WO1985002705A1

WO1985002705A1 - Electronic musical instrument

Info

Publication number: WO1985002705A1
Application number: PCT/GB1984/000422
Authority: WO
Inventors: David Simmons
Original assignee: Stepp Electronics Limited
Priority date: 1983-12-09
Filing date: 1984-12-07
Publication date: 1985-06-20
Also published as: GB8332906D0; EP0199724A1; AU3675684A

Abstract

An electronic guitar synthesizer has provision for "bending" the note upwards or downwards. A sensor detects lateral deviation of the selected fret string in each direction relative to a rest undeviated position and produces a signal representing the direction and amount of the deviation. In one example an l.e.d. (181) and a photo detector (182) are aligned on opposite sides of the string (180) with the string off-centre when undeviated. Provision is also made for detecting the position of a strum or pluck on the strum strings by comparing the amplitude of movement at opposite ends of the string.

Description

ELECTRONIC MUSICAL INSTRUMENT

The present invention relates to an electronic musical instrument. Various forms of musical instrument are known which may be described as electronic and are generally characterized in that the musical notes or tones that are generated by the instrument are electron¬ ically generated by an oscillator circuit. Music synthesizers of this general kind most commonly have a keyboard, somewhat in the manner of a piano or organ, by which they can be operated or played, together with a number of additional controls in the form of switches and control knobs or sliders. These additional controls are commonly preset by the player before playing a melody on the keyboard. Resetting of these additional controls during the course of the playing of a melody is possible though often difficult. Synthesizers with two separate keyboards are known enabling different sounds to be generated by each keyboard during the course of the play of one piece of music.

It is also known to form an electronic music synthesizer in the form generally of a guitar or other stringed instrument which can be strummed, plucked or bowed. In such "guitar-like" instruments the selection of tones to be generated by the electronic circuits of the instrument is controlled by switches provided on a neck of the instrument to simulate the usual fingerboard. The initiation or timing of the notes generated by the circuitry of the instrument can then be controlled by additional switches or sensors detecting a plucking or strumming action.

Various switching arrangements have been proposed. U.S. Patent 3666875 to Ranzato describes theprovision of individual key switches along the neck of the instrument simulating the usual fret fingering positions on the fingerboard of a guitar. Additional keys are provided at the strumming or plucking position of the guitar to enable the control of the timing of notes generated by the instrument with the fingers of the right hand of a right- handed player of the instrument. As an alternative, U.S. Patent 3662641 to Allen describes the use of touch sensitive switches along the fingerboard simulating the fret fingering positions. Short string members or elements combined with vibration sensors are provided for detecting the strumming or plucking action to control the tone generation circuits of the instrument.

Most commonly, however, in prior art arrangements, the "fret switches" simulating the fingerboard have been formed by the provision of electrically conductive fret bars! at the usual positions along the neck of the instru¬ ment in combination with electrically conductive string

OMPI elements extending along the neck over the fret bars in simulation of the usual strings of a guitar. A particular tone for generation by the electronic circ¬ uitry of the instrument can then be selected by the usual fingering action on the fingerboard depressing a selected string against a selected fret bar to make electrical contact between them. Such an arrangement is described in U.S. Patent 4372187 to Berg. Additionally Berg uses separate short string members or elements for use with the strum or plucking detectors formed in Berg as variable- reluctance activators. Such an arrangement as described by Berg which provides string elements along the neck of the instrument and also string elements in the strumming or plucking region has, at least in some respects, a number of advantages in that the instrument can have a familiar feel to the player in that he is controlling string elements with both hands in a manner similar to the playing of an ordinary guitar. However, the arrangement using electrical connections between conductive strings and fret bars for the fret switches has a number of drawbacks. It has been found that the electrical conn¬ ections made by this arrangement tend to be unreliable and furthermore the alignment of the string element over the fret bars is quite critical, almost as critical as the requirements of an ordinary guitar. Wrong alignment can result in a string element making contact accidentally with a fret bar below, nearer the bridge, in addition_ to the bar against which the string is being intentionally depressed. Furthermore, it is quite normal for the string element to make contact not only with the intended fret bar but also the bar above it, that is nearer the top end of the neck. Indeed this fact has been used in an attempt to overcome some of the problems associated with fret bar to string element switching by requiring the string to make contact with two adjacent fret bars before selecting for generation the note associated with the lower of the contacted fret bars, ie, that nearest the bridge.

It is believed that the aforementioned problems associated with the various prior art forms of fret switches in "guitar synthesizers" has resulted in such instruments failing to find wide appeal amongst musicians.

Nevertheless, it is helieved that a guitar synthesizer that had reliable fret switches, had a playing response closely simulating that of a stringed guitar and enabled many of the playing nuances of a stringed guitar to be replicated, would find wide appeal. It is an object of the present invention to provide an electronic musical instrument,^' which can be played in simulation of the playing of a guitar whilst generating musical tones synthetically, and provides a novel detection arrangement enabling the note or tone generated by the instrument to be modified or "bent" by the player pushing or pulling a selected string over the fingerboard, in a manner simulating the pitch, bending technique popular with, guitarists.

