Abstract:
A classroom sound amplification system adapted for providing information aiding at diagnosing possible erroneous or inappropriate conditions or configurations of the system is disclosed. The system comprises a microphone device converting a voice to a sound signal and connecting to a sound processing device processing the sound signal and generating a processed sound signal, and a speaker device connecting to the sound processing device and converting the processed sound signal to a processed voice. The sound processing device may further comprise a feedback cancellation unit identifying acoustical feedback in the sound signal and removing the acoustical feedback in the sound signal. Communication with the parts of the system carried by a moving person may be wireless.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a sound amplification system, in particular a classroom amplification system, i.e. a system used for enhancing the sound so as to increase the learning for students, such as a public address sound system or an assistive learning system. The invention relates specifically to the maintenance of such systems. The invention further relates to minimization or cancellation of acoustical feedback in such systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present account of the prior art relates to one of the areas of application of the invention, classroom sound amplification systems. 
         [0003]    Generally, state of the art classroom sound systems comprise a microphone worn by a teacher and connected to an amplifier, which amplifies the teacher&#39;s voice and communicates an amplified signal to a set of speakers situated in the classroom. As the teaching format has evolved from classical lectures given from a generally fixed position in front of a blackboard to computer power point presentations and a moving teacher moving around in the classroom, the requirements of a classroom sound amplification system has simultaneously increased. A multitude of technical features can be included in such a system, e.g. features relating to the distribution and quality of sound, such as e.g. acoustical feedback compensation but also other features relating to a combination with stationary or mobile audio and/or visual units. Such combinations can make the system relatively complex. 
         [0004]    For example, the movement of the teacher requires the classroom sound amplification system to be able to compensate for acoustical feedback generated when the teacher, for example, moves the microphone closer to one of the speakers. 
         [0005]    The troubleshooting of an installed system can be difficult, and e.g. involve drawing the user&#39;s attention to checklist&#39;s containing typical errors and/or wrong or inappropriate system settings, etc., and if insufficient to solve the problem anyway may require that part of or the whole system is sent in to the manufacturer or to a service site for evaluation. Alternatively, it may require that a technician goes to the place of installation. In some cases, systems thus evaluated are found fully functional, and the conclusion is that the mal-function is due to some sort of inappropriate or erroneous configuration of the system. This is obviously time consuming and costly, and imposes down-time of the system, all of which is degrading the perceived value of the classroom amplification system. 
       SUMMARY OF THE INVENTION 
       [0006]    An object of the present invention is to provide an improved sound amplification system, e.g. a classroom amplification system overcoming drawbacks of prior art sound systems. 
         [0007]    It is a further object to provide a system that is simpler to maintain. 
         [0008]    It is a further object of embodiments of the present invention to improve the learning of students in a classroom environment so that a greater number of students benefit from the teaching. 
         [0009]    A particular advantage of embodiments of the present invention is to enable the teacher to move freely and un-hindered around amongst the students while the voice is being processed and distributed by the sound amplification system. 
         [0010]    A particular feature of embodiments of the present invention is the provision of a transmission of images concurrently with transmission of a teacher&#39;s voice. 
         [0011]    An object of embodiments of the present invention is to provide a sound system having a simple and effective means for eliminating acoustical feedback, and which requires only a few processing steps. 
         [0012]    A particular feature of the present invention is utilization of an understanding of the statistical distribution of a speech signal in the frequency domain. 
         [0013]    One or more of the above objects are achieved by a sound amplification system (e.g. a classroom sound amplification system) comprising a microphone device adapted to convert a an acoustical sound (e.g. a voice or a combination of a voice and other sounds, e.g. music) to a (e.g. electric) sound signal and connecting to a sound processing device adapted to process said sound signal and to generate a processed sound signal, and a speaker device connecting to said sound processing device and adapted to convert said processed sound signal to a processed sound, and further one or more Audio- and/or Video-devices and a control device, the control comprising a data processing unit, a memory and optionally a communications interface, wherein the microphone device, the sound processing device, the speaker device and the one or more Audio- and/or Video-devices are connected to or form part of said control device allowing the control device to collect operational information concerning the operation and/or status of various devices of the system (including the A-V-devices) by monitoring predefined operational parameters at various points in time and by storing such information in said memory. 
