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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an improved method and apparatus
for determining and visually displaying the frequency of a vibratory
element of a musical instrument. Throughout this specification, the term
"vibratory element" is employed in a general sense to include all
frequency producing means whether mechanical, electrical, or otherwise.
2. Description of the Prior Art
All musical instruments of the acoustical variety and especially
multistringed instruments such as guitars, violins, and pianos, require
periodic, even daily, tuning to insure that they consistently reproduce a
proper pitch when played. In the past, in the case of the piano, this
periodic tuning has been accomplished manually by a skilled craftsman
employing a set of tuning forks to provide audible reference frequencies.
Being of simpler construction than the piano, instruments such as the
guitar and the violin are not generally tuned by such a special skilled
craftsman, but rely upon the skill of the individual musician for their
tuning. In any event, the use of tuning forks is inherently an inaccurate
method, is slow and tedious, and in the case of multistringed instruments
such as pianos, requires skill far beyond that routinely available in
today's society.
Because of this situation, electronic devices have been developed to
provide such periodic tuning. Known devices generally provide information
in the form of a frequency difference between an input signal as generated
by a vibratory element, such as a string of a guitar, and the correct or
desired frequency to be generated by that element. In these instances,
when the frequency difference becomes small or zero, the element is
properly tuned. Examples of some of the known devices are disclosed in the
U.S. Patents to Allen, U.S. Pat. No. 3,881,389, Iannone, U.S. Pat. No.
3,896,697, Rosado, U.S. Pat. No. 4,018,124, Arpino, U.S. Pat. No.
4,041,831, and Calvin, U.S. Pat. Nos. 4,078,469 and 4,122,751. As
disclosed, these devices utilize visual indicators which are sometimes in
the form of meters or lights which turn on or off depending on whether or
not the vibratory element is in tune, digital displays of frequency
deviations, and use in one instance, of a stroboscope to display frequency
deviation as apparent movement of dark and light spots on a disk. The
patent to Mackworth-Young, U.S. Pat. No. 3,631,756, discloses an indicator
in the form commonly known as a "magic-eye" according to which fluorescing
sectors are moved towards or away from one another depending on whether
the vibratory element is approaching or retreating from a desired tuned
frequency.
These patents are generally representative of the prior art and, although
they were deemed to be advances in the state of the art at the time that
they were conceived and reduced to practice, they exhibit a number of
drawbacks which have been considered during the development of the present
invention. For example, in many instances, the known devices utilize
complicated electrical or electronic circuitry which necessarily results
in a high initial cost and are subsequently expensive to maintain.
However, a major drawback of those devices described in the patents
recited above is the fact that the information displayed begins to
degenerate at the instant the string is plucked with the result that such
information is of questionable accuracy after the initial value is
displayed. Thereafter, the musician is not able to rely on the information
displayed, but is forced to guess the actual value albeit based to some
extent on the information displayed. An additional drawback of the known
devices is the fact that they do not generally inform the musician of the
particular frequency of the vibratory element being examined; rather, they
inform the musician of the difference between the frequency of the
vibratory element, as actuated, and the desired frequency for that
element. In most instances, a competent musician is aware of the general
frequency range for a particular vibratory element, although he may not
know the exact frequency for that element. In any event, most musicians
would rather be informed of the particular frequency being generated by an
activated element and make the appropriate adjustment to bring it into
tune, than to know only the frequency deviation between the actual and
desired frequency.
SUMMARY OF THE INVENTION
It was with recognition of these needs and of the state of the prior art
that the present invention was conceived and has been reduced to practice.
The present invention, then, relates generally to a method and apparatus
including electronic circuitry for tuning a vibratory element of a musical
instrument. The vibratory element may be, for example, the strings of a
guitar, violin, or piano, or any other acoustically tuneable musical
instrument. When a tuneable vibratory element of the instrument is
actuated, the vibrations thereby created are converted into an electrical
signal. This signal is operated upon to eliminate harmonic components, is
sampled for a duration of one second, and is visually displayed on a
readout device as a frequency registered in units of cycles per second. If
the tunable element is actuated again, the display is zeroed and the
frequency of the new signal will be displayed in place of the frequency of
the previous signal, and if the tunable element is not actuated again
within a predetermined period of time, twenty seconds, for example, the
display on the readout device will return to zero.
