U.S. patent number 3,662,641 [Application Number 05/077,280] was granted by the patent office on 1972-05-16 for electronic musical apparatus.
Invention is credited to Joseph Stevens Allen, Zeb Vance Bulla, Jr..
United States Patent |
3,662,641 |
Allen , et al. |
May 16, 1972 |
ELECTRONIC MUSICAL APPARATUS
Abstract
An electronic musical instrument in which the fingerboard of a
guitar is replaced by capacitive touch contact switches simulating
all of the fret positions of a string. The touch plates are coupled
to various oscillators and the output frequency is amplitude
modulated by a transducer produced output signal from a set of
strings which are plucked. This output signal is stretched and
shaped as desired to modulate the audio frequency signal and
produce the final musical output.
Inventors: |
Allen; Joseph Stevens
(Atherton, CA), Bulla, Jr.; Zeb Vance (Nashville, TN) |
Family
ID: |
22137148 |
Appl.
No.: |
05/077,280 |
Filed: |
October 1, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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864024 |
Oct 6, 1969 |
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Current U.S.
Class: |
84/722; 84/702;
984/346 |
Current CPC
Class: |
G10H
1/342 (20130101); G10H 2220/301 (20130101) |
Current International
Class: |
G10H
1/34 (20060101); G01h 001/00 () |
Field of
Search: |
;84/1.01,1.14,1.16,1.17P,1.24 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Electronics World, Vol. 65, No. 1, Jan. 1961, pp. 29-32; 125, "A
Transistorized Teremin,".
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Primary Examiner: Miller; J. D.
Assistant Examiner: Skudy; R.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of copending
application, Ser. No. 864,024, filed Oct. 6, 1969, in the names of
J. Stevens Allen and Zeb Vance Bulla.
Claims
What we claim is:
1. Electronic musical apparatus comprising, string means adapted
for bowing or plucking, a plurality of discrete touch actuated
switch means for simulating the fingerboard of a stringed musical
instrument each of said switch means corresponding to a
predetermined audio frequency signal, oscillator means coupled to
said switch means and responsive to the selective actuation of any
one of said switch means for generating said predetermined audio
frequency signal corresponding to the switch means which has been
actuated, transducer means in proximity to said string means
responsive to the physical displacement of said string means; and
modulating means coupled to said oscillator means and transducer
means and responsive to the actuation of said string means into
vibration concurrently with the actuation of said one switch means
for modulating said audio frequency signal.
2. Electronic musical apparatus as in claim 1 where said switch
means include fixed wire segments for forming virtual capacitors
when a human finger is placed in proximity with a segment.
3. Electronic musical apparatus as in claim 1 where said switch
means include touch actuating means arranged in a straight line
corresponding to the various fingering positions of a string in the
same physical location.
4. Electronic musical apparatus as in claim 1 where said modulating
means includes waveshape modifying means for modifying the output
of said transducer means.
5. Electronic musical apparatus as in claim 1 including tuning
means for said oscillating means located in a position
corresponding to the tuning machine of the simulated
fingerboard.
6. Electronic musical apparatus as in claim 1 where said plurality
of switch means include a common radio frequency oscillator for
generating an alternating signal which charges virtual capacitors
formed by touching a predetermined portion of said switch
means.
7. Electronic musical apparatus as in claim 1 where said switch
means includes means coupled to said modulating means and
responsive to the deactivation of said switch means to disable said
modulating means.
8. Electronic musical apparatus as in claim 1 where said modulating
means includes first and second series coupled balanced modulators
said modulators providing a logarithmic modulation
characteristic.
9. Electronic musical apparatus as in claim 1 where said transducer
means includes first transducer means primarily responsive to
longitudinal mode vibrations of said string means and includes
second transducer means primarily responsive to transverse mode
vibrations of said string means.
10. Electronic musical apparatus as in claim 1 where said
transducer means includes piezoelectric elements mechanically
coupled to said string means.
11. Electronic musical apparatus as in claim 1 including harmonic
control means coupled to said oscillator means for modifying the
harmonic content of the audio frequency signal output of said
oscillator means said harmonic control means including variable
integration means.
