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Description  |
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Background of the Invention
This invention relates to improvements in musical instruments and more
particularly to an electronic musical instrument for simulating a stringed
instrument.
On a conventional guitar, whether it is an acoustical type or an
electrically amplified type, the sounds originate from vibrating strings
which are set in motion by a picking or strumming action. A note is
selected by playing an open string or by fingering a string on a
particular fret position on the neck of the instrument. This action serves
to change the vibrating length of the string thereby producing the
vibrating frequency of the desired tone. Chords are played by picking,
plucking or strumming more than one string, either sequentially or with
one stroke of the hand. Accordingly, a conventional guitar is played by
fingering the strings on the neck of the instrument with one hand, while
picking or strumming the strings with the other hand.
While stringless guitar-like musical instruments have been disclosed, for
example in U.S. Pat. Nos. 3,340,343, 3,555,166, and 3,666,875, these
instruments in addition to having a plurality of finger actuated switches
located in a fret-board type of arrangement on the neck of the instrument,
also includes means located on the body of the instrument, requiring it to
be played much like a keyboard instrument, e.g. an accordian wherein
manual depressions of an element is required.
The present invention on the other hand is directed to a stringless
instrument, which can be played using similar techniques to those
described above for a conventional guitar. Furthermore, a player who has
learned to play a conventional guitar can play an instrument according to
the subject invention immediately without having to relearn new fingering
positions for either the neck of the instrument or for the body of the
instrument, meaning that melodies and chords and combinations thereof can
be picked or strummed with a conventional plectrum as well as plucked or
strummed with the hand in the conventional manner.
Summary
Briefly, the subject invention is directed to an electrically controlled
musical instrument embodying self-contained electronic tone generation
modulation and amplification circuitry for the production of musical
sounds by means of a plurality of relatively thin flexible blade type
switch actuator members which are mounted on edge and are located on the
front surface of the body of the instrument in line with a fret-board
switch assembly. The outward edge of each actuator resembles the cross
section of a string and is adapted to be plucked, strummed, struck or
bowed. Each flexible blade type actuator is adapted to be flexed in either
direction, causing closure of one or more leaf type electrical switches
which are adapted to control the amplified output of an electronic
oscillator circuit whose fundamental operating frequency is adapted to be
further varied in accordance with the operation of finger actuated fret
switches located on the neck of the instrument.
The preferred embodiment of this invention will be disclosed primarily in
terms of a guitar-like musical instrument which comprises one of the
"lute" classes of strummable string instruments. It will also become
apparent that other instruments in the lute class can be simulated in the
same manner. Furthermore, the inventive concept can be used for electronic
simulation of "viol" class of musical stringed instruments such as the
violin, cello and other instruments which are played with a bow as well as
those plucked with the hand.
It can be seen, therefore, that the primary object of the present invention
is to provide a stringless musical instrument which can be played as
though it were, in fact, a stringed musical instrument.
Other objects and advantages will become immediately apparent as the
following specification is considered in conjunction with the accompanying
drawings.
Brief Description of the Drawings
FIG. 1 is a top plan view of a guitar-like musical instrument broadly
illustrating the preferred embodiment of the subject invention;
FIG. 2 is a fragmentary cross sectional view taken along the lines 2--2 of
the neck portion of the instrument shown in FIG. 1 and being illustrative
of one fret-key switch assembly;
FIG. 3 is an end sectional view of the fret-key switch assembly shown in
FIG. 2 taken along the lines 3--3;
FIG. 4 is a partial side elevational view of the body portion of the
instrument shown in FIG. 1;
FIG. 5 is a top plan view of an assembly of plural flexible blade type
actuator members mounted on the body of the instrument for simulating
individual strings;
FIG. 6 is an exploded end view of one of the flexible blade actuator
members shown in FIG. 5 together with respective switch contact assemblies
on either side thereof;
FIGS. 7A and 7B are illustrative side and end planar views of the type of
flexible blade assembly utilized for lute type instruments;
FIGS. 8A and 8B are side and end planar views of the type of flexible blade
assembly utilized for viol type instruments; and
FIG. 9 is an electrical schematic diagram illustrative of the circuit
details for one of six flexible actuator blade members and its
interconnection with the remaining five simulated strings to form a
complete electronic system for generating musical sounds.
