Patent Publication Number: US-10777180-B2

Title: Apparatus for a reed instrument

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of the U.S. patent application Ser. No. 16/258,333, filed Jan. 25, 2019, which is a continuation of U.S. patent application Ser. No. 15/746,723, filed Jan. 22, 2018, now U.S. Pat. No. 10,229,663, which is a national stage entry under 35 U.S.C. 371 of PCT Patent Application No. PCT/GB2016/052267, filed Jul. 25, 2016, which claims priority to the United Kingdom Patent Application No. 1513036.2, filed Jul. 23, 2015, the entire contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an apparatus that allows a player to quietly play a reed instrument, e.g. while practising. 
     The normal method of playing a reed instrument (e.g. clarinet, oboe, saxophone, bassoon) is well known. The user blows such that the reed vibrates, thus introducing a complex set of tones into the instrument. A resonant cavity is provided, having a plurality of keys. Depending upon which key(s) are depressed, resonance is produced such that a standing acoustic wave is formed that matches the resonance of the cavity. In this way the traditionally known notes are formed. 
     Typically when practising, it is desirable to reduce the noise output of reed instruments out of courtesy for those in the vicinity. 
     US 2014/0224100 A1 describes a system for use with bagpipes in which the normal reed is replaced with transducer apparatus comprising a speaker and a microphone. The speaker delivers sound to an air chamber of the bagpipes, the speaker being driven by a test signal comprising a periodic signal consisting of linear chirps, each linear chirp comprising only frequencies above 16 Khz, i.e. outside the audible range. The microphone detects the sound delivered to the air chamber and then the signal played by the speaker is correlated with the signal detected by the microphone to yield the response function of the acoustic system and thereby the musical note played by the instrument. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a system for representing sounds of a reed instrument according to claim  1 . 
     The use of a pressure sensor enables the control of timing of operation of the system e.g. in the output of sound by the microphone to the air chamber or the output of synthesized musical notes. 
     Preferably the signal sent by the pressure sensor to the processing unit additionally indicates how hard the user is blowing through the mouthpiece. This can be used to vary volume of the synthesized musical note output or to recognise an octave shift which can be achieved in some reed instruments by the player blowing hard. Also the air pressure variations may be used to modulate the synthesized sounds, e.g. to recognise when the player is applying a vibrato breath input to the reed instrument and in response import a vibrato into the synthesized sounds. 
     Other preferred features of the system of the invention are set out in claims  3  to  23 . 
     Preferably, the excitation unit is arranged to drive the speaker to produce sound at a volume chosen based on an amount of ambient noise. For example, the volume may be chosen to exceed ambient noise by a predetermined amount. The level of ambient noise may be measured using any known sensor, but is preferably measured using the microphone or by a separate ambient noise microphone measuring noise outside of the instrument. In one embodiment the user can select an operating mode in which the volume of sound produced by the excitation means can be manually selected. 
     The present invention allows a musician to practice with the system fitted to the reed instrument, without the generation of any significant noises which may disturb people nearby. 
     The output means may be one or more of: an interface for a computer; a wireless device for exchanging data over short distances using short-wavelength UHF radio waves; a MIDI (musical instrument data interface) connection; an HD protocol interface; and/or a transmitter. 
     The speaker and microphone may be mounted on a housing, the housing being adapted for attachment to an air chamber of a reed instrument such that the speaker and microphone are in communication with the air chamber. This allows for the system to be easily retrofitted to a musician&#39;s instrument. The speaker and microphone may be mounted on an inner surface of the housing in communication with a cavity formed therein, the housing being adapted for attachment to an air chamber of a reed instrument such that the speaker and microphone are in communication with the air chamber. Preferably the housing is adapted for attachment to a mouthpiece of a reed instrument and the housing is arranged to form a barrier between the mouthpiece and the air chamber. 
     In another preferred embodiment, the speaker and microphone may be mounted on a housing, the housing being adapted for attachment to an air chamber of a reed instrument such that the speaker and microphone are in communication with the air chamber; the housing forms a mouthpiece; a bore extends through the mouthpiece, the bore being separate from the cavity. 
     In yet another preferred embodiment, the mouthpiece may comprise a tip with an opening in communication with its bore. The mouthpiece comprises a false reed (in place of a normal reed) extending along the mouthpiece and, optionally, arranged to close the tip of the mouthpiece (although this is not essential). The false reed may be rigid so as not to vibrate when the user blows. The false reed has formed therein an air-pressure groove or air-pressure relief passage extending to a bleed hole formed in the false reed. This can be retrofitted onto existing instruments, and the air-pressure relief groove or passage can allow for the ejection of condensed moisture. 
     The air pressure sensor may be provided in the bore or in the air-pressure relief groove or passage. This allows the system to detect when the user is blowing and only play tones at these times. Additionally, as mentioned above, the strength of the blowing can be factored into the generation of the output signal and/or a vibrato input breath recognised and a vibrato element incorporated in the synthesized musical note. 
     The processing unit may be arranged to receive the measurement signal, recognise a played note from the measurement signal and then synthesize a corresponding musical note, the synthesis taking account of both the air pressure in the bore and a characteristic of a difference between the sound produced by the speaker and the sound received by the microphone. 
     The processor may generate an output signal by synthesising the sound of a reed instrument, with the frequency of the synthesised sound being based on frequency content of the measurement signal and also based on the air pressure sensed by the air pressure sensor, and with the amplitude of the synthesised sound being based on the air pressure sensed by the air pressure sensor. 
     The present invention also provides a method as claimed in claim  24  an apparatus for use in such a method as claimed in claim  25 . 
     The present invention further provides transducer apparatus as claimed in claim  26 . Such transducer apparatus provides a unit conveniently attachable to a reed instrument in place of a reed which will allow a player to practice playing the reed instrument without the generation of any significant noise which might trouble others in the vicinity. Preferred features of the transducer apparatus are set out in claims  27  to  34 . The transducer apparatus can form part of a practice system as claimed in claims  35  and  36 . The communication between the transducer apparatus and a laptop, tablet or personal computer or a smartphone allows for a better learning experience for the player practicing playing of the reed instrument, e.g. graphical representations of played musical notes can be compared against graphical representations of ‘ideal’ played musical notes. Also musical scores and training exercises can be presented to the player. 
     The present invention provides an electronic system for determining a musical note played by a reed instrument as claimed in claim  37 , with a preferred feature of this system given in claim  38 . The system of both claims allows the sound delivered by the speaker to be a low scarcely audible level, since ambient noise is removed from the measurement signal. 
     The present invention provides an electronic system for determining a musical note played by a reed instrument as claimed in claim  39 , with preferred features of the system given in claims  40 ,  41  and  42 . The system of all three claims uses an exponential chirp which has a lowest frequency in the audible range, corresponding at least approximately to a lowest musical note playable by a reed instrument. In contrast the system of US 2014/0224100 A1 uses a chirp which a linear rather than an exponential chirp and one that only comprises frequencies above 16 Khz, i.e. above the audible range of frequencies. Using a linear chirp means that only a smaller range of frequencies can be included in the chirp and this does not allow for recognition of a shift of frequencies occasioned in a reed instrument e.g. by the use of a register shift key. The prior art uses a high energy signal outside the audible range, whereas the present invention uses a low volume signal including frequencies in the audible range. This can provide the effect of playing a near-silent instrument while providing for reliable musical note recognition. 
     The present invention provides an electronic system for determining a musical note played by a reed instrument as claimed in claim  43 , with preferred features of the system given in claims  44 ,  45  and  46 . The selection of an excitation signal with components corresponding to played notes allows for reliable musical note detection from the measurement signal and allows for use of a filter bank with filters tuned to the relevant musical notes. This can provide the effect of playing a near-silent instrument while allowing for reliable musical note detection. 
