Abstract:
A musical apparatus that outputs a musical control signal modulated in real-time by the interruption of laser beams in an operational space. These interruptions of laser beams are transduced by appropriate circuitry into electrical signals common to electronic musical equipment, for example MIDI clock data. The signals may be used to control the tempo of a musical performance, or may control some other parameters. The system includes interpretive circuitry for recognizing gestures from the accepted canon of musical conducting.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO COMPUTER PROGRAM LISTING COMPACT DISC APPENDIX 
     A source code appendix, Appendix A, is included. This appendix resides on two duplicate CD-R discs. The discs are entitled “Callaway Appendix A,” and each disc contains two ascii-format source code files for the Zilog Z8 microcontroller: “SOURCE.TXT,” and “INCLUDE.INC.” 
     BACKGROUND OF THE INVENTION 
     This invention is an apparatus that allows a musical conductor to practice conducting a piece of music with no orchestra present. 
     Modem and classical music can be transcribed into MIDI (Musical Instrument Digital Interface) computer files as ‘digital’ music. Unlike CDs or MP3s, MIDI files do not contain any actual sound data. MIDI files consist only of a list of note events, which are made into sounds by a synthesizer. For example, the opening phrase ‘Happy birthday to you” would contain 6 discrete note events. 
     MIDI files contain multiple instruments, where an instrument consists of a specific list of note events. A string quartet MIDI file has four instruments, and therefore four distinct lists of note events. A solo piano MIDI file has only one instrument. 
     Synchronization—Controlling MIDI Tempo with an External Signai 
     A software MIDI player can play back music much like a CD player. A ‘play’ button in MIDI player software starts the music, and a ‘stop’ button ends it. During the playback, the note events for each instrument are sent separately to a synthesizer. 
     Popular software MIDI players allow flexible control of musical tempo for applications more complex than simple playback. One application that requires special tempo control is synchronization. Synchronization is necessary when a MIDI player must be locked in simultaneous playback with another machine. For example, a MIDI player can be synchronized to a video recorder. When the video recorder begins playback, it sends a control signal to the MIDI player. The control signal from the video recorder controls the speed (or tempo) of the MIDI player&#39;s playback. When the video recorder stops, the MIDI player stops. When the video player changes speeds, the control signal causes the MIDI player to change speeds as well. The control signal is made up of individual timing markers, or ‘MIDI Beat Clocks.’ MIDI Beat Clocks are subdivisions of musical beats. Every musical beat is subdivided into twenty-four MIDI Beat Clocks. This means that the video recorder, or other controlling machine, must send exactly twenty-four MIDI Beat Clocks for the MIDI Player to advance its music by one beat. 
     Using Synchronization to Allow Real-Time Human Conducting 
     A human conductor can control the tempo of a MIDI file with a device that generates synchronization data. A conducting device allows a user to establish tempo in real time, with the music following in synchronization. The conducting device translates this activity into MIDI Beat Clocks, which are sent to a MIDI player. The MIDI player derives its tempo from the incoming MIDI Beat Clocks as if it were synchronized to a video recorder. When the user speeds up the tempo, the MIDI Time Code also speeds up, and the MIDI player plays back the music more quickly. 
     Devices that Generate MIDI Beat Clocks 
     Over the last 20 years, conducting devices have been popular projects in the academic world. However, very few conducting devices have been brought to market. No conducting device that has been introduced has been widely embraced by musicians. However, other electronic instruments flourish in the marketplace. Digital pianos, wind instruments, and motion-detecting sound modules such as the Theremin are in wide use among modern musicians. 
     The Radio Baton 
     A system for tracking musical gestures, disclosed in 1990 in U.S. Pat. No. 4,980,519 by Matthews, incorporated batons that contained radio transmitters. As the batons moved about in three-dimensional space, their motion was detected by an ‘antenna board’ lying beneath them. The antenna board received signals sent from the two batons using multiple radio receivers. By comparing the relative strength of the received signals, a computer could calculate XYZ position coordinates for the two batons. This position data was sent as a control signal to a computer running musical software. The control signal could be configured to govern a variety of musical signals, including tempo. The complexity of this system caused it to be expensive. 
     Lightning II 