A further object of the present invention is to provide a sensing and decoding arrangement enabling real time control of a functional parameter of the tone generating circuits of the instrument in accordance with the position at which the instrument is strummed or plucked.

According to one aspect of the invention there is provided an electronic musical instrument having a neck part with a fingerboard, generally simulating the neck and fingerboard of a stringed musical instrument, the neck part having at least one string element tensioned along the neck part overlying the fingerboard and being arranged to provide electrical switches in at least one column corresponding to the fret fingering positions of a string represented by said string element, whereby a respective said switch can be actuated by depressing the string element with a finger against the underlying fingerboard at a selected fret fingering position along the string element; respective electronic tone generating circuitry responsive to selective actuation of the switches in the or each, column of. switches to enable the generation of a predetermined audio tone signal corresponding to the respective switch in the column which is actuated; and

OMPI pitch, bend detecting means responsive to deviation of the or each, respective string element laterally from a rest position, and parallel to the fingerboard, to provide a pitch, bend signal, said pitch bend detecting means being arranged to detect the lateral position of the string element over a range of lateral positions on both sides of the rest, undeviated position of the string element, whereby a parameter of the pitch bend signal is indicative of the sense of the deviation from the rest position, the tone generating circuitry being responsive to the pitch bend signal to raise or lower said predetermined audio tone respectively depending on said sense of the deviation of the string element indicated by the pitch bend signal. It will be appreciated that for ordinary stringed instruments, which rely on the length and tension of a string to determine the frequency of the generated tone, the only form of pitch bend possible is an upward bend since deviation of the string by the player results in an increase in tension in the string. On the other hand, the above referred aspect of this invention enables both upward and downward bends to be produced by the instrument. For example, the player may produce an upward bend by pushing the string with his fret finger and a downward bend by pulling the string. The above referred pitch, bend detecting means may comprise, for the or each, string element, a string position detector located and arranged to detect said lateral position at a point between supporting points between which the string element is freely suspended in tension.

In one arrangement, the or each string position detector comprises a photo-detector, having a sensitive surface, and a light source located on opposite sides of the associated string element so that the amount of the sensitive surface of the detector which is occluded from the light source by the string element is dependent on said lateral position of the element. Preferably the light source and detector are spaced apart on opposite sides of the string element in a direction perpendicular to the fingerboard surface and are located asymmetrically relative to the string element so that with the string element in the rest position a portion only to one side of the detector surface is occluded and a deviation of the string element in one direction increases the occluded portion whereas deviation in the other direction reduces the occluded portion.

Alternatively, the light source and detector may be spaced apart on opposite sides of the string element in the direction parallel to the fingerboard surface, and are such that, with the string element in the rest position.

OMPI v$ IPO a portion only of the detector surface is occluded even when the light source and detector are located symmetri¬ cally relative to the string element, deviation of the string element moving the element towards or away from the detector surface and varying the size of the occluded portion accordingly.

In another arrangement, the or each string position detector comprises a linear Hall effect device and a magnet located on opposite sides of the associated string element, the string element being made of a ferro¬ magnetic material, whereby the conduction characteristic of the Hall effect device, is dependent on said lateral position of the element.

The above described preferred embodiments of the present invention are particularly applicable to an example of the invention in which the fingerboard comprises a plurality of pressure actuated electrical switches forming the surface of the fingerboard and with the contacts of the switches entirely within the neck beneath the surface of the fingerboard. Such switches may for example take the form of membrane switches.

However, the generality of the above described aspect of the present invention is equally applicable to other forms of fret switching.

OMPI In a further aspect of the present invention,

an electronic musical instrument has a neck part with

a fingerboard, generally simulating the neck and

fingerboard of a stringed instrument, the neck part

comprising a plurality of electrical switches arranged

in at least one column along the neck part and

corresponding to the fret fingering positions of a

string, whereby a selected said switch can be actuated

by the finger of a person playing the instrument;