     The present invention provides an electronic system for determining a musical note played by a reed instrument as claimed in claim  47 , with preferred features of the system given in claims  48  and  49 . The systems claimed employ a feedback arrangement in which the excitation signal is adapted following an initial detection of a played musical note so that it contains frequencies better suited to detection of the played musical note in the measurement signal. This can provide the effect of playing a near-silent instrument while allowing for reliable musical note detection. 
     The present invention provides a method of practising playing of a reed instrument as claimed in claim  50 , with preferred versions of the method set out in claims  51  to  58 . Further methods of practising playing of a reed instrument are provided as claimed in claims  59  and  60 . The methods allow a player to easily and quickly convert his/her own reed instrument into a version which allows near silent practice. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention, and to show how the same may be put into effect, reference is now made, by way of example only, to the accompanying drawings in which: 
         FIG. 1  is a simplified cross-sectional view of a conventional clarinet; 
         FIG. 2  is a cross-sectional view of the barrel section of a clarinet according to an embodiment of the present invention; 
         FIG. 3  is an cross-sectional view of a mouthpiece for a clarinet according to another embodiment of the present invention; 
         FIG. 4  is a schematic representation of an electronic control unit as used by any of the described embodiments of the invention; 
         FIG. 5 a    shows another embodiment of the present invention; 
         FIG. 5 b    shows a preferred version of  FIG. 5   a;    
         FIG. 6  shows a false reed for use in the embodiments of  FIGS. 5 a    and  5   b;    
         FIGS. 7 a  and 7 b    both show a perspective view of transducer apparatus for use with a reed instrument according to an embodiment of the invention; 
         FIG. 8  is a perspective underneath view of the transducer apparatus of  FIGS. 7 a    and  7   b:    
         FIG. 9  is a first end view of the transducer apparatus of  FIGS. 7 a , 7 b    and  8 ; 
         FIG. 10  is a second end view of the transducer apparatus of  FIGS. 7 a    to  9 ; 
         FIG. 11  is a view of one side of a component of the transducer apparatus of  FIGS. 7 a    to  10 . 
     
    
    
     DETAILED DESCRIPTION 
     While the detailed description will be made with reference to a clarinet, it will be appreciated that this is by way of example only and the present invention can be used with any suitable wind instrument (in particular, a reed instrument). 
     The acoustics of reed instruments, e.g. clarinet, oboe, saxophone, bassoon are well known. The player provides wind energy such that the reed vibrates thus introducing a variety of tones into the instrument. Depending upon which key(s) are depressed a resonant cavity is produced in the air chamber of the instrument such that a standing acoustic wave is set up matching the resonance of the cavity, and the result is the sound which is recognised aurally as the played musical note. The terms first harmonic and fundamental are often used as alternative terms for the lowest frequency component of the played musical note; i.e. the frequency which is aurally perceived. 
     With reference to  FIG. 1 , there is shown a simplified cross-section of a part of a typical clarinet  10 . Shown in figure is a mouthpiece  11  which is substantially cylindrical and hollow. At a proximal end of the mouthpiece, a reed  12  is attached to the mouthpiece  11  with a ligature (not shown). At a distal end, the mouthpiece  11  has a cutaway section of reduced outer diameter. Embedded in this section is a tenon cork  13  which extends around the periphery of the reduced diameter section. 
     The clarinet  10  also comprises a barrel  14  (also known as a socket) which is again cylindrical and hollow. The barrel  14  has an outer and an inner diameter substantially similar to those of the mouthpiece  11 . A section of the inner diameter of the barrel  14  is removed at a proximal end thereof so as to seal with the tenon cork  13  of the mouthpiece  11 . 
     A distal end of the barrel  14  engages with an upper joint  16  of the clarinet  10 . Again a section of the inner diameter of the barrel  14  is removed at the distal end thereof so as to seal with a tenon cork  19  of the upper joint  16 . The upper joint  16  is provided with a plurality of tone holes, only two of which are shown at  17 A,  17 B, over which are mounted tone hole rings and keys  18 A,  18 B. The keys can either be in an undepressed state  18 A, or a depressed state  18 B, to uncover or cover the holes  17 A,  17 B, respectively. The upper joint  16  is then in turn attached to a lower joint and a bell (not shown) to form the completed clarinet. These components define a cylindrical air chamber  15  which extends throughout the clarinet  10 . 
     To play the clarinet  10  a user blows into the mouthpiece  11 , causing the reed  12  to vibrate. Standing waves are formed in the air chamber  15 , which is shaped such that these correspond to the commonly known musical scale. Opening and closing of the holes  17 A,  17 B alters the shape of the generated standing wave, and hence the musical note produced. 
     In a first embodiment of the present invention, the barrel  14  of  FIG. 1  is replaced with the barrel  20  of  FIG. 2 . This barrel  20  comprises a speaker  28  and a microphone  26 , both of which are provided in the air chamber  15 . As shown in  FIG. 4 , the speaker  28  is driven by an excitation unit  101  (part of an electronic processing unit  100 ) to produce a sound. The sound may be particularly quiet, or may be outside of the frequency range of human hearing. The sound must be suitable for forming an acoustic wave in the air chamber  15  which is characteristic of the combination of keys  18 A,  18 B which are depressed. The sound delivered by the speaker  28  to the air chamber  15  is modified by the acoustic transfer function of the air chamber  15 . The sound in the air chamber  15  (which will include the sound delivered by the speaker  28  to the air chamber) is measured by the microphone  26 , which outputs a measurement signal representing the measured sound. The acoustic transfer function of the air chamber  15  is set by the player of the reed instrument, by opening and closing the tone holes (e.g.  17 A,  17 B) which are located along the length of the instrument and which connect the air chamber  15  of the instrument to the exterior of the instrument at a plurality of different locations spaced out along the length of the air chamber  15 , as will be further described later. These tone holes (e.g.  17 A,  17 B) may be opened and closed directly by fingers of a player of the reed instrument or by tone hole rings which are connected to keys manually controlled by a player of the reed instrument. The combination of open and closed tone holes (e.g.  17 A,  17 B) selected by the player dictates what musical note is played by the instrument. In normal use of the reed instrument the vibration of the reed  12  by the player blowing across the reed  12  generates a sound which is then modified by the acoustic transfer function of the air chamber  15  to generate a music note output from the reed instrument, typically via a bell portion at an end of the air chamber  15  opposite to the mouthpiece  11  of the reed instrument. The timing, tone and volume of the sound produced will also be affected by when and how hard the player of the reed instrument blows into the mouthpiece  11  of the instrument  10 . 
     The present invention recognises that it often hard for players of reed instruments to practice without unduly disturbing others and so provides an arrangement by which the player can still blow into the mouthpiece  11  and open and close the tone holes (e.g.  17 A,  17 B) in the normal manner, but without generating sound that will disturb others. Instead the speaker  28  will deliver a largely or totally inaudible sound to the air chamber  15  of the instrument  10 , which will be modified by the acoustic function of the air chamber  15  as selected by the player by opening and closing the tone holes (e.g.  17 A,  17 B), the modified sound then forming part of the sound in the air chamber  15  which is received by the microphone  16 , which will output a measurement signal from which can be determined which musical note has been selected by the player of the instrument by the opening and closing of the tone holes  17 A, 17 B. The measurement signal can be then used by the system to produce a sound delivered e.g. by headphones to the player, so that the player can hear the musical note played without the instrument producing a sound which would disturb others. As will be described below, a pressure sensor separate and independent from the microphone can be used to determine when and how hard the player is blowing into the mouthpiece  11  (which will not have a functioning reed), so that the timing and volume of the musical notes delivered as sound, e.g. via headphones to the player, can be varied accordingly. 