12. Electronic musical apparatus as in claim 11 where said variable
integration means comprise a capacitor coupled across a balanced
modulator said modulator including variable gain control means to
vary the effective capacitance value of said capacitor.
13. Electronic musical apparatus as in claim 11 where said harmonic
modulator is coupled and responsive to said transducer means.
14. Electronic musical apparatus as in claim 11 where said
oscillator means produce sawtooth type signals and said variable
integration means attenuate high harmonics of said sawtooth
signals.
15. Electronic musical apparatus as in claim 1 including tuning
means for said oscillator means said tuning means being coupled to
a common junction and together with means for warying the voltage
level of said junction to simultaneously vary the frequencies of
the audio frequency signals generated by said oscillator means.
16. Electronic musical apparatus as in claim 15 where said means
for varying said voltage level includes a potentiometer.
17. Electronic musical apparatus as in claim 15 together with foot
pedal means for controlling said potentiometer.
18. Electronic musical apparatus as in claim 15 where said means
for varying said voltage level includes continuous potentiometer
means and detented potentiometer means and option switch means for
selecting one of said potentiometer means.
19. Electronic musical apparatus as in claim 1 where said
oscillator means includes at least one unijunction transistor.
20. Electronic musical apparatus comprising, transducer means
adapted for actuation by a human hand, a plurality of touch
actuated switch means each including a fixed wire segment for
forming a virtual capacitor with a human finger, each of said
switch means corresponding to a predetermined audio frequency
signal, oscillator means coupled to said switch means and
responsive to the selective actuation of any one of said switch
means for generating an audio frequency signal corresponding to the
switch means which has been actuated; and modulating means coupled
to said oscillator means and transducer means and responsive to the
actuation of said transducer means concurrently with the actuation
of said one switch means for modulating said audio frequency
signal.
21. Electronic musical apparatus as in claim 20 where said
modulating means includes harmonic control means coupled to said
oscillator means for modifying the harmonic content of the audio
frequency signal output of said oscillator means said harmonic
control means including a variable symmetry chopper driven by said
oscillator means for producing a pulse type output signal having a
variable pulse width.
22. Electronic musical apparatus as in claim 21 together with
control means coupled to said chopper for varying said pulse
width.
23. Electronic musical apparatus as in claim 21 where said chopper
includes a saturated differential amplifier.
24. Electronic musical apparatus as in claim 21 where said
oscillator means produces sawtooth type signals and said chopper
clips said sawtooth signals to produce said pulse type output
signal.
25. Electronic musical apparatus as in claim 21 where said chopper
is coupled and responsive to said transducer means for varying the
pulse width of said output signal.
26. Electronic musical apparatus as in claim 20 where said touch
actuated switch means includes means responsive to the skin
pressure of a finger on a wire segment of said switch means for
modifying the frequency of said audio frequency signal of said
oscillator means.
27. Electronic musical apparatus as in claim 26 where said touch
actuated switch means includes a radio frequency oscillator for
generating an alternating signal which charges virtual capacitors
formed by said finger touching said wire segment said radio
frequency oscillator having an input current proportional to said
skin pressure said switch means also including control means
responsive to said input current for proportionately modulating
said frequency of said audio frequency signal.
28. Electronic musical apparatus as in claim 20 together with
filtering means having an input coupled to the modulated output of
said modulating means and an output to audio transducer means.
29. Electronic musical apparatus as in claim 28 where said
filtering means has a frequency filtering characteristic which is
variable to provide control of the timbre of said audio
frequency.
30. Electronic musical apparatus as in claim 29 where said
filtering means includes a plurality of .pi. sections comprising an
inductor and two capacitor legs together with switching means for
coupling said input and output to any two adjacent .pi. sections at
any one time for providing said variation of said filtering
characteristic.
31. Electronic musical apparatus as in claim 28 together with
impedance means coupled to said input of said filtering means
having an impedance different from the characteristic impedance of
said filtering means.
32. Electronic musical apparatus as in claim 31 where said
impedance means is variable to provide for control of the richness
of said audio frequency.