     The ‘Lightning II’ MIDI controller was a baton-based system for tracking motion and gestures. It operated by deriving XYZ position coordinates from strobing LEDs. Two handheld batons each contained LEDs that strobed at unique fixed frequencies. An external array of optical sensors used triangulation to calculate XYZ position coordinates for the two batons. This system was expensive and fragile, and the batons were so heavy as to be objectionable to musical conductors. (see http:/www.buchla.com/lightning/descript.html) 
     The Digital Baton 
     A hand-held conducting device, disclosed in 1999 in U.S. Pat. No. 5,875,257 by Marrin, used internal accelerometers and strobing LEDs to detect conducting gestures. The device provided multiple control signals for the conducting of music, including tempo and volume. This system used a heavy baton, so that it could not accommodate extended conducting sessions. 
     The Conductor&#39;s Jacket 
     A custom-fitted jacket, developed by Nakra, contains biometric sensors. The jacket measures body motion and muscle action, and a computer combines these measurements to create a control signal. The control signal is used to govern a variety of musical parameters in live performance, including tempo, volume, and dynamics. This system is expensive and requires heavy calibration for each user. (see http:/web.media.mit.edu/˜marrin/CIM.htm) 
     Roland Dimension Beam 
     A system that detected the position of a hand in an operational space was disclosed in 1998 in U.S. Pat. No. 5,998,727 by Takahashi et al. The system used optical sensors to collect light reflected from the hand, and estimated the position of the hand through a process of triangulation. The system allowed a user to define specific MIDI parameters, and to control them with the signal generated through the optical triangulation. Both the sources of light and the optical detectors were contained in a single enclosure. Because of the crude method of triangulation used to detect the position of the hand, this system allowed only rough control of analog parameters, and not precise triggering of events. Triggering was particularly infeasible if a baton, instead of a hand, was used. 
     Every system that has been designed for conducting to date has suffered from some combination of the following disadvantages: 
     Heavy or bulky interfaces 
     Elements that must be worn on the body 
     Poor tracking of beats (i.e. beats are missed or skipped) 
     High cost ($1,200-$20,000) 
     Complex hardware installations 
     A user&#39;s most common objection to a conducting device is typically its weight. Conducting a symphony or opera can be a 4-hour endeavor, and conductors often favor super lightweight batons in performance. Some conductors decline to use batons, even though this makes them less visible to musicians. The handheld component of most conducting devices weigh over 10 ounces, while a conductor&#39;s baton weighs 1-5 ounces. 
     Objects and Advantages 
     In contrast to past efforts, the present device distinguishes itself by: 
     a. Allowing the user to hold any baton, or no baton; 
     b. Enabling simple manufacture and calibration, with few complex assembly steps or parameters requiring calibration; 
     c. Manufacturability at a cost typical of digital instruments (e.g. keyboards) 
     d. Providing lower sensitivity to false triggers. 
     e. Providing high beat resolution. Whether the musical gestures are made rapidly or very slowly, triggering is consistent. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a device for detecting the gestures of a musical conductor. The system uses a laser beam projected into an optical sensor. When a conductor&#39;s baton breaks the laser beam, the device sends a control signal to a computer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing discussion will be understood more readily from the following detailed description of the invention, when taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of an apparatus for detecting conducting gestures in accordance with the invention; 
     FIG. 2 is a schematic illustration of the operative components of a detection unit for use in the apparatus of FIG. 1; 
     FIG. 3 diagrammatically illustrates a musical pattern of gestures called “4/4 time;” 
     FIG. 4 diagrammatically illustrates a musical pattern of gestures called “3/4 time.” 
     FIG. 5 is a logic flow diagram of a microcontroller embodiment of the conducting device. 
     FIG. 6 is a logic flow diagram of the states of a system of sequential logic  704 . 
     FIG. 7 is a perspective view of an alternate apparatus of a lattice of laser beams. 
     FIG. 8 is a graphical view of a ‘consistent tempo’ operational contingency. 
     FIG. 9 is a graphical view of a ‘decreasing tempo’ operational contingency. 
     FIG. 10 is a graphical view of an ‘increasing tempo’ operational contingency. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 LIST OF REFERENCE NUMBERALS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 100 
                 laser projector 
               