     The apparatus of the first embodiment has an operating mode for playing the instrument in a manner that is substantially inaudible, for instance the apparatus may be arranged to limit the power output of an excitation unit  101  (see  FIG. 4 ) to drive the speaker  28  to produce sound at a low volume. The low volume may be selected based on a measurement of ambient sound. The measurement of ambient sound may be taken by the microphone  26 . Alternatively an additional microphone can be provided which is directed not into the air chamber  15 , but instead is directed outwardly of the instrument  10  to directly measure the ambient sound outside the musical instrument  10 . 
     For example, the power output of the speaker  28  may be chosen to be greater or less than the measured ambient sound level by a predetermined amount or by a predetermined factor. 
     Preferably, when the measurement of ambient sound is taken by the microphone  26  (or by a second ambient noise microphone), the power output of the speaker  28  is chosen to be greater than the measured ambient sound level by a predetermined amount or by a predetermined factor. In such embodiments, the power output of the speaker  28  may be a factor of two or more times the power of the ambient noise received by the microphone  26  (or the second ambient noise microphone). 
     In this way, the selection of power output can be configured (for a given instrument) such that the sound produced by the speaker  28  is expressed by the reed instrument at a level that will effectively allow the instrument to be played quietly such that it cannot be heard over the sound of the ambient noise. 
     In a preferred embodiment the apparatus is arranged to excite the speaker  28  such that the frequency of sound produced by the speaker  28  is between 20 Hz and 20 KHz. The excitation signal sent to the speaker  28  preferably comprises a series of exponential chirps. The chirp will preferably excite a selected range of audible frequencies equally. Each chirp is preferably an exponential chirp, sometimes called an exponentially scanned chirp or a geometric chirp, but could be a concatenated set of sine-waves at carefully selected frequencies. In an exponential chirp the frequency of the signal varies exponentially as a function of time: f(t)=f 0 k t , where f 0  is the starting frequency (at t=0) and k is the rate of exponential change in frequency. Unlike a linear chirp, an exponential chirp has an exponentially increasing frequency rate. The exponential chirp will provide equal frequency discrimination to each musical note of the instrument and therefore address the issue that the signal to noise ratio can be higher for some musical notes due to the presence of ambient noise, which could otherwise lead to poor musical note recognition. 
     The microphone  26  then picks up the acoustic waveform in the air chamber  15 , which will contain the waveform output by the speaker  28  modified by the acoustic transfer function of the air chamber  15 , such acoustic transfer function being selected by the player of the reed instrument by the opening and closing of tone holes. This signal is passed to the processor  102  (see  FIG. 4 ). The processor  102  analyses this signal to detect which musical note is being played. The processor  102  compares the frequency domain analysis of the measurement signal with a set of stored frequency domain analyses, each of which correlates with a musical note played by the reed instrument. The processor  102  determines for each measurement signal the Pearson correlation coefficient between the measurement signal and the set of stored signals to select the stored signal which most closely correlates with the measurement signal. The stored signal selected in this way will correlate with a musical note played by the reed instrument. The processor  102  incorporates a synthesizer ( 220  in  FIG. 8 ) which generates a signal embodying this musical note to output means  103 . The output means  103  is then connected via amplifier  111  to headphones  112  in order to reproduce the synthesized musical note to the user wearing the headphones  112 . Alternatively, or in addition, wireless transmission means  116 ,  118  may be incorporated in the apparatus such as wireless transmission means using the Bluetooth® wireless technology standard for exchanging data over short distance distances (e.g. using short-wavelength UHF radio waves in the ISM (industrial, scientific and medical) radio band from 2.4 to 2.485 GHz). The wireless transmission means will transmit a signal for use by the headphones  112 . 
     Whist it is possible that the invention could be implemented and used with a conventional reed still in place and the user refraining from blowing, it will be more typical that to implement the invention the mouthpiece of the reed instrument will be replaced by a modified mouthpiece which is part of the apparatus of the invention or, more preferably, the regular mouthpiece of the instrument will be modified by removing the regular reed and replacing this with a reed substitute according to the invention, as will be described more fully later. In this manner the user can practice the instrument very quietly without disturbing others within earshot. Optionally, a vent hole is provided either in the modified mouthpiece or in the substitute reed to ensure that the user feels the same resistance to blowing as would be felt with a normal mouthpiece. 
       FIG. 6  shows one way in which a substitute reed  212  may be provided. The tip of the regular mouthpiece  11  of the reed instrument comprises an opening in communication with the bore of the mouthpiece. The substitute reed  212  may be applied to the mouthpiece in place of the normal reed  12 . It will be a stiff non-vibrating reed. The substitute reed  212  may, optionally, be configured to close the opening at the tip of the mouthpiece  11 . Advantageously, the substitute reed  212  may have formed therein an air-relief groove  213  along a surface of the substitute reed  212 , or an air-relief passage extending through the substitute reed  212 , from a first location to a bleed hole  214 . The first location is selected to receive a flow of breath from the user. 
     If a groove  213  is provided (as shown in  FIG. 6 ), this can cooperate with the mouthpiece to collectively form an air-relief passage. This can give a player the impression that he/she is playing the instrument normally, but without allowing excitation of the air chamber. A pressure sensor  37  can be mounted in the passage  213  (for example, as an alternative to the location of the sensor  37  in  FIGS. 5 a  and 5 b   ). 
     The pressure sensor  37  may send a signal to indicate when and/or how hard and/or in what manner (e.g. vibrato) the player is blowing through the passage  213 . The substitute reed  212  of  FIG. 6  will typically be used in conjunction with the apparatus of  FIG. 5A  or  FIG. 5B . The use of the substitute reed  212  will remove the need for the passage  313  in the apparatus of  FIG. 5A  and  FIG. 5B . 
     While the embodiment of  FIG. 4  depicts an output signal being transmitted to headphones  112 , the signal may be sent to any suitable device such as, but not limited to, speakers, an internet connection, mixing console or games console. The signal generated does not necessarily have to be used by the device to mimic the output of the reed instrument being played. It could, for instance, be used as part of a computer game in which the user is rewarded for playing the correct note at the correct time, or an instrument different from that being played could be synthesized. 
       FIG. 3  depicts an alternative embodiment of the present invention. In this embodiment a new mouthpiece  30  is provided. The mouthpiece  30  comprises speaker  28  and microphone  26  which act as per the previous embodiment. In this embodiment, the bore  35  does not have an opening at the proximal end of the mouthpiece, so the air chamber is sealed off the mouthpiece end thereof. Instead, a small bore  32  is provided through the mouthpiece  30 , which has an outlet to the exterior of the mouthpiece  30 . This bore  32  may be shaped so as to mimic the usual air-pressure characteristics of the clarinet  10  as it is being played. The bore  32  does not communicate with the air chamber  35 . 
     The bore  32  is provided with a pressure sensor  37 , which sends a signal to the processor  102  (see  FIG. 4 ) to indicate when and/or how hard the user is blowing through the mouthpiece  30 . The processor  102  then uses this data to decide when to initiate the speaker  28 , and/or the microphone  26  and/or generation by the synthesizer  220  (see  FIG. 8 ) of a musical note output signal, and/or operation of the output means  103 . The signal may also be used to alter the characteristics of the synthesized music note signal, such as representing a higher pitch when a high pressure is sensed or introducing a vibrato element to the synthesized musical note. 
     A further alternative is shown in  FIG. 5 a   .  FIG. 5 a    shows transducer apparatus for attachment between the mouthpiece  11  and a main body of an instrument (e.g. an upper joint of a clarinet). In  FIG. 5 a   , the transducer apparatus is formed in the shape of and as a replacement to a barrel  14  of a clarinet. The  FIG. 5 a    transducer apparatus comprises a barrier to isolate the mouthpiece  11  from the air chamber  15  in the main body of the instrument. The speaker  28  and microphone  26  are arranged to be in communication with the air chamber  15  in the main body of the instrument, while the pressure sensor  37  is arranged to be in communication with the mouthpiece  11 . For example, the speaker  28  and microphone  26  may be mounted on the opposite side of the barrier to the side on which the pressure sensor  37  is mounted. 