Description of the Preferred Embodiment
Referring now to the drawings and more particularly to FIG. 1, there is
disclosed a top plan view of a guitar-type instrument 10 consisting of a
body portion 12 and a neck portion 14. Along the neck portion 14 of the
instrument 10 is fret switch assembly including a plurality of keys 16
arranged in sets along the face of the finger board 18. Such apparatus is
well known to those skilled in the art, a typical example being shown for
example in the above referenced U.S. Pat. Nos. 3,555,166 and 3,666,875.
On the upper face 20 of the body portion 12 is located an assembly 22 of
six identical string simulation means which will be discussed in detail to
permit a player experienced with a conventional stringed instrument to
immediately play the subject instrument with similar hand and finger
motions applied to the assembly 22 in addition to those established for
the fret-switch keys 16 on the finger board 18. Reference numeral 24 as
shown in FIG. 6 generally designates one of six identical flexible blade
type switch actuator members 24.sub.1, 24.sub.2 . . . 24.sub.6. This
arrangement is shown in detail in FIG. 5. The actuator members are
generally rectangular in shape as depicted in FIGS. 7A and 8A and are
relatively thin so as to permit flexure transversely to their longitudinal
dimension. As shown in FIG. 7A, the upper edge 26.sub.1 of member 24.sub.1
runs lengthwise for a predetermined distance terminating in rounded
corners 28. The members 24.sub.1 . . . 24.sub.6 are of uniform thickness
and when viewed from above as shown in FIG. 5, are analogous to the cross
section of a musical string located thereat in a conventional guitar-like
instrument.
Thus the flexible blade type elements 24.sub.1 -24.sub.6 can be picked with
a conventional type plectrum, plucked with fingers, or strummed by both
means with one stroke of the hand in either direction in a normal manner.
Accordingly, conventional finger, hand and arm motions familiar to the
musician experienced with conventional stringed instruments are used. It
should be noted that the assembly 22 is preferably located at the
conventional waist region of the instrument body 12 on the longitudinal
axis of the instrument and that each flexible blade element 24.sub.1 . . .
24.sub.6 is parallely aligned with the neck portion 14 in the same manner
as the string it is intended to simulate. While mention of the fact that
the actuators 24.sub.1 . . . 24.sub.6 are generally rectangular in shape,
1 is to be made that they are of sufficient length along the longitudinal
axis of the instrument to avoid the need to search for their location when
picking or strumming since searching tends to detract from the normal
motions already cultivated by an experienced player of a conventional
instrument, particularly so in view of the fact that the body portion 12
is observed to a much lesser extent than the neck portion 14.
A plurality of knobs 30, 32 and 34 are conveniently arranged on the face 20
of the body portion 12 for effecting tone control, harmonic control and a
combination of the volume control as well as an on/off switch,
respectively. Reference numeral 36 is intended to designate a suitable
indicator light to indicate the power status of the instrument. Also,
shown in FIG. 1 on the surface 20 of the body portion 12 is reference
numeral 38 which is intended to designate a muting switch pad associated
with electronic circuitry, not shown, which is used to provide abrupt
sound cut off similar to that accomplished when usable string vibrations
are stopped with the hand. For lute type instruments, it is preferred that
the muting switch pad 38 be located to serve as a rest for the heel of the
picking hand so that it can be depressed for muting instantly without
having to hunt for the pad.