         [0014]    The term “processed” is in this context to be construed as amplifying a signal according to a transfer function; i.e. the gain is not necessarily constant throughout a frequency bandwidth, or throughout time. Further, the term “processor” or “processing device/unit” is in this context to be construed as a unit capable of performing a wide range of mathematical processes such as achieved by a microprocessor, a microcontroller, a central processing unit, and/or a digital signal processor. Hence the processor is capable of implementing a transfer function for a sound signal, i.e. providing a required gain in accordance with frequency. 
         [0015]    The terms “a” and “an” used in connection with elements of the invention are in this context to be construed as one or more, a plurality, or a multiplicity of elements. 
         [0016]    It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other stated features, integers, steps, components or groups thereof. 
         [0017]    In an embodiment, one or more Audio- and/or Video-devices comprise a further microphone device or a further speaker device. In an embodiment, one or more Audio- and/or Video-devices comprise a DVD-player or a personal computer with display and/or loudspeaker and/or microphone, a smart board, etc. 
         [0018]    In an embodiment, the operational information can be inspected directly (in real time or retrieved at a later point in time) via a display unit or be exchanged with another unit or system, e.g. via a fixed transmission line or a network, e.g. the Internet. 
         [0019]    In a particular embodiment, the sound amplification system is a classroom sound or voice amplification system, where a microphone device is worn by a person, e.g. a teacher, who may be stationary or move around in the classroom. 
         [0020]    The presence of computing power and memory in a classroom amplification system allows the retrieval of performance data over time of any character, assumed to have an influence on system performance, including some of the following operational information:
       usage patterns
           use-/down-time (to determine and analyze the use pattern in a particular class room, in a particular period)   how often the system has been muted (to determine how often (or how large a fraction of the time) the teacher voice has been amplified within the class),   how long time mobile units have been charged (serving as a troubleshooting aid for the manufactures service department),   how often (or how large a fraction of the time) other media were run using the system (to determine metrics or trends for the use of multimedia in classrooms),   
           incidences of interference (to help determine the possible root cause of interference from other signal sources in a particular installation),   incidences of feedback (to help determine the optimum placement of speakers in the room and to aid the troubleshooting of installations. This information can also be used to evaluate the effectiveness of the amplification system),   static noise (noise in the receiver, this can help aid in troubleshooting the installation, such as a failure in the squelch circuit),   incidences where microphone went into clipping,   battery status in stationary and mobile units,
           battery charging/discharging rate,   
           settings of user-controls on the system,   microphone input levels (to determine if the microphone is being worn correctly),   presence of auxiliary input/output (to determine when the unit would come out of standby mode),       
 
         [0035]    Such status information, which is helpful in evaluating the system and at least some of which is or can be made self-diagnosing, can thus be retrieved either directly from the system memory (or from another storage medium to which the data are transferred), when units are shipped in to a service centre for repairs, or remotely when such data are transmitted to a service centre (e.g. in real time or streamed via a WLAN/Internet connection). 
         [0036]    In an embodiment, operational data are collected from a monitored device via a USB interface to a control device (e.g. a PC or Mac). In an embodiment, data are stored in a log-file on the control device. In an embodiment, operational data are collected from a monitored device via a wired or wireless local area network. In an embodiment, operational data are collected from a monitored device via the Internet, the monitored device having an IP-address assigned. 
         [0037]    In an embodiment, the control device is a PC or MAC computer (personal computer). In an embodiment, the control device functions as a media hub of a classroom sound amplification system tying together the various parts of the system and e.g. including a projector and/or a high-bandwidth network connection. This has the advantage that all sorts of content and media can be downloaded, manipulated, created and played (on the relevant device/unit) via the control device. Further, during a lesson—in addition to amplifying the teacher&#39;s voice—different media could be controlled and played through the classroom sound amplification system (e.g. computer assisted presentations, audio files, video files, smart board sessions, etc.). 
         [0038]    In a particular embodiment, the system is adapted to forward operational information to a predefined receiving unit (e.g. a local or remote service unit or centre). In a particular embodiment, the system is adapted to forward such operational information at regular intervals in time, e.g. once a day (e.g. during idle periods, e.g. nightly, e.g. via e-mail). In a particular embodiment, the system is adapted to forward such operational information automatically based on predefined criteria or the system comprises an activator (e.g. a ‘help button’ implemented in hardware or software) allowing a user to activate such forwarding. In a particular embodiment, the predefined criteria comprise one or more conditions for dysfunction of the system. 