               
                   
                 102 
                 vector laser beam 
               
               
                   
                 104 
                 horizontal laser beam 
               
               
                   
                 106 
                 vertical laser beam 
               
               
                   
                 108 
                 collimated laser diode 
               
               
                   
                 110 
                 conductor&#39;s baton 
               
               
                   
                 200 
                 tower 
               
               
                   
                 202 
                 mirror 
               
               
                   
                 204 
                 pivot 
               
               
                   
                 206 
                 armature 
               
               
                   
                 208 
                 base 
               
               
                   
                 300 
                 tower 
               
               
                   
                 302 
                 mirror 
               
               
                   
                 304 
                 pivot 
               
               
                   
                 306 
                 armature 
               
               
                   
                 308 
                 base 
               
               
                   
                 400 
                 laser detector 
               
               
                   
                 402 
                 aperture 
               
               
                   
                 406 
                 MIDI connector 
               
               
                   
                 410 
                 power LED 
               
               
                   
                 420 
                 ‘laser alignment’ LED 
               
               
                   
                 430 
                 ‘first beat’ LED 
               
               
                   
                 450 
                 mode switch 
               
               
                   
                 500 
                 set of ‘4/4’ gestures 
               
               
                   
                 510 
                 first beat 
               
               
                   
                 520 
                 second beat 
               
               
                   
                 530 
                 third beat 
               
               
                   
                 540 
                 fourth beat 
               
               
                   
                 600 
                 set of ‘3/4’ gestures 
               
               
                   
                 610 
                 first beat 
               
               
                   
                 620 
                 second beat 
               
               
                   
                 630 
                 third beat 
               
               
                   
                 700 
                 optical sensor 
               
               
                   
                 702 
                 one-shot trigger 
               
               
                   
                 704 
                 sequential logic 
               
               
                   
                 706 
                 timer 
               
               
                   
                 708 
                 divider 
               
               
                   
                 710 
                 MIDI Encoder 
               
               
                   
                 712 
                 computer MIDI port 
               
               
                   
                 714 
                 MIDI software player 
               
               
                   
                   
               
             
          
         
       
