Signal controller for a musical instrument

A signal controller for a musical instrument such as a guitar includes a liquid-filled tilt-sensor that has means to cause a variation in electrical resistance that is exploited by control circuitry to vary one or more qualities of the signal of the musical instrument. Such a signal may be a volume control, a tone control, a balance control and/or an effects control.

FIELD OF THE INVENTION

This invention relates to the control of hand-held electrical or electronic musical instruments.

CROSS-REFERENCES TO RELATED APPLICATIONS

This regular U.S. patent application is based on and claims the benefit of United Kingdom provisional patent application Ser. No. 0129084.0, filed Dec. 5, 2001, and United Kingdom regular patent application Ser. No. 0226173.3, filed Nov. 8, 2002 the entire disclosures of which are relied upon and incorporated by reference herein.

DESCRIPTION OF THE RELATED ART

The signal generated by hand-held electrical or electronic musical instruments may be treated in a number of ways, it may have its volume and tone adjusted, and may be subjected to a range of effects such as: reverberation; echo; wah-wah and chorus.

Since most hand-held instruments need to be played with both hands, it is not easy for the player to adjust such signal treatment. Typically the player must either pause briefly to adjust a manual control such as a volume knob, or must use foot-pedals to adjust the signal treatment. Foot-pedals restrict the player's movement and may distract the player from the performance. In U.S. Pat. No. 4,078,467 Kawachi Kiyoshi describes a volume controller in which a pendulum acts as a tilt-sensor and affects the value of a variable circuit element. That invention allowed a musician to control the volume of a musical instrument by tilting it to a particular degree.

One of the features of the inventive concept is a simple technique by which the sound qualities of a hand-held musical instrument's signal can be altered through variation of the angle at which the instrument is held. Tilting of an instrument requires little conscious effort on the part of the player and is a simple and instinctive way to achieve changes in sound quality.

The spirit-level is a familiar example of a device that indicates tilt. This principle has given rise to a number of liquid filled tilt-sensors which exhibit a variation of electrical resistance according to the degree by which the sensor is tilted. The liquid filled tilt-sensor referred to herein may be any one of several types, the liquid being typically either an electrolyte or mercury.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a signal controller comprising a liquid activated tilt-sensor which causes a variation of electrical resistance and circuitry to exploit said variation in such a way as to alter the treatment of a signal of a musical instrument.

According to a second aspect of the present invention there is provided a musical instrument including a signal controller to control tone of the musical instrument by using a tilt-sensor which causes a variation of electrical resistance and circuitry to exploit the variation in such a way as to alter the tone.

According to a third aspect of the present invention there is provided a musical instrument including a signal controller to control balance of the musical instrument by using a tilt-sensor which causes a variation of electrical resistance and circuitry to exploit the variation in such a way as to alter the balance.

According to a fourth aspect of the present invention there is provided a musical instrument including a signal controller to control effects of the musical instrument by using a tilt-sensor which causes a variation of electrical resistance and circuitry to exploit the variation in such a way as to alter the effects.

Suitable means can be provided to mount components of the signal controller. Means can be provided to adjust the signal controller.

The invention allows a wide range of signal treatments to be controlled, including, but not limited to: volume control; equalisation; balance between multiple signal sources; balance between multiple signal destinations; and the control of electronic effects circuitry.

DETAILED DESCRIPTION

In the following detailed description, reference will be made to the accompanying drawings, in which identical functional elements are designated with like numerals. The aforementioned accompanying drawings show by way of illustration, and not by way of limitation, specific implementations consistent with principles of the present invention. These implementations are described in sufficient detail to enable those skilled in the art to practice the invention and it is to be understood that other implementations may be utilized and that structural changes may be made without departing from the scope and spirit of present invention. The following detailed description is, therefore, not to be construed in a limited sense.

The signal qualities of a portable musical instrument may be controlled by the tilt of the instrument by incorporating the present invention in the instrument's signal path. This is shown as a functional diagram in FIG.1. The liquid filled tilt-sensor1causes a variation in electrical resistance that is exploited by the control circuitry to vary one or more qualities of the instrument's signal.