respective electronic tone generating circuitry

responsive to selective actuation of the switches in

the or each column of switches to enable the

generation of a predetermined audio tone signal

corresponding to the respective switch in the column

which is actuated, and further including at least one

dynamic control input whereby a parameter of the audio tone signal can be controlled by a control signal applied thereto; a respective elongate strum element corresponding to the or each said column of switches and actuatable by a strumming or plucking action in simulation of the strumming or plucking action on the corresponding string of a stringed instrument; a respective sensing means associated with the or each strum element to produce a trigger signal in response to actuation of the strum element by a strumming or plucking action to trigger the respective tone generating circuitry, the sensing means including strum position means responsive to signals generated by a strumming or plucking action to produce a strum position signal which is indicative of the position of said strumming or plucking action along said elongate element; and means supplying said strum position signal to the dynamic control input of the respective electronic tone generating circuitry to effect dynamic control of said parameter of the audio tone signal in response to said position of said strumming or plucking action. This aspect of the invention provides a very useful feature which may for example be used to simulate the variations in tonal quality which can be obtained when strumming or plucking strings of an ordinary guitar at different places along the length of the strings. For example plucking or strumming near the bridge of the guitar produces a "twangy" tone with a substantially greater content of higher harmonics than strumming or plucking the strings further away from the bridge near the base of the neck. The strum position signal generate in the above aspect of the invention can be used to control an appropriate parameter in the electronic tone generating circuitry to simulate this variation in tonal quality. However, alternatively, the strum position signal may be used to control any selected parameter of the tone signal produced by the instrument. For example, the tone generating circuitry of the instrument may have a number of parameter control inputs which are normally preset, very conveniently by a microprocessor. The microprocessor can be programmed with a number of setting selections so that resetting of the tone generating circuitry is accomplished simply by instructing the microprocessor which combination of settings to apply. The various combinations of settings can be stored in the microprocessor memory for example to simulate the sounds of various instruments such as mandolin , guitar, piano, etc. In a particularly remarkable embodiment of the present invention, the strum position signal may be supplied to the microprocessor as real time data whereby the microprocessor responds to the value indicated by the strum position signal by almost instantaneously selecting an appropriate combination of settings from programme memory. In this way, the instrument can be arranged to sound for example like a mandolin when strummed or plucked near the bridge, and like a piano when strummed or plucked away from the bridge near the base of the neck. Such flexibility during the actual playing of the instrument is something quite new in music synthesizers.

Preferably, the or each elongate strum element is formed as a flexible string member suspended in tension between supporting points, and the sensing means comprises a pair of sensors located at sensing points spaced apart along the string member and also spaced from said supp¬ orting points, the sensors being arranged to produce a pair of signals representative of the instantaneous deviation at the respective sensing points of the string from rest when strummed or plucked, and wherein the strum position means is responsive to said pair of signals to produce said strum position signal. The strum position means, for the or each said string member, may include a comparator connected to generate an enable signal when the instantaneous deviation represented by one of said pair of signals exceeds a predetermined threshold value, and a sample and hold circuit triggered by said enable sig¬ nal to sample the value at the corresponding moment of deviation as represented by the other of said pair of sig- nals and to hold said sampled value as the strum position signal. Conveniently each of said sensors comprises a photo- electric device, having a sensitive surface, and a light source located on opposite sides of the associated flexible string member so that the amount of the sensitive surface of the detector which is occluded from the light source by the string member is varied on deviation of the member from a rest position.

An example of the present invention will now be described in greater detail and with reference to the accompanying drawings in which:

Figure 1 is a perspective view of an electronic musical instrument embodying the present invention and in a form simulating a guitar;

Figure 2 is a more detailed perspective view, partly in cross section, of the neck part of the guitar¬ like instrument of Figure 1, illustrating the construction of the fingerboard;

Figure 3 is an enlarged sectional view taken along line III-III of Figure 2;

OMPI Figure 4 is a simplified block diagram of a sensor arrangement employed with, the string members used for sensing a strumming or plucking action on the instrument;

Figure 5 is a simplified block diagram of the sensor arrangement used for detecting pitch bend signals on the string elements extending along the neck part of the instrument;

Figure 6 is a detailed cross sectional view illustrating a preferred form of sensor used for gener- ating pitch bend signals;

Figure 7 is a graphical representation of the response of the sensor of Figure 6.

Figure 8 is a circuit diagram illustrating a level shifting circuit for use with the pitch bend sensor of Figure 6 ;

Figure 9 is a detailed cross sectional view of a sensor used in association with strum string members for detecting a strum or plucking action;

Figure 10 is a graphical representation of the response of the sensor of Figure 9;

Figure 11 is a circuit diagram illustrating a filter and buffer element for use with the strum sensor of Figure 9 and generating a trigger signal for the tone generating circuitry;

Figure 12 is a circuit diagram of an arrangement for generating a strum position signal from the outputs of the two sensors illustrated in Figure 11 and

Figure 13 is a graphical representation illustrating the operation of the strum position sensor of Figure 12.

