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BACKGROUND OF THE INVENTION
The present invention relates to an electronic stringed instrument.
In an electronic stringed instrument, it is necessary that a fret position
of a given string depressed by a player's finger is discriminated to
specify a pitch of a musical tone to be produced, and at the same time, a
picking timing is detected to determine timings of sounding of the musical
tone.
A conventional method of detecting a fret position in the process for
producing musical tones in such an electronic stringed instrument will be
described with reference to FIG. 1. When a player depresses a string 1
with his finger at a desired position on a fingerboard so as to generate a
specific musical tone, the string 1 is brought into contact with the
specific fret and the length of the string 1 to be picked is determined.
However, according to the conventional method, at this moment, the fret
position is not discriminated. The fret position is discriminated after
the player picks the string 1. More specifically, when the string 1 is
picked, the string 1 vibrates in a period corresponding to the string
length. The vibrations of the string 1 are converted by an electromagnetic
pickup 2 into an electrical signal having a waveshape similar to the
vibrations of the string 1. This electrical signal is waveshaped by a
low-pass filter 3. A peak detector 4 detects the peak in amplitude of the
waveshaped signal. A pulse converter 5 generates pulses in synchronism
with the detection result of the peak detector 4. A pulse interval
measuring circuit 6 measures an interval of pulses generated in
synchronism with peak detection. The pulse interval measuring circuit 6
generates a digital signal corresponding to the pulse interval. A value
represented by this digital signal corresponds to the fundamental
frequency of the string 1 and also represents the position of the fret
which which the string 1 is in contact. A tone generator 7 generates a
musical tone signal on the basis of this digital signal. A sound system 8
produces a musical tone represented by the musical tone signal.
In the conventional arrangement described above, the position of the fret
with which the string 1 is in contact is detected on the basis of the
period of vibration of the picked string 1. At least a period
corresponding to a possible maximum vibration period of the string 1 must
be preset for detecting the peak. For example, a period of about 1/80
second is required for a typical six-string guitar. In addition, the
vibrations of the string 1 immediately after picking have a large harmonic
overtone component ratio, and this ratio causes variations in peak.
Therefore, the initial peak is not used for discriminating the fret
position, and the fret position is detected according to the second or
subsequent peak at which the harmonic overtone component ratio is rapidly
reduced. In the conventional arrangement, it takes a relatively long
period of time until a musical tone is produced by the sound system after
the player picks the string 1. The player experiences an unnatural
feeling.
In an electronic stringed instrument having a plurality of strings 1, the
vibration of the strings 1 are converted into electrical signals by
electromagnetic pickups respectively corresponding to the strings 1. A
magnetic field formed by each electromagnetic pickup 2 is adversely
affected by not only the string 1 assigned thereto but also by adjacent
strings. The fret position may therefore be erroneously discriminated.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an
electronic stringed instrument for accurately detecting a position of a
fret with which a string depressed by a player's finger is in contact.
It is another object of the present invention to provide an electronic
stringed instrument having a short response time for producing a musical
tone.
In order to achieve the above objects of the present invention, there is
provided an electronic stringed instrument comprising: an instrument body;
a string which is stretched above the instrument body; a plurality of
metal frets which are provided on the instrument body and below the string
so that a player's depression of the string causes contact between the
string and one or ones of the plurality of metal frets; ultrasonic
transmitting/receiving means, provided on the instrument body and coupled
to a specific point of the string, for generating an ultrasonic wave so
that the ultrasonic wave is propagated through the string toward the
nearest fret to the specific point among the fret or frets contacting the
string and for receiving an echo wave which is a reflected wave of the
ultrasonic wave from the nearest fret; and fret discriminating means
connected to the ultrasonic transmitting/receiving means for
discriminating the nearest fret among the plurality of metal frets
according to a time difference between generation of the ultrasonic wave
and the receipt of the echo wave and for generating a fret signal
representing the nearest fret.