The apparatus, as disclosed, indicates the actual frequency of a tunable
vibratory element when actuated, as when a guitar string is plucked, and
allows sufficient time for the musician to adjust or tune the element to
the known, desired, frequency of that element. A primary feature of the
invention, then, is that the indicated value remains displayed for a
period of time sufficient to enable the musician to compare the displayed
value to the standard value desired and thereby tune the element.
Furthermore, if the musician actuates the same element while the previous
value remains displayed, the new value will preempt the previous value and
will itself be displayed and remain for a predetermined period of time or
until it is, in turn, preempted. The invention is adaptable to both
acoustical instruments and to electrically powered instruments, is highly
accurate, is instantaneous in its operation, is compact, portable, and is
light in weight. Additionally, the invention utilizes existing or
state-of-the-art materials and components such that it is inexpensive to
manufacture and maintain.
Other and further features of the invention will become apparent from the
following description taken in conjunction with the following drawings. It
is to be understood that both the foregoing general description and the
following detailed description are exemplary and explanatory but are not
restrictive of the invention. The accompanying drawings which are
incorporated in and constitute a part of this invention, illustrate one
embodiment of the invention, and together with the description, serve to
explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a perspective view of the invention illustrating the invention in
operation and electrically connected to both an electrical guitar and an
acoustical guitar;
FIG. 2 is a block diagram disclosing a system for measuring the vibration
frequency of a vibratory element according to the present invention; and
FIG. 3 is a schematic diagram of the electronic circitry illustrative of
portions of the block diagram illustrated in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Refer now to the drawings and initially to FIG. 1 which generally
illustrates the invention as it is used in conjunction with stringed
instruments. As illustrated, the invention is in the form of a tuning
device 20 comprised of electronic circuitry and components, to be
described, enclosed within a casing 22. As will be described in greater
detail below, the tuning device 20 serves to inform a musician of the
frequency value of a plucked string on a musical instrument such as a
guitar. FIG. 1 illustrates both an electrical guitar 24 and an acoustical
guitar 26, and the invention is applicable to either variety of
instrument. It is further noteworthy that the invention is applicable to
substantially any instrument having a vibratory element, strings or
otherwise, and the invention should not be construed as being limited only
to guitars or, indeed, stringed instruments.
A top panel 28 of the casing 22 is preferably provided with a legend as
indicated by a bracket 30 providing the frequency and the notes associated
with each string. As indicated, there are six such frequencies or notes,
the guitar being a six stringed instrument, by definition. The electrical
guitar 24 is electrically connected to the device 20 by means of a lead 32
extending between an output jack 34 on the guitar and an input jack 36
appropriately provided on a front panel 38 of the casing 22. The output
jack 34 is electrically connected to a pick-up head (not illustrated)
which serves to convert the movement of a string 40 into an electrical
signal which can then be read at the output jack 34.
A string selector dial 42 is also suitably mounted on the front panel 38
and is selectively moveable to any one of six positions, each position
being associated with a different string of the guitar 24. That is, by
turning the string selector dial to the numeral "6", the pick-up for the
associated string 40 is then being monitored and selectively processed by
the circuitry within the tuning device 20. Thereupon, the device 20 is
energized by means of a power switch 44 connecting its internal electronic
circuitry to a suitable source of power.
With string selector dial 42 appropriately rotated to the number "6"
position relating to that particular string whose frequency is to be
determined, as shown in FIG. 1, that string is then plucked in the "open"
position. The "open" position means that no fingers are placed on a fret
46 nor does any other object touch the string along its free length. A
display 48, which may be of the digital variety provided in the front
panel 38 of the casing 22, thereupon indicates a frequency value
equivalent to the musical note at which the string is presently set. This
value remains on the display for a moderate period of time, for example,
for a period of 20 seconds or until the string is plucked again. If the
number appearing on the display is not the same as the number appropriate
for the particular string as indicated on the top panel 28, the musician
turns a tuning peg 50 on the headpiece 52 of the guitar for that
respective string and continues to pluck the string and adjust the tuning
peg until the value indicated by the display 48 corresponds to the desired
value for the string. This same procedure is used for tuning each of the
remaining five strings.