A possible embodiment of aspects of the present invention is illustrated generally in Figure 1. The illustrated embodiment is in the general form of a guitar, particularly an electric guitar (rather than an acoustic guitar) . It should be stressed that the present invention is not concerned with an instrument which relies on the frequency of vibration of strings to determine the frequency of output tones generated by the instrument. In this respect the present instrument is quite different from the usual electric guitar. The present instrument has electronic tone generating

circuitry which relies on, for example, voltage controlled

oscillators for determining the frequency of the output tones and sounds of the instrument. The voltage controlled oscillators within the instrument may be mounted on circuit boards housed in a body part 10 of the instrument. Preset controls are provided on the body part 10, eg, in the form of control knobs 11 and 12 and selecting keys 13. Additionally, the present functional setting of the electronic tone generators can be displayed eg, by electronic displays 14. The instrument can be played in a manner simulating the playing of the usual electric or acoustic guitar, ie, with a player strumming or plucking strum string elements 15 with the right hand whilst fingering fret string elements 16 with the left hand. However, in this-example of the indention, the fingering

action on the fret string element 16 is arranged to operate electric switches within the fingerboard 17 of the instrument thereby controlling the output tones to be generated by the tone generating circuitry. The triggering or initiation of the sounds from the tone generating circuitry can be subject to the control of the strumming or plucking action on the strum string members 15. Referring to Figures 2 and 3, the particular form of this example of the neck part of the illustrated instru¬ ment is shown in more detail. The neck part illustrated generally at 20 is formed of an elongate structural element 21 providing the necessary rigidity and strength for the neck part, housed in a channel shaped housing member 22 defining the rear of the neck. The neck has a fingerboard 23 in which are located a plurality of pressure responsive switches. The switches are arranged in columns corresponding to the normal strings of an ordinary electric or acoustic guitar with the switches of one column corresponding to the separate fret fingering positions of the string. The switches are formed as membrane switches and comprise a substrate board 24 of a relatively rigid electrically insulating material having deposited thereon metalised regions 25 forming the contacts of each of the switches. The contacts formed by the metalised regions on the board 24 are physically spaced so as to be electrically isolated from one another on the board. Overlying the substrate board 24 is an electrically insulating spacer membrane 26 which has formed through it apertures 27. The apertures 27 are each aligned accurately to overly the metalised regions 25 forming each of the switch contacts. A flexible contacting sheet 28 in turn overlies the spacer membrane 26 and has electrically conductive metalised regions 29 formed on an underface thereof directed towards the substrate board 24 through the apertures 27. Overlying the entire assembly of switches forming the fingerboard there is provided an insulating flexible sheet 30 which may be formed of a polycarbonate plastics material. A selected one of the switches formed in the fingerboard 23 can be operated by pressing on the flexible polycarbonate sheet 30 in an appropriate position so as to deform the sheet 30 together with the underlying flexible sheet 28 to bring the contacting layer 29 into electrical contact with the metalised region 25 of the selected switch. Electrical contact is thereby provided between the individual contacts of the switch by means of the contacting region 29, thus closing the switch.

Running along the length of the neck oart 20 are provided string elements 31 which simulate the usual strings of a guitar. However, in examples of the present invention, the string elements 31 may be intentionally damped so that any vibration of the elements 31 plays no part in selection of the tones or sound frequencies generated by the instrument. The string elements 31 are suspended in tension between supporting points 32 and 33 at the head end and base of the neck part respectively (see Figure 1) . The string elements 31 are when in a state of

OMPI rest, undeviated by any finger pressure by the player, spaced above the surface of the fingerboard 23. When playing the instrument, a player depresses the string element 31 down onto the surface of the fingerboard 23 and by the pressure thereby exerted by the finger and the string element itself onto the fingerboard surface, operates a selected underlying switch. It will be appreciated that in this example of the invention, there is no requirement for any electrical contact to be made between the string elements 31 and any part of the finger¬ board surface. The electrical switches are formed entirely beneath the surface of the fingerboard 23 and the string elements 31 are provided rather to give the player of the guitar the usual tactile response with which he would be familiar from the playing of ordinary electric or acoustic guitars.

In order to enable the player of the instrument to identify the correct fret position, raised pips 34 may be provided on the fingerboard surface. The pips 34 may be made by embossing the polycarbonate sheet 30 forming the surface layer of the fingerboard. The pips 34 are provided in rows as illustrated in Figure 2, generally corresponding to the positions of the fret bars that would be provided on an ordinary acoustic or electric guitar. The rows of pips 34 are positioned on the fingerboard surface so that a player of the instrument can feel with his fingers where to depress an appropriate string element 31 down onto the fingerboard surface and thereby operate an underlying switch. The pips 34 of each row of pips are located substantially equally spaced between the string elements 31. In this way, the pips 34 additionally provide a tactile response to the player of the guitar whereby the player will be able to limit any "bending" he may apply to the string element 31, in order to achieve pitch bend as will be described in more detail later, so as to avoid inadvertently operating an adjacent switch in the next column of switches associated with the next string element.

The organisation and interconnection of the various switches in the fingerboard of the neck part of the instrument can vary. However, in one example, each switch is formed of a pair of interdigitated contact elements formed on the insulating substrate board 24. In the illustrated embodiment, there are six columns: fswitches simulating the six strings of a typical guitar. It will be appreciated that different numbers of columns of switches could be provided. In this exam^ple of the invention, a total of twenty-four switches are provided in each column corresponding to twenty-four different fret fingering positions capable of providing two full octaves of tones on each column. Appropriate electronic circuitry is provided

for scanning the various switches to address each

switch in turn, column by column.