The present invention is based on an assumption that a propagation time of
an ultrasonic wave to be propagated through a string is proportional to a
string length. An ultrasonic transmitting/receiving means intermittently
transmits an ultrasonic wave. The ultrasonic wave propagates from one end
to the other end of the string. When the player wishes to produce a
specific musical tone and depresses a predetermined position of the
string, the string is brought into contact with at least one of the
plurality of frets so that a string length is defined by this fret. The
ultrasonic wave propagating from one end to the other end of the string is
reflected by the fret with which the string is in contact, and an echo is
generated. The echo propagates from the fret to one end of the string and
is received by the ultrasonic transmitting/receiving means. The fret
discriminating means discriminates the fret position according to the
ultrasonic wave intermittently transmitted from the ultrasonic
transmitting/receiving means and the echo received thereto. Therefore, the
time required for discriminating the fret is the ultrasonic propagation
time for which the ultrasonic wave reciprocates between one end of the
string and the fret with which this string is contact. The fret
discrimination time is not associated with the string diameter. In
addition, the speed of the ultrasonic wave propagating through a solid
object is very high. The player normally depresses the string before
picking it. Therefore, the musical tone can be produced substantially
simultaneously with picking of the string, and the musical tone upon
picking can be obtained in a short response time.
The ultrasonic wave propagates through the medium, unlike in the case of a
magnetic field. The ultrasonic wave is attenuated upon propagation through
the medium. Even if another ultrasonic source is located near the
ultrasonic transmitting/receiving means, it is substantially free from the
influence of an ultrasonic source nearby. Therefore, the fret
discriminating means can accurately discriminate the fret position
according to only the ultrasonic wave transmitted thereby and the echo
derived from the transmitted ultrasonic wave.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a conventional fret discriminating means;
FIG. 2 is a schematic side view of an electronic stringed instrument
according to an embodiment of the present invention;
FIG. 3 is a front view showing a bridge holder of the stringed instrument
in FIG. 1;
FIG. 4 is a plan view showing the bridge holder in FIG. 3;
FIG. 5 is a block diagram of the stringed instrument in FIG. 1;
FIGS. 6A to 6I are timing charts for explaining the operation of the
stringed instrument in FIG. 1;
FIG. 7 is a block diagram of a receiver in FIG. 5;
FIG. 8 is a block diagram showing a modification of a signal discriminator
in the stringed instrument in FIG. 1;
FIG. 9 is a block diagram showing a modification of the receiver in FIG. 5;
FIG. 10 is a side view showing a stringed instrument according to another
embodiment of the present invention;
FIG. 11 is a block diagram of the stringed instrument in FIG. 10;
FIGS. 12A to 12G are timing charts for explaining the operation of the
stringed instrument in FIG. 10;
FIG. 13 is a side view showing a stringed instrument according to still
another embodiment of the present invention;
FIG. 14 is a side view showing a damping means in the stringed instrument
in FIG. 13;
FIG. 15 is a plan view showing the damping means in FIG. 15;
FIG. 16 is a graph for explaining attenuation of ultrasonic vibrations; and
FIG. 17 is a perspective view showing a modification the piezoelectric
element according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2 shows an embodiment wherein the present invention is applied to a
six-string guitar. Referring to FIG. 2, reference numeral 11 denotes a
guitar body. N metal frets 13.sub.1, 13.sub.2, . . . , 13.sub.n are fixed
on a fingerboard 130 in a direction perpendicular to the longitudinal
direction of the fingerboard 130, and the fingerboard 130 is fixed on a
neck 12 connected to the body 11. Bare steel strings 15.sub.1, 15.sub.2, .