         [0039]    In a particular embodiment, the system comprises a set of predefined criteria for the monitored operational parameters representing un-allowed or inappropriate configurations of the system. An un-allowed operational parameter could e.g. be a maximum allowable de-charging rate for battery powered units, a value superseding the maximum value indicating that replacement of batteries are required. Another example could be maximum volume control settings, values superseding the maximum values indicating an improper setup or installation. 
         [0040]    In a particular embodiment, the system is adapted to create a system status signal based on a comparison of the monitored operational parameters and said predefined criteria. Such system status signal could indicate whether or not the system is in a state of error, and if so, in which part (or device) such erroneous state is present. In a particular embodiment, the system microcontroller in the control device is configured to go through a self-test mode upon power up, and if certain state-parameters are outside normal limits an error code is generated. In an embodiment, the error code equals the system status signal. 
         [0041]    In a particular embodiment, the system is adapted to forward such operational information automatically to a predefined unit or system based on and/or in response to a comparison with said predefined criteria. Such unit or system can be a part of the sound amplification system or located remotely, e.g. at a service centre, where a technician can attend to the information and take proper action. 
         [0042]    In a particular embodiment, the system is adapted to create a diagnosis based on a comparison of the monitored operational parameters and said predefined criteria, thereby creating a self-diagnosing system. 
         [0043]    In a particular embodiment, the system is adapted to provide that a wearer of a microphone device of the system and whose voice is to be processed and distributed by the system is able to move freely within the normal area of function of the system without being limited in movement by cable wiring to the microphone device and possible other devices integrated therewith. 
         [0044]    In a particular embodiment, the classroom sound amplification system is wireless. A wireless system implies that the wearer of the microphone device (e.g. a teacher) and whose voice is to be processed and distributed by the system is able to move freely (including not being limited in movement by cable wiring to the microphone device (and possible other devices integrated therewith, e.g. a sound processing device). In other words, the direct communication from the part of the system carried by a wearer of a microphone device of the system to other parts of the system is wireless. 
         [0045]    In a particular embodiment, the system comprises more than one microphone device, e.g. 2, 3, 4, 5 or more. In an embodiment, each microphone can be individually activated in the system. In an embodiment, no more than one microphone device can be active at a given time. In an embodiment, more than one microphone device can be active at a given time. In an embodiment, the system is adapted to process a human voice. In an embodiment, the system is adapted to process a voice or a combination of a voice and other sounds, e.g. music. 
         [0046]    In a particular embodiment, the sound processing device comprises a feedback cancellation unit adapted to identify acoustical feedback in said sound signal and to remove said acoustical feedback in said sound signal. 
         [0047]    The feedback cancellation unit may comprise a calculating element adapted to calculate a threshold value based on mean magnitude and standard deviation of the sound signal. The feedback cancellation unit may further comprise a FFT element adapted to transform the sound signal into frequency domain, and a peak identification element adapted to identify a peak in the sound signal in frequency domain and to generate a peak signal. The feedback cancellation unit may further comprise a comparator adapted to compare the threshold value with the peak signal and to generate a control signal identifying frequency of the peak. The feedback cancellation unit may further comprise a programmable notch-filter unit adapted to receive the control signal and operable to filter out a bandwidth of the sound signal in accordance with the control signal thereby generating the processed sound signal. 
         [0048]    The classroom sound system may, advantageously, utilize the fact that vocal sound has a Gaussian distribution in the time domain and the fact that most energy is of the vocal sound is within one standard deviation from the centre frequency. Hence the classroom sound system is particularly useful in situations where vocal sound is to be amplified such as in a classroom. 
         [0049]    The microphone device may comprise a microphone transmitter adapted to transmit the sound signal wirelessly to the sound processing device in accordance with a communication protocol. The communication protocol may be a proprietary protocol or a protocol such as Bluetooth, WLAN, WiMax, Wi-Fi, or other standardized protocols. The microphone transmitter, advantageously, enables the teacher to freely move around in the classroom and provide support for students at their tables or desks. However, having the teacher moving around in the classroom increases the possibility of the occurrence of acoustical feedback since the position of the microphone relative the speaker device may be too close. Hence prior art classroom amplification systems with wireless microphones inherently experience acoustical feedback creating a howling sound from the speakers. The feedback cancellation unit thus, advantageously, ensures dynamic removal of acoustical feedback. 