The procedure in the instance of the acoustical guitar 26 is similar to
that just described with respect to the electrical guitar 24. However, in
this instance, a suitable pick-up 54 is applied to the guitar 26 and, in
turn, connected to a lead 56. Thus, with the lead 56 connected to the
input 36 of the tuning device 20, vibrations resulting from a plucked
string on the guitar 26 will be translated into an electrical signal and
read on the display 48.
In its broadest terms, the electronic circuitry within the tuning device
20, which will be described below, performs generally according to a
sequence defined by the following steps: first, obtaining an input from a
vibratory element, that is, a string 40, and converting the output into an
electrical signal; second, deriving and providing as an output those
portions of the electrical signal which are present within a generally
narrow predetermined frequency range; third, monitoring the output from
the second step for a first predetermined period of time; fourth,
eliminating any further input from the second step for a second
predetermined period of time; and fifth, visually displaying the frequency
of the vibratory element for no longer than the second predetermined
period of time.
The sequence just recited may include an additional, or sixth, step of
returning a display mechanism utilized for visually displaying the
frequency of the vibratory element to a zero condition after lapse of the
second predetermined period of time. Also, the sequence may include a
seventh step of resetting the display mechanism utilized for visually
displaying the frequency of the vibratory element to a zero condition
prior to displaying a frequency for a new input. This seventh step may be
in place of, or in addition to, the sixth step.
In accordance with the invention, the apparatus to be disclosed comprises
input means for converting into an electrical signal substantially of sine
wave shape the acoustic vibrations of a tunable element of the instrument;
filter means for deriving and providing as an output those portions of
said electrical signal which are present within a generally narrow
predetermined frequency range; display means operable to provide a visual
indication of the frequency of the vibratory element; a first one-shot
pulse generator operable to provide an output timing pulse of
predetermined limited duration; actuating means responsive to said output
of said filter means when said output is greater than a predetermined
level for operating said first one-shot pulse generator; sample and hold
means operable to receive the output from said filter means for operating
said display means; first switch means for electronically connecting said
filter means and said sample and hold means resulting in operation of said
sample and hold means by the output from said filter means and responsive
to operation of said first pulse generator for opening said first switch
means and electronically disconnecting said filter means and said input
means; a second one-shot pulse generator responsive to the output timing
pulse from said first pulse generator operable to provide an output timing
pulse of extended duration; and second switch means responsive to
operation of said second pulse generator for change to a conductive state
to electronically connect said sample and hold means and said display
means resulting in operation of said display means for a predetermined
extended period of time.
As embodied herein, the invention will be initially described with the aid
of FIG. 2 which presents a block diagram of the basic invention.
Subsequently, reference will be made to FIG. 3 which presents specific
electronic circuitry illustrative of portions of the block diagram.
Accordingly, with initial reference to FIG. 2, the sound produced when the
guitar string 40 is plucked is received by a pick-up 58 and fed to the
input 36 of the device 20 (FIG. 1) as previously described. The sound of
the plucked string is converted by the pick-up 58 into an electrical
signal substantially of sine wave shape as represented by the reference
numeral 60. An impedance match circuit 62 (utilizing, for example, a Radio
Shack 843LF353N15, or equivalent, and associated components) thereupon
matches the impedance of the signal 60 to that of the following circuit,
the output from the circuit 62 being generally indicated as a signal 64. A
two-stage auto gain control 66 (utilizing, for example, a National LM324N,
or equivalent, and associated components) serves to receive the signal 64
and maintain it as a steady amplitude represented by a signal 68 as the
movement of the string 40 decays. Blocks 70 and 72 together comprise a
state variable active bandpass filter (utilizing, for example, a National
LM324N, or equivalent, and associated components) which is adjustable for
the basic narrow bandwidth of frequencies of each of the six strings. The
purpose of the filter 70, 72 is to eliminate the harmonic frequencies
which are generated by a string when plucked and disallows any frequencies
from adjacent strings inadvertently being processed. The result is a sharp
signal 74 or, in other words, those portions of the electrical signal 68
which are present within a generally narrow predetermined frequency range.
For example, if the frequency being sought is 330 cps, the filter 70, 72
might allow passage of those portions of an electrical signal within a
frequency range approximately between 310 cps and 350 cps.
After the signal 74 is operated upon in a manner which will be described
below, the frequency of that signal will be visually provided by the
display 48 to which reference has previously been made as being located on
the front panel 38 of the casing 22.
