transmission is again assumed to occur in his specific situation of use. According to the invention the second threshold value  151   b  is less than the first threshold value. 
         [0030]    Optionally the values selected by the user for the first and second duration  221 ,  222  as well as the first and second threshold values  151   a,    151   b  can be stored jointly with an item of information about the respective situation of use so that the stored values can be later used again without a renewed manual input. The information about the situation of use can include for example the location of an event. 
         [0031]      FIG. 3  shows a flow chart relating to operation of the digital wireless audio transmission unit according to the invention. During the transmission the received data packets are continuously processed and in that respect in step S 10  in the sample counter the number of the received sample values and in the error counter the number of the errors detected in that case are summed up. At the query S 11  the procedure then involves checking whether the end of the time window just being considered is reached. If the end of the time window is not reached then the flow progresses to step S 13  and operation of the audio transmission system is not influenced. If however the end of the time window is reached then the flow progresses to step S 12  where the error rate ER is calculated by division of the value of the error counter by the value of the sample counter and then both counters are reset to the value zero. In addition the end of the following time window is established, in which case firstly the length of the time window which has just expired is used again. The query S 14  then involves checking whether the system is in the “muted” state. If that is the case then query S 15  involves checking whether the error rate ER is below the second threshold value  151   b.  If that is not the case the system remains in the “muted” state and processing continues unchanged with the step S 19 . If however it is established at the query S 15  that the error rate ER is below the second threshold value  151   b  then the system is put into the “unmuted” state in step S 17  by the audio output being activated and the duration to be used for the next time window is set to the first duration  221  and used for establishing the next window end before the process proceeds at step S 19 . 
         [0032]    If it were established at the query S 14  that the system is not in the “muted” state then the process continues at the query S 16 . There a check is made to ascertain whether the error rate ER is above the first threshold value  151   a.  If that is not the case the system then remains in the “unmuted” state and processing proceeds unchanged at the step S 13 . If however it is established at the query S 16  that the error rate ER is above the first threshold value  151   a  then the system is put into the “muted” state in step S 18  by the audio output being deactivated and the duration to be used for the next time window is set at the second duration  222  and is used for establishing the next window end before the process proceeds at step S 19 . 
         [0033]    According to the invention wireless audio real time streaming is effected for example from a digital wireless microphone as the transmitter. In that respect the invention concerns in particular the wireless receiver which receives the audio data from the digital wireless microphone. 
         [0034]    According to the invention the decoder  120  converts the received streaming data into audio samples or audio data. The audio data or samples are then passed to the audio processing unit  130  where further audio processing or conversion possibly takes place. For that purpose the audio processing unit  130  is capable of activating or deactivating the output audio signal and can thus mute the system. 
         [0035]    According to the invention the high frequency analysis unit  110  can detect errors in the wireless transmission for example by a CRC mechanism. 
         [0036]    According to the invention the decoder  120  can implement error concealment. The second items of error information  122  can include information as to whether error concealment by the decoder  120  was successful or required. 
         [0037]    The error detection unit  140  can have two different sampling times and two different threshold values. A first time interval can be associated with the first threshold value  151   a  and a second time interval can be associated with the second threshold value  151   b.    
         [0038]    While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the inventions as defined in the following claim.