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The device incorporates systems and components relating to: Musical conducting, Laser optics, light reflection, light detection, analog circuits, microcontrollers, and MIDI (musical instrument digital interface) 
     FIG. 1 shows a perspective view of a preferred embodiment of the device. 
     A laser projector  100  contains a collimated laser diode  108  and projects a vertical beam of laser radiation  102  on to a mirror  202 . Mirror  202  is positioned at an angle of 45? to vertical beam  102 , and gives rise to a horizontal laser reflection  104 , which is incident upon a mirror  302 . Mirror  302  is positioned at an angle of 45? to horizontal reflection  104 , and gives rise to a vertical laser reflection  106 , which is incident upon an optical sensor  700  housed in a detection unit  400  and exposed through an aperture  402 . 
     Two towers  200  and  300  are identical in construction, and suspend mirrors  202  and  302 . Towers  200  and  300  should lie approximately 30 inches apart. Two supports  208  and  308  should be weighted appropriately so that they provide stability for the towers, or approximately five pounds. Two armatures  206  and  306  are right-angled sections of rigid material, for example steel, approximately 36 inches in total length, or 18 inches in each dimension. Rigidity of armatures  206  and  306  is critical because the incidence of laser reflection  106  upon optical sensor  700  relies upon a constant and invariant alignment of mirrors  202  and  302 . Mirrors  202  and  302  are mounted on two rotary pivots  204  and  304 , allowing alignment of the mirrors with respect to their incident laser beams  102  and  104 . Pivots  202  and  302  should provide ample rotary resistance so that mirrors  202  and  302  can be adjusted by a hand, and so that they maintain their alignment after adjustment is complete. 
     Detection unit  400  is an enclosure with an aperture  402  on its top side. Aperture  402  exposes an upward-facing optical detector  700  that is electrically connected to the system of FIG.  2 . Three LED indicators  410 ,  420 , and  430  are mounted on one side of detection unit  400 . An output connector  406  for transmission of MIDI (Musical Instrument Digital Interface) signals is mounted on one side of the detection unit. 
     Refer now to FIG. 2, a schematic illustration of the detection unit. Each of the elements [ 700 ,  702 ,  704 ,  706 ,  708 ,  710 ,  712 , and  714 ] is serially interconnected, with the output signal of each element being transmitted to the next element as an input signal. 
     Note that throughout the remainder of the specification and claims, the terms ‘interruptions’ and ‘laser interruptions’ will be used frequently. In the context of the present apparatus, interruptions of laser beams  102 ,  104 , and  106  arise from the intentional gestures of a user. These gestures may represent musical beats. For the systematic discussion of the apparatus, the terms ‘interruptions’ or ‘laser interruptions’ will always be used to discuss gestures made by the user. 
     The purpose of optical sensor  700  is to detect interruptions of laser beams  102 ,  104 , and  106 . The optical sensor must be configured so that it creates a distinct shift in output voltage when laser beams  102 ,  104 , or  106  are interrupted. If the optical sensor is too sensitive to ambient light, its state will not change during laser interruptions. An acceptable realization of the optical sensor consists of a Fairchild Semiconductor L14G1 Hermetic Silicon Phototransistor configured in series with a pull-up resistor of resistance 60 k? and a supply voltage of 5 volts. When a laser beam is incident upon the phototransistor, the voltage at the node shared by the phototransistor and the resistor is 0 volts. When the laser beam is not incident upon the optical sensor, the voltage at same node is 5 volts. This configuration allows the detection of laser interruptions in environments of low to average ambient light. Optical sensor  700  is connected to LED indicator  420 , which illuminates when vertical laser beam  106  is incident upon the optical sensor. LED  420  enables simple alignment and adjustment of the mirror pivots and laser beams, because it remains unlit when the laser beams are not correctly aligned. 
     The output of optical sensor  700  produces the input signal for a one shot trigger  702 . The one-shot trigger exists to reject false triggers, or unintended interruptions of laser beams  102 ,  104 , or  106 . False triggers can occur if a hand or other object is used to interrupt the laser beams. When the hand passes through a laser beam, a trigger signal is generated when the first finger of the hand interrupts the laser. A second, spurious trigger can be generated by a second finger interrupting the laser. One-shot trigger  702  rejects this type of undesired trigger signal by the following method. Upon the occurrence of a trigger signal, the one-shot trigger transmits a fixed-width rectangular pulse. This pulse could be 1 ms in duration. During and after the transmission of the rectangular pulse, the one-shot trigger applies a holdoff window. The holdoff window is a period of time during which incoming trigger signals are ignored. The holdoff window could be 100 ms in duration. Thus, when a trigger signal occurs, one-shot  702  will reject spurious signals occurring less than about 100 ms after the trigger signal. 