Referring now to FIG. 2, there is disclosed the details of one typical
fret-switch key 16 shown in FIG. 1. A switch actuator member 40 is held in
its unactuated position against the underside of the fingerboard 18 by
means of resilient foam material components 42 which are located at either
ends of the element 40. The durometer softness of the material from which
the foam material is comprised is selected to provide a comfortable feel
to the player, with considerations including low finger pressure but not
so low that undesired actuation can take place. A further consideration is
to provide a pre-travel of the member 40 downward before a pair of
electrical switch contacts 44 and 46 are closed. The spring leaf
configuration of member 44 permits over-travel after the switch contacts
close. The pre-travel aids to prevent unwanted sounds from emanating when
the element 40 is inadvertently depressed by the fingers while using them
for guidance or while straddling them in a manner which is normal for
playing stringed instruments. The over-travel is provided for improved
electrical contact and to minimize finger fatigue, which may occur sooner
when stopped by an unyielding switch key.
Further to this end, it is preferred that the key element 40 be permitted
to be depressed so that the upper surface 48 is nearly flush with the
fingerboard surface 50, permitting only enough protrusion to feel it for
guidance when it is fully depressed. Accordingly, when one of the key
elements 40 is depressed, it is guided to the proper location over the
contact member 44 by means of angulated guides which form an integral part
of the contact mounts 52 as shown in FIG. 3. These guides permit a freedom
of fit for the key element 40 in its finger-board slot so as to provide a
bind-free action.
An insulating board member 54 is used for mounting the contact mount 52
with spacer bars 56 between each fret position. A multiple pin connector,
not shown, is utilized at the end of the mounting board member 54 where it
meets the body portion 12 to interface the fret-key switch elements 16
with electronic circuitry shown in schematic form in FIG. 9 contained
inside of the body portion 12 of the instrument.
The major improvement of the subject invention consists in the actuator
assembly 22 briefly referred to above and its related electronic
circuitry. Associated with each actuator element 24.sub.1, 24.sub.2 . . .
24.sub.6 is an assembly of six leaf type switches arranged so that three
switches are located on each side of an actuator. Referring now to FIG. 6
which is intended to typically illustrate one element 24 of the six
identical structures 24.sub.1 . . . 24.sub.6, flexible leaf type
electrical contact strips 58.sub.a, 58.sub.b, 58.sub.c and 58.sub.d are
located on one side of the actuator 24 to form one set of switch contacts
58. Mutual separation of the contact strips is provided by means of
electrical insulator members 60.sub.a, 60.sub.b, 60.sub.c and 60.sub.d. In
a like manner, on the opposite side of the element 24 are electrical leaf
type contact strips 62.sub.a, 62.sub.b, 62.sub.c and 62.sub.d and being
separated from each other by means of the insulator elements 64.sub.a,
64.sub.b , 64.sub.c and 64.sub.d . These form the other set of switch
contacts 62. The insulator elements 60.sub.a . . . 60.sub.d and 64.sub.a .
. . 64.sub.d are preferably comprised of, for example, thin plastic
strips.
Additional insulation is provided by insulating sleeves 66 and 68 on a pair
of contact mounting screws 70 and 72 with which nuts 74 and 76
respectively engage to hold the whole assembly together as shown, for
example, in FIG. 7B. The lower terminal portions of the switch contacts
58.sub.a . . . 58.sub.d and 62.sub.a . . . 62.sub.d comprise tab portions
78.sub.a, 78.sub.b, 78.sub.c and 78.sub.d and 80.sub.a, 80.sub.b, 80.sub.c
and 80.sub.d for making electrical connections to the electrical circuit
elements shown in schematic form in FIG. 9.
The flexible actuator type switch assembly shown in FIG. 6 can be mounted
singly or in multiples, depending on the type of instrument desired. The
arrangement shown in FIGS. 7A and 7B discloses a six member configuration
for simulating a lute-type instrument while the configuration shown in
FIGS. 8A and 8B comprise a four member configuration simulating a
viol-type instrument. In either case the switch assemblies are ganged and
spaced apart from one another utilizing an end frame 82, a plurality of
spacers 84 and mounting screws and nuts 86 and 88.