Referring again to Figure 1, sensors are provided to detect strumming or plucking actions on the string

members 15 of the instrument. In the present example

these strum detectors comprise two individual

detecting elements provided near opposite ends of

each string member 15, so that for each string

there is one strum detector near the support

OMP points 60 of the string at the base of the neck part of the instrument and another detector at the support point 61 of the string iretfcer at the "bridge" end of the rretrber. These pairs of strum detectors are illustrated diagraπiratically in Figure 4 at 62 and 63. The sensors 62 and 63 are arranged to provide electrical signals which indicate the amplitude of deviation of the string at the respective detection points from a rest position. It may be appreciated therefore that, with the two detec¬ tors near opposite ends of each string member 15 , the relative amplitudes of the detection signals produced are indicative of the position along the strum string member at which the strumming or plucking action takes place. For example a strumming or plucking action near the neck end detector 62 produces a greater amplitude signal from these detector 62 than that from the detector 63. Difference circuits 64 are provided and will be described in greater detail later, which produce an output signal representative of the difference in these amplitudes , thereby being indicative of the position along the string member between the detection points at which the strumming or plucking action took place . The outputs from the difference circuits 64 are held in holding circuit 65 for supplying of control signals to the tone generating circuits as will be described. Additionally, signals are derived directly from at least one of the sensors 62 or 63 for supply, preferably by appropriate buffering and pulse shaping circuits to the tone generating circuits to control the initiation and timing of the audio signals produced by the generating circuits .

As was mentioned briefly above , the string elements 31 extending along the neck part of the instrument may not only provide an appropriate tactile feedback to the player of the instrument assisting in location of selected switches beneath the fingerboard, but also can enable the player to control the instrument to provide "pitch bend" in a manner which will be familiar to guitar players . Pitch bend is normally applied to acoustic or electric guitars by the player deflecting the string depressed against a selected fret bar sideways along the fret bar so as. to increase the tension of the string, thereby raising its tone . In the present example of this invention , and as illustrated in Figure 5 , sensors 70 are provided to detect lateral deviation, parallel to the fingerboard surface , of the string elements 31 , thereby to provide controlling inputs to the tone generating circuits to modify the output tone .

The sensors 70 are arranged to detect lateral deviation of the string elements 31 in either direction , ie , either pushing or pulling the string, and to control the tone generator to raise the pitch of the generated tone in response to pushing of the string and to lower the pitch in response to pulling of the string. Appropriate sensors and circuitry for this purpose will be described in more detail later. The sensors 70 are conveniently provided near the ends of the string elements 31 just spaced from supporting points 71 of the strings Csee Figure 11 at the base of the neck part of the instrument.

It will be appreciated that an appropriate address scanning arrangement is required to enable each individual switch on the fingerboard to be separately addressed to identify whether it is opened or closed. In accordance with the usual way of playing a guitar-like instrument, it can be expected that only one switch will be closed in each column, corresponding to each string.

Control signals identifying any switch closed in each column are provided to the tone generating circuits to set up the appropriate tones for generation.

Additional circuitry may be provided for detecting when either the fret string elements 16 or the strum string members 15 are being touched by the player of the instrument. This touch detection can usefully provide signals which can control the tone generating circuitry to simulate the damping and snubbing actions which will be familiar to players of ordinary acoustic and electric guitars. For such an arrangement, the fret string element 16 and the strum string members 15 are made of an electrically conductive material. A separate tone generating circuit, or voice, is provided for each column of switches Cor stringl provided on the fingerboard of the instrument and each, such tone generating circuit is controlled by the switches of the corresponding column on the fingerboard and the sensors associated with the corresponding strum string member.

The tone generating circuit is also controlled dynamically by the pitch bend signals from sensor 70 and by the strum position signal from the holding circuit 65. The strum position signals can be used to control the pulse width of pulse signals which are generated in the generating circuit to build up the desired tonal quality and harmonic content. In this way, the harmonic content of the audio output signal from the generator can be varied during the playing of the instrument in accordance with the position along the strum string members that the string members are plucked or strummed. For example it may be arranged that the pulse width is reduced in response to strumming or plucking the strum string members near the bridge end of the strings, and increased in response to strumming near the neck end of these string members. This has the effect of increasing the higher harmonic content of the audio output signal from the generator which can simulate the increased "twangy" sound normally experienced with acoustic and electric guitars when strumming or plucking near the bridge. It is important to note that the strum position signal can indicate the position of strumming or plucking over substantially the full length of the strum string member and can thereby provide an additional "degree of freedom" to the player of the instrument. Not only can the individual notes and the timing of these notes be selected by the player during the playing of the instrument, but also the tonal quality of each note so selected can be determined and changed with a considerable degree of precision.