FIG. 2illustrates the tilting of a hand-held instrument through an angle, and the effect this has on a potentiometric tilt-sensor mounted on the instrument. To aid in the understanding of circuit design issues, an example tilt-sensor is shown consisting of a mercury bead3which may be thought of as the potentiometer's wiper, whose distance from the respective terminals4and5on a resistive carbon track determines the resistance between wiper and terminal.

It will be seen that as the angle changes, the position of the mercury remains static, and the proportion of carbon-track6between mercury wiper3, and terminal4changes. This changing resistance value is exploited by the embodiments of the invention which are considered in the following paragraphs. Other types of liquid-filled tilt-sensors may be similarly employed.

The controller may be used to vary the volume of a musical instrument such as an electric guitar. The controller is inserted in the signal path between the signal source, typically the guitar's pickups, and the signal destination, typically an amplifier. This is illustrated schematically in FIG.3. As the guitar's tilt is varied so the resultant volume changes. The tilt-sensor acts as a potential-divider having a common terminal5, an input terminal4and a wiper terminal3.

Similarly the controller may be used to provide a tone control as illustrated in FIG.4. As the instrument's tilt is varied, so the treble component of the signal varies.

The controller may be used to alter the balance between signal sources. One application would be to allow a guitar player to select which of two pickups is dominant when changing from accompaniment to solo playing. This is illustrated in FIG.5.

In FIG.8andFIG. 9the controller is used to vary the respective levels of a series of effects devices. This embodiment will now be considered in detail.

InFIG. 9the musical instrument12is shown connected to the effects controller2through audio-cable52. The controller is connected to amplification or recording equipment through cable37. All the interconnecting cables shown inFIG. 9are conventional, monophonic audio cables.

The effects pedals33and34are governed by the tilt-sensor1. At one extreme of the tilt-sensor's range effects pedal33is not attenuated, and effects pedal34is heavily attenuated. Conversely at the opposite extreme of the tilt-sensor range, effects pedal34is not attenuated, and effects pedal33is. In this way the treatment of the signal may be varied to any desired combination of two effects. For instance, a musician might choose to apply reverberation at the beginning of a performance, later changing to a chorus effect, finally combining chorus and reverberation at the end of the performance by tilting the instrument to the intermediate angle8in FIG.2.

The way in which this variation is controlled is shown in FIG.8. The first stage of the circuit exploits the fact that the instrument cable52can be used to carry both the normal audio signal, and a controlling DC signal, so long as these two are separated by later stages. The DC control signal21is injected into the instrument cable52. The resistor20and tilt-sensor1form a potential-divider, so that variation of1causes a variation of DC voltage at their junction. The instrument pickup23serves to complete this potential-divider circuit, presenting as it does a relatively small DC resistance.

From an AC perspective the signal generated by the instrument's pickup or pickups is largely unaffected by variable-resistor1, since bypass-capacitor22provides a low-impedance path to audio frequencies.

The two signal components are segregated by AC-filter25and DC de-coupler24such that only the audio signal is passed to the signal inputs of the VCAs29and30, and only the DC voltage is passed to the buffer26.

The left-hand connection to each the VCAs29and30is for the input signal, the lower connection is for the controlling voltage, and the upper connection is for the output. It will be seen that the shapers27and28are connected to the control terminals of the VCAs29and30respectively.

The operation of this embodiment can be appreciated by first imagining the shaper circuits27and28to be inverting amplifiers. By adjusting the tilt-sensor1to a high resistance value a high voltage would be produced by shaper27and a low voltage by shaper28. Conversely by reducing the value of 1, a low voltage would be produced by shaper27and a high voltage by28. Thus by adjusting the value of resistance, the respective output levels of the two VCAs can be varied in any combination.