Accordingly then, each of the actuators 24.sub.1 . . . 24.sub.6 are
comprised of thin flexible spring-like material which are mounted on edge
and project above the electrical contact strips and are free to bend or
deflect when a force normal to the upper playing surface is applied. Since
the contacts are mounted to the lower portion of the actuators which is
firmly held, it is possible to bend the upper portion of the actuator by
applying a small force until, for example, electrical pole piece 58.sub.a
as shown in FIG. 6 contacts element 58.sub.b, affecting a closing of one
pair of switch contacts. Initial movement in the other direction causes
elements 62.sub.a and 62.sub.b to make contact. Additional incremental
forces will cause additional sequential contact closures to take place,
namely element 58.sub.c would contact element 58.sub.b and 58.sub.d would
make contact with element 58.sub.c and so forth. When the force is
removed, the actuator 24 and any contacts closed will return to their
original upright normally open condition as shown in FIG. 6. These events
will take place when the deflecting force is applied in either direction
normal to the plane face and nearer the top edge of the actuator 24. By
this means the same magnitude of force applied in either direction will
close the same number of switch contacts and removal of the force will
allow the contacts to spring back to their open state.
From the foregoing description it can be seen that if a guitar player for
example uses a conventional type plectrum to deflect the actuator 24 shown
in FIG. 6, first in one direction and then the other, the picking action
of a conventional guitar is simulated. The actuators 24.sub.1 . . .
24.sub.6 as shown in FIG. 7B, for example, may be deflected with a thumb
or fingers or a combination of both to provide a plucking action or when
desirable, a complete set of actuators 24.sub.1 . . . 24.sub.6 can be
strummed with one sweeping motion of the hand in either direction which is
normal. It should be emphasized here that all of the action described can
be performed by a musician already familiar with the guitar without having
to relearn new techniques or fingering positions.
With respect to the configuration for implementing the type of string
instruments in the "viol" class which includes those instruments
characteristically played with a fiddler's bow such as a violin, cello,
etc. reference to FIGS. 8A and 8B indicates that the upper edges of four
flexible actuators 24.sub.1 . . . 24.sub.4 are arranged in an arched
profile similar to the bridge of a violin making it possible to be played
with a fiddler's type of bow, not shown, to contact, when desired, only
one simulated string at a time. Such a configuration is possible because
the electronic circuitry shown in FIG. 9, to be discussed subsequently, in
addition to being utilized in connection with a guitar-type instrument, is
also designed such that: (1) the "attack" portion of an audio frequency
envelope is produced upon the initial deflection of an actuator 24.sub.1 .
. . 24.sub.4 rather than upon release as is customary; (2) the sound is
sustained for as long as the deflection of the actuator is maintained by
the dynamic friction of the moving bow; and (3) the sound dampens
gradually when the actuator is allowed to return to its normal state upon
lifting of the fiddler's bow. Assuming that the actuator elements 24.sub.1
. . . 24.sub.4 are made of thin flexible metallic material such that the
coefficient of friction at the thin top edge 26 is inadequate for proper
bowing, the edge may be capped with a plastic or similar edging or beading
elements 90.sub.1 . . . 90.sub.4 to provide a proper friction factor.
Alternatively, the actuator elements 24.sub.1 . . . 24.sub.4 etc. may be
made from a plastic or similar material which has been selected for
optimum flexibility and optimum friction factor. Accordingly, the subject
invention is not intended to be limited to the simulation of stringed
instruments of the lute class only, but rather it is intended to include
the simulation of other instruments in which the strings are played by
picking, plucking, strumming, bowing and also by known percussive methods.