     The output of one-shot  702  produces the input signal for a system of sequential logic  704 . The sequential logic could also be called a finite state machine. The purpose of the sequential logic is to map a pattern of laser interruptions on to a sequence of musical beats. The sequential logic is able to propagate or permit laser interruptions that represent beats, while suppressing or ignoring laser interruptions that represent non-beats. FIG. 6 is a diagram showing the state transitions of the sequential logic. FIG. 6 shows the operation of the sequential logic in two distinct musical time signatures or ‘modes’: 3/4 mode (3 beats per measure) and 4/4 mode (4 beats per measure). The correct operational mode of the sequential logic is selected with a toggle switch  450 , which has two positions. The two positions of the toggle switch are labeled ‘4/4’ and ‘3/4.’ An LED  430  is controlled by the sequential logic. This LED is called the ‘first beat’ LED and illuminates to notify the user that the next laser interruption will be mapped on to the first musical beat of the active musical time signature. 
     The output of sequential logic  704  produces an input signal for a timer  706 . The purpose of the timer is to determine the elapsed time between two laser interruptions. Whenever the timer receives a stop signal, it measures the time elapsed since the preceding laser interruption. Every laser interruption causes the timer to stop, register its elapsed time, and immediately restart. The timer should be capable of measuring pulses as short as 200 ms, for a very fast tempo. It should also be capable of measuring pulses as long as 4 or 5 seconds, for a very slow tempo. The output signal transmitted by timer  706  is a measured time interval T x . This interval can be represented as a digital signal. 
     The output of the timer produces an input signal for a divider  708 . The purpose of the divider is to divide the time interval measured by timer  706  by the number twenty-four. Thus, the output of the timer is a time interval T x /24. 
     The output signal of divider  708  is sent to a MIDI encoder  710 . The MIDI encoder transmits one MIDI Beat Clock (F 8  hexadecimal) for every elapsed time interval of T x /24. Thus, the MIDI encoder transmits 24 MIDI Beat Clocks for every valid trigger signal received by optical sensor  700 . Referring briefly to FIG. 6, the MIDI encoder can accommodate three distinct musical contingencies, as follows: 
     The output signal of divider  708  is sent to a MIDI encoder  710 . The purpose of the MIDI encoder is to transmit 24 MIDI Beat Clocks for each laser interruption. During a given interval T x /24, the MIDI Beat Clocks will be sent at intervals of T x /24. Note that MIDI Beat Clocks are transmitted at a rate determined by the interval between the two most recent laser interruptions. As a result, the system ‘predicts’ the rate at which MIDI Beat Clocks should be transmitted on the basis of past information. 
     Consistent Tempo 
     When every laser interruption occurs exactly T x  seconds after the preceding laser interruption, the relationship between laser interruptions and MIDI Beat Clocks will be similar to FIG.  8 . In this contingency, the frequency at which MIDI Beat Clocks are transmitted is constant. However, the frequency of laser interruptions is an unknown signal generated by the user. Accordingly, the frequency of laser interruptions can increase and decrease. 
     Decreasing Tempo 
     When the frequency of laser interruptions decreases, the relationship between laser interruptions and MIDI Beat Clocks will be similar to FIG.  9 . In this contingency, two laser interruptions will occur at an interval of T x . Following this, the MIDI Encoder will transmit 24 MIDI Beat Clocks at a frequency of T x /24. In this contingency, the user will not issue a new laser interruption for some time after the MIDI Encoder has transmitted the 24 MIDI Beat Clocks. The entire time elapsed during the transmittal of the 24 MIDI Beat Clocks and the subsequent time until the user issues a new laser interruption is called interval T x+1 . Note that interval T x+1  does not terminate until a new laser interruption occurs, resulting in the transmittal of the first MIDI Beat Clock of interval T x+2 . 
     Increasing Tempo 
     When the frequency of laser interruptions increases, the relationship between laser interruptions and MIDI Beat Clocks will be similar to FIG.  10 . In this contingency, two laser interruptions will occur at an interval of T x . Following this, the MIDI Encoder will begin to transmit MIDI Beat Clocks at a frequency of T x /24. However, the user will issue a new laser interruption before 24 MIDI Beat Clocks have been transmitted. This means that the user has ‘demanded’ that interval T x+2  begin before interval T x+1  has ended. To accommodate this, the MIDI Encoder immediately ‘purges’ the remaining MIDI Beat Clocks of interval T x+1  by transmitting them at an absolute maximum frequency. For example consider FIG.  10 . Interval T x  determines the frequency of the MIDI Beat Clocks transmitted during interval T x+1 . However, after only  17  MIDI Beat Clocks, interval T x+1  is interrupted by a new laser interruption. As a result, the MIDI Encoder immediately sends 7 MIDI Beat Clocks at a maximum rate of 3 MIDI Beat Clocks per millisecond. This completes the transmittal of the 24 MIDI Beat Clocks of interval T x+1  in a delay too short for the user to perceive. After the transmittal of these 7 MIDI Beat Clocks, the MIDI Encoder begins transmitting a new group of MIDI Beat Clocks. This signifies the beginning of interval T x+2 . These MIDI Beat Clocks are transmitted at a rate determined by the length of interval T x+1 . 
     The MIDI Beat Clocks are transmitted via the MIDI protocol to a computer with MIDI input capability  712 . The computer  712  delivers the MIDI Beat Clocks to a software MIDI player  714  capable of playing MIDI files and synchronizing to MIDI Beat Clocks. Software MIDI Player  714  uses the MIDI Beat Clocks to regulate the tempo of a pre-recorded MIDI file. For every 24 MIDI Beat Clocks it receives, the software MIDI player plays one beat of music from the pre-recorded MIDI file. Thus, the signal that is generated when the user interrupts the laser beams controls the tempo of a musical piece. 
     LED  410  is a power indicator, and illuminates when the device is powered. 
     Solid State Embodiment 