The VCA outputs feed the effects circuits33and34. The output levels of the effects circuits reflect the level of signal from their respective VCA. Thus when the signals are combined by the mixer38, the dominance of one effect or the other will be determined by the setting of the tilt-sensor.

A number of other embodiments of the invention will be apparent using this technique. One being to mix treated and untreated signals, another would involve feeding two separate audio channels from the outputs of the two VCAs allowing stereo panning between two channels. A further embodiment would replace the effects devices with filters to allow the tone of the instrument to be controlled. Yet another embodiment would be to connect an effects device such as a fuzz box or overdrive between the decoupler24and one VCA29or30to allow the volume of a saturated signal to be adjusted.

To achieve satisfactory operation, several design issues need to be addressed which now be considered, each of the components inFIG. 6will become apparent in the description.

The first design consideration relates to symmetry of output from the two VCAs29and30.FIG. 2shows a guitar whose playing angle is varied between the angles7and9. At angle9the VCA29should be fully on, providing unity gain, and VCA30fully off providing no gain. At angle7VCA29should be off and30should be fully on.

To achieve symmetry, the VCAs must be fed complementary control voltages as indicated by41and42in FIG.6. This demands that the more negative the control voltage, the higher the gain of the VCA, but that any control voltage more positive than −0.5 volts will result in zero gain. A control voltage of −1.5 volts will provide unity gain. It is not desirable to increase the gain of either VCA beyond unity, since a complementary response is desired in order to pan uniformly from one VCA to the other.

In the example inFIG. 2, 30 degrees of range represents only ⅙ of the range of the sensor. The lower boundary of operation is enforced by the limit on the movement of the mercury3. However, increasing the angle from 9 to 10 will increase the distance indicated by 6 and thus increase the resistance. It is necessary to prevent this further change in resistance from affecting the output of the VCAs. This limiting is achieved by the shaper27.

Consider again the output from shaper27if it were simply an inverting amplifier. An increase in elevation of the sensor would lead to an increase in its resistance, this in turn increasing the voltage input to the buffer26. Both the buffer26and shaper27invert their inputs, thus the output from the shaper increases with elevation as indicated by40in FIG.6. The required response however, is indicated by41, such that an increase in elevation beyond 30 degrees does not result in any further increase in voltage. Once this is assured, the second shaper28can simply subtract the output of shaper27from a constant value to achieve the complementary response42.

Referring toFIG. 10, the desired response is achieved by the inclusion of the Zener diode Db. The diode has no effect on the output voltage of the amplifier A1until the Zener voltage is reached, this being −0.5 volts relative to ground. Any output voltage more positive than that is clamped down to −0.5 volts by the diode.

The shaper28inFIG. 10uses A2to subtract the output voltage of27from the constant value −2 volts giving the complementary response42in FIG.6. The Resistors R8and R9inFIG. 10provide the required −2 volts, the resistors R19and R20providing a 1:1 feedback ratio for unity gain.

The second design issue relates to the sensitivity of the circuit to variation of tilt-sensor1. One individual may wish the operating range to be achieved with a 30 degree span, while another may prefer a 45 degree span.

A desirable feature of the controller, therefore, is a fully variable sensitivity control. The sensitivity indicated by41inFIG. 6can be decreased to that indicated by43inFIG. 7by setting the non-inverting input of A1inFIG. 10to be more negative, since a wider range of input voltage is then required before the clamping threshold of D1is reached. The resistor network R5, R6and R7is used to vary the voltage applied to A1.

It will be seen that the sensitivity has thus been decreased by 15 degrees. An undesirable side effect of this is that the maximum output, has been increased by 0.5 volts. This would increase VCA gain, and require the musician to make a compensatory change in volume settings whenever sensitivity was adjusted.

The resistor network R3, R4and R1are used to automatically compensate for the increase in output. R4and R5represent a dual-gang potentiometer causing gain to be reduced proportionally as amplifier sensitivity is reduced. It will be seen that the maximum gain possible is (R4+R3)/R1and the minimum gain possible is R3/(R4+R1), the resistor configuration shown provides a very uniform relationship of gain in response to variation of R5.