A major feature of the assembly 22 in its various embodiments as shown in
FIGS. 5 through 8B is the capability of producing "expressive" variations
in sound volume as a function of the amount of actuator deflection of any
element 24.sub.1 . . . 24.sub.n-1, 24.sub.n. It can be seen, for example,
with reference to FIG. 6 that two sets 58 and 62 of three switches each
are adapted to provide three levels of expressive sound volume. The
closest strip 58.sub.a and 62.sub.a on either side of the contact 24 is
used as a pole piece to provide a fixed supply potential V.sub.2 (FIG. 9)
to the remaining three contact strips 58.sub.b, 58.sub.c and 58.sub.d and
62.sub.b, 62.sub.c and 62.sub.d, respectively. When the actuator 24
deflects either strip 58.sub.a or 62.sub.a to its nearest contact 58.sub.b
or 62.sub.b the lowest level of sound will be produced. As the deflection
is increased, the second contact 58.sub.c or 62.sub.c is closed and a
third 58.sub.d or 62.sub.d in turn. As each contact closes against its
neighbor, the expressive sound volume increases to a higher level as will
be shown. Although three levels of expressive sound volume are
illustrated, it should be noted that if additional contacts are included
in the stack, then additional sound levels can be provided. This provision
of variations in sound volume enables the musician to perform with
"expression" using dynamic techniques similar to those applied to a
conventional string instrument, i.e. a greater string deflection produces
a greater volume of sound. Another important feature of the subject
invention is the capability of sustaining the sound when desired by the
musician during a musical score or as a part of it without resorting to
manipulation of other controls. This is accomplished by holding one or
more of the simulated strings, i.e. actuators 24.sub.1 . . . 24.sub.n in
the deflected position in either direction. When they are released, the
sound will dampen out gradually. Also, "sustain" effects can be applied
with increasing or decreasing sound volume while the finger board keys 16
shown in FIG. 1 are run through a musical sequence or while a particular
note or chord is held. The resulting advantage of this sustaining feature
is twofold, namely it provides an additional form of "expression" for the
musician when desired without detracting from the normal method of playing
the instrument, and the musician can change the sound of the same
instrument instantly to sound like a plucked string instrument, an organ,
or even a violin type instrument.
In addition to the normal type of tone control provided by the knob 30 as
shown in FIG. 1, a harmonic control is also provided by means of the knob
32. With the control knob 32, the sounds are made to vary in a manner
which may be described as "timbre", "color", "presence", etc. which when
used in conjunction with the tone control knob 30, can produce a wide
range of tonal "voice" variations. The uniqueness of this harmonic control
function lies in the simplicity of the circuit and its implementation
which will now be described.
Referring now to the schematic diagram shown in FIG. 9, the basic audio
frequency signals to be generated in accordance with the aforementioned
assembly 22 can be provided by any waveform generating circuitry which can
provide time varying waveforms, e.g. triangular or sawtooth type
waveforms, at the fundamental frequencies required for each open string
tone and the required incremental frequencies for each fret tone. In its
preferred embodiment, the basic frequencies are generated in the subject
invention by six relaxation oscillator circuits 92.sub.1, 92.sub.2,
92.sub.3, 92.sub.4, 92.sub.5 and 92.sub.6, which are identical insofar as
circuit configuration is concerned but the relative frequency determining
values of the components differ. Accordingly, only one of the oscillator
circuits 92.sub.1 is shown in detail and is configured basically about a
programmable unijunction transistor 94, n-p-n junction transistor 95 and a
plurality of fret-key switches 16.sub.1, 16.sub.2 . . . 16.sub.n-1 and
16.sub.n which are used to select desired increments of resistances
96.sub.1, 96.sub.2 . . . 96.sub.n-1 and 96.sub.n to form a specific RC
time constant with the fixed capacitor 98 to control the oscillator
frequency. Smaller frequency changes are made by a variable resistance
element 100 which is utilized for simulated string "tuning" purposes. The
design parameters for this type of oscillator circuit are well defined in
any typical programmable unijunction transistor manufacturer's brochure,
e.g. G.E. application notes AN60-20 dated 1/71 at page 4 and AN90-93 dated
1/72 at page 12. The programmability feature of this type of circuit is
well known to have been used as a means of organ tone generation. The
fundamental or "open string" frequency of the oscillator circuit 92.sub.1
is obtained when a fixed supply potential V.sub.1 appearing at terminal
102 and coupled to circuit junction 104 is applied to circuit junction 106
common to capacitor 98 through the total series combination of resistances
96.sub.1 . . . 96.sub.n which occurs when all of the fret-switches
16.sub.1 . . . 16.sub.n are in their open condition. When the upper
fret-switch 16.sub.1 is closed, the voltage V.sub.1 appearing at junction
104 is applied at junction 108, excluding the upper resistor 96.sub.1 from
the RC time constant to thereby produce the next higher tone frequency.
