Plectrum for a string instrument, a transmitter/receiver arrangement and a signal processing apparatus

A plectrum for a stringed musical instrument having a plurality of conductive strings is provided with a non-conductive body and a conductive tip. The conductive tip is sized so as to fleetingly contact a string when the string is plucked with a plectrum. The tip is electrically connected to a monitoring circuitry which provides a triggering signal each time the tip contacts any of the strings. A transmitter and receiver arrangement is provided to monitor the contact of the tip with the strings and generate the triggering signal. The triggering signal is in turn received by a signal processing apparatus which modifies the audio signal output from the stringed musical instrument under control of the triggering signal.

FIELD OF THE INVENTION

The present invention relates to string instruments having a plurality of conductive strings, for example electric guitars. In particular, the present invention relates to a plectrum for use with such string instruments, a transmitter/receiver arrangement adapted for use with the plectrum and a signal processing apparatus also adapted for use with the plectrum.

The invention has been developed primarily for use in digital processing of the audio output from a string instrument and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use. For example, the triggering signal derived from the present invention can also be used to drive effects other than audio effects, for example lighting effects being synchronised with music played upon the string instrument.

BACKGROUND TO THE INVENTION

Known techniques for processing an audio signal derived from string instruments are limited by the difficulty of providing an accurate triggering signal to enable event-driven signal processing techniques. Accordingly, most signal processing techniques currently used in real-time with string instruments are continuous in the sense that a signal processing process is not stopped and started on an event basis. Typical audio effect processes such as echo, reverberation, phasing, panning, chorus and flanging are usually continuous in nature since the effect is applied to the audio signal continuously for as long as the effect is desired.

An attempt to provide a triggering signal to enable more sophisticated signal processing is described in U.S. Pat. No. 4,235.144. This prior art document discloses a conductive pick connected to a contact sensor which senses conductive contact between the strings of the guitar and the conductive pick. In this arrangement, breaking contact between the pick and the string initiates a special musical effect.

It has been appreciated by the inventor of the present invention however that this prior art arrangement suffers numerous technical defects to the extent that it cannot be successfully employed to provide a triggering signal reliable enough to enable sophisticated event-driven signal processing. In particular, the inventor of the present invention has discovered that the conductive contact between the string and the prior art conductive pick can be subject to numerous imperfections leading to false triggering. This can be exacerbated by the habit of some string instrument players of resting their pick on the string before actually plucking the string. As the prior art arrangement triggers from the moment when conductive contact between the pick and the string is broken, the imperfect conductive connection can result in false triggering. Other factors leading to imperfect triggering by the prior art arrangement of U.S. Pat. No. 4,235,144 include: a string and/or the pick may be tamished, thereby inhibiting stable conductive contact; the pressure of the pick on the string may not be constant due to the player touching the pick against the string lightly; and larger gauge strings in particular can be vibrating quite vigorously towards and away from the pick, thereby initiating and breaking conductive contact prior to plucking of the string. Whilst this imperfect triggering may suffice for the relatively simple effects outlined in the abovementioned U.S. patent, it has been found by the inventor of the present application not to suffice for slightly more sophisticated triggering such as MIDI triggering, Control Voltage and Gate triggering, in other words, the type of triggering required for the signal processing provided by modern synthesizers.

OBJECT OF THE INVENTION

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a plectrum for a string instrument having a plurality of conductive strings, said plectrum including:

a non-conductive body defining a gripping portion and a plucking portion; and

a conductive tip protruding just beyond an edge of said plucking portion, an outer surface of said tip being sized so as to fleetingly contact a string of said instrument when said string is plucked by said plucking portion, said tip further being capable of operative association with electronic monitoring circuitry adapted to provide a triggering signal each time the tip contacts any one of said strings.

Preferably the tip is electrically connected to a first wire embedded within the body which is, in turn, electrically connected to a second wire external of the body and extending from a point on the body remote of the plucking portion.

In the preferred embodiment the tip protrudes from an outer edge of the plucking portion by no more than 1 mm and the perimeter length of the tip is no greater than 8 mm.

According to a second aspect of the invention there is provided a transmitter/receiver arrangement adapted for use with a plectrum as described above, said arrangement including a transmitter having a signal generator electrically connectable to said tip such that, when said tip fleetingly connects with said string during plucking, the transmitter produces a signal which is detectable by receiver circuitry, said receiver circuitry being operatively associated with said electronic monitoring circuitry so as to provide said triggering signal.