         [0050]    The sound processing device may comprise a sound processing transmitter adapted to transmit the processed sound signal wirelessly to the speaker device in accordance with a communication protocol. The communication protocol may be a proprietary protocol or a protocol such as Bluetooth, WLAN, WiMax, Wi-Fi, or other standardized protocols. The sound processing transmitter thus enables for wireless connection to a speaker device. This further flexibility in movement of the teacher carrying a microphone wirelessly connecting to the sound processing device, which is wirelessly transmitting to a movable speaker device, further increases the possibility for the occurrence of acoustical feedback. Hence the feedback cancellation unit ensures the mobility of the speaker devices as well as the microphone by dynamically removing acoustical feedback when detected. 
         [0051]    The speaker device and/or an Audio- and/or Video-device of the system may comprise an interactive white-board. The interactive white-board offer computer-interactive presentation, which offers images together with audio such as the teacher&#39;s processed voice. Having the teacher facing an interactive white-board equipped with speakers further increases the possibility of occurrences of acoustical feedback, which, advantageously, is prohibited by the feedback cancellation unit according to the first aspect of the present invention. 
         [0052]    The speaker device may comprise a personal computer wirelessly connecting to the sound processing transmitter and/or microphone transmitter and adapted to receive images concurrent to the speaker device generating the processed voice. Hence the personal computer may provide visual support during classes such as, for example, power point shows or other presentational data. The personal computer may comprise a laptop or desktop general purpose computer. 
         [0053]    The speaker device may be integral with the personal computer or be external devices plugged to the personal computer. Hence the personal computer allows the teacher to communicate with the students in a classroom by having the microphone device connecting directly to the students&#39; personal computers, while simultaneously presenting visual material either directly, or streamed to the students personal computers. 
         [0054]    The personal computer may comprise a wireless receiver connecting to the sound processing transmitter. Hence the wireless receiver may be implemented by a PCMCI card inserted into the personal computer such as WLAN, Wi-Fi, WiMax or Bluetooth. 
         [0055]    The personal computer may connect to projecting means adapted to display a visual presentation. The personal computer may further connect to a communications network such as a local area network (LAN), wide area network (WAN), metropolitan area network (MAN), or an internetwork (e.g. the Internet), which communications network is adapted to forward the processed sound signal. The communications network may interconnect the personal computer to a plurality of speaker devices and/or further personal computers. Hence the personal computer may act as a media hub of a classroom. 
         [0056]    The personal computer may comprise the sound processing device. The sound processing device may be implemented in the personal computer as a software program. 
         [0057]    The programmable notch-filter may comprise a leaky integrator operable to control attack time of said programmable notch-filter. The leaky integrator ensures that the notch-filter gradually reduces the sound signal in the frequency domain in a bandwidth of the notch-filter so that artifacts introduced by steep edged notch-filters are avoided. The leaky integrator is computationally efficient for the sound system since it requires only three mathematical operations. 
         [0058]    Further, the leaky integrator may be operable to control the attack times of the programmable notch-filter in accordance with frequency. That is, the leaky integrator may be adapted to be operable having a first attack time for a first frequency bandwidth and having a second attack time for a second frequency bandwidth. Thus the leaky integrator may e.g. be operable having a long attack time in the high frequency part of said sound signal in said first frequency bandwidth and having a short attack time in the low frequency part of said sound signal in said second frequency bandwidth. 
         [0059]    The term “attack time” is in this context to be construed as the time it takes for the programmable notch-filter from receiving a control signal to fully engaging the filter. Further, “attack time” is in this context to be construed as similar to “release time” being the opposite, namely the time it takes for the programmable notch-filter from receiving a control signal to fully disengaging the filter. 
         [0060]    The processor (or sound processing device) may further comprise a counter unit adapted to count a number of frequencies of said sound signal in the frequency domain having magnitudes above said threshold value. The counter unit may be adapted to provide a gain control signal to said processor when the count of said frequencies is above a predetermined number. Hence, the processor when receiving the gain control signal may reduce gain throughout the frequency spectrum. This is, particularly, advantageous since by identifying a plurality of frequencies in the sound signal in the frequency domain may demonstrate an acoustical feedback is present. For example, the predetermined number may be in the range between 2 to 10 such as 3. 
         [0061]    The programmable notch-filter may be operable to establish a number of parallel notch-filters each having a selected operating bandwidth. Obviously, any number of parallel notch-filters may be established each having a selected operating bandwidth and centre frequency; however, the number may be limited to the predetermined number defined above. 