     A further version of transducer apparatus according to the present invention is shown in  FIG. 5 b   . In this variant, a barrier between the mouthpiece and the remainder of the instrument comprises a housing containing a battery for powering the transducer apparatus and also the electronic processing unit  100  of the device (including one or more of the excitation unit  101 , the processor  102 , the output means  103 , and the memory  104 ). There may additionally be provided in or on the housing: a charging and/or communication connection point (such as a micro-USB connector), which may be part of, or additional to, the output means  103 ; a socket for headphones; controls for activating the device or its various features; and/or a status display (such as one or more LEDs). 
     Whilst the transducer apparatus shown with in  FIG. 5 a    has two female connectors (for connection to male connectors of the main body and mouthpiece) and the transducer apparatus of  FIG. 5 b    has one male and one female connector, each of the shown transducer apparatus may be configured to have any combination of male and/or female connectors necessary to interfit with a desired reed instrument. The transducer apparatus of  FIG. 5 a    is designed to replace a barrel of a clarinet, whilst the transducer apparatus of  FIG. 5 b    could be provided in addition to a barrel of a clarinet (preferably, between the barrel and the mouthpiece, where sizes are typically standardised). 
     Each of transducer apparatus of  FIGS. 5 a  and 5 b    may have formed therein a passage  313  from the mouthpiece side to a bleed hole  214 . This can give players the impression that they are playing the instrument normally, but without allowing them to excite the air chamber  15  themselves. The pressure sensor could be mounted in the passage  313 . 
       FIG. 4  shows a schematic representation of a system for synthesizing the sound of a reed instrument. The system of  FIG. 4  may be used with either of the structural arrangements given above or any of the embodiments mentioned below. There are a variety of well-known techniques for analysing a resonant cavity to measure or estimate its resonance. These include, but are not limited to, application of maximum length sequences, time-domain reflectometry, swept sine analysis, chirp analysis, and mixed sine analysis. Irrespective of the embodiment, or the processing approach, it has been found to be advantageous for the speaker  28  and the microphone  26  to be separated by a distance of less than 5 cm. 
     In some embodiments of the invention, a method based upon the application of simple sine tones is used. A stimulus frame comprises tones chosen for each of the possible notes of the clarinet  10  (or other reed instrument). The tones can be applied discretely or contiguously one after another. Each tone may be formed of more than one frequency component. A stimulus-frame comprises the tones arranged in a known order. 
     The stimulus-frame is applied as an excitation to the loudspeaker  28 . Excitation may be carried out periodically, or may commence after an event (such as when the pressure sensor  37  senses the user has blown into the mouthpiece). The microphone  26  picks up the stimulus-frame and the resonances generated and passes this information to the processor  102 . The processor applies a filter bank or fast Fourier transform in order to measure the intensity of the received sound signal at different frequencies. From the intensity measurements it is possible to identify the musical note played by the player of the reed instrument. 
     The processor  102  may use data from the pressure sensor  37  to decide when to initiate the speaker  28 , and/or the microphone  26  and/or generation of the output signal, and/or operation of the output means  103 . The signal may also be used to alter the characteristics of the output signal generated by the synthesizer  220  (see  FIG. 8 ) incorporated in the processor  102 , such as representing a higher pitch when a high pressure is sensed. In preferred embodiments, the speaker  28  may be continually active during operation. For example, the speaker  28  may be driven to produce a repeated sequence of sounds. In this case, the processor  102  can use the signal from the pressure sensor  37  to restart the sequence. Also air pressure variations measured by the pressure sensor  37  may be used to modulate the synthesized musical note generated by the synthesizer ( 220  in  FIG. 8 ), e.g. to recognise when the player is applying a vibrato breath input to the reed instrument and in response import a vibrato into the synthesized musical note. 
     A predetermined set of stimulus-frames may be stored in memory  104 . 
     The system may be programmed to learn the response of the instrument  10  to one or each tone within a stimulus-frame. For example, the user may be instructed by a user interface to depress the keys  18  required to play one or more notes (perhaps, all possible notes) in order to characterise the resonance of the instrument  10 . Whilst each key  18  is depressed, the excitation unit  101  excites the loudspeaker  28  with a stimulus-frame and the response is received using the microphone  26 . The processor  102  can analyse the received response and use this to store a representation of the played musical note in memory  104 . In this way, the system can adapt to the particular instrument  10  to which it is applied. 
     Alternatively, or in addition, the learning process can be used to adapt the stimulus-frame. For example, if the microphone  26  receives sound energy having a primary fundamental frequency (e.g., the lowest received frequency) that is higher than that of a tone transmitted by the speaker  28 , the processor may increase the frequency of that tone of the stimulus frame, or all of the tones of the stimulus frame, by a factor equal the ratio of the primary fundamental frequency received by the microphone  26  to the tone that was transmitted by the speaker  28 . 
     Alternatively the processing unit  100  comprising the excitation unit  101 , the processor  102 , the output means  103  and the memory  104 , can generate from the measurement signal sent by the microphone  26  to the processor  102  an output signal comprising a time series of data characterising a difference between the sound produced by the speaker  28  driven by the excitation unit  101  and the sound received by the microphone  26 . The excitation signal produces by the excitation unit  101  can be relayed to the processor  102  to allow direct comparison with the measurement signal received by the processor  102  from the microphone  26 . The difference is indicative of the acoustic transfer function of the air chamber  15  and this is turn indicates the musical note played by the player; thus the processor  103  can select the musical note played, e.g. by comparing the indicated acoustic transfer function with a series of acoustic transfer functions stored in the memory  104  (each of which would be associated with a particular musical note). The synthesizer  220  (see  FIG. 8 ) of the processor  102  can then synthesize the musical note selected to be output by the output means  103  e.g. to the headphones  112 . 
     When a player is playing the instrument  10  of the embodiment of  FIG. 2 , the player may adopt the usual pose, but need not blow into the instrument. Alternatively, the reed of the mouthpiece may be removed so that the player can blow without forming a note that can resonate. In this case, the synthesis of a musical note may be triggered by a key press (either a key  18  of the instrument, or a separate key provided for this purpose). Micro-switches could be associated with one or more keys to allow this, with the micro-switches sending key position signals to the processing unit  100  for use thereby. 
     When a user is playing the instrument  10  of the embodiment of  FIG. 3 , the user will blow into the instrument, but the flow of air will not reach the air chamber  15 . The air pressure sensor  37  will sense the change in pressure and provide a pressure signal to the processor  102 . The pressure signal  102  can be used to indicate when a note should be synthesized. For example, synthesis of a note may be commenced when the air pressure sensor  37  senses a pressure exceeding a threshold and ceased when the pressure drops below a/the threshold. 
     The pressure signal  102  can also be used to trigger the excitation of the loudspeaker  28 . For example, the excitation may be triggered when the air pressure sensor  37  senses a pressure exceeding a threshold and continued until the pressure drops below a/the threshold. When the stimulus-frame method is used, the stimulus frames may be repeated during the excitation. In embodiments in which the speaker  28  continually produces a repeated sequence of sounds, the processor  102  can use the signal from the pressure sensor  37  to restart the sequence. 
     The pressure signal also represents the volume of note intended to be played by the user. The processor  102  instructs the output means  103  to synthesize a note having a volume that depends on the sensed pressure. 
     For some instruments  10 , the pressure of air provided by the user can also affect the note played. In some embodiments, the synthesizer ( 220  in  FIG. 8 ) in the processor  102  will synthesize a note having a pitch that depends on the sensed pressure. Furthermore the pressure signal can indicate when the player is applying a vibrato to the reed instrument and when this is detected then the synthesizer ( 220  in  FIG. 8 ) will generate a musical note signal incorporating a vibrato element. 