     The system of FIG. 2 can be realized using commercially available integrated circuits and passive circuit elements. Optical sensor  700  can be a phototransistor that becomes conductive when exposed to light. The optical sensor can be configured in series with a pull-up resistor of resistance 60 k? and a supply voltage of 5 volts. One-shot trigger  702  can be a typical IC non-retriggerable one-shot with an external RC network to determine the one-shot holdoff time. This holdoff time should be short enough to occur during a fast musical beat, and also long enough to reject spurious triggers from the optical sensor. A holdoff time of about 100 ms is appropriate. Spurious triggers might occur if a hand is used to interrupt the laser beams. When the hand passes through a laser beam, a first trigger can be derived from the first finger of the hand interrupting the laser. A second, spurious trigger can be generated by a second finger. One-shot trigger  702  rejects this second trigger. 
     Sequential logic  704  can comprise a binary counter that counts repeatedly up to the number of beats per measure in the musical composition and a network of combinational logic with a single output node. The combinational logic should be configured to produce a TRUE output signal when an interruption maps to an actual musical beat. The combinational logic should also produce a FALSE output signal when an interruption maps to a non-beat. The Boolean output of the combinational logic stage should drive one input of a two-input AND gate. The second input of the AND gate should be connected to the output of the one-shot trigger  702 . Thus, the sequential logic discriminates every interruption of the laser beams. Interruptions that represent beats are propagated past the combinational logic. Interruptions that represent non-beats are systematically ‘ignored’ by the sequential logic. 
     The timer  706  can be a 16-bit digital counter that is both stopped and started by each non-ignored laser interruption. The output signal of the timer will be a digital signal representing the elapsed count T x . 
     The divider  708  can be a clocked digital divider. The divider must be capable of accommodating a dividend of 16 bits. The divider must also be capable of completing a division operation quickly enough to accommodate a fast tempo, or approximately 5 ms. The output signal of the divider will be a digital signal representing the divided time T x /24. 
     The MIDI encoder  710  can be a UART (universal asynchronous receiver/transmitter) common to the MIDI art. It should be capable of sending a MIDI Beat Clock for every quantity of elapsed time T x /24. 
     The MIDI computer  712  can be any commercially available personal computer with an attached MIDI input means. MIDI input means might comprise a MIDI interface connected to the computer via USB, a serial cable, or a Firewire cable. 
     The MIDI software player  714  can be any commercially available MIDI application supporting synchronization via MIDI Beat Clocks or MIDI Realtime Messages. One such software player is Mark of the Unicorn&#39;s Performer. 
     Microcontroller Embodiment 
     A convenient embodiment of the invention uses a programmed microcontroller (e.g. the Zilog Z 8 ) to incorporate the one-shot trigger  702 , the sequential logic  704 , the timer  706 , the divider  708 , and the MIDI encoder  710 . Object code for the programming of such a device is included in an appendix. 
     In the microcontroller embodiment, the optical sensor is mapped to an interrupt vector. Whenever a laser interruption occurs, an interrupt routine runs and restarts a timer internal to the microcontroller. 
     The one-shot timer is incorporated into the microcontroller embodiment through a software ‘wait’ or ‘delay’ routine. This routine is executed every time a laser interruption occurs, and it causes subsequent laser interruptions to be ignored for some interval of time. A distinct advantage of the microcontroller embodiment of the conducting device is that the holdoff window can be scaled with the current tempo. Thus, for very slow tempos, when the user&#39;s hand or baton is likely to be moving very slowly, the holdoff time can be longer than for fast tempos. 
     The logic diagram of FIG. 5 is programmed into the microcontroller, so that the sequential logic  704  is incorporated. 
     Operation of the Invention 
     To conduct music with the device, the user begins by configuring the device components. The user positions the laser projector  100 , the towers  200  and  300 , and the laser receiver  400 . The user then adjusts the pivots  202  and  302  so that the vertical laser beam  106  enters the aperture  402  of the laser receiver  400 . 
     When configured, the device resembles the system of FIG.  1 . The user toggles switch  450  into either its 4/4 setting or its 3/4 setting. For example, if the music were written in an ‘even’ time signature, (e.g. 4/4 or 4/2) the user would toggle the switch into 4/4 mode. If the music were written in an ‘odd’ time signature, (e.g. 3/2 or 3/4 or 6/8) the user would toggle the switch into 3/4 mode. 
     The following descriptions describe patterns typical to a musical conductor who is right-handed and conducts with her right hand. A conductor using left-handed gestures would reverse the left/right gestures outlined below. Some reference components are shown in FIG.  2 . 
     Operation of an ‘Even’ Time Signature of Four Beats 
     The following description relates to a piece of music in the 4/4 time signature, as shown in FIG.  3 . In this time signature, the musical beats are counted “1, 2, 3, 4, 1, 2, 3, 4 . . .” Each set of four beats constitutes a ‘measure.’ 
     The user interrupts the horizontal laser beam  104  with an initial upward stroke (x) of a hand or baton (x). This interruption does not represent an actual beat, but a preparatory beat. The interruption of horizontal beam  104  causes the voltage at the optical sensor to drop. This voltage drop functions as a control signal to start timer  706 . The timer will record the elapsed time until the next interruption of the laser. 