         [0062]    The programmable notch-filter may be operable to receive the sound signal in the time domain or to receive the sound signal in the frequency domain. The configuration of the programmable notch-filter is thus not limiting to the sound system. 
         [0063]    In addition, the programmable notch-filter may comprise amplifying means adapted to amplify the sound signal in accordance with a predetermined transfer function. The programmable notch-filter may be implemented as an active filter such as an infinite impulse response filter. 
         [0064]    In an aspect of the invention a method of operating a sound amplification system is provided, the method comprising 
         [0065]    a) providing a microphone device adapted to convert an acoustical sound to an electrical sound signal, 
         [0066]    b) providing a sound processing device adapted to process said sound signal and to generate a processed sound signal, 
         [0067]    c) providing a speaker device adapted to convert said processed sound signal to a processed sound, 
         [0068]    d) providing one or more Audio- and/or Video-devices, and 
         [0069]    e) providing a control device comprising a data processing unit, a memory and optionally a communications interface, 
         [0070]    f) connecting the microphone device, the sound processing device, the speaker device and the one or more Audio- and/or Video-devices to said control device, thereby allowing the control device to collect operational information concerning the operation and/or status of various devices of the system; 
         [0071]    g) monitoring predefined operational parameters of said devices at various points in time and storing such information in the memory of the control device. 
         [0072]    In a particular embodiment, the system comprises a communications interface allowing the system (e.g. the control device) to communicate with local or remote units or systems, e.g. a service centre. 
         [0073]    In a particular embodiment, the system is adapted to forward the operational information to a predefined receiving unit or system. 
         [0074]    In a particular embodiment, a set of predefined criteria for the monitored operational parameters representing un-allowed or alarming values or inappropriate configurations of the system is defined. 
         [0075]    In a particular embodiment, said set of predefined criteria is stored in the memory of the control device. 
         [0076]    In a particular embodiment, a system status signal based on a comparison of the monitored operational parameters and said predefined criteria is created. 
         [0077]    In a particular embodiment, said operational information is forwarded automatically to a predefined unit or system in response to a comparison with said predefined criteria. 
         [0078]    In a particular embodiment, a system diagnosis is created based on a comparison of the monitored operational parameters and said predefined criteria, thereby creating a self-diagnosing system. 
         [0079]    In a particular embodiment, a wearer of a microphone device of the system and whose voice is to be processed and distributed by the system is able to move freely within the normal area of function of the system without being limited in movement by cable wiring to the microphone device and possible other devices integrated therewith. 
         [0080]    In a particular embodiment, the direct communication from a part of the system carried by a wearer of a microphone device of the system to other parts of the system is wireless. 
         [0081]    In a particular embodiment, the operations performed by the microphone device, the sound processing device and the speaker device comprise: 
         [0082]    (a) converting an acoustical sound to an electrical sound signal, 
         [0083]    (b) calculating a threshold value based on mean magnitude and standard deviation of said sound signal, 
         [0084]    (c) transforming said sound signal into frequency domain, 
         [0085]    (d) identifying a peak in said sound signal in frequency domain and generating a peak signal, 
         [0086]    (e) comparing said threshold value with said peak signal and generating a control signal identifying frequency of said peak when said peak signal is above said threshold value, 
         [0087]    (f) filtering out a bandwidth of said sound signal according to said control signal thereby generating a filtered sound signal, 
         [0088]    (g) processing said filtered sound signal and generating a processed sound signal, 
         [0089]    (h) communicating said processed sound signal to a speaker device, 
         [0090]    (i) converting said processed sound signal to a processed acoustical sound. 
         [0091]    In an aspect of the invention use of a system according to the invention and as described above, in the detailed description and in the claims is provided. 
         [0092]    In a particular embodiment the system is used as a classroom sound amplification system. In a particular embodiment the sound includes a voice. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0093]    The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawing, wherein: 
           [0094]      FIG. 1 , shows a block diagram of a sound system according to a first embodiment of the present invention; 
           [0095]      FIG. 2 , shows a block diagram of a sound processor for the sound system according to a first and presently preferred embodiment of the present invention; 
           [0096]      FIG. 3 , shows a further block diagram of a sound processor for the sound system according to a second embodiment of the present invention; 
           [0097]      FIG. 4 , shows a further block diagram of a sound processor for the sound system according to a third embodiment of the present invention; 
           [0098]      FIG. 5 , shows a further block diagram of a sound processor for the sound system according to a fourth embodiment of the present invention; 
           [0099]      FIG. 6 , shows an overview of a classroom amplification system according to an embodiment of the present invention; and 
           [0100]      FIG. 7 , shows a block diagram of classroom amplification system according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0101]    In the following description of the various embodiments, reference is made to the accompanying figures, which show by way of illustration how the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention. 