     Irrespective of how the microphone  26 , speaker  28 , and optional air pressure sensor  37 , are mounted (i.e. as in the case of  FIG. 2, 3, 5 or 6 ), the system may work in the same way. The system can be applied in a variety of ways, including the following. 
     Quiet play: the system may be provided with a quiet operating mode in which the excitation unit  101  is arranged to drive the speaker  28  to produce sound at a volume selected based on a measurement of ambient sound. The measurement of ambient sound may be taken by the microphone  26  (or a separate and independent ambient noise microphone). In this way, the instrument can be “played” by the user (either without blowing, or with the breath redirected as in  FIGS. 3, 5, and 6 ) without generating sound via the instrument in the normal way, but such that the output means  103  produces an output signal that can drive headphones or the like for playing the synthesized sound to the user. Thus, the user can practice quietly. 
     Game interface: the output means  103  may be adapted to provide a signal to a computer programmed to challenge the user to play a certain piece of music. The computer may display in real-time the notes played and/or score the ability of the user to play the piece of music, based on timing and/or frequency of the signal produced by the microphone  26 . This may optionally also apply the quiet operating mode. 
     Virtual orchestra: the output means  103  may be adapted to provide a signal to a communications device (e.g., an internet connection). The communications device may receive signals from other such devices and/or other types of instrument and synthesize the sound of a plurality of instruments playing simultaneously. Again, this may optionally also apply the quiet operating mode. 
       FIGS. 7 a    to  11  show a transducer apparatus  200  according to a further embodiment of the invention. The transducer apparatus  200  is configured to be attachable to a mouthpiece  201  of a reed instrument, e.g. a clarinet, in place of the reed of the instrument. Typically a reed instrument will have a ligature which is used to releasably secure a reed in place on the mouthpiece  201 . To use the transducer assembly  200  a player will loosen the ligature and release and remove the reed from the mouthpiece  201  (perhaps along with ligature). Then the transducer apparatus  200  is secured to the mouthpiece  201  in place of the reed, as shown in  FIGS. 7 a  and 7 b   . The transducer apparatus has a collar  202 , typically moulded from a plastic material, which is attached to a reed replacement section  203  of the apparatus. The reed replacement section  203  is also typically moulded from a plastic material and is U-shaped when viewed end on, as can be seen in  FIGS. 9 and 10 . In  FIGS. 9 and 10  it can be seen that the collar  202  is also U-shaped when the apparatus is viewed end on. The collar  202  and reed replacement section  203  encircle the mouthpiece  201  when the transducer apparatus  200  is mounted on the mouthpiece  201 , with the collar  202  extending over and engaging an ‘upper’ external surface of the mouthpiece  201  (‘upper’ in the sense that when the reed instrument is played in a conventional manner then the surface will point in an upward direction) and the collar  202  thereby securing the reed replacement section  203  to the mouthpiece in place of the reed normally secured to the mouthpiece  201 . The reed replacement section  203  when secured in place will occupy the site on the mouthpiece usually occupied by a reed. An inwardly facing surface of the reed replacement section (facing inwardly toward the mouthpiece) engages and abuts a ‘lower’ external surface of the mouthpiece  201 . 
     The transducer apparatus  200  has a printed circuit board  204  on which is mounted various electronic components which together provide the processing unit ( 217  in  FIGS. 7 a    to  10 ,  100  in  FIG. 4 ), the function of which has been described above and will be further described later. The printed circuit board  204  is attached to an exterior surface of the reed replacement section  203  which in use faces away from the mouthpiece  201 . 
     As can be seen in  FIGS. 9 and 10  the transducer apparatus  200  is provided with an arm  205  which is attached to the reed replacement section  203  and extends away therefrom, toward the collar  202 . In use, when the transducer apparatus  200  is secured to the mouthpiece  201 , the arm  205  will extend through an aperture in the lower external surface of the mouthpiece  201 , into an air chamber  15  of the reed instrument.  FIG. 9  shows a face  206  of the arm  205  which faces in use toward an end of the mouthpiece  201  engaged by lips of player.  FIG. 10  shows a face  207  of the arm  205  which is uses faces away from the end of the mouthpiece  201  engaged by the lips of the player, e.g. a face  207  which faces towards the bell of a clarinet. 
     The arm  205  provides a housing for a speaker  208  and a microphone  209 , as can be seen in  FIG. 10 , both of which open on to the face  207  of the arm  205 . The speaker  208  in use will be positioned substantially centrally in the circular cross-section bore of the mouthpiece  201 . The microphone  209  is located between the speaker  208  and the reed replacement section. Both the speaker  208  and the microphone  209  are connected electrically to the processing unit  217  by wires extending through the arm  205 . A U-shaped barrier  210  extends out from the face  207  and shields the microphone  209  from the speaker  208  to reduce the amount of sound output from the speaker  208  that ‘short circuits’ directly to the microphone  209 . 
     The reed replacement section  203  has an air passage that extends therethrough from an inlet  211  shown in  FIG. 9  to an outlet  213  shown in  FIG. 11 , which shows the lower external face of the reed replacement section  203 . In use the player of the reed instrument will blow through the inlet  211 . The passage between the inlet  211  and the outlet  213  is shaped and sized to provide a resistance to the air flow that will be similar to that experienced by the player of the instrument when playing the instrument with the reed attached. A pressure sensor  212  is housed in the reed replacement section  203  and measures air pressure in the passage between the inlet  211  and outlet  213 . The pressure sensor  212  generates a pressure signal indicating when and how hard and in what manner (e.g. vibrato) the player blows into the passage. The pressure sensor is connected to the processing unit ( 217  in  FIGS. 7 a    to  10 ,  100  in  FIG. 4 ) provided by the electronics on the printed circuit board  204 . 
     The transducer apparatus  200  is also provided with an ambient noise microphone  214  which faces outwardly of the apparatus  200  and which receives ambient sound surrounding the apparatus  200 . The ambient noise microphone  214  produces an ambient noise signal which is relayed to the electronic signal processing unit ( 217  in  FIGS. 7 a    to  10 ,  100  in  FIG. 4 ) provided by the electronic components of the printed circuit board  204 . 
     Batteries  215  and  216 , preferably rechargeable, are provided on the printed circuit board  204  to power the electronic components on the board  204 . Also a wireless transmitter  218  is provided to wirelessly transmit an output signal from the transducer apparatus  200 , e.g. to the be received by a receiver of wireless headphones. 
     In use the transducer apparatus  200  will be mounted on the mouthpiece  201  of the reed instrument in place of a reed. The player will then blow through the inlet  211  of the apparatus while manually operating keys of the reed instrument to open and close tone holes of the instrument and thereby select a note to be played by the instrument. The blowing through the inlet  211  will be detected by the pressure sensor  212  which will send a pressure signal to the processing unit provided by the electronics on the printed circuit board  204 . The processing unit ( 100 , 217 ), in response to the pressure signal indicating blowing of the player, will activate the excitation unit ( 101 , 222 ) of the processing unit ( 100 ,  217 ) to output an excitation signal to the speaker  208 , which will then output sound to the air chamber  15  of the reed instrument. The frequency and/or amplitude of the excitation signal can be varied by the excitation unit ( 101 , 222 ) having regard to the pressure signal output by the pressure sensor  212 , so as to take account of how hard the player is blowing. Also air pressure variations measured by the pressure sensor  212  may be used to modulate the synthesized sounds, e.g. to recognise when the player is applying a vibrato breath input to the reed instrument and in response import a vibrato into the synthesized sounds. The frequency and/or amplitude of the excitation signal can also be varied by the excitation unit ( 101 , 222 ) having regard to the ambient noise signal output by the ambient noise microphone  214 , e.g. to make sure that the level of sound output by the speaker  208  is at least greater than preprogrammed minimum above the level of the ambient noise. 