Preferably the transmitter is mountable to a person playing the instrument, for example by means of a strap mounted to the wrist of the person. The transmitter is preferably electrically connectable to the plectrum by the second wire.

According to a third aspect of the invention there is provided a transmitter adapted for use with a plectrum as described above, said transmitter having a radio frequency signal generator electrically connectable to said tip such that, when said tip fleetingly connects with said string during plucking, the tip injects a radio frequency signal into the string.

According to a fourth aspect of the invention there is provided a receiver adapted for use with the transmitter as described above including receiver circuitry being tuned to said radio frequency so as to detect the radio frequency signal injected into the string, the receiver being operatively associated with said electronic monitoring circuitry so as to provide said triggering signal.

According to another aspect of the invention there is provided a signal processing apparatus adapted to process an audio signal derived from a string instrument having a plurality of conductive strings being plucked by the plectrum described above, said apparatus including:

a first input to receive said audio signal;

a second input to receive a triggering signal which includes a plurality of triggering pulses, each indicative of a plucking of any of said strings by said plectrum tip;

signal processing circuitry adapted to perform a plurality of different processes, each process modifying the audio signal, said circuitry being electrically connected to said first and second inputs, and wherein said signal processing circuitry is adapted to vary the particular process used to modify the audio signal according to a predefined relationship with said triggering signal; and

an output electrically connected to said signal processing circuitry for outputting a modified audio signal.

In one preferred embodiment the predefined relationship is such that the process is varied each time an integral number of triggering pulses are received. For example, this integral number may be 1, in other words the process applied to the audio signal is varied each time a triggering pulse is received.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the plectrum4shown inFIGS. 1to5includes a non-conductive body5having a gripping portion6and a plucking portion7. The body5is constructed of a plastics material in the preferred embodiment. A conductive tip8protrudes just beyond an edge9of the plucking portion7. The outer surface of the tip8is sized so as to fleetingly contact a string10of the instrument11as the string10is plucked by the plucking portion7. This is best shown in the progressive plucking action illustrated in FIG.5. In particular, contact between the tip8and the string10occurs at step D of FIG.5. The tip8is capable of operative association with electronic monitoring circuitry12, an embodiment of which is shown in FIG.10. The details of the operative association between the tip8and the electronic monitoring circuitry12will be described in more detail later in this document. The electronic monitoring circuitry12is adapted to provide a triggering signal shown as signal G inFIG. 15each time the tip8contacts any of the strings10of the instrument11.

This inventive arrangement has been found to provide far more reliable triggering than that provided by the prior art. Additionally, because the tip8only contacts the string10during the instant of plucking, it is possible for the electronic monitoring circuitry12to monitor for any moment that conductive contact between the tip8and the wire10is made, rather than monitoring for the moment when conductive contact is broken, as in the prior art.

The geometry of the non-conductive body5and the barely exposed tip8is such that a player can rest the plectrum against a string, as shown in views B and C ofFIG. 5prior to plucking without the tip8contacting the string10, and therefore without causing any false triggering. Additionally, as the electronic monitoring circuitry12of the preferred embodiment monitors for the instant that conductive contact is made, rather than broken, it is possible for the arrangement of the present invention to provide a triggering signal wherein each triggering pulse is initiated an instantaneous moment before a string10is actually plucked. This advantageously effectively provides a lead time which can be offset against any lag time that may exist in the audio signal processing apparatus to help ensure that the audio signal processing apparatus is in a required state prior to, or at the moment of, receiving the audio input resulting from the plucking of the string.

The tip8is electrically connected to a first wire13which may be embedded within the body5. In other embodiments (not illustrated), the tip8is an integral part of the wire13. The first wire13is, in turn, electrically connected to a second wire14external of the body5. The second wire14extends from a point15of the body5remote of the plucking portion7.

In one embodiment the first and second wires13and14are formed from a preshrunk polyester (not illustrated) upon which silver conductive ink is screen printed to provide a conductive surface. This advantageously provides a strong conductor which is sufficiently thin to be embedded within the body5, or applied thereto as a surface coating. Additionally, the pre-shrunk polyester can be manufactured with a width which can be attached to the plectrum4such that the width is aligned with the body5. This provides ergonomic advantages by contributing to freedom of movement of the plectrum. The width is preferably between 2 mm and 8 mm, and in the preferred embodiment is approximately 3.5 mm.