A signal shaping circuit 76 operates on its input signal 74 (which is of
sine wave shape) to produce an output signal 78 which is of square wave
form but at the same basic frequency as the input signal. A
frequency/voltage converter 80 serves to operate on the signal 78 and
produce a d.c. output which is proportional to the frequency of the signal
78. A sample and hold circuit 82 operates on the output signal from the
frequency/voltage converter 80, the signal being directed via a first
electronic switch 84 and averages and holds that output signal and gates
it to a digital voltmeter 86 through a second electronic switch 88. Such
gating through the switches 84 and 88 must be achieved at the proper time
as will be disclosed below.
To this end, it is noteworthy that a peak detector 90 receives the signal
74, and generates an output signal 92 which is representative of the
initial oscillations of the string 40. A level detector 94, which operates
in conjunction with the peak detector 90, generates an output signal 96
which occurs at a trip point 98 of the signal 92 and triggers a first
one-shot pulse generator circuit 100 which is operational for a duration
of one second to change the switch 84 to the conductive state. The
trailing edge of an output signal 102 from the circuit 100 triggers a
second one-shot pulse generator circuit 104 which is operational for a
duration of twenty seconds. An output signal 106 from the circuit 104
thereby serves to remove the ground signal that zeroes the display and
changes the switch 88 to the conductive state for the predetermined
interval of twenty seconds so as to permit the output from the sample and
hold circuit 82 to be fed to the digital voltmeter 86 and indicated on the
display 48 for that period of time.
When the twenty-second, or other desired predetermined interval of time,
has passed, the electronic switch 88 will again open eliminating the
signal to the digital volt meter 86 and returning the display 48 to a zero
condition. In the event the string 40 is plucked again before the
twenty-second interval has passed, in a manner which will be discussed
more completely below, the electronic switch 88 is again opened
momentarily to return the display 48 to a zero condition before providing
a visual indication of the updated information.
Thus, the pulse generator 100 is operable to provide an output timing pulse
of predetermined limited duration, one-second, for example, and the peak
detector 90 and level detector 94 together serve as actuating means
responsive to the output of the filter means 70, 72 when that output is
greater than a predetermined level, as determined by the trip point 98,
for operating the pulse generator 100. Simultaneously, the sample and hold
means 82 is operable to receive the output from the filter means 70, 72
(through the converter 80) for operating the display means 48.
Furthermore, the first switch means 84 electronically connects the filter
means 70, 72 and the sample and hold means 82 resulting in operation of
the sample and hold means by the output from the filter means but in
response to operation of the pulse generator 100 electronically opens the
first switch means 84 thereby electronically disconnecting the sample and
hold means 82 from the input. Additionally, a second pulse generator 104
is responsive to the output timing pulse from the pulse generator 100 to
provide an output timing pulse of extended duration (for example, twenty
seconds) and the second switch means 88 is responsive to operation of the
second pulse generator 104 for change to a conductive state to
electronically connect the sample and hold means 82 and the display means
48 resulting in operation of the display means for a predetermined
extended period of time.
In accordance with the invention being generally as previously described,
said apparatus includes blanking means operable to change said second
switch means to the non-conductive state to thereby electronically
disconnect said sample and hold means and zero said display means upon
introduction to said input means of a subsequent acoustic vibration within
the predetermined extended period of time. As embodied herein, with
continued reference to FIGS. 2 and 3, it will be understood that if the
string is again plucked during the twenty second interval, a negative
signal is routed through a blanking circuit 107 which in turn terminates
the twenty second pulse causing a switch 181 (FIG. 3) to apply a ground
potential to the display 48 thus causing it to display zero. It must be
noted at this time that the signal out of the blanking circuit 107 will
have an effect on changing the state of the display only during the twenty
seconds of display time, therefore constituting it as a reset circuit
only.
In accordance with the invention being generally as previously described,
said input means includes a moveable vibratory element of a musical
instrument of the acoustic variety operable to produce acoustic vibrations
when moved and a pickup responsive to operation of said vibratory element
for generating an electrical signal of sine wave shape corresponding to
the acoustic vibrations produced by said vibratory element. As embodied
herein, with particular reference to FIG. 1, it will be appreciated, as
previously described, that a musical instrument to be tuned may be of the
acoustical variety, such as the acoustical guitar 26. As disclosed, a
suitable pickup 54 is physically attached to the guitar 26, and is, in
turn, connected to a lead 56 whereby vibrations resulting from a plucked
string on the guitar 26 will be translated into an electrical signal and
eventually read on the display 48.