     The microphone  209  will receive sound in the air chamber  15  and output a measurement signal to the processing unit ( 217  in  FIGS. 7 a    to  10 ,  100  in  FIG. 4 ). The processing unit ( 217 , 100 ) will compare the measurement signal or a spectrum thereof will pre-stored signals or pre-stored spectra, stored in a memory unit  219  on the printed circuit board  204  (also shown as  104  in  FIG. 4 ) to find a best match (this could be done after removing from the measurement signal the ambient noise indicated by the ambient noise signal provided by the ambient noise microphone  214 ). Each of the pre-stored signals or spectra will correspond with a musical note. By finding a best match of the measurement signal or a spectrum thereof with the pre-stored signals or spectra the processing unit thereby determines the musical note played by the player of the reed instrument. The processor  102  incorporates a synthesizer  220  (see  FIG. 8 ) which synthesizes an output signal representing the detected musical note. This synthesized musical note is output by the output means  103 , e.g. via a wireless transmitter  218  (shown in  FIG. 8 ) to wireless headphones, so that the player can hear the selected note output by the headphones. The processing unit ( 100 , 217 ) can additionally use the pressure signal and the ambient noise signal in the process of detecting what musical note has been selected and/or what musical note signal is synthesized and output (for instance the amplitude of the output signal might be varied in response to the pressure signal, since the pressure signal will indicate the strength of breath of the player and hence the loudness of the musical note desired by the player). 
     The transducer apparatus as described above has the following advantages:
         i) It is a unit easily capable of being fitted to and removed from a mouthpiece of a standard reed instrument replacing the reed, or could be permanently fitted to a spare (inexpensive) mouthpiece.   ii) It has an integral pressure sensor which allows volume modulation of the excitation signal output by the speaker and also allows control of when a synthesized musical note is output. Also a pressure signal output by the pressure sensor can indicate when a vibrato air pressure is applied to the reed instrument and this allows a vibrato element to be incorporated in the synthesized musical note.   iii) It has integral embedded signal processing and wireless signal output.   iv) It allows communication of data to a laptop, tablet or personal computer/computer tablet/smart-phone application, with can run software providing a graphical user interface, including a visual display on a screen of live musical note spectra.   v) It can be provided optionally with a player operated integral excitation volume control.   vi) It can be provided with an ambient noise sensing microphone which allows integral ambient noise cancellation from the air chamber microphone measurement signal. It is preferred that the ambient noise microphone is as close to the instrument as possible to give an accurate ambient noise reading   vii) Its processing unit ( 100 ,  217 ) comprises an integral synthesizer ( 220  in  FIG. 8 ) providing a synthesized musical note output for aural feedback to the player.   viii) It comprises and is powered by an internal battery and so does not requires leads connected to the unit which might inhibit the mobility of the player of the reed instrument.   ix) It advantageously processes the microphone signal in electronics mounted on the reed instrument and hence close to microphone to keep low any latency in the system and to minimise data transmission costs and losses.       

     The invention as described in the embodiment above introduces an electronic stimulus by means of a small speaker  208  built in the transducer apparatus  200 , placed near the connection of the mouth-piece to the remainder of the instrument. The stimulus is chosen such that the resonance produced by depressing any combination of key(s) causes the acoustic waveform, as picked up by at least one small microphone, e.g. the microphone  209  described above, preferably placed close to the stimulus provided by the speaker  208 , to change. Therefore analysis of the acoustic waveform, when converted into an electric measurement signal by microphone  208 , and/or derivatives of the signal, allows the identification of the intended note associated with the played key positions. 
     The stimulus provided via the speaker  208  can be provided with very little energy and yet with appropriate processing of the measurement signal, the intended note can still be recognised. This can provide to the player of the reed instrument the effect of playing a near-silent instrument. 
     The identification of the intended notes preferably gives rise to the synthesis of a musical note, typically, but not necessarily, chosen to mimic the type of reed instrument played. This electronic sound synthesis will be carried out by the sound synthesizer  220  provided on the printed circuit board  204 . The synthesized sound will be relayed to headphones or other electronic interfaces such that a synthetic acoustic representation of the notes played by the instrument is heard by the player. Electronic processing can provide this feedback to the player in close to real-time, such that the instrument can be played in a natural way without undue latencies. Thus the player can practice the instrument very quietly without disturbing others within earshot. 
     The mouthpiece  201  of the instrument is modified by use of the transducer apparatus  200  to replace the reed typically mounted on the mouthpiece  201  of the reed instrument. The player expresses air into a small aperture provided by the inlet  211  to a passage which ends in a permanently open vent hole providing the outlet  213  to the outside of the instrument, typically in the vicinity of a junction between the mouthpiece  201  and a remainder of the reed instrument. The purpose of the vent hole is preferably two-fold; to mimic the normal playing air-pressure experienced by the player; and to provide a path for condensed moisture egress. Alternatively a second vent hole may be provided which is sealed until opened via a small key to allow for the ejection of condensed moisture. The dimensions of the or each vent hole are chosen to mimic the normal range of pressures exerted when playing a conventional instrument. 
     As mentioned above the air pressure within the passage between the inlet  211  and outlet  213  is detected by the pressure sensor  212 . Typically an analogue signal representing the measured pressure is provided to the electronic processing unit shown as  100  in  FIG. 4  and as  217  in  FIGS. 7 a    to  10 . The absolute value of, or changes in, air pressure may be used to initiate application of the stimulus, and/or processing of the microphone signal(s) and/or generation of the synthesized mimic sound. The air pressure variations may also be used to modulate the synthesized sound e.g. when vibrato is applied. There is no air passage between inlet  211  and the remainder of the instrument, so the breath of the player cannot reach the air chamber  15  of the reed instrument. 
     The electronic processing unit ( 100 , 217 ) will use one or more of a variety of well-known techniques for analysing the measurement signal in order to discover a transfer function of the resonant cavity provided by the air chamber  15  of the reed instrument, and thereby the intended note, working either in the time domain or the frequency domain. These techniques include application of maximum length sequences either on an individual or repetitive basis, time-domain reflectometry, swept sine analysis, chirp analysis, and mixed sine analysis. 
     An embodiment based on the consecutive application of simple sine tones will now be described, but alternate processing methods may be used. 
     In the preferred embodiment the stimulus signal sent to the speaker, e.g. speaker  208 , will be a stimulus-frame comprised of tone fragments chosen for each of the possible musical notes of the instrument. The tones can be applied discretely or contiguously following on from each other. Each of the tone fragments may be comprised of more than one frequency component. The tone fragments are arranged in a known order to comprise the stimulus-frame. The stimulus-frame is applied as an excitation to the speaker (e.g.  208 ) typically being initiated by the player blowing into the instrument (as detected by the pressure sensor  212 ). A signal comprising a version of the stimulus-frame as modified by the acoustic transfer function of the air chamber (as set by any played keys and resonances generated thereby) is picked up by the microphone  209 . The time-domain measurement signal is processed, e.g. by a filter bank or fast Fourier transform (fft), to provide a set of measurements at known frequencies. The frequency measures allow recognition of the played note, either by comparison with pre-stored frequency measurements of played notes or by comparison with stored frequency measurements obtained via machine learning techniques. Knowledge of ordering and timing within the stimulus-frame may be used to assist in the recognition process. 
     The stimulus-frame typically is applied repetitively on a round-robin basis for the period that air-pressure is maintained by the player (as sensed by the pressure sensor  212 ). The application of the stimulus frame will be stopped when the pressure sensor  212  gives an pressure signal indicating that the player has stopped blowing and the application of the stimulus frame will be re-started upon detection of a newly timed note as indicated by pressure sensor  212 . The timing of a played note output signal, output by a component of the processing unit ( 217  in  FIGS. 7 a    to  10 ,  100  in  FIG. 4 ), on identification of a played note, is preferably determined by a combination of the recognition of the played note and the measured air-pressure. The played note output signal is then input to synthesis software run on the synthesizer  220  such that a mimic of the played note is output by the synthesizer  220  of the processing unit ( 217  in  FIGS. 7 a    to  10 ,  100  in  FIG. 4 ), the synthesized musical note signal and the timing thereof are offered back to the player typically for instance via wireless headphones. 