The tip8preferably protrudes from the outer edge9of the plucking portion7by no more than 1 mm. In the preferred embodiment, the distance by which the tip8protrudes is 0.5 mm. This dimension can be best appreciated with reference to FIG.3and in particular to the perpendicular distance separating lines16marked thereon. In the preferred embodiment the perimeter length of the tip8is no greater than 8 mm and the dimension used in the preferred embodiment is 2 mm. This dimension can be best appreciated fromFIG. 2a,and in particular from the distance separating lines17marked thereon. The width of the tip8is preferably no greater than the width of the pick and in the preferred embodiment is 0.5mm. This can be best seen with reference to FIG.3and in particular to the perpendicular distance separating lines18marked thereon. This dimension is less than the corresponding width of the body5. An outer edge22of the tip8is shaped to generally correspond to the shape of the outer edge of the plucking region7from which the tip8extends.

As best shown inFIG. 2, the body5of the plectrum4is generally a triangular shape. The region adjacent first apex19defines the plucking portion7and the tip8is disposed at the first apex19. The second wire14extends from, or adjacent to, one of the other apexes, in this case, apex20. In other embodiments, the second wire14extends from other regions of the body5of the plectrum4. The region adjacent apexes20and21defines the gripping portion6.

The electronic monitoring circuitry12is adapted to detect the initiation of conductive contact between the tip8and the string10and to use said contact as the basis for the triggering signal. The switch which is effectively formed by the plectrum4and the string10is shown in an open state in FIG.4.

FIG. 6depicts a schematic representation of the transmitter23, a receiver24and a preferred embodiment of a transmitter/receiver arrangement whereby said transmitter23communicates to said receiver24. The transmitter23includes a signal generator25which is electrically connectable to the tip8. In one embodiment, the tip8is connected to a radio frequency signal generator25via the first and second wires, the second wire terminating in a plug which is mateable with a socket provided upon the transmitter23. When the tip8fleetingly connects with the string10during plucking, as shown inFIG. 5, the tip8injects a radio frequency signal shown as signal A inFIG. 11into the string10. The radio frequency signal (signal A) is detectable by receiver circuitry26which is tuned to the signal. The receiver24is operatively associated with electronic monitoring circuitry12so as to provide the triggering signal (signal G).

In another embodiment (not illustrated), the electrical connection between the tip8and the transmitter23is achieved by means of capacitive coupling. It will be appreciated by those skilled in the art that other methods of electrical connection may also be used.

In the illustrated preferred embodiment the transmitter23is mountable to a person27playing the instrument11. In particular, the transmitter23is disposed upon, or housed within, a strap28mountable to a wrist of the person27. The strap of the preferred embodiment is held in place by hook and eye fasteners (also known as “velcro”), although clearly other fastening means may be employed. The strap28includes means to house or mount a battery (not illustrated) to power the radio frequency signal generator25. This allows the player27of the instrument11greater freedom of movement as compared to having the plectrum4hard wired to circuitry win the receiver which would require a long cable from the plectrum to the receiver.

As illustrated inFIG. 9, the transmitter circuitry of the preferred embodiment makes radio frequency grounding connections labelled RGND or +3V. This may be achieved by allowing one of the terminal connections of the battery to make direct connection with the skin of a user. Such a radio frequency ground connection has been found by the inventor to provide a significantly stronger signal, if such is desired.

The strings10of the instrument11are electrically connected to an instrument-ground29, which is, in turn, electrically connected to the receiver24, and in particular to the receiver circuitry26. The instrument-ground29is normally included as a part of the audio cable.

The radio frequency generator25is capable of producing a signal A as shown in FIG.11. This signal is a waveform at a carrier frequency which preferably lies within the range of 100 KHz to 30MHz, and in the preferred embodiment is 3.545 MHz.