. . 15.sub.6 having different diameters are kept taut between tuning keys
12a fixed at the head at the distal end of the neck 12 and a tailpiece 14
extending on the body 11. Six ceramic piezoelectric elements 16.sub.1,
16.sub.2, . . . 16.sub.6 as the ultrasonic transmitting/receiving means
are separated from each other and mounted near the tailpiece 14. The
strings 15.sub.1 to 15.sub.6 are respectively in contact with the
piezoelectric elements 16.sub.1 to 16.sub.6. As is best shown in FIGS. 3
and 4, a pair of bolts 18A extend on the body 11 so as to cause a bridge
holder 17 to be vertically movable. The bridge holder 17 is urged by the
elastic forces of the strings 15.sub.1 to 15.sub.6 against nuts 18
threadably engaged with the pair of bolts 18A. In order to adjust the
height of the bridge holder 17, the nuts 18 are turned. Holes each having
a rectangular cross section are vertically formed from the upper surface
of the bridge holder 17 and are spaced apart from each other at a
predetermined pitch. Adjusting screws 19.sub.1, 19.sub.2, . . . 19.sub.6
extend parallel to the strings 15.sub.1, 15.sub.2, . . . 15.sub.6 through
the holes. The heads of the adjusting screws 19.sub.1 to 19.sub.6 project
from one side surface of the bridge holder 17 such that the screws
19.sub.1 to 19.sub.6 can be turned with a screwdriver. Bridges 20.sub.1,
20.sub.2 , . . . 20.sub.6 carrying the piezoelectric elements 16.sub.1 to
16.sub.6 are threadably engaged with the adjusting screws 19.sub.1 to
19.sub.6 extending through the holes formed in the bridge holder 17. By
turning the screws 19.sub.1 to 19.sub.6, the bridges 20.sub.1 to 20.sub.6
are moved parallel to the strings 15.sub.1 to 15.sub.6, respectively. The
pivotal movement of the bridges 20.sub.1 to 20.sub.6 is defined by the
edges of the holes in a direction parallel to the strings. Upon rotation
of the adjusting screws 19.sub.1 to 19.sub.6, the bridges 20.sub.1 to
20.sub.6 can be moved within the above-mentioned range in the axial
direction of the adjusting screws 19.sub.1 to 19.sub.6, i.e., the
extending direction of the strings 15.sub.1 to 15.sub.6 . A common damper
23 is arranged between the tailpiece 14 and the bridges 20.sub.1 to
20.sub.6. The damper 23 is made of rubber for absorbing vibrations of the
strings. Electromagnetic pickups 21.sub.1, 21.sub.2, . . . 21.sub.6 are
arranged between the piezoelectric elements 16.sub.1, 16.sub.2, . . .
16.sub.6 and the frets 13.sub.1, 13.sub.2, . . . 13.sub.n fixed on the
fingerboard 130 of the neck 12 so as to respectively correspond to the
strings 15.sub.1, 15.sub.2, . . . 15.sub.6 (i.e., independently). The
electromagnetic pickups 21.sub.1, 21.sub.2, . . . 21.sub.6 detect
vibrations of the corresponding strings 15.sub.1, 15.sub.2, . . . 15.sub.6
picked by the player. As a result of the detection, each electromagnetic
pickup supplies a picking signal KON to a tone generator 47. The
piezoelectric elements 16.sub.1 to 16.sub.6 are connected to a fret
discriminating means 22. A rubber damper 24 is arranged at the end of the
fingerboard 130 near each key 12a to absorb the string vibrations when the
string is not held on the fret.
The electrical circuit connected to the piezoelectric elements 16.sub.1 to
16.sub.6 and the electromagnetic pickups 21.sub.1 to 21.sub.6 will be
described with reference to FIGS. 5 to 7. The electrical circuit in FIGS.
5 to 7 is arranged for each one of the strings 15.sub.1 to 15.sub.6. In
the following description, one (associated with the string 15.sub.1) of
the electrical circuits will be exemplified. Predetermined RF pulses (or
pulses including the RF wave) P1 are generated by a pulse generator 31 at
an interval of 3 to 10 msec. The RF pulses are applied from a transmitter
32 to the piezoelectric element 16.sub.1 (time t1 in FIG. 6A). The
piezoelectric element 16.sub.1 generates an ultrasonic wave having a
frequency of 400 kHz to 1 MHz (in the case of bare wires). The ultrasonic
wave propagates through the string 15.sub.1. When the player wishes a
specific musical tone to depress the string 15.sub.1 at a predetermined
position of the neck 12, the string is brought into contact with at least
one of the frets 13.sub.1 to 13.sub.n according to the depression position
of the string 15.sub.1. The ultrasonic wave is reflected by one of the
metal frets 13.sub.1 to 13.sub.n which is in contact with the string
15.sub.1, so that an echo is generated.