Referring now to Figures 6, 7 and 8 a preferred form of pitch bend sensor such as indicated at 70 in Figure 5 will be described. Figure 6 is a greatly enlarged view illustrating a pitch bend sensor detecting the position of one of the fret string elements shown in cross section at 180. The string element 180 is illustrated in Figure 6 in the rest, or undeviated position. The pitch bend sensors for each of the fret string elements are located near, but spaced slightly away from, the supporting points of the string elements at the base end of the neck. Each sensor comprises a light emitting diode 181 and a photoelectric detector, typically a photo- transistor 182. The diode 181 and detector 182 are mounted rigidly with respect to the body of the instrument so as to be aligned on opposite sides of the string 180 and perpendicular to the plane of the fingerboard of the instrument. Thus, the usual pitch bending action by a player of the instrument produces a lateral movement of the string 180 in the directions of arrows 183 and 184 in Figure 6. ^τ**e arrangement is such that the string elements 16 normally overlie the fingerboard surface spaced but sufficiently close to the surface so that when depressed onto the surface to operate a selected finger- board switch , there is negligible deviation of the string element 180 at the location of the pitch bend sensor towards and away from the photo- detector 182. On the other hand, the usual lateral movement of the string associated with pitch bending , produces a detectable degree of movement of the string element 180 at the position of the sensor .

As is shown in Figure 6 , when the string element is at rest, and undeviated , it is arranged to be off-set relative to the centre line between the light emitting diode 181 and photo-detector 182 so that a part 185 , preferably about half of the sensitive surface 186 of the photo-detector 182 is occluded from the light emitting diode 181. It can be seen , then , that movement of the string element 180 in one direction 183 exposes more of the surface 186 of the detector to light from the diode

181 , whereas movement in the opposite direction 184 reduces the exposed surface area. The resultant output from the detector 182 can be as illustrated graphically in Figure 7.

Preferably the output voltage from the detector 182 is level adjusted by a circuit such as illustrated in Figure 8. The positive going voltage from the detector 182 which can vary over the range illustrated in Figure 7 is supplied to the non-inverting input of an operational amplifier 190 and the inverting input of the amplifier is supplied with a DC bias from a potential divider 191 so that the output of the operational amplifier can swing both negative and positive on either side of zero volts corresponding to the rest position of the string element. The output of the operational amplifier on line 192 can then be supplied directly to the pitch bend input of the tone generating circuit .

Referring now to Figures 9 and 10 a sensor arrangement is illustrated which can be used as the strum or pluck sensors on the strum string elements as shown in Figure 4. An arrangement similar to that for the pitch bend illustrated in Figure 6 is used for the strum sensor and is illustrated in Figure 9. A light emitting diode 195 and an opposed photo-detector 196 are provided on opposite sides of each strum string member, shown in Figure 9 in cross section at 197. One such sensor as illustrated in Figure 9 is provided near each end of each strum string member to constitute the separate sensors 62 and 63 shown

OMPI l IPO in Figure 4. The sensors are located near but spaced a short distance away from the supporting points at the end of the strum string members. For all the strum sensors, the light emitting diode 195 and detector 196 can be located with the string member 197 aligned centrally between them when at rest so^"as substantially completely to occlude the sensitive surface 198 of the detector 196 from light from the diode 195. Then, deviation of the string member 197 in either direction, such as illustrated in dotted lines at 199, can result in an increase in the area of the sensitive surface 198 which is exposed to light from the diode 195. The resultant output charact¬ eristic of the detector 196 is illustrated graphically in Figure 10 where the minimum voltage from the detector 196 corresponds to the rest position of the string member. The amplitude of deviation of the string member from the rest position can be determined up to maximum displacements from either side of the rest position, corresponding to complete exposure of the detector 196. Figure 11 illustrates the two sensors identified as A and B, located near opposite supporting points 200 and 201 of the strum string member 202. Output voltages from the detectors 196 of the two sensors A and B are fed on lines 203 and 204 to a strum position detector 205 arranged to generate therefrom a signal on a line 206 indicative of the position along the string member 202 at which the strum

UMΠ iφ WIPO or plucking action took place. Additionally, the signal from the sensor A is fed on a line 207 via a high pass filter comprising a series capacitor 208 and shunt resistor 209 to a buffer amplifier 210, the output of which constitutes the trigger pulse supplied on a line 159 to trigger the envelope generator 149 of the corresponding tone generating circuit. It will be appreciated that the amplitude of the signal from the sensor A fed on line 207 is dependent not only on the strength with which the string member 202 is plucked or strummed but also the distance of the plucking or strumming action from the supporting point 200. Accordingly, it may be preferable to supply a corresponding output from the sensor B to a second high pass filter and buffer amplifier circuit similar to that shown in Figure 11 and then to sum the analogue outputs of the two circuits to produce a trigger signal which has an amplitude substantially independent of the position along the string member 202 of the corresponding strumming or plucking action. Figure 12 illustrates an example of the strum position detector 205 in greater detail. The output signals from the two sensors A and B are fed to the circuit of Figure 12 on lines 220 and 221 respectively. The output signal from the sensor B is fed to a comparator 222 having its other input held at a predetermined voltage level defining a threshold voltage. The output of the

OMPI comparator 222 changes state when the voltage signal from the sensor B exceeds a predetermined threshold voltage , and the resultant pulse signal developed on the line 223 operates gate 224 so that the voltage level at that instant on the line 220 from the sensor A is stored on a capacitor 225 . The value of this voltage across capacitor 225 is fed to the output line 206 via a buffer 226 .