In accordance with the invention being generally as previously described,
said input means includes a moveable vibratory element of a musical
instrument of the electrical variety operable to produce electrical
signals corresponding to the movement thereof and a suitable pickup
responsive to operation of said vibratory element for generating an
electrical signal of sine wave shape corresponding to the electrical
signals produced by said vibratory element.
As embodied herein, with continuing reference to FIG. 1, it has been
previously explained that the electrical guitar 24 is electrically
connected to the device 20 by means of a lead 32 extending between the
output jack 34 on the guitar and an input jack 36 appropriately provided
on the front panel 38 of the casing 22. In this fashion, the output jack
34 is electrically connected to a pickup head (not illustrated) which
serves to convert the movement of the string 40 into an electrical signal
which can then be read at the output jack 34, and eventually, on the
display 48.
In accordance with the invention being generally as previously described,
shaping means are provided for converting the sine wave shaped output of
said filter means into the form of a square wave; and converter means are
operative to provide a d.c. output proportional to the frequency of the
square wave output from said shaping means; and said sample and hold means
is operable to receive the d.c. output from said converter means for
operating said display means and said first switch means electronically
connects said converter means and said sample and hold means resulting in
operation of said sample and hold means by the d.c. output from said
converter means and is responsive to operation of said first pulse
generator for changing said first switch means to a non-conductive state
and electronically disconnecting said filter means and said input means.
As embodied herein, with reference once again to FIG. 2 the circuit 76
serves to reshape the sine wave signal 74 into a square wave signal 78 and
the frequency/voltage converter circuit 80 serves to provide a d.c. output
signal proportional to the frequency of the square wave output 78 from the
signal shaping circuit 76. Furthermore, the sample and hold circuit 82 is
operable to receive the d.c. output from the converter circuit 80 for
operating the display 48. In this regard, the first switch 84
electronically connects the converter circuit 80 and the sample and hold
circuit 82 resulting in operation of the sample and hold circuit by the
d.c. output from the converter 80 and is responsive to operation of the
first pulse generator 100 for its opening, thereby electronically
disconnecting the converter circuit 80 from the sample and hold circuit
82.
Although the basic concept of the invention should be reasonably well
understood by the reader at this stage of the disclosure, it is considered
that it would be of benefit to disclose one form of electronic circuitry
which can be used to achieve the results expressed by the inventor. To
this end, attention is directed to FIG. 3 which is a schematic diagram of
the electronic circuitry illustrative of portions of the block diagram
illustrated in FIG. 2.
With reference now to FIGS. 2 and 3, consider initially the electrical path
taken by a signal passing by way of the frequency/voltage converter 80,
first switch 84, sample and hold circuit 82, the second switch 88, the
digital voltmeter 86, and terminating at the display 48. The
frequency/voltage converter 80 may be a Radio Shack 9400 CJ, or
equivalent, whose output, as previously explained, is proportional to the
frequency of its input at a pin 108. The first electronic switch 84
receives and passes the d.c. level output from the converter 80 when the
switch control voltage at a pin 110 is high for a period of one second.
The d.c. output thereby passed by the switch 84 charges a high quality
capacitor 112 through a resistor 114 for a period of ten time constants
(five time constants generally being required for a full charge on a
capacitor) to thereby insure a full charge on the capacitor. This d.c.
level signal is then fed to a pin 116 of the second electronic switch 88
via a high impedance source follower 118 (Radio Schack Dual BI-FET OP AMP
843LF353N15, or equivalent, and associated components) which is employed
to prevent the capacitor 112 from discharging.
The d.c. signal out of the source follower 118, as previously explained, is
fed through the electronic switch 88 via pin 116 and a pin 120 and on to
the digital voltmeter 86 when the control signal at a pin 122 of the
switch 88 is high for a duration of twenty seconds. However, before this
signal can be sent to the digital voltmeter 86, a pin 124 of the
electronic switch 181 has to go low to remove the ground level at a pin
126 which is used to zero the display 48.