Prior to generation of the echo, when the RF pulse P1 is generated, a drive
pulse generator 34 in a receiver 33 in FIG. 7 supplies a set signal S1 to
a set terminal S of an RS flip-flop 35 (FIG. 6B). The RS flip-flop 35
supplies a gate enable signal S2 to a gate 36 (FIG. 6C) to open the gate
36. An output from a clock generator 37 for generating a clock signal C1
(FIG. 6D) is supplied as an output (FIG. 6E) of the gate 36 to a counter
38 while the gate enable signal S2 is supplied to the gate 36 (FIG. 6E).
The counter 38 counts pulses of the clock signal C1 supplied from the
clock generator 37.
When the echo reaches the piezoelectric element 16.sub.1 at time t2, the
piezoelectric element 16.sub.1 generates an electrical signal S3 (FIG. 6F)
having a waveform similar to that of the echo. The electrical signal S3 is
then supplied to the receiver 33. In the receiver 33, an amplifier 39A in
FIG. 7 amplifies the electrical signal S3. When the player picks a string
(as will be described later), a high-pass filter (HPF) 40 eliminates a
low-frequency component caused by string vibrations from the electrical
signal S3. Thereafter, a pulse signal P2 (FIG. 6G) which goes high during
the ON duration of the echo in response to the electrical signal S3 is
output from a signal detector 41. The signal P2 is supplied to a reset
terminal R of the RS flip-flop 35 through an OR gate 42. As a result, the
gate enable signal S2 supplied from the RF flip-flop 35 goes low (FIG.
6C). The gate 36 is disabled and the counter 38 stops counting the clocks.
Therefore, the counter 38 stores the number of clocks output between time
t1 and time t2 (FIG. 6E). A falling differentiator 43 generates a pulse
signal P3 (FIG. 6H) which rises at the trailing edge of the gate enable
signal S2. The count of the counter 38 is latched by a latch 44 in
response to the pulse signal P3. The pulse signal P3 is also supplied to a
delay circuit 45. At time t3 delayed from time t2 by a predetermined
period of time, a delayed pulse P4 from the delay circuit 45 is supplied
to a reset terminal RS of the counter 38, so that the counter 38 is ready
for the next counting cycle. If the player does not depress the string
15.sub.1 at any position and then the echo is not generated, the counter
38 overflows. An overflow signal OF from the counter 38 is supplied to an
OR gate 42 (FIG. 4) in the receiver 33 to reset the RS flip-flop 35.
The count of the counter 38 which is transferred to the latch 44 is
converted into a key code signal KC by a data conversion table 46. The
tone generator 47 specifies a pitch of a musical tone to be produced,
according to the key code signal KC. When the electromagnetic pickup
21.sub.1 detects string picking and the picking signal KON upon its
detection is supplied from the electromagnetic pickup 21 to the tone
generator 47, a musical tone signal is generated according to the
instruction from a musical tone control switch circuit 48 and is supplied
to a sound system including an amplifier 49 and a loudspeaker 50. The
sound system produces the musical tone having a pitch corresponding to the
discriminated fret position.
According to this embodiment, the position of the fret with which one of
the strings 15.sub.1 to 15.sub.6 is in contact is discriminated according
to the propagation time of the ultrasonic wave through the corresponding
one of the strings 15.sub.1 to 15.sub.6 regardless of the string
vibrations upon picking. The position of the fret contacting one of the
strings 15.sub.1 to 15.sub.6 is discriminated in an ultrasonic reciprocal
propagation time between one of the piezoelectric elements 16.sub.1 to
16.sub.6 and one of the frets 13.sub.1 to 13.sub.n which contacts the
depressed string. In addition, since the fret position can be
discriminated prior to picking, a musical tone having a pitch
corresponding to the position of the fret contacting the string can be
generated simultaneously when the player picks the string. The ultrasonic
wave propagating through the strings 15.sub.1 to 15.sub.6 cannot be
transferred to the piezoelectric elements 16.sub.1 to 16.sub.6 without
being through the bridges 20.sub.1 to 20.sub.6, the adjusting screws
19.sub.1 to 19.sub.6, and the bridge holder 17, the ultrasonic wave is
greatly attenuated. The piezoelectric elements 16.sub.1 to 16.sub.6 do not
therefore receive the influence from the ultrasonic wave propagating
through the adjacent strings 15.sub.1 to 15.sub.6.