     Next, the user delivers a downward (vertical) stroke  510  of the baton, interrupting horizontal laser beam  104 . This stroke constitutes the first beat of the first measure of the musical passage. When the optical sensor transmits the control signal resulting from this stroke, the timer stops and restarts. The amount of time recorded by the timer constitutes the predicted duration of the first beat. MIDI Encoder  710  begins to send MIDI Beat Clock signals to computer  712  at a rate of 24 per beat, or one signal every (1/24) of the time recorded by the timer. 
     Next, the user delivers a left-moving (horizontal) stroke  520  of the baton, interrupting horizontal laser beam  106 . This stroke constitutes the second beat of the first measure of the musical passage. When the optical sensor transmits the control signal resulting from this stroke, the timer stops and restarts. The amount of time recorded by the timer constitutes the predicted duration of the second beat. MIDI Encoder  710  begins to send MIDI Beat Clock signals to computer  712  at a rate of 24 per beat, or one signal every (1/24) of the time recorded by the timer. 
     Next, the user delivers a right-moving (horizontal) stroke  530  of the baton, interrupting horizontal laser beam  106 . This stroke constitutes the third beat of the first measure of the musical passage. When the optical sensor transmits the control signal resulting from this stroke, the timer stops and restarts. The amount of time recorded by the timer constitutes the predicted duration of the third beat. MIDI Encoder  710  begins to send MIDI Beat Clock signals to computer  712  at a rate of 24 per beat, or one signal every (1/24) of the time recorded by the timer. 
     Next, the user delivers an upward (vertical) stroke  540  of the baton, interrupting horizontal laser beam  104 . This stroke constitutes the fourth beat of the first measure of the musical passage. When the optical sensor transmits the control signal resulting from this stroke, the timer stops and restarts. The amount of time recorded by the timer constitutes the predicted duration of the fourth beat. MIDI Encoder  710  begins to send MIDI Beat clock signals to computer  712  at a rate of 24 per beat, or one signal every (1/24) of the time recorded by the timer. 
     The user has thusly conducted the first four beats (or first measure) of the musical passage. To begin the second measure of the piece, the user delivers a downward (vertical) stroke of the baton  510 , interrupting horizontal laser beam  104 . This stroke constitutes the first beat of the second measure. Each measure of the musical passage can be conducted using the fundamental four gestures outlined above. These gestures form the common pattern that musical conductors use to conduct music in 4/4 time signature. 
     Operation of an ‘Odd’ Time Signature of Three Beats 
     The following description relates to a piece of music in the 3/4 time signature, as shown in FIG.  4 . In this time signature, the musical beats are counted “1,2,3,1,2,3 . . .” Each set of three beats constitutes a ‘measure.’ The user must configure the device for operation in this odd time signature by depressing the footswitch. 
     The user interrupts the horizontal laser beam  104  with an initial upward stroke (x) of a hand or baton (x). This interruption does not represent an actual beat, but a preparatory beat. The interruption of horizontal beam  104  causes the voltage at the optical sensor to drop. This voltage drop functions as a control signal to start timer  706 . The timer will record the elapsed time until the next interruption of the laser. 
     Next, the user delivers a downward (vertical) stroke  610  of the baton, interrupting horizontal laser beam  104 . This stroke constitutes the first beat of the first measure of the musical passage. When the optical sensor transmits the control signal resulting from this stroke, the timer stops and restarts. The amount of time recorded by the timer constitutes the predicted duration of the first beat. MIDI Encoder  710  begins to send MIDI Beat Clock signals to computer  712  at a rate of 24 per beat, or one signal every (1/24) of the time recorded by the timer. 
     Next, the user delivers a rightward-moving (horizontal) stroke  620  of the baton, interrupting vertical laser beam  102 . This stroke constitutes the second beat of the first measure of the musical passage. When the optical sensor transmits the control signal resulting from this stroke, the timer stops and restarts. The amount of time recorded by the timer constitutes the predicted duration of the second beat. MIDI Encoder  710  begins to send MIDI Beat Clock signals to computer  712  at a rate of 24 per beat, or one signal every (1/24) of the time recorded by the timer. 
     Next, the user delivers an upward (vertical) stroke  630  of the baton, interrupting vertical laser beam  102  and horizontal laser beam  104 . This stroke constitutes the third beat of the first measure of the musical passage. When the optical sensor transmits the control signal resulting from the interruption of vertical laser beam  102 , the control signal is suppressed by sequential logic  704 , and never reaches timer  706 . When the optical sensor transmits the control signal resulting from the interruption of horizontal laser beam  104 , the timer stops and restarts. The amount of time recorded by the timer constitutes the predicted duration of the third beat. MIDI Encoder  710  begins to send MIDI Beat Clock signals to computer  712  at a rate of 24 per beat, or one signal every (1/24) of the time recorded by the timer. 
     The user has thusly conducted the first three beats (or first measure) of the musical passage. To begin the second measure of the piece, the user delivers a downward (vertical) stroke of the baton  610 , interrupting the horizontal laser beam. This stroke constitutes the first beat of the second measure. Each measure of the musical passage can be conducted using the fundamental three gestures outlined above. These gestures form the common pattern that musical conductors use to conduct music in 3/4 time signature. 