Description
BACKGROUND OF THE INVENTION
The present invention is directed in general to an electronic
musical apparatus and more particularly to musical apparatus of the
stringed type.
With the advent of solid state electronics the use of electronic
amplification for stringed instruments has been widespread. This
amplification has also included echo or reverberation effects
accomplished by introducing a time delay in one channel of
amplification.
The present invention is directed in general to an electronic
musical apparatus and more particularly to musical apparatus of the
stringed type.
With the advent of solid state electronics the use of electronic
amplification for stringed instruments has been widespread. This
amplification has also included echo or reverberation effects
accomplished by introducing a time delay in one channel of
amplification.
However, except for the elimination of an acoustic sounding box,
stringed instruments such as the guitar have been essentially
unchanged in their basic construction. In other words, present
amplified instruments have not provided a design in the music
producing and amplification portions which have been truly
integrated.
It is, therefore, a general object of the invention to provide an
improved electronic musical apparatus in which the electronic
portion is integrated with the music producing portion of the
apparatus.
It is another object of the invention to provide apparatus as above
which produces novel musical sounds and effects and greatly
increases the versatility of standard stringed instruments when
modified in accordance with the invention.
In accordance with the above objects there is provided electrical
musical apparatus comprising transducer means adapted for actuation
by a human hand. A plurality of touch actuated switch means are
provided each corresponding to a predetermined audio frequency
signal. Oscillator means are coupled to the switch means and are
responsive to the selective actuation of any one of the switch
means for generating an audio frequency signal corresponding to the
switch means which has been actuated. Modulating means are coupled
to the oscillator means and transducer means are responsive to the
actuation of the transducer means concurrently with the actuation
of one switch means for modulating the audio frequency signal.
FIG. 1 is a schematic representation of a musical instrument
embodying the present invention along with a schematic block
diagram illustrating the associated electronic portion of the
invention;
FIG. 2 is a detailed circuit schematic of a portion of FIG. 1;
FIG. 3 is a detailed circuit schematic of another portion of FIG.
1;
FIG. 4 is a circuit characteristic useful in understanding the
present invention;
FIG. 5 is a block diagram showing a modification of the circuit of
FIG. 1;
FIG. 6 is a block diagram showing another modification of the
circuit of FIG. 1;
FIG. 7 is a block diagram illustrating a modification of the output
circuit of FIG. 1;
FIG. 7A is a detailed schematic of a block of FIG. 7; and
FIG. 8 is a cross-sectional view of a modification of the stringing
arrangement of FIG. 1.
Referring first to FIG. 1, the present invention is shown in its
preferred embodiment as a guitar 10 which, as will be explained in
detail below, has been modified in accordance with the principles
of the present invention. However, it should be understood that the
present invention is applicable to any stringed instrument. Guitar
10 includes typical portions such as a neck 11 with a fingerboard
12, a head 13 having tuning machines 14a- f and a table portion 16
having stretch strings 17a-f mounted around rubber studs 18 by
springs 19. The strings are arranged so they may be plucked by
fingers or a plectrum. Strings 17a-f do not extend over the
fingerboard to the tuning machines 14a-f. Instead they are short
and lie only on the table 16.
The displacement of the strings is picked up by two sets of
piezoelectric transducers 21 and 22. The individual transducers are
constructed similarly to photograph pickups. Transducer set 21
physically contacts strings 17 slightly in front of studs 18 to
cause them to be primarily responsive to transverse mode vibrations
of the strings. Transducer set 22 contacts portions of strings 17
which are wrapped around studs 18 and are thus primarily responsive
to longitudinal mode vibrations.
As will be clearly apparent, the frequency of the musical signal is
not dependent upon the strings; rather only the amplitude and
partially the rise and fall duration of the musical sound is
determined by the strings 17a-f. Moreover, by controlling the
location at which the strings are plucked, the longitudinal or
transverse modes can be emphasized to achieve special sound
effects. For example, plucking near the transverse mode transducer
21 will produce a twanging effect.