Pitch data in place of the key code signal KC may be stored in the data
conversion table 46 and may be supplied to the tone generator 47.
The dynamic range (e.g., 10 V) of the RF pulse P1 applied from the
transmitter 32 to the piezoelectric element 16.sub.1 greatly differs from
that (e.g., 0.6 V) of the electrical signal S3 based on the echo generated
upon reflection of the ultrasonic wave by the fret. Therefore, separate
discriminators may be arranged in the transmitter 32 and the receiver 33,
respectively. Alternatively, a signal discriminator 60 shown in FIG. 8 may
be arranged. More specifically, since the RF pulse P1 supplied from the
transmitter 32 has a wide dynamic range, the DC component of the pulse P1
is removed by a capacitor 61, and the pulse P1 then passes through a pair
of parallel diodes 62 and 63 reverse-biased with each other. The resultant
pulse is then applied to the piezoelectric element 16.sub.1. Since the RF
pulse P1 is also supplied through diodes 64 and 65, the pulse cannot be
detected as the electrical signal S3 by the receiver 33. The electrical
signal S3 generated by the piezoelectric element 16.sub.1 has a narrow
dynamic range and does not pass through the diodes 64 and 65. The DC
component of the signal S3 is eliminated by a capacitor 66, and the
resultant pulse is supplied to the receiver 33. However, since the
electrical circuit S3 does not pass through the diodes 62 and 63, it
cannot be applied to the transmitter 32. Threshold levels of the diodes
62, 63, 64, and 65 fall within the range between the dynamic ranges of the
RF pulse P1 and the electrical signal S3.
The pulse generator 31, the transmitter 32, the receiver 33, the gate 36,
the clock generator 37, the counter 38, the falling differentiator 43, the
latch 44, the delay circuit 45, and the data conversion table 46 are
arranged for each one of the strings 15.sub.1 to 15.sub.6. However, the RF
pulses P1 may be generated by a single pulse generator 31 and sequentially
supplied to the piezoelectric elements 16.sub.1 to 16.sub.6, and the
echoes from the strings 15.sub.1 to 15.sub.6 may be processed by a single
receiver 33, a single gate, a single clock generator 37, a single counter
38, a single falling differentiator, a single latch 44, a single delay
circuit 45, and a single data conversion table 46 in a time-divisional
manner. If fret position detection is time-divisionally performed, the
arrangement of the fret discriminating means can be simplified.
As shown in FIG. 9, the receiver 33 may be connected in parallel with the
high-pass filter 40 and a low-pass filter (LPF) 61. A picking component
may be extracted from the electrical signal S3 or separately from the
signal S3. The picking component extracted by the low-pass filter 61 is
supplied to the tone generator 47. The picking components are extracted
from the electrical signals S3 from the piezoelectric elements 16.sub.1 to
16.sub.6 to obtain picking signals KON, thereby eliminating the
electromagnetic pickups 21.sub.1 to 21.sub.6 and thus simplifying the
construction.
In the electronic stringed instrument of FIG. 2, the picking timings are
discriminated on the basis of the low-frequency vibrations detected by the
electromagnetic pickups. The fret is discriminated according to the
propagation time of the ultrasonic signal propagating in the string
through the piezoelectric element. Two types of vibration detecting means
(i.e., the piezoelectric element and the electromagnetic pickup) must be
arranged in the instrument body, thus complicating the construction and
increasing the manufacturing cost of the electronic stringed instrument.
In order to solve the problem described above, a single detecting means is
provided for detecting the picking timing and discriminating the fret
contacting the picked string, as shown in FIGS. 10 to 12.
Another embodiment of the present invention will be described with
reference to FIGS. 10 to 12G. The same reference numerals as in FIG. 2
denote the same parts and functions in FIG. 10 to 12G. Referring to FIGS.