As best shown inFIG. 6, the instrument-ground29is electrically connected to the receiver-ground30, the connection31effectively forming an electrical short between the grounds29and30at audio frequencies such as those generated by the instrument11, however the connection31also effectively forms a first tuned receiver between the grounds29and30, the tuned receiver being broadly tuned at the carrier frequency. The connection31is an inductor (labelled L1in FIG.6and labelled L11inFIG. 10) and a capacitor (labelled C1in FIG.6and C26inFIG. 10) wired in parallel between the instrument-ground29and the receiver-ground30. The 3.545 MHz radio frequency that is coupled into the resonate circuit31appears as a voltage at connection29, this voltage is illustrated inFIG. 12signal B. Signal B is coupled through the capacitor C27into the amplifier circuitry28which is comprised of Q1, R34, R35, R36, R37and C23. This 3.545 MHz amplified signal is then coupled through C22onto the base of transistor Q3which forms a non-linear mixer along with R42, R38, R39, and R43, circuitry34. A 4.00 MHz local oscillator signal is generated from circuitry33. This circuitry comprises U8, C57, C58, R73and X5. Such an arrangement allows the local oscillator frequency to be easily changed by using a different frequency crystal X5, along with a corresponding change to the frequency of the transmitter. Such a change may become necessary if two identical preferred embodiments are operating at close quarters and interfering with each other. The output (U5pin2) is coupled onto the emitter of Q3through the capacitor C34. The resulting Signal C as appears on the collector of Q3has a frequency component that is equal to the difference between the 3.545 MHz carrier frequency and the 4.00 MHz local oscillator. This difference is known as the intermediate frequency and in the preferred embodiment is a waveform having a 455 KHz component as shown in FIG.13. The amplitude of the 455 KHz frequency component is directly proportional to the amplitude of the 3.545 MHz carrier radio frequency. The band pass filter as described next selectively passes only the 455 KHz frequency so in effect the circuitry has selectivity for the frequency of 3.545 MHz. This helps in the rejection of broad spectrum noise which could potentially interfere with the operation of the device. This technique is known as a superheterodyne receiver. This gives Signal C as shown in FIG.13. Signal C is then passed through a selective band pass filter35tuned at the intermediate frequency. In the preferred embodiment, the selective band pass filter35is comprised of a ceramic resonator labelled X2in FIG.10. The output of the selective band pass filter35is signal D as shown in FIG.14. Signal D is present in the electronic monitoring circuit only when the tip8of the plectrum4is in contact with the string10. This is shown inFIG. 15where intermittent bursts of signal D are shown.

The signal is then amplified by Q4as shown in FIG.10. The degree of amplification is varied by potentiometer VR2. This allows the user to adjust the signal strength, which affects the sensitivity of the system to outside interference. If the gain is too low the system may miss triggers, however if it is too high false triggers may be caused by outside electromagnetic interference.

The signal is then passed through a detector circuit36which is made up of Q5, R50& C42as also shown in FIG.10. The output of Q5is the envelope of the intermediate frequency component which is proportional to the radio frequency signal. This is shown as signal E in FIG.15. The envelope has brief pulses37which substantially correspond to the period of time for which the plectrum tip8is in contact with the string10. This signal is then AC coupled and amplified by U58as shown in FIG.10. The brief pulses37are then time-stretched so as to provide a modified signal (signal F shown inFIG. 15) having time-stretched pulses38which, because of their longer duration, are not missed by the microprocessor to which the signal is subsequently fed. The time-stretching of the pulses37is performed by D15, C45, R54and R57as shown in FIG.10.

The electronic monitoring circuitry12includes a microprocessor39adapted to receive said modified signal (signal F) and to perform an analogue-to-digital conversion thereto using U2so as to produce a digital representation of signal F. The microprocessor39is further adapted to detect positive transients40in the digital version of the signal and to generate a triggering signal (signal G) by correlating each of the positive transients40with an initial contact of the plectrum tip8with the string10. In other words, each time the plectrum tip8initially makes conductive contact with the string10, instantaneously before the moment of plucking, the electronic monitoring circuitry is adapted to output a triggering signal responsive to said contact. The triggering signal (signal G) provided by one preferred embodiment of the invention is of the MIDI (Musical Instrument Digital Interface) type. An alternative embodiment outputs a triggering signal consisting of a control voltage and a gate signal (this alternative triggering signal is not illustrated). The triggering signal is fed from the receiver24via triggering cable41as shown in FIG.8.

Put simply, when a transient40of sufficient amplitude is detected, a pick event is deemed to have happened and the associated controlled signals are then generated to provide a triggering signal.