Fingerboard 12 instead of having strings and being fretted to
produce a variation in musical pitch consists of columns of touch
plates 26a-f in the form of wire segments which correspond to or
simulate the strings which would otherwise be in those column
locations. In addition, each of the simulated string columns 26a-f
correspond to the tuning machines 14a-f and may in fact be tuned in
the same manner as a typical stringed guitar. More specifically,
each touch wire column 26a-f is arranged in a straight line and
each touch wire designated 27 simulates a specific fingering
position of a string in the same physical location. Thus, the
spacing and configuration of the touch wire 27 would be varied
depending upon the type of stringed instrument being simulated. For
example, with a classical guitar the touch wires 27 would be spaced
farther apart because of the wider neck of that guitar as opposed
to a "folk" type guitar with a narrower neck.
Each touch wire 27 is coupled to an individual switch 28 which is
activated when a finger of the player is placed on the wire. This
action places a virtual capacitor in the associated circuitry in a
well-known manner. FIG. 1 shows switches 28 coupled to only touch
wire column 26f. However, all touch wires would be connected to
their own touch sensitive switches.
Each column 26a-f of touch wires 27 and their associated
touch-actuated switches 28 are associated with an oscillator 29. As
shown in FIG. 1 the subscript of the oscillator 29f corresponds to
the simulated string; namely 26f. Touch actuated switches 28 are
coupled to oscillator 29f through a series of resistors 31f which
includes a V.sub.RF voltage supply on one end. V.sub.RF is provided
by a radio frequency oscillator 30 having an input power source +V
coupled through a resistor 33. The output R.F. signal modulates a
+V voltage supply which is a.c. isolated by a choke coil 34.
Oscillator 29f is also coupled to a corresponding tuning machine
14f which includes a variable resistor 32f which, as will be
explained in detail below, controls the basic frequency of
oscillation of oscillator 29f. The remaining tuning machines 14a-f
would be coupled to their respective oscillators 29a-e (not shown).
All of the oscillators 29a-f are respectively coupled to an
isolation amplifier 35a-f which prevents the loading of the
associated oscillators 29a-f by the subsequent circuits. Amplifier
35f is coupled into a balanced modulator 36f through series
resistors 37f and 38f. The balanced modulator is of a type
commercially available as a unit and produces no output in the
absence of a modulating input on line 39f.
Harmonic control means are coupled between resistors 37f and 38f
and include a balanced reactance modulator 41f having a capacitor
42f across its signal input, V.sub.in, and output terminals,
V.sub.out, 43f and 44f and a third modulation input terminal 46f
coupled to a potentiometer 47f. Output terminal 44f is coupled
between resistors 37f and 38f.
Potentiometer 47f provides either a null or zero input or is
variable between +V and -V voltage as indicated. Such inputs when
applied to modulating input control terminal 46f varies the gain of
the modulator 41f and in turn the value of capacitor 42f is
illustrated in FIG. 4. At 0 voltage gain (-.infin. dB) where
V.sub.out =0 the true value of the capacitor (C .times. 1) is in
the circuit; at unity gain inverted where V.sub.out = -V.sub.in the
effective value is doubled (C .times. 2); and at unity gain not
inverted where V.sub.out = V.sub.in the value is zero (C .times.
0).
Harmonic control is effected by variation in the effective value of
capacitor 42f which smooths or integrates the triangular waveform
output of oscillator 29 by attenuating its higher harmonics.
The audio signal from oscillator 29f and modulator 36f is coupled
through and modulated by a series connected balanced modulator 51f
having a modulation input 52f. The series cascading of the
modulators forms a combined modulation characteristic which is
logarithmic. Since the response of the human ear to sound is
non-linear a logarithmic characteristic partially compensates for
this nonlinearity. The above combination also produces a better
null than a signal modulator.
Both modulators 36a-f and 51a-f are respectively responsive to the
bowing or plucking of string means 17a-f to modulate the audio
frequency signals from the oscillators 29a-f in accordance with the
displacement of the strings 17a-f. Specifically, modulator 36f is
responsive to signals from transducer set 21 which are coupled to
its modulation input 39f through a stretching and shaping unit 53f.