         [0102]      FIG. 1 , shows a block diagram of a sound system according to the first embodiment of the present invention and designated in entirety by reference numeral  100 . The sound system  100  comprises a microphone unit  102  converting a sound to an analogue electrical sound signal. The analogue electrical sound signal is communicated through a first communication path  104  to an analogue-to-digital (A/D) converter  106 , which converts the analogue electrical sound signal into a digital sound signal. The digital sound signal is communicated through a second communication path  108  to a sound processor  110 , which processes the digital signal in accordance with a predetermined transfer function. The second communication path  108  may be a multi-channel bus. The sound processor  110  generates a processed digital signal and communicates this through a third communication path  112  to a digital-to-analogue (D/A) converter  114 . The third communication path  112  may be identical to the second communication path  108  i.e. a controlled multi-channel bus. The D/A converter  114  converts the processed digital signal into a processed analogue signal and communicates this through a fourth communication path  116  to a driver  118 . Finally, the driver  118  is connected to a loud speaker  120  through a fifth communication path  122  and is adapted to drive the loud speaker  112  to present a processed sound. 
         [0103]    A large part of the sound system  100  may in fact be implemented as integrated elements so that the sound system  100  comprises the microphone unit  102 , the speaker unit  120  and a digital signal processor  124 . 
         [0104]    A control device  107  for gathering operational information (such as parameters that may be used to judge the operational status of the device in question) of the devices of the system is connected to each of the monitored devices. 
         [0105]    The sound processor  110  as shown in  FIG. 2  comprises an input buffer unit  202  adapted to buffer the digital signals into a number (N) of frames, which are communicated to a FFT unit  204  transforming the frames into frequency domain signals and to a threshold calculation unit  206  adapted to calculate a threshold value from the frame based on mean magnitude (m) and standard deviation (σ) of the frames. For example the threshold value may be determined in accordance with formula 1 below. 
         [0000]      Threshold_value= m+α·σ   (Formula 1), 
         [0000]    where “m” is the mean magnitude of the frame, “α” is a multiplication factor and “σ” is standard deviation of the frame. The calculation of the threshold value may further be adjusted by a bias. The multiplication factor “α” may have any real number; however the presently preferred number is 2, since this provides for most of the energy of the frame if the frame contain vocal information. 
         [0106]    The transformed frame is forwarded from the FFT unit  204  to a peak identification unit  208  adapted to identify peaks in the transformed frame and to generate a peak signal for each peak identified in the transformed frame. 
         [0107]    The peak signal provides information of magnitude and frequency of the peak. The peak identification unit  208  may be configured to identify any number of peaks such as in the range one to ten, for example identifying the three largest peaks in each transformed frame. The peak identification unit  208  may comprise a counter for counting number of peaks and may be adapted to generate a flag signal when the number of peaks identified equals a pre-selected number. 
         [0108]    The threshold calculation unit  206  generates a threshold signal for each frame and forwards the threshold signal to a comparator unit  210 , which compares the threshold signal to the peak signals received from the peak identification unit  208 . 
         [0109]    The calculation of the mean magnitude of the frequency spectrum in a frame may advantageously be established by a squared addition of the real and imaginary parts of the digital signals. Further, the calculation of the mean magnitude of the digital signals may advantageously be established by a vector magnitude computation such as suggested by Richard G. Lyons in “Understanding Digital Signal Processing” 2nd edition (the αMax+βMin method). It should be understood that any calculation or estimation know to a person skilled in the art may be employed. 
         [0110]    The comparator unit  210  generates a filter control signal in case the peak signal is greater than the threshold value, which filter control signal is forwarded to a filter/amplifier unit  212 . The filter/amplifier unit  212  comprises a programmable notch-filter  214  and an amplifier  216 , and is adapted to receive the digital sound signal and filter the digital sound signal according to the filter control signal by means of the programmable notch-filter  214 , and to amplify the potentially filtered digital sound signal according to a predetermined transfer function by means of the amplifier  216 . In this context the term “amplify” is to be construed as increasing or decreasing any particular frequency regions. 