By reference to the graphical representation of Figure 13 it can be seen that the circuit of Figure 12 provides on line 206 an output voltage which can be substantially independent of the strength with which the string member is plucked or strummed but representative only of the position along the length of a string member at which the plucking or strumming action took place . The string member at rest is indicated in Figure 13 by the horizontal line extending between - the support point 200 near the neck of the instrument and 201 corresponding to the bridge of the instrument. The positions along the string member of the sensors A and B are indicated by the vertical dashed lines 230 and 231. If the string member is plucked or strummed at a position X along the string as indicated in Figure 13 , the string member must be deviated in the manner shown by the two lines 232 and 233 before the output from the sensor B near the bridge 201 exceeds the threshold level of the comparator 222. At that instant, the corresponding output of the sensor A, identified at

OMPI 234 in Figure 13, is stored on the capacitor 225 and buffered onto the output line 206. The corresponding string deviation for a strumming action at position Y, roughly halfway between the sensors A and B, is indicated by the lines 235 and 236, and it can be seen that the output signal from the sensor A on triggering of the comparator 222 is now at a lower value 237. Similarly, the deviation of the string member for a plucking or strumming action at position Z is shown to produce a stored and buffered value of 238 of the sensor A. Thus the circuit arrangement of Figure 12 can produce an output voltage on line 206 indicative of the position along the string element at which the plucking or strumming action takes place. It should be noted that the amount of deviation shown in Figure 13 is very greatly exagerated for clarity. It will be appreciated that the threshold level must be set sufficiently low that it will be less than the corresponding deviation of the string member at sensor B for a strumming or plucking action near the sensor and of the minimum force to be position detectable.

Alternative circuits and arrangements for detecting the position of the strumming action along the length of the string member can be envisaged. For example, separate peak detection circuits may be employed responsive to the output signals from each of the sensors A and B to produce corresponding voltage levels. An appropriate ratio detector can then be employed to determine the ratio of these voltage levels to provide an indication of the strum position. Instead of the optical sensors as illustrated in figure 9, other sensing devices may be used for the strum sensors, such as Hall effect devices or capacitative detectors.

Claims

CLAIMS;

1, An electronic musical instrument having a neck part with a fingerboard, generally simulating the neck and fingerboard of a stringed musical instrument, the neck part having at least one string element tensioned along the neck part overlying the fingerboard and being arranged to provide electrical switches in at least one column corresponding to the fret fingering positions of a string represented by said string element, whereby a respective said switch can be actuated by depressing the string element with a finger against the underlying fingerboard at a selected fret fingering position along the string element; respective electronic tone generating circuitry responsive to selective actuation of the switches in the or each column of switches to enable the generation of a predetermined respective switch in the column which is actuated; and pitch bend detecting means responsive to deviation of the or each respective string element laterally from a rest position, and parallel to the fingerboard, to provide a pitch bend signal, said pitch bend detecting means being arranged to detect the lateral position of the string element over a range of lateral positions on both sides of the rest, undeviated position of the string element.

OMPI whereby a parameter of the pitch, bend signal is indicative of the sense of the deviation from the rest position, the tone generating circuitry being responsive to the pitch bend signal to raise or lower said predetermined audio tone respectively depending on said sense of the deviation of the string element indicated by the pitch bend signal.

2. An electronic musical instrument as claimed in Claim 1, wherein the pitch bend detecting means comprises, for the or each string element, a string position detector located and arranged to detect said lateral position at a point between supporting points between which the string element is freely suspended in tension.

3. An electronic musical instrument as claimed in Claim 2, wherein the or each string position detector comprises a photo-electric detector, having a sensitive surface, and a light source located on opposite sides of the associated string element so that the amount of the sensitive surface of the detector which is occluded from the light source by the string element is dependent on said lateral position of the element.

OMPI 4. An electronic musical instrument as claimed in Claim 3 wherein the light source and detector are spaced apart on opposite sides of the string element in a direction perpendicular to the fingerboard surface, and are located asymmetrically relative to the string element so that with the string element in the rest position a portion only to one side of the detector surface is occluded and deviation of the string element in one direction increases the occluded portion whereas deviation in the other direction reduces the occluded portion.