     Operation of Other Time Signatures 
     The operation outlined above was relevant to pieces of music in the 4/4 time signature and the 3/4 time signature. A piece of music can theoretically be written in any time signature. A time signature consists of a quantity of beats per measure (the top number) and the length of one beat (bottom number). 
     The 2/4 time signature: This time signature is typically conducted with a downward stroke and an upward stroke. The device can be configured for this mode the same way it can be configured for operation in the 4/4 time signature. 
     The 2/2 time signature: This time signature is typically conducted with a downward stroke and an upward stroke. The device can be configured for this mode the same way it can be configured for operation in the 4/4 time signature. 
     The 3/2 time signature: This time signature is typically conducted with a downward stroke, a rightward stroke, and an upward stroke. The device can be configured for this mode the same way it can be configured for operation in the 3/4 time signature. 
     Uncommon time signatures: Suppose a piece of music were written in the 5/4 time signature. Suppose also that a user desires to conduct the piece of music using the following gestures: down, left, right, left, up. To accommodate this operation, the device could use a map to associate each ‘cut’ (interruption of a laser beam) with one of six expected cuts. The first cut would map to the first beat, and the second cut would map to the second beat. The third and fourth cuts would map to the third and fourth beats. The fifth cut would be unique in that it would not map to a beat. The fifth cut would be treated as rhythmically insignificant. The sixth cut, being the last cut in the map, would map to the fifth beat. 
     Description and Operation-Alternate Embodiments 
     One alternate embodiment uses multiple parallel laser beams to detect motion of a baton or a hand, as shown in FIG.  7 . Instead of detecting beats via interruptions of laser beams, this embodiment relies upon a lattice of laser beams to track the motion of a hand or baton. When a user conducts music with a baton, he breaks the laser beams of the lattice sequentially. However, when the user reaches a beat, he reverses the direction of the baton, creating a peak. This change of direction will result in one beam being broken twice in a row, and this will trigger a new beat. The construction of this embodiment is more elaborate than that of the main embodiment, because this embodiment requires that many lasers be aligned so that they project laser beams into optical sensors. 
     Conclusion, Ramifications, and Scope 
     Thus the reader will see that the present device is an efficiently operated, simply constructed conducting device. It is capable of accommodating many conducting patterns and tempos. 
     While the preceding description is specific, it does not intend to limit the scope of the invention. While the preferred embodiment of the conducting device has been described in detail, there are other possible variations and improvements that maintain the essence of the present invention. For example: 
     An embodiment of the device might use multiple laser projectors and multiple optical sensors to more exclusively discriminate beats. For example, two laser projectors could project beams into two optical sensors. 
     An embodiment of the device might use computer software to make predictions about the length of upcoming beats. These predictions might be based upon patterns recognized in previous beats or groups of beats. For example, a user might persist in making beats ‘1’ and ‘3’ of a piece of music in the 4/4 time signature longer, and beats ‘2’ and ‘4’ shorter. Software incorporated in the device might recognize this pattern and use it to adjust the length of new beats. 
     An embodiment of the device might derive velocity information from the laser interruptions by measuring the amount of time for which the laser beam is interrupted. 
     An embodiment of the device might rely on special MIDI player software to incorporate the function of the sequential logic  704 . In this embodiment, the user would not be required to toggle the mode switch  450 , because the MIDI player would automatically ignore laser interruptions that did not represent beats. 
     An embodiment of the device might incorporate the laser projector  100  into the laser detection unit  400 . The laser projector would project a beam out of the detection unit, and the beam would be bounced back into the detection unit by a system of mirrors. 
     An embodiment of the device might send MIDI signals other than MIDI Beat Clocks. For example, the MIDI Encoder  710  could send a single note signal for each beat, rather than 24 equally spaced MIDI Beat Clocks. This embodiment could be useful for diversifying the functionality of the device, so that it could be used to trigger various MIDI signals in addition to tempo. 
     An embodiment of the device could replace the mirrors  202  and  302  with prisms. 
     An embodiment of the device could replace the laser projector  100 , the towers  200  and  300 , and the detection unit  400  with units designed to be mounted permanently in a musical space. 
     An embodiment of the device could incorporate the laser projector  100 , the towers  200  and  300 , and the detection unit  400  into a single unit suitable for easy transport. 
     An embodiment of the device could allow automated configuration of the laser. The laser projector  100 , or the mirror pivots  202  and  302 , or the optical sensor  700 , or any combination thereof might be guided by servo motors. 
     An embodiment of the device might incorporate an entire ‘kit’ of mirror elements, laser projectors, optical sensors, and configurable sequential logic. This kit could be configured by a user to detect any set of conducting gestures or any tempo.