         [0111]    The filter/amplifier unit  212  may be implemented as an active filter such as an infinite impulse response (IIR) filter. 
         [0112]    The programmable notch-filter  214  may comprise a leaky integrator adapted to provide a gradual engagement of the notch-filter  214  so as to avoid artifacts caused by the notch-filter&#39;s  214  sharp edges to be generated. For example, the leaky integrator may be operable so that the effect of the notch-filter is engaged and disengaged slowly. The leaky integrator may be implemented by any means know to a person skilled in the art. 
         [0113]    In case the peak identification unit  208  identifies a maximum number of peaks within a frame the comparator  210  generates an alert signal, which causes the filter/amplifier unit  212  to reduce gain of the amplifier  216 . The effect of the reduction of the gain is monitored on the following frames. That is, if the peak identification unit  208  fails to identify new peaks in the next frames then the gain is gradually increased. 
         [0114]      FIG. 3 , shows a block diagram of a sound processor  110 ′ according to a second embodiment of the present invention, which comprises the same elements of the sound processor  110  and these are referenced by the same numerals. The sound processor  110 ′ differs from the sound processor  110  by having the FFT unit  204  transforming the frames into frequency domain signals, which are then communicated to the threshold calculation unit  206  in this case being adapted to calculate a threshold value from the frame based on mean magnitude and standard deviation of the frequency spectrum of the frame. 
         [0115]      FIG. 3 , shows a block diagram of a sound processor  110 ″ according to a second embodiment of the present invention. The sound processor  110 ′ comprises the same elements of the sound processor  110  and  110 ′ and these are referenced by the same numerals. The sound processor  110 ″, however, differs from the sound processor  110 ′ by having the filter/amplifier unit  212  receive frames from the buffer unit  202  and thus perform filtering and amplifying operations on the frames rather than directly on the digital sound signal. 
         [0116]      FIG. 4 , shows a further block diagram of a sound processor  110 ′″ according to a third embodiment of the present invention. The sound processor  110 ′″ comprises the same elements of the sound processors  110 ,  110 ′ and  110 ″ and these are referenced by the same numerals. The sound processor  110 ″, however, differs from the sound processors  110  and  110 ′ by having a filter/amplification unit  300  receiving the sound signal in the frequency domain from the FFT unit  204  and thus performing the filtering and amplifying operations on the sound signal in the frequency domain rather than on the digital sound signal or on the frames. The filter/amplification unit  300  further comprises an inverse FFT unit  302  for inverting the processed sound signal in the frequency domain back into a processed sound signal in the time domain. 
         [0117]      FIG. 6  shows a classroom designated in entirety by reference numeral  600 . In the classroom  600  a teacher  602  speaks to an audience of students  604 . The teacher  602  carries a microphone device around the neck or attached on a collar of a coat or shirt. The microphone device converts the sound from the teacher  602  to an electric sound signal. The microphone device comprises a transmitter for transmitting the sound signal to a signal processing device  606  receiving the sound signal and performing processing of the sound signal e.g. filtering and amplification. The signal processing device  606  may comprise a transmitter for (wirelessly) transmitting the processed sound signal to speaker devices  608 ,  610 ,  612  and  614 . Alternatively or additionally, the signal processing device  606  may forward the processed signal to the speaker devices  608 ,  610 ,  612  and  614  by wire. The sound system comprises a control device  607  for monitoring the operational history and status of other devices of the system. The control device is electrically or optically connected to other devices of the system to be monitored either via electrical or optical wiring or via wireless connections (e.g. radio frequency or infra red light communication). The signal processing device  606  may e.g. be a part of the control device  607 , the processing functions possibly being implemented as a software routine run on said control device, e.g. a PC. 
         [0118]    The control device is connected to a service centre via a dedicated connection or via a network. 
         [0119]      FIG. 7 , shows a classroom amplification system according to an embodiment of the present invention and designated in entirety by reference numeral  700 . The classroom amplification system  700  positioned in a classroom  702  comprises a wearable microphone unit  704  connecting wirelessly to a control device (here a computer)  706  acting as a hub for a plurality of computers  708 . Alternatively the connection between microphone unit and computer may be wired. The computer  706  connects to the plurality of computers  708  through a communications bus  710 , which may be implemented as a hardwired local area network or a wireless local area network, such as Bluetooth, Wi-Fi or WiMax. The microphone unit  704  may also directly connect wirelessly to a plurality of students&#39; personal computers or ultra mobile personal computers (UMPC), acting as local speakers and/or storage devices. The plurality of computers  708  may, for example, connect to the communications bus  710  by means of a PCMCI card. 