•5. An electronic musical instrument as claimed in Claim 3, wherein the light source and detector are spaced apart on opposite sides of the string element in a direction parallel to the fingerboard surface, and are such that, with the string element in the rest position, a portion only of the detector surface is occluded even when the light source and detector are located symmet¬ rically relative to the string element, deviation of the string element moving the element towards or away from the detector surface and varying the size of the occluded portion accordingly.

6. An electronic musical instrument as claimed in Claim 2, wherein the or each string position detector comprises a linear Hall effect device and a magnet located on opposite sides of the associated string element, the string element being made of a ferroinagnetic material, whereby the conduction characteristic of the Hall effect device is dependent on said lateral position of the element.

7. An electronic musical instrument having a neck part with a fingerboard, generally simulating the neck and fingerboard of a stringed musical instrument, the neck part comprising a plurality of electrical switches arranged in at least one column along the neck part and corresponding to the fret fingering positions of a string and at least one string element tensioned along the neck part to overly the fingerboard, whereby a selected said switch can be actuated by depressing the string element with a finger against the underlying fingerboard at a position along the string element to actuated the switch; respective electronic tone generating circuitry responsive to selective actuation of the switches in the or each column of switches to enable the generation of a predetermined audio tone signal corresponding to the respective switch in the column which is actuated; and pitch bend detecting means responsive to deviation of the or each respective string element laterally from a rest position, and parallel to the fingerboard, to provide a pitch bend signal, the pitch bend detecting means comprising, for the or each string element, a string position detector located and arranged to detect the lateral position of the string element, at a point between supporting points between which the string element is freely suspended in tension, over a range of lateral positions on both sides of the rest, undeviated, position of the string element, whereby a parameter of the pitch bend signal is indicative of the snese of the deviation from the rest position, the tone generating circuitry being responsive to the pitch bend signal to raise or lower said predetermined audio tone respectively depending on said sense of the deviation of the string element indicated by the pitch bend signal.

8. An electronic musical instrument having a neck part with a fingerboard, -generally simulating the neck and fingerboard of a stringed instrument, the neck part comprising a plurality of electrical switches arranged in at least one column along the neck part and corres¬ ponding to the fret fingering positions of a string, whereby a selected said switch can be actuated by the finger of a person playing the instrument; respective electronic tone generating circuitry responsive to selective actuation of the switches in the or each column of switches to enable the generation of a predetermined audio tone signal corresponding to the respective switch in the column which is actuated, and further including at least one dynamic control input whereby a parameter of the audio tone signal can be controlled by a control signal applied thereto; a respective elongate strum element corresponding to the or each said column of switches and actuatable by a strumming or plucking action in simulation of the strumming or plucking action on the corresponding string of a stringed instrument; respective sensing means associatedwith the or each strum element to produce a trigger signal in response to actuation of the strum element by a strumming or plucking action to trigger the respective tone generating circuitry, the sensing means including strum position means responsive

OMPI to signals generated by a strumming or plucking action to produce a strum position signal which is indicative of the position of said strumming or plucking action along said elongate element; and means supplying said strum position signal to the dynamic control input of the respective electronic tone generating circuitry to βffeet dynamic control of said parameter of the audio tone signal in response to said position of said strumming or plucking action.

9. An electronic musical instrument as claimed in Claim 8, wherein the or each elongate strum element is formed as a flexible string member freely suspended in tension between supporting points, and the sensing means comprises a pair of sensors located at sensing points spaced apart along the string member and also spaced from said supporting points, the sensors being arranged to produce a pair of signals representative of the instant¬ aneous deviation at the respective sensing points of the string from rest when strummed or plucked, and wherein the strum position means is responsive to said pair of signals to produce said strum position signal.

10. An electronic musical instrument as claimed in Claim 9, wherein the strum position means, for the or each said string member, includes a comparator connected to generate an enable signal when the instantaneous deviation represented by one of said pair of signals

OMPI exceeds a predetermined threshold value, and a sample and hold circuit triggered by said enable signal to sample the value at the corresponding moment of deviation as represented by the other of said pair of signals and to hold said sampled value as the strum position signal.

11* An electronic musical instrument as claimed in either of Claims 9 and 10 wherein each of said sensors comprises a photo-electric device, having a sensitive surface, and a light source located on opposite sides of the associated flexible string member so that the amount of the sensitive surface of the detector which is occluded from the light source by the string member is varied on deviation of the member from a rest position.

12. An electronic musical instrument as claimed in any of Claims 8 to 11 wherein said electronic tone generating circuitry includes controllable oscillator means having a plurality of parameter control inputs enabling the setting of corresponding parameters of the audio tone signal generated by the circuitry to provide a desired tonal quality, and there is provided a micro¬ processor and associated memory arranged for generating selected predetermined combinations of parameter control signals for supply to said parameter control inputs, the microprocessor being arranged to receive data defining changes in said strum position signal and programmed to respond in real time to said changes to alter the selected combination of parameter control signals .

13 , An electronic musical instrument substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings .

OMPI