Therefore, eliminating each additional resistor 96.sub.2, 96.sub.3, etc.
in succession results in incrementally higher toner changes for
successively higher fret positions. With this configuration, depressing
one or more fret key 16 of the same set will produce the tone only of the
highest fret key 16.sub.n depressed. In summary, the function of the
fingerboard key switches is to apply the voltage V.sub.1 to the resistor
termination which will produce the desired tone.
The output of the programmable unijunction oscillator 92.sub.1 which
appears at junction 106 is coupled to a respective class C type modulating
output amplifier circuit 108.sub.1 which includes transistor 110. The
purpose of the modulation amplifier 108.sub.1 is to receive a variable
frequency audio tone signal having a constant amplitude or envelope from
the audio frequency oscillator voice"1, reshape it to a form which
contains enriched harmonics, amplify the new tone signal, and then
modulate the signal envelope to simulate the desired sound or "voice of
the musical instrument being simulated. The output of the oscillator
92.sub.1 is fed to the base of the transistor 110 by means of resistor 112
and coupling capacitor 114. Reshaping is provided by the base bias for
class C operation provided by a network consisting of resistors 116 and
118 and the variable resistance 120 coupled back to the supply potential
V.sub.1. The variable resistance 120 is adapted to be mechanically coupled
to the control knob 32 shown in FIG. 1. When the variable resistor 120 is
adjusted for zero resistance and the actuator 24.sub.1, for example is
deflected, an audio tone signal comprised of narrow low duty cycle
rectangular pulses is produced at the collector junction 122 of transistor
110 which is very rich in both odd and even harmonics. If the resistance
120 is varied to provide an increasing resistance, the pulse-width of the
tone signal will increase up to a maximum duty cycle of 50% or less,
thereby approaching a square wave, which is less rich in harmonics than a
narrow rectangular pulse, containing only the odd harmonics. By this means
the harmonic content of the output waveform or the "timbre" of the voice
signal appearing at junction 122 is made variable. The net effect of this
harmonic control achieved by means of varying the resistance 120 is to
provide a wide range of instrumental voices and pleasing sound effects
when desired by the musician without resorting to extraneous electronic
circuits.
It should be pointed out, however, that no audio output will be produced
until such time that the actuator 24.sub.1 closes one or more of the
switch contact elements 58.sub.a . . . 58.sub.d or 62.sub.a . . . 62.sub.d
to couple a supply potential V.sub.2 from terminal 121 to the collector
circuit of transistor 110. This supply potential is provided from the
fixed DC source 126 via the switch 128 and resistor 129 or when desired
from an external source, not shown, coupled to the connector 127.
Deflecting the actuator 24.sub.1 in either direction produces a pulsed or
sustained output waveform envelope of the audio frequency as desired by
the musician depending upon whether the actuator is momentarily deflected
or held in a deflected position. Instrument "voice" modulation, however,
is provided by the network 130 which is a compensated balanced bridge
attenuator network and the manner in which the actuator 24.sub.1 is moved.