         [0120]    The communications bus  710  may further connect to a displaying means  712 , such as a projector or an intelligent whiteboard also known as smart board. The displaying means  712  may be utilized for presentation of images or text relating to the teaching of students. For example, the teacher may utilize the displaying means  712  for presentation of a power point show of text and/or pictures illustrating the subject to be taught. The displaying means  712  comprise one or more speaker units  714  and  716  presenting the processed voice of the teacher or additional audio determined by the teacher. For example, the teacher may desire to illustrate a certain pronunciation of a word or a particular piece of music and include this in the presentation. 
         [0121]    Similarly, the plurality of computers  708  may each comprise a speaker unit  718  presenting the processed voice of the teacher or additional audio determined by the teacher. 
         [0122]    The microphone unit  704  comprises a microphone  720  for converting the voice of the teacher to a sound signal, a sound processing device  722 , such as a digital signal processor, for processing the sound signal in accordance with a transfer function, and an antenna  724  wirelessly transmitting the processed sound signal to the computer  706  via antenna  726 . 
         [0123]    The control device  706  (here a computer such as a PC) is connected to other devices either via wired or wireless connections to monitor their operational status. The operational information is e.g. gathered at regular intervals in time, e.g. once every hour, and stored in a memory of the control device. A table of un-acceptable operational values of relevant parameters for each of the monitored devices of the system is stored in a memory of the control device. At certain intervals in time, e.g. once every hour, the stored values of the gathered operational information are compared to the un-acceptable operational values of relevant parameters for each of the monitored devices. In case of one or more of the operational parameters falling in an un-acceptable range, such parameter(s) and the relevant device(s) are identified and an alarm is flagged. A message, at least containing the identified parameter(s) and device(s) is transmitted to a service centre for evaluation by a technician, possibly together with information on the configuration of the system, and further operational information, e.g. a number (e.g. 10) of the last stored sets of operational parameters (for facilitating the debugging job of the technician). 
         [0124]    Generally, state of the art classroom sound systems involve a microphone worn by a teacher and wirelessly connected to an amplifier, which amplifies the teacher&#39;s voice and communicates an amplified signal to a set of speakers situated in the classroom (or possible in another room, physically separate from the classroom where the teacher is located). 
         [0125]    To establish the wireless link, different technologies have been used over time. For convenience and cost reasons most often common commercially available wireless technologies from providers of RF-components or RF-circuits are used. Examples of classic technologies are analog modulated technologies, the carrier-wave typically being either an RF (radiofrequency) or IR (infrared). These are characterized by being low-complexity, in-expensive proven solutions, offering simple on-way communication links. 
         [0126]    As new and more advanced wireless technologies are being commercially available, these have also found their way into the classrooms sound systems. 
         [0127]    The global drive for more and more wireless communication lines, with higher and higher density of users, are putting ever increasing pressure on bandwidth, speed, and cost. The classical technologies do not meet these requirements, and a plethora of new digital wireless technologies have emerged in the past decade. The sheer volume of products these technologies are used in is driving the cost down of these very sophisticated technologies. Examples of these technologies are Bluetooth, DECT, IEEE.802.11-compliant technologies, WiBree, ZigBee, etc. And more will come. 
         [0128]    It is therefore a natural development that some of these technologies also find use in classroom sound systems. 
         [0129]    What they can offer is hassle-free set-up in high density installations, like a school-wide installation. These classrooms are often in need of several channels for team-teaching and student pass-around microphones, which is where the digital technology offers an advantage. 
         [0130]    These technologies are most often having a bi-directional exchange of control signals that “negotiates” the communication protocol between the units set up to communicate with each other. Should disturbance occur in the current band/timeslot, they can agree to move to a un-disturbed place in the ether. Likewise audio can be exchanged in both directions. Obviously the teacher&#39;s voice can be carried over the wireless link. But the microphone worn by the teacher can also perform as a receiver, receiving classroom activity remotely, response from student pass-around microphones or team teaching units, or receive audio passed through the classroom sound system from external sources. 
         [0131]    Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject-matter defined in the following claims.