The third design issue concerns possible phase inversion by the effects devices33or34. The mixer38is used to re-combine the signal after treatment by these effects, providing a single output signal. It is quite possible that an effects device could invert the phase of the signal. This would cause the mixer to act as a differential amplifier, which is unlikely to be desirable. Accordingly a suitable audio mixer with inverting, as well as a non-inverting inputs is required.

The purpose of those components inFIG. 10not previously described is as follows: The capacitors C1and C9constitute the AC filter indicated by25in FIG.8. R18, TR2and R24constitute the buffer26inFIG. 6, this being a conventional common-source JFET circuit.

29is a VCA. It is a common emitter circuit using an NPN bipolar transistor. R13provides a base bias voltage, and the combination of R14and R13attenuate the input signal. Instead of the emitter resistor R15being tied to ground, it governs the emitter current in response to the control voltage being applied to it, such that the more negative the control voltage, the greater the VCA gain. Bypass-capacitor C2maximises AC amplification, and C4de-couples the DC from the output path31. The constituent parts of VCA30function in the same way as29.

D4and R21provide the small DC voltage source21. C7and C8constitute the DC de-coupler24. The value of capacitor22should be high enough to present little impedance to the audio frequency signal generated by the pickup23. However this must be weighed against a low time-constant of capacitor22and resistor20, since high-values would result in slow responsiveness to variation of the tilt-sensor1.

Example component values are shown in the table below.

The inclination of the tilt-sensor should be adjustable. This allows individual musicians to choose the playing angle representing the low end of operation of the sensor. The angle will generally be within a few degrees of the horizontal plane, indicated by7in FIG.2.

A suitable means for mounting the tilt-sensor is illustrated inFIG. 11, an electric-guitar being used as an example. Capacitor22and shielding are omitted for clarity.

The ¼ inch jack-socket11receives the instrument cable. The ¼ inch jack-plug53is connected to the guitar's pickup socket. The guitar's strap-pin is passed through the hole in mounting-pate56, as shown by arrow58. The mounting-plate is thus secured between the butt of the guitar and the strap-pin's screw-head.

An arm59is attached to the mounting-plate. The tilt-sensor1is attached to a ‘forearm’60. The arm and ‘forearm’ are connected using a bolt passed through holes in each, following arrow55. Tightening a nut on this bolt, the forearm may be secured in any position desired on the path indicated by arrow57. Several similar means of mounting the tilt-sensor, and allowing adjustment of its orientation will be apparent.

It should be noted that the use of DC as a control signal, as shown inFIG. 8represents only one variation of this embodiment. Ultrasonic AC might be a feasible alternative, if, for instance, an electrolytic tilt-sensor were employed.

In summary the present invention provides a simple means by which the sound qualities of a portable musical instrument's signal can be altered by varying the angle at which the instrument is held. This offers several advantages to a player. For example, by using the controller shown inFIG. 3, a musician could enhance a performance by appropriate variations in volume. By using the controller shown inFIG. 8, the musician could vary the respective levels of various effects devices during the performance, or perform stereo panning across a stage.

It will be appreciated that the pendulum operated volume controller of U.S. Pat. No. 4,078,467 suffered from two disadvantages that the present invention is intended to address. Firstly, the present invention allows more than just volume to be controlled: any quality of the instrument's signal that can be affected by a variable-resistor may likewise be controlled by the present invention. Secondly pendulum controlled tilt-sensors, having moving parts, are relatively costly to manufacture, and potentially prone to failure and accordingly a liquid filled tilt-sensor is employed in the present invention.

It should be understood that processes and techniques described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components. Further, various types of general purpose devices may be used in accordance with the teachings described herein. It may also prove advantageous to construct specialized apparatus to perform the method steps described herein.

The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations of mechanical and electronic components including, without limitation, hardware, software, and firmware will be suitable for practicing the present invention.