     It is desirable to provide the player with low-latency feedback of the played note, especially for low frequency notes where a single cycle of the fundamental frequency may take tens of milliseconds. A combination of electronic processing techniques may be applied to detect such notes with low latency by applying a tone or tones at different frequencies to the fundamental such that the played note may still be detected from the response. 
     On some reed instruments the played note is changed by means of one or more register or octave-key(s) opening at least one additional ‘vent’, or alternatively by ‘over-blowing’ (i.e. the player blowing at a significantly higher pressure) such that a harmonic sounds rather than the fundamental. Over-blowing may be detected by the pressure sensor  212  through the additional air-pressure exerted. Use of a register or octave-key causes the resonant frequency of the fundamental to move slightly without significantly affecting the frequency of the higher harmonics and thus provides a basis for recognition through the measurement signal provided by the microphone  209 . Alternatively the position of the register or octave-key could be detected via a variety of conventional methods, e.g. by use of a magnetic switch or a micro-switch. 
     In a further embodiment the excitation signal sent to the speaker  208  is an exponential chirp running from 20 Hz to 20 kHz. The signal will include a lowest frequency in the range 20 Hz to 200 Hz. This signal excites the air chamber of the reed instrument via the loudspeaker on a repetitive basis, thus forming a stimulus-frame. The starting frequency of the scan is chosen to be below the lowest fundamental (first harmonic) of the instrument, roughly 150 Hz in the case of a Bflat clarinet. 
     It should be noted that on many reed instruments the opening associated with the register key is physically small in relation to the other key openings. This has the effect of the opening being largely transparent to high frequencies since the phase of the waveform reverses before significant sound energy can escape through the small hole. It is important that the bottom scan frequency of the chirp signal provided by the stimulus-frame sent to the microphone is at least as low as the lowest fundamental frequency of the instrument, e.g. ˜150 Hz on a standard Bflat clarinet. 
     The sound present in the air chamber  15  is sensed by the microphone  209  and assembled into a frame of data lasting exactly the same length as the exponential chirp excitation signal (which provides the stimulus-frame). Thus the frames of microphone data and the chirp are synchronised. 
     An FFT is performed upon the frame of data in the measurement signal provided by the microphone  209  and a magnitude spectrum is thereby generated in a standard way. 
     The transducer apparatus in this embodiment preferably has a training mode in which the player successively plays all the notes of the instrument and the resultant magnitude spectrum of the measurement signals provided by the microphone are stored correlated to the notes being played. Preferably the transducer apparatus is provided with a signal receiver as well as its signal transmitter and thereby communicates with a laptop, tablet or personal computer or a smartphone running application software that enables player control of the transducer apparatus. The application software allows the player to select the training mode of the transducer apparatus. Typically the memory unit ( 104 ,  219 ) of the apparatus will allow three different sets of musical note data to be stored. The player will select a set and then will select a musical note for storing in the set. The player will manually operate the relevant keys of the instrument to play the relevant musical note and will then use the application software to initiate recording of the measurement signal from the microphone  209 . The transducer apparatus will then cycle through a plurality of cycles of generation of an excitation signal and will average the measurement signals obtained over these cycles to obtain a good reference response for the relevant musical note. The process is then repeated for each musical note played by the instrument. When all musical notes have been played and reference spectra stored, then the processing unit ( 217  in  FIGS. 7 a    to  10 ,  100  in  FIG. 4 ) has a set of stored spectra in memory ( 104 ,  219 ) which comprise a training set. Several (e.g. three) training sets may be generated (e.g. for different instruments), for later selection by the player. The laptop, tablet or personal computer or smartphone will preferably have a screen and will display a graphical representation of each played musical note as indicated by the measurement signal. This will enable a review of the stored spectra and a repeat of the learning process of the training mode if any defective musical note data is seen by the player. 
     Rather than use application software on a separate laptop, tablet or personal computer or smartphone, the software could be run by the electronic processing unit ( 100 ,  217 ) of the transducer apparatus  200  itself and manually operable controls, e.g. buttons, provided on the transducer apparatus  200 , along with a small visual display, e.g. LEDs, that provides an indication of the selected operating mode of the apparatus  200 , musical note selected and data set selected. 
     An accelerometer  221  (see  FIG. 8 ) could be provided in the transducer apparatus  200  to sense motion of the transducer apparatus  200  and then the player could move the instrument to select the input of the next musical note in the training mode, thus removing any need for the player to remove his/her from the instrument between playing of musical notes. Alternatively, the electronic processing unit ( 100 , 217 ) or a laptop, tablet or personal computer or smartphone in communication therewith could be arranged to recognise a voice command such as ‘NEXT’ received e.g. through the ambient noise microphone  214  or a microphone of the laptop, tablet or personal computer or smartphone. As a further alternative, the pressure signal provided by the pressure sensor  212  could be used in the process, recognising an event of a player stopping blowing and next starting blowing (after a suitable time interval) as a cue to move from learning one musical note to the moving to learning the next musical note. 
     When the transducer apparatus  200  is then operated in play mode a pre-stored training set is pre-selected. The selection can be made using application software running on a laptop, tablet or personal computer or on a smartphone in communication with the transducer apparatus. Alternatively the transducer apparatus  200  could be provided with manually operable controls to allow the selection. The magnitude spectrum is generated from the measurement signal as above, but instead of being stored as a training set it is compared with each of the spectra in the training set (each stored spectrum in a training set representing a single played note). A variety of techniques may be used for the comparison, e.g. a least squares difference technique or a maximised Pearson second moment of correlation technique. Additionally machine learning techniques may applied to the comparison such that the comparison and or training sets adjusted over time to improve the discrimination between notes. 
     It is convenient to use only the magnitude spectrum of the measurement signal from a simple understanding and visualisation perspective, but the full complex spectrum of both phase and amplitude information (with twice as much data) could also be used, in order to improve the reliability of musical note recognition. However, the use of just the magnitude spectrum has the advantage of speed of processing and transmission, since the magnitude spectrum is about 50% of the data of the full complex spectrum. References to ‘spectra’ in the specification and claims should be considered as references to: magnitude spectra only; phase spectra only; a combination of phase and amplitude spectra; and/or complex spectra from which magnitude and phase are derivable. 
     In an alternative embodiment a filter bank, ideally with centre frequencies logarithmically spaced, could be used to generate a magnitude spectrum, instead of using a Fast Fourier Transform technique. The centre frequencies of the filters in the back can be selected in order to give improved results, by selecting them to correspond with the frequencies of the musical notes played by the reed instrument. 
     Thus the outcome of the signal processing is a recognised note, per frame (or chirp) of excitation. The minimum latency is thus the length of the chirp plus the time to generate the spectra and carry out the recognition process against the training set. The processing unit ( 217  of  FIGS. 7 a    to  10 ,  100  of  FIG. 4 ) of the preferred embodiment typically runs at 93 ms for the excitation signal and ˜30 ms for the signal processing of the measurement signal. It is desirable to reduce the latency even further; an FFT approach this will typically reduce the spectral resolution since fewer points will be considered, assuming a constant sample rate. With a filter bank approach there will be less processing time available and the filters will have less time to respond, but the spectral resolution need not necessarily be reduced. 