The audio signal (not illustrated) generated by the instrument11is applied to amplifier U3C via resistor R13as shown in FIG.10. This circuitry50is adapted to store maximum amplitudes of the audio signal from the instrument11. In other words, each time a string10of the instrument11is plucked, the receiver circuitry stores a maximum amplitude of the resulting audio signal. The circuitry of U3B, U3D, D4, D7and C15(as indicated onFIG. 10) holds said maximum amplitude. The electronic monitoring circuitry12includes a microprocessor39(which may be the same microprocessor mentioned previously, or may be a separate microprocessor) which is adapted to measure the stored amplitude and to output a value corresponding to the amplitude. In some embodiments this value is digital and in other embodiments it is analogue. The value is effectively an output corresponding to the force with which the string10is plucked. This information can be transmitted to an audio effects system so that effects can respond to the intensity with which a string10is plucked. In some embodiments, the electronic monitoring circuitry12and the receiver circuitry50are adapted to measure and record the maximum amplitude of the audio signal each time the tip8contacts a string10. In other embodiments, circuitry12and50is adapted to measure the maximum amplitudes occurring during predefined time intervals.

With reference to FIG.17. the signal processing apparatus42processes the audio signal derived from the string instrument11. In some preferred embodiments all signal processing is performed digitally, in other preferred embodiments the signal processing may be exclusively analogue, or a combination of digital and analogue. The signal processing apparatus42is adapted to function in conjunction with the plectrum of the present invention. The apparatus42includes a first input43to receive the audio signal from the string instrument11. The second input44receives the triggering signal (signal G) which includes a plurality of triggering pulses, each indicative of a plucking of any of the strings10by the plectrum tip8. The apparatus42houses signal processing circuitry45which is adapted to perform a plurality of different processes, each process modifying the audio signal. For example, some of the processes may be relatively straight forward modifications to provide effects such as echo, reverberation, phasing, panning, chorus and flanging. However more sophisticated and elaborate processes may be provided by altering one more parameter values and/or one or more effects algorithms which are, in turn, used by the signal processing circuitry45to modify the audio signal. The signal processing circuitry45is electrically connected via wires46to the first and second inputs respectively,43and44. The signal processing circuitry45is adapted to vary the particular process used to modify the audio signal according to a predefined relationship with the triggering signal. In other words, the signal processing circuitry45has a number of different processes or “effects”, which can be varied based upon the triggering signal. The apparatus42also includes an output47electrically connected to the digital signal processing circuitry45via wire46for outputting the modified audio signal (not illustrated).

The predefined relationship between the triggering signal and the varying of the particular process used to modify the audio signal can be adjusted as required. For example, in one embodiment, the particular process used to modify the audio signal is varied each time an integral number of triggering pulses are received. In another embodiment, the integral number is 1, meaning that the particular process used to modify the audio signal is varied each time a triggering pulse is received by the signal processing circuitry45. This is shown schematically in FIG.16. It would be appreciated by those skilled in the art, however, that other predefined relationships may be used for example making a first variation to the particular process after a first number of triggering pulses are received, followed by a second variation to the particular process after a second number of triggering pulses are received, and so on.

During the transition from a first process to a second process, the first process is progressively faded out and the second process is simultaneously progressively faded in. This transitional arrangement is illustrated inFIG. 16where the horizontal axis represents time and the vertical axis represents the degree to which a particular process is used to modify the audio signal. At the time when a triggering pulse is received48, the degree to which the first process49is applied to the audio signal begins to decrease and, simultaneously, the degree to which the second process50is applied to the audio signal is increased. This provides a smooth transition between processes. As can be seen inFIG. 16, the same fade-in, fade-out technique is used each time a subsequent variation of a process is made. The transition commences upon receipt of a triggering pulse such that each transition is initiated substantially at each moment the tip8first contacts the plectrum during plucking. As described above, triggering from the moment of initial contact (rather than the moment of which contact is broken as in the prior art) advantageously provides a brief lead-in time before the string10of the instrument11is actually plucked. This enables any delay that may be introduced by the signal processing circuitry45to be off-set against the “head start” provided by the triggering signal.

The preferred embodiment of the signal processing apparatus42includes provision for at least one of the operative characteristics of one or more of said processes to be variable dependent upon the maximum amplitude of the audio signal each time the plectrum4contacts a string10. The signal processing apparatus42includes a third input51to receive a value indicative of a maximum amplitude of the audio signal from the microprocessor39. The third input51is adapted to feed the value to the signal processing circuitry35via a wire52. The operative characteristics of the processes which may be varied include factors such as the parameters and/or the algorithms used to modify the audio signal. In some embodiments, the function of the second and third inputs,44and51, is performed by a single input (not illustrated) which is adapted to receive and de-code an information stream having information relating to both the triggering and the maximum amplitude.