10 to 12G, an instrument body 11, tuning keys 12a, a tailpiece 14, six
strings 15.sub.1 to 15.sub.6 having different diameters and kept taut
between the tuning keys 12a and the tailpiece 14, n frets 13.sub.1 to
13.sub.n fixed on a neck 12 of the body 1 in a direction substantially
perpendicular to the strings 15.sub.1 to 15.sub.6, and a bridge holder 17
extending on the body 11 at the tailpiece 14 side and having ceramic
piezoelectric elements 16.sub.1 to 16.sub.6 corresponding to the strings
15.sub.1 to 15.sub.6 are substantially the same as those of FIG. 2. The
piezoelectric elements 16.sub.1 to 16.sub.6 are in direct contact with the
strings 15.sub.1 to 15.sub.6, respectively. The piezoelectric elements
16.sub.1 to 16.sub.6 generate ultrasonic signals in response to drive
pulses P1 as a first electric signal supplied from a pitch data generating
means 137 and transmit the ultrasonic signals to the corresponding strings
15.sub.1 to 15.sub.6. The ultrasonic signals transmitted to the strings
15.sub.1 to 15.sub.6 propagate toward the frets 13.sub.1 to 13.sub.n
through the strings 15.sub.1 to 15.sub.6. The ultrasonic signals are
reflected by the frets contacting the corresponding strings, so that the
corresponding echoes are generated. The echoes propagate back to the
piezoelectric elements through the strings and are converted by the
piezoelectric elements into reflection signals S11 as a second electrical
signal.
Each reflection signal S11 is supplied to the pitch data generating means
137. The pitch data generating means 137 counts the time interval between
the sending timing of the drive pulse P1 and the reception timing of the
reflection signal S11. The frets which caused generation of the echoes are
discriminated according to the count results. The frets discriminated by
the echoes represent pitches of the desired musical tones. The pitch data
generating means 137 generates a pitch signal S12 representing the pitch
of the tone to be produced. The pitch signal S12 is supplied to a musical
tone signal generator 139.
When the player wishes to produce one or more musical tones and depresses
one or more strings 15.sub.1 to 15.sub.6, the picked strings are vibrated
at low frequencies. The low-frequency vibrations are converted into
low-frequency picking signals S13 as third electrical signals by the
corresponding ones of the piezoelectric elements 16.sub.1 to 16.sub.6.
Each picking signal S13 is detected by a picking data generating means
141. The picking data generating means 141 supplies a volume signal S14
representing a musical tone volume and a duration signal S15 representing
the duration of the musical tone according to the picking signal S13 to
the musical tone signal generator 139. As a result, the musical tone
generator 139 generates a musical tone signal S16 according to the pitch
signal S2, the volume signal S14, and the duration signal S15. The musical
tone signal S16 is supplied to a sound system including an amplifier 49
and a loudspeaker 50, thereby producing a musical tone.
The detailed arrangements and operations of the pitch data generating means
137 and the picking data generating mean 141 will be described with
reference to FIGS. 11 to 12G. Although the circuit in FIG. 11 is arranged
for each one of the piezoelectric elements 16.sub.1 to 16.sub.6, the
circuit arranged for the piezoelectric element 16.sub.1 is exemplified in
the following description. Referring to FIG. 11, reference numeral 101
denotes a pulse generator for generating a drive pulse P1. When the drive
pulse P1 is supplied from the pulse generator 101 to the piezoelectric
element 16.sub.1 and a monostable multivibrator 105 through a transmitter
103 (FIG. 12A), the piezoelectric element 16.sub.1 generates an ultrasonic
wave in response to the drive pulse P1, and the ultrasonic wave is
transmitted to the string 15.sub.1 (N in FIG. 12D represents self-excited
noise of the piezoelectric element 16.sub.1) The ultrasonic wave
transmitted to the string 15.sub.1 propagates through the string 15.sub.1
toward the frets 13.sub.n, . . . 13.sub.1. The ultrasonic wave is
reflected by one of the frets 13.sub.1 to 13.sub.n which is in contact
with the string 15.sub.1, and the corresponding echo is generated. The
echo propagates back through the string 15.sub.1 toward the piezoelectric
element 16.sub.1.