This unit modifies the output of transducer set 21 by stretching
the output waveform, the amount of stretching being varied by a
control 54f, and delaying the production of the signal by means of
a delay attack control 56f.
Similarly, input 52f of modulator 51f is coupled to transducer set
22 through a stretching and shaping unit 57f having stretch and
delay control 58f and 59f.
The final modulated outputs of all balanced modulators 51a-f are
coupled to an amplifier 60 and speaker 61.
Means for muting the audio output of the apparatus is provided by
the associated circuitry of R.F. oscillator 30. A capacitor 62
coupled to the +V power input of the oscillator is responsive to
the change in power requirements when the touch activated switches
are deactivated. The resultant change in stored charge is coupled
through a conductor 63 to stretching and shaping circuits 53a-f,
57a-f causing these circuits in turn to disable the modulators
36a-f, 51a-f; in other words, zero modulation is produced on inputs
39a-f and 52a-f. Details of the muting circuit are shown in FIG.
3.
Several alternative schemes are also available for muting. For
example, a threshold circuit may be placed in line 63 so that
muting will occur only if a predetermined number of switches 28 are
deactivated. For a more complete control arrangement each simulated
string column 26a-f may have a separate R.F. oscillator 30 with
individual muting controls.
Simultaneous tuning of all simulated strings (or a simulated
"capo") is achieved in the present invention by connecting variable
resistors 32a-f to a common junction 66 and varying the voltage
level of the junction. This simultaneously shifts the frequencies
of oscillators 29a-f by a common amount. An option switch 67
coupled to junction 66 to either a foot pedal operated continuous
potentiometer 68 or a detented potentiometer 69. Foot pedal 68 may,
of course, be detented if desired.
Special effects can be achieved by feeding an a.c. signal to the
junction 68 in effect modulate the tuning voltage. Also either or
both tuning potentiometers may be ganged with other electronic
musical apparatus embodying the present invention to in effect
allow an entire band to easily tune to various musical keys.
In operation, the electronic musical apparatus of the present
invention is initially tuned by varying the knobs on tuning
machines 14a-f. Oscillators 29a-f, in effect, produce the
fundamental mode frequencies which would be produced by unfretted
strings. Movement of the finger up the fingerboard 12 along a given
column of touch segments 27 gradually cuts out resistors of
resistor string 31 to increase the frequency of oscillation of
oscillator 29 in the same manner and proportion as an actual string
which is fretted. More specifically, for example, the oscillator 29
vibrates at the fundamental frequency of the string which it
represents and then as the touch segments 27 are activated it will
increase in frequency in accordance with the touch segment
corresponding to that fret position.
The use of simulated tuning machines 14a-f and touch wire columns
26a-f, in the same location as they would be for an actual stringed
guitar, makes adaptation to the electronic musical apparatus of the
present invention extremely easy for the experienced player of an
actual stringed instrument.
The specific audio frequency signal or combination of frequency
signals which are applied to the modulators 39 and 51 by
oscillators 29a-f are modulated by the displacement of the strings
17a-f. This displacement is represented as an electrical waveform
which can be stretched in time by means of stretching adjustments
54, 58 or the delay attack controls 56, 59 to achieve special
effects. The outputs of stretching and shaping circuits 53f and 57f
are also coupled to the input terminal 46 of balanced reactance
modulator 41 to cause the harmonic content of the audio output to
vary in accordance with the modulation signal.
FIG. 2 shows greater details of a touch-sensitive switch 28 along
with oscillator 29f. The capacitance produced when the finger
touches the touch plate 27 is shown by a virtual capacitor 70. This
capacitor is coupled into the switch 28 between diodes 71 and 72
through a d.c. blocking capacitor 73 which guards against shocks to
the player of the apparatus and also protects the diodes and
transistors against accidental grounding. Diode 72 is coupled to
the base of a transistor Q1 and diode 71 to the emitter of Q1. The
emitter of Q1 is also coupled through a d.c. blocking capacitor 74
to the radio frequency oscillator 30. This may be of a frequency of
from 1 to 75 megahertz and provides for operation of the
touch-sensitive switch in a manner well-known in the art. The
collector of Q1 is coupled to a resistor string 31f coupled in turn
to oscillator 29f; more specifically to the emitter of an
unijunction transistor Q2.