     As with the other preferred embodiments, the recognised note is synthesized immediately and fed back to the player via wired headphones. Alternatively the synthesized musical note may be transmitted to be used by application software running on a laptop, tablet or personal computer or smartphone or other connected processor. The connection may be wired or preferably wireless using a variety of means, e.g. Bluetooth®. Parameters which are not critical to operation but which are useful, e.g. the magnitude spectrum, may also be passed to the application software for every frame. Thus the application software can generate an output on a display screen which allows the player to see a visual effect in the frequency spectrum of playing deficiencies of the player e.g. a failure to totally close a hole. This allows a player to adjust his/her playing and thereby improve his/her skill. 
     In a further embodiment of the invention an alternate method of excitation signal generation and processing the measurement signal is implemented in which an excitation signal is produced comprising of a rich mixture of frequencies, typically harmonically linked. The measurement signal is analysed by means of a filter-bank or fft to provide a complex frequency spectrum. Then the complex frequency spectrum is run through a recognition algorithm in order to provide a first early indication of the played note. This could be via a variety of recognition techniques including those described above. The first early indication of the played note is then used to dynamically modify the mixture of frequencies of the excitation signal in order to better discriminate the played note. Thus the recognition process is aided by feeding back spectral stimuli which are suited to emphasising the played note. The steps are repeated on a continuous basis, perhaps even on a sample by sample basis. A recognition algorithm provides the played note as an additional output signal. 
     In the further embodiment the content of the excitation signal is modified to aid the recognition process. This has parallels with what happens in the conventional playing of a reed instrument in that the reed provides a harmonic rich stimulus which will be modified by the acoustic feedback of the reed instrument, thus reinforcing the production of the played note. However, there are downsides in that a mixture of frequencies as an excitation signal will fundamentally produce a system with a lower signal to noise ratio (SNR) than that using a chirp covering the same frequencies, as described above. This is because the amplitude at any one frequency is necessarily compromised by the other frequencies present if the summed waveform has to occupy the same maximum amplitude. For instance if the excitation signal comprises a mixture of 32 equally weighted frequencies, then the overall amplitude of the sum of the frequencies will be 1/32 of that achievable with a scanned chirp over the same frequency range and this will reflect in the SNR of the system. This is why use of a scanned chirp as an excitation signal, as described above, has an inherent superior SNR; but the use of a mixture of frequencies in the excitation signal which is then enhanced might enable the apparatus to have an acceptably low latency between the note being played and the note being recognised by the apparatus. 
     With suitable communications, application software running on an device external to the instrument and/or the transducer apparatus may also be used to provide a backup/restore facility for the complete set of instrument data, and especially the training sets. The application software may also be used to demonstrate to the user the correct spectrum by displaying the spectrum for the respective note from the training set. The displayed correct spectrum can be displayed alongside the spectrum of the musical note currently played, to allow a comparison. 
     Since the musical note and its volume are available to the application software per frame, a variety of means may be used to present the played note to the player, These include a simple textual description of the note, e.g. G #3, or a (typically a more sophisticated) synthesis of the note providing aural feedback, or a moving music score showing or highlighting the note played, or a MIDI connection to standard music production software e.g. Sibelius, for display of the live note or generation of the score. 
     The application software running on a laptop, tablet or personal computer or smartphone in communication with the transducer apparatus and/or as part of the overall system of the invention will allow: display on a visual display unit of a graphical representation of a frequency of a played note; the selection of a set of data stored in memory for use in the detection of a played note by the apparatus; player control of volume of sound output by the speaker; adjustment of gain of the pressure sensor; adjustment of volume of playback of the synthesized musical note; selection of a training mode or a playing mode operation of the apparatus; selection of a musical note to be learned by the apparatus during the training mode; a visual indication of progress or completion of the learning of a set of musical notes during the training mode; storage in the memory of the laptop, tablet or personal computer or smartphone (or in cloud memory accessed by any of them) of the set of data stored in the on-board memory of the transducer apparatus, which in turn will export (e.g. for restoration purposes) of set of data to the on-board memory ( 104 ,  219 ) of the transducer apparatus  200 ; a graphical representation, e.g. in alphanumeric characters, of the played note; a musical note by musical note graphical display of the spectra of the played notes, allowing continuous review by the player; generation of e.g. pdf files of spectra. The application software could additionally be provided with feature enabling download and display of musical scores and exercises to help those players learning to play an instrument. 
     Whilst above the identification of a played note and the synthesis of a musical note is carried out by electronics on-board to the transducer apparatus, these processes could be carried out by separate electronics physically distant from but in communication with the apparatus mounted on the instrument or indeed by the application software running on the laptop, tablet or personal computer or smartphone. The generation of the excitation signal could also occur in the separate electronics physically distant from but in communication with the apparatus mounted on the instrument or by the application software running on the laptop, tablet or personal computer or smartphone. 
     In modifications of the embodiments described above at least a second channel of processing is provided with one of more independent ambient noise microphone(s)  214 , which can be placed on the printed circuit board  204 . The independent ambient noise microphone(s)  214  will measure sound external to the air chamber  15 . This provides two possibilities:
         a) The external microphone signal(s) may be used to reduce external ambient noise, either directly by providing an ambient noise signal processed with the measurement signal provided by the internal microphone  209  to remove the ambient noise from the measurement signal prior to e.g. FFT processing and recognition. Alternatively the complex or magnitude spectrum of the ambient signal can be generated and removed from the respective spectrum of the measurement signal provided by the microphone  209 .   b) The external microphone signal(s) may alternatively or additionally be used to reduce the effect of ambient noise upon the note recognition process by dynamically increasing the volume of the speaker  208  to help overcome the ambient noise on a frame by frame basis.       

     The transducer apparatus  200  will preferably retain in memory ( 104 ,  219 ) the master state of the processing and all parameters, e.g. a chosen training set. Thus the transducer apparatus  200  is programmed to update the process implemented thereby for all parameter changes. In many cases the changes will have been initiated by application software on the laptop, tablet or personal computer or smartphone, e.g. choice of training note. However, the transducer apparatus  200  will also generate changes to state locally, e.g. the pressure currently applied as noted by the pressure sensor  212  or the note currently most recently recognised. 
     The embodiments of the invention above could be modified by the addition of an accelerometer included in the apparatus. The signal from the accelerometer would indicate movement of the reed instrument and thereby provide the player with expression control and/or automatic power-up/power-down governed by instrument movement. This control could be implemented either in the electronics mounted to the reed instrument or in application software run on a laptop, tablet or personal computer or smartphone in communication with the device mounted on the reed instrument. 
     Whilst above an electronic processing unit ( 100 ,  217 ) is included in the device coupled to the reed instrument which provides both an excitation signal and outputs a synthesized musical note, a fast communication link between the instrument mounted device and a laptop, tablet or personal computer or smartphone would permit application software on the laptop, tablet or personal computer or smartphone to generate the excitation signal which is then relayed to the speaker mounted on the instrument and to receive the measurement signal from the microphone and detect therefrom the musical note played and to synthesize the musical note played e.g. by a speaker of the laptop, tablet or personal computer or smartphone or relayed to headphones worn by the player. A microphone built into the laptop, tablet or personal computer or smartphone could be used as the ambient noise microphone. The laptop, tablet or personal computer or smartphone would also receive signals from a pressure sensor and/or an accelerometer when they are used. 
     The synthesized musical notes sent e.g. to headphones worn by a player of the reed instrument could mimic the reed instrument played or could be musical notes arranged to mimic sounds of a completely different instrument. In this way an experienced player of a reed instrument could by way of the invention play his/her reed instrument and thereby generate the sound of a e.g. a played guitar. This sound could be heard by the player only by way of headphones or broadcast to an audience via loudspeakers. This can be particularly useful for the practice of certain reed instruments, e.g. bass reed instruments are very large and expensive, since being able to practice a piece of music on a Bflat clarinet fitted with the present invention will be far more convenient in many circumstances (e.g. when travelling) than practising on the bass instrument itself.