The monostable multivibrator 105 generates a one-shot pulse P2 in response
to the drive pulse P1. The one-shot pulse P2 is supplied to a pitch
designation circuit 107 (FIG. 12B). The pitch designation circuit 107
causes its built-in counter 107a to count clocks in response to the
one-shot pulse P2 (FIG. 12C). When the echo reaches the piezoelectric
element 15.sub.1 at time t2, the piezoelectric element 15.sub.1 generates
the reflection signal S11 derived from the echo (FIG. 12D). The reflection
signal S11 is amplified by an amplifier 109, and the amplified signal is
supplied to a high-pass filter 111 and a low-pass filter 113. Since the
reflection signal S11 is generated on the basis of the echo of the
ultrasonic signal, its frequency is very high. Therefore, the reflection
signal S11 passes through only the high-pass filter 111, and the filtered
signal is supplied to the pitch designation circuit 107. The counter 107a
in the pitch designation circuit 107 stops counting the clocks, and the
current count is held thereby (FIG. 12C). The count corresponds to a time
interval between the sending timing of the drive pulse P1 and the
reception timing of the reflection signal S11, thereby representing the
fret which generated the echo. The pitch designation circuit 107 supplies
the pitch signal S2 representing the pitch of the musical tone to the
musical tone generator 139 according to the count.
When the player picks the string 15.sub.1 to produce a desired musical tone
after the pitch of the musical tone to be produced is determined, the
string 15.sub.1 is vibrated at a low frequency. The string vibrations are
converted into the low-frequency picking signal S13 by the piezoelectric
element 16.sub.1 at time t3 (FIG. 12D). The picking signal S13 is
amplified by an amplifier 109, and the amplified signal is filtered
through only a low-pass filter 113. The filtered signal is then supplied
to a waveshaper 115. The waveshaper 115 extracts an envelope of the
picking signal S13 (FIG. 12E). A speed detector 117 in the next stage
holds a peak value obtained after a lapse of a predetermined period of
time. The volume signal S14 is formed according to the value (FIG. 12F).
In general, if the string is strongly picked, the amplitude of the picked
string is increased. The peak value obtained after the lapse of the
predetermined period of time is proportional to the picking strength and
to the volume level of the musical tone. An output from the waveshaper 115
is also supplied to a duration discriminator 119 so that the peak value is
compared with a threshold value Vth. If the output from the waveshaper 115
exceeds the threshold value Vth at time t4, the duration signal S5 output
from the duration discriminator 119 goes high. When the output from the
waveshaper 115 is lower than the threshold value Vth at time t5, the
duration signal S5 goes low (FIG. 12G).
While the duration signal S15 is kept high, a switch circuit 121 is turned
on and then the volume signal S14 is supplied to a voltage-controlled
amplifier (VCA) 123. The musical tone generator 139 receives the output
from the amplifier 123 and the pitch signal S12 and generates a musical
tone signal having predetermined pitch and volume levels. The musical tone
signal is supplied to the sound system.
In the electronic stringed instrument of this embodiment, the piezoelectric
elements 16.sub.1 to 16.sub.6 can be used to generate the reflection
signal S11 and the picking signal S13, thereby simplifying the overall
construction and reducing the manufacturing cost.
In the above embodiment, the volume signal S14 and the duration signal S15
are generated by the picking data generating means 141. However, the
present invention is not limited to these signals. For example, a signal
associated with other string picking may be generated.
In the embodiment of FIG. 10, the material and structure of the strings are
selected to minimize attenuation of the ultrasonic signals propagating
through the string. However, the echo of the ultrasonic signal generated
in response to the drive pulse P1 applied to the piezoelectric element is
not greatly attenuated, but converted into the electrical signal E1 by the
piezoelectric element. The signal E1 is used to discriminate the fret
which has generated the echo. However, with this arrangement, while the
echo propagates through the string, a secondary echo is generated, and
then noise N2 is generated on the basis of the second echo. Furthermore,
noise N3 is generated on the basis of the ternary echo. The secondary and
subsequent echoes are not normally greatly attenuated. It is difficult to
discriminate the electrical signal E1 from the noise N2 or N3. In order to
accurately discriminate the fret which has generated the echo, the pulse
interval must be increased.
FIGS. 13 to 15 show still another embodiment for solving the above problem.
The same reference numerals as in FIGS. 2 to 4 denote the same parts and
functions in FIGS. 13 to 15. Referring to FIGS. 13 to 15, six strings
15.sub.1 to 15.sub.6 having different diameters are kept tout on an
instrument body 11 between tuning keys 12a and a tailpiece 14. N frets
13.sub.1 to 13.sub.n are fixed on a neck 12 of the body 11 in a direction
substantially perpendicular to the strings 15.sub.1 to 15.sub.6. The
strings 15.sub.1 to 15.sub.6 can be brought into contact with these frets.