If the musician simply picked the actuator 24.sub.1 so that it is allowed
to spring back like a string, a sound like a plucked string will be
produced; however, if he deflects and holds the actuator 24.sub.1 in a
deflected position, he can sustain the tone to produce tones like an organ
or other tone sustaining instruments, including "viol" types. The
amplitude of the modulating waveform and therefore the sound volume is
varied by the amount of deflection of the actuator 24.sub.1. As shown,
three amplitude levels are available to the musician for sound volume
expression purposes and they are proportional to the amount of deflection
analogous to deflecting a musical string.
When the actuator 24.sub.1 is deflected to close the first contact pair
58.sub.a and 58.sub.b, for example, or 62.sub.a and 62.sub.b, a step input
voltage V.sub.2 is applied to circuit junction 132 of the compensated
attenuator network 130 comprised of resistors 134 and 136 and capacitors
138 and 140. This type of circuit is disclosed, for example, in the
publication entitled "Pulse, Digital and Switching Waveforms", Millman and
Taub, published by McGraw Hill, 1965, at pp. 50-54. By this means a fast
rising voltage pulse derived from the supply voltage V.sub.2 occurs at
circuit junction 142 which is coupled to the collector of transistor 110
via collector load resistor 144 and forms an abrupt leading edge "attack"
portion of the modulating waveform and to charge the decay time storage
capacitor 146. In the process, the attenuator capacitors 138 and 140 are
also charged from the supply potential V.sub.2 . Upon release of the
actuator 24.sub.1, the voltage source V.sub.2 is cut off. Therefore, the
only voltage remaining is supplied by one or more charged capacitors 138,
140 and 146. These capacitors discharge to ground 148 through the
collector to emitter circuit of transistor 110 via the collector load
resistor 144.
In doing so, a decaying envelope of the oscillator 92.sub.1 frequency
appears at the collector junction 122 which closely simulates the
gradually dampened waveform produced by the sound of a plucked string
instrument. If on the other hand the actuator 24.sub.1 is held to keep one
or more of its associated switch contacts closed, the voltage V.sub.2 will
be maintained and an output tone will be sustained for so long as it is
held in the deflected position. Also after any sustained effect is
terminated, the gradually dampened edge of the waveform will be produced
by one or more of the discharging capacitors 138, 140 and 146. It should
be noted also that a muting switch, not shown, can be used to curtail the
decaying trailing edge when desired by the musician. Such a device, for
example, would be a shorting switch for instantly discharging all three
capacitors 138, 140 and 146 to ground. The switch actuator for such a
device would be the muting pad actuator 38 shown in FIG. 1.
The modulating pulse generally used to simulate the sound of a plucked
string for a stringless guitar-like instrument had in the past been a
fixed wave shape and any changes in the wave shape when provisions were
included had to be preset. As illustrated in the foregoing description,
the pulse waveform generated by the subject invention can be varied in
pulsewidth and/or amplitude purely as a function of the picking, plucking
or strumming action of the actuators 24.sub.1, 24.sub.2, etc. by a
musician. This versatility is made possible by providing for a fast rising
leading edge (attack) for the amplitude modulating pulse of the voltage
V.sub.2 immediately upon the initial deflection of the actuator rather
than after it is released as is customary.
As noted above, the fast rising leading edge required to simulate the
percussive sound of a plucked string instrument is produced by the network
130 consisting of the bridge formed by resistors 134, 136 and capacitors
138 and 140 connected to the resistor 144 and capacitor 146. When the
actuator 24.sub.1 is deflected slightly to close its first pair of switch
contacts 58.sub.a and 58.sub.b, for example, an impulse current is
produced at junction 142 when a step voltage input V.sub.2 is applied to
the circuit junction 132. Under these conditions, capacitors 138 and 140
behave like short circuits such that the rise time of the step voltage
appearing at circuit junction 132 is very nearly reproduced at circuit
junction 142 while the final value voltage is attenuated by two stages of
a simple passive resistive network made up of resistors 134 and 136. When
the actuator 24.sub.1 is deflected further until the next contact
58.sub.c, for example is closed, the voltage V.sub.2 is applied at circuit
junction 150. At this point only one stage of resistive attenuation
provided by resistor 136 remains ahead of circuit junction 142. Therefore,
the amplitude of the signal at junction 142 is greater than when the
voltage V.sub.2 is applied to circuit junction 132, the result being an
increase in sound volume. It can be seen then that when the actuator
24.sub.1 is deflected so that the third contact 58.sub.d is closed, the
voltage source V.sub.2 is applied directly to circuit junction 142 with no
attenuation. For this case, the amplitude of the output signal and
therefore the volume of the sound produced at the collector junction 122
will be at its maximum value.