With a discussion of the path of a signal from the frequency/voltage
converter 80 to the display 48 now as a background, consider the path of a
signal from the state variable filter 70, 72 to the display 48. The a.c.
signal output of the state variable filter 70, 72 is fed to a peak
detector circuit 90 and charges a capacitor 128 through a resistor 130
from ground to a maximum of 1.5 volts less the IR drop across a diode 132
(IN 914, or equivalent). A resistor 134 is used to discharge the capacitor
128 when the signal is removed from it. The resistor 130 is preferably of
a low value to prevent any short spikes in the signal from triggering the
level detector 94, partially represented as a quad op amp (National LM
324N, or equivalent, and associated components). With this arrangement, it
would require a chain of pulses to charge the capacitor 128 to a level
sufficient to trigger the level detector instead of a random noise spike.
An output pin 138 of the inverting level detector 136 (National LM 324N,
or equivalent, and associated components) changes state from +5 volts d.c.
to -5 volts d.c. when the value of a signal at an input pin 140 exceeds
the setting on a pin 142. A resistor 144 provides hysteresis so as to
prevent oscillations in the signal from being processed. The level change
on pin 138 from +5 to -5 volts d.c. causes a capacitor 146 to
instantaneously change to a -5 volts d.c. The -5 volts d.c. pulse is
thereupon inverted by a hex inverter 148 to give a positive pulse 150 at a
pin 152.
The pulse 150 instantaneously discharges a capacitor 154 through a diode
156 (IN 914, or equivalent). The circuit arrangement is such that the
capacitor 154 slowly charges through a resistor 158, the time constant of
the capacitor 154 and the resistor 158 being set for one second. The
resulting positive one second pulse is then inverted by a hex inverter 160
resulting in a negative one second pulse 162 at its output pin 164. A
capacitor 166 is provided to prevent oscillations when the inverter 160
operates on the signal to change its state.
The signal 162 is routed to a quad op amp 168 (National LM324N, or
equivalent) which is configured as an inverting comparator and used to
wave shape the one second pulse into a square wave signal 170 which is
used to turn on the electronic switch 84 as previously discussed.
A signal across a capacitor 182 of the pulse generator 100 first goes
positive on the leading edge of the one second pulse, then goes negative
with the trailing edge of the one second pulse. The negative going signal
then triggers a hex inverter 184 (Radio Shack SIL4049BC, or equivalent)
which in turn puts out a positive pulse 186 at a pin 188. This pulse 186
instantaneously discharges a capacitor 174 and also shuts off a hex
inverter 178 (Radio Shack SIL 4049BC, or equivalent). At this point, the
capacitor 174 begins to charge through a resistor 190, taking
approximately twenty seconds to charge to the trip point of the inverter
178. During this twenty second interval, the pin 180 assumes a negative
state which is applied to pin 124 of electronic switch 181, thereby
opening the switch 181 which removes the ground potential to the digital
voltmeter 86 and causes a pin 191 of a hex inverter 192 (Radio Shack
SIL4049BC, or equivalent) to go positive and is applied to pin 122 of
electronic switch 88 which allows the d.c. value on a capacitor 112, after
one second of sampling time, to be displayed through the digital voltmeter
86.
The signal 162 is also routed to the twenty second pulse generator 104
through the diode 172 to instantaneously charge the capacitor 174. Such a
procedure serves to terminate the twenty second output by applying -5
volts d.c. to the pin 176 of the hex inverter 178 which inverts the signal
and applies the +5 volts d.c. from the output pin 180 to the electronic
switch 181. This, in turn, serves to apply a ground potential to the
digital voltmeter 86 thereby restoring the display 48 to a zero condition.
Thus, it should now be clear that when a string 40 is plucked in the open
position, the display 48 of the tuning device 20 will exhibit a digital
value equivalent to the frequency of the musical note at which the string
is set. This value will remain on the display 48 for approximately 20
seconds or until the string is plucked again. After a period of 20 seconds
has passed, the value appearing on the display 48 will return to zero. If
the string 40 is plucked again within the 20-second interval during which
a value is presently appearing on the display, the new value will preempt
the previous value. After the passage of 20 seconds from the time the
string was last plucked, the value on the display will become zero.
The invention, in its broader aspects, is not limited to the specific
details shown and described; departures may be made from such details
without departing from the principles of the invention and without
sacrificing its chief advantages.
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