A bridge holder 17 is fixed on the body 11 at the tailpiece 14 side. The
bridge holder 17 supports six ceramic piezoelectric elements 116.sub.1 to
116.sub.6 as the piezoelectric transducer means. The piezoelectric
elements 116.sub.1 to 116.sub.6 are in direct contact with the strings
15.sub.1 to 15.sub.6, respectively. The piezoelectric elements 116.sub.1
to 116.sub.6 can generate ultrasonic vibrations in response to drive
pulses P1 as a first electric signal supplied from a fret discriminator
37. The ultrasonic vibrations are transmitted to the corresponding strings
15.sub.1 to 15.sub.6. The ultrasonic vibrations propagate as ultrasonic
signals through the strings 15.sub.1 to 15.sub.6 toward the frets 13.sub.n
to 13.sub.1. The ultrasonic signals are reflected at positions where frets
are in contact with the corresponding strings, so that the corresponding
echoes are generated. The echoes propagate back to the piezoelectric
elements 116.sub.1 to 116.sub.6 through the strings 15.sub.1 to 15.sub.6.
The echoes are converted into reflection signals S1 as second electrical
signals by the piezoelectric elements 116.sub.1 to 116.sub.6. Each
reflection signal S1 is supplied to the fret discriminator 37. The fret
discriminator 37 counts a time interval between a sending timing of the
drive pulse P1 and a reception timing of the reflection signal S1, thereby
discriminating each fret contacting the corresponding string. The frets
13.sub.1 to 13.sub.n which generate the echoes represent pitches of the
desired musical tones. The fret discriminator 37 generates a pitch signal
S2 representing a pitch of a tone to be produced, according to the fret
position discrimination result. The pitch signal S2 is sent to a tone
generator 39.
When the player wishes desired musical tones and picks the strings 15.sub.1
to 15.sub.6, the strings 15.sub.1 to 15.sub.6 are vibrated at low
frequencies. The low-frequency vibrations are picked up by electromagnetic
pickups 21.sub.1 to 21.sub.6 respectively arranged for the strings
15.sub.1 to 15.sub.6. Picking signals KON based on the detection results
are supplied to the tone generator 39. In response to each picking signal
KON, the tone generator 39 generates a musical tone signal S3 according to
the pitch signal S2. The musical tone signal S3 is generated to the sound
system including an amplifier 49 and a loudspeaker 53. Therefore, a
musical tone is produced.
The arrangement of a damping means 155 will be described. The damping means
155 is fixed on the body 11 near the electromagnetic pickups 21.sub.1 to
21.sub.6. The detailed arrangement of the damping means is illustrated in
FIGS. 14 and 15. A pair of studs 157 and 159 extending on the body 11 are
slidably fitted at both ends of a support member 161. Six plate members
63.sub.1 to 63.sub.6 respectively corresponding to the strings 15.sub.1 to
15.sub.6 are disposed on the upper surface of the support member 16.sub.1.
One end of each of the plate members 63.sub.1 to 63.sub.6 is coupled by a
pin 62 to the support member 161. The other end of each of the plate
members 63.sub.1 to 63.sub.6 is threadably engaged with a corresponding
one of screws 75.sub.1 to 75.sub.6. When the screws 75.sub.1 to 75.sub.6
are threadably fitted in the plate members 63.sub.1 to 63.sub.6,
respectively, the other end (the end spaced apart from the corresponding
pin 62) of each of the plate members 63.sub.1 to 63.sub.6 comes near a
corresponding one of the strings 15.sub.1 to 15.sub.6. Dampers 87.sub.1 to
87.sub.6 are adhered to the centers of the plate members 63.sub.1 to
63.sub.6, respectively. When the other end of each of the plate members
63.sub.1 to 63.sub.6 comes near the corresponding one of the strings
15.sub.1 to 15.sub.6, the dampers 87.sub.1 to 87.sub.6 are brought into
contact with the strings 15.sub.1 to 15.sub.6. As | | |