Accordingly, the compensated balanced bridge attenuator network 130 is
adapted to provide leading edge conditioning (attack) for the modulation
envelope as well as the trailing edge conditioning (decay) thereof in
response to the selective actuation of the switch contacts associated with
the actuator 24.sub.1. Control of the envelope amplitude for expressive
sound volume as well as envelope width extension for control of sustained
effects is thus provided. It should be pointed out that variations of the
circuit configurations can readily be made to provide additional control
of the functions described such as modulation envelope attack and decay
time variations or additional special effects such as vibrato, etc.
without departing from the spirit and scope of the invention. The output
of the modulation amplifier 108.sub.1 as well as the other five amplifiers
108.sub.2 . . . 108.sub.6 are coupled in parallel to a common summing
junction point 152 by means of the summing resistors 154.sub.1 . . .
154.sub.6. The common circuit junction 152 is coupled to an output jack
156 by means of a volume control potentiometer 158 which is adapted to be
mechanically coupled to the control knob 34 shown in FIG. 1 and a variable
RC tone control circuit including capacitor 160 and a variable resistor
162 which is adapted to be connected to the control knob 30 also shown in
FIG. 1.
When desirable, the on/off switch 128 can be made an integral part of the
volume control potentiometer 158 coupled to the knob 34 shown in FIG. 1.
Additionally, a zener diode 166 as shown in FIG. 9 is utilized to provide
a stable voltage reference for the supply potential V.sub.1 which is
required for the oscillator circuitry 92.sub.1 . . . 92.sub.6 as well as
for the variable resistor 120 utilized in the biasing circuitry for the
transistor 110, for example. The other source voltage V.sub.2 may vary due
to different types of DC supply means coupled to the input power connector
127 or because of a partially discharged battery 126. Accordingly, the
supply potential V.sub.2 is used only for functions that are relatively
insensitive to voltage variations such as capacitor charging amplitude
modulation and sound amplification, etc. The remainder of the power supply
circuitry includes a current limiting resistor 168, two filter capacitors
170 and 172. As noted above and as shown in FIG. 1, the indicator light 36
which may be, for example, a light emitting diode, may be used as a visual
indicator of power status. It can be applied to indicate a power on/off
status or a low battery condition, depending upon the desires of the user.
Also a miniature battery condition meter may be used in place of the
indicator light as desired.
In conclusion then, respective oscillators and modulation amplifiers are
associated with each flexible actuator and a group of leaf type switches
actuated thereby are summed at the junction 152 by means of the six
summing resistors 154.sub.1 . . . 154.sub.6 and coupled to the output jack
156. This output can then be amplified as desired by an amplifier within
the body of the instrument with or without a built-in speaker or it can be
amplified by an external musical instrument amplifier and speaker system.
Typically the output jack 156 is intended to be connected to a standard
electrically amplified guitar-type musical instrument amplifier or
equivalent. If on the other hand the present invention is configured as a
viol type instrument, the signal output would be coupled to a suitable
musical instrument amplifier associated with such type of apparatus.
While the subject invention has been shown and described with a certain
degree of particularity, it is not desired that the present disclosure be
interpreted in a limiting sense, since it is desired that all
modifications, alterations and variations coming within the spirit and
scope of the present invention are meant to be included.
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