A capacitor 76 is also coupled to the emitter of Q2 and provides
the basic free-running frequency of the oscillator. One of the
input terminals of Q2 is grounded and the other connected between
series connected resistors 77 and 78. These resistors are also
coupled to the respective tuning machine resistors 32a-f (in this
case 32f) to vary the biasing of Q2 to determine the oscillation
frequency of oscillator 29f in combination with capacitor 76. More
specifically, the discharge point of capacitor 76 is determined by
Q2 and its charging rate is determined by the number of resistors
in resistor string 31f. The fewer in number of resistors the faster
the charging rate; therefore, the higher the frequency the higher
the pitch. Oscillator 29 because of the above construction produces
a sawtooth type output. In addition, the use of a unijunction type
transistor allows the frequency of oscillation to be linearly
varied with the above change in resistance.
The output of oscillator 29f is coupled to an isolation amplifier
in the form of a field effect transistor whose purpose is to
prevent the loading of the oscillator by the subsequent balanced
modulators.
A typical stretching and shaping circuit is shown in greater detail
in FIG. 3. The output from transducers 21 or 22 is coupled into a
transistor Q3 which is coupled to waveshaping circuits which
include a potentiometer 81 and a switch 82 which may be switched
between three capacitors 83, 84 and 85. The potentiometer and
switch may be joined together as shown by the dashed line 46 which
will in effect be the stretch switches 54, 58 of FIG. 1. The output
of waveshaping circuit 81, 82 is coupled into the base input of a
transistor Q4. The emitter output of Q4 is coupled to a switch 86
which also includes three capacitors to provide for delay of the
signal which is then coupled to balanced modulators 36, 51.
The shaping circuit of FIG. 3 may be elaborated on and modified
extensively. For example, resonant circuits and feedback circuits
may be used when desired.
In order to achieve a greater degree of harmonic control of the
output of oscillator 29, a variable symmetry chopper circuit may be
used in place of balanced modulator 41f and capacitor 42f. Such a
modification of the circuit of FIG. 1 is illustrated in FIG. 5
where the output of an isolation amplifier 35f, which is in the
form of a triangular waveshape 101, is coupled to a variable
symmetry chopper 102f. This chopper is driven by the oscillator 29f
and produces a pulse type output 102 on an output line 103 which is
coupled to balanced modulator 36f.
Chopper 102f is actually in the form of a saturated differential
amplifier and includes transistors 104 and 105 having their
emitters coupled together and to a negative voltage source and
their collectors coupled through resistors to a common positive
voltage source. A Schmitt trigger circuit may alternatively be
used. However, the base input of transistor 105 is coupled to
potentiometer 47f along with the outputs of stretching and shaping
circuit 52f and 53f to vary the point on the waveshape 101 at which
the chopper clips. This causes a variation in the symmetry of the
pulse train 102 as illustrated by the dashed outline 107. In other
words, the actual pulse width of pulse train 102 is varied in
accordance with the control input voltage on the base of transistor
105 to provide pulses of variable width.
In accordance with well known Fourier analysis a change in width
will change the harmonic content of the pulse train 102 with a
greater width producing lower harmonics and the narrower width
producing a higher ratio of upper harmonics. Thus, by variation of
the pulse width the harmonic content of various stringed
instruments can be approximated. Moreover, since the control input
to the base of transistor 105 is also coupled to the output of the
stretching and shaping circuits 52f and 53f a variable harmonic
content can be produced during the plucking of a single string.
This can produce, for example, a familiar twanging sound.
Another variation in circuitry which allows the user of the musical
apparatus to supply a tremolo or vibrato is illustrated in FIG. 6.
Here the RF oscillator 30 is shown with its input current being
supplied from a positive voltage source through resistor 33.
Variation of the skin pressure produced by the finger on one of the
touch plates 27 shown in FIG. 1 causes a change in the input
current of the RF oscillator and the voltage on resistor 33.
Further in accordance with the invention a control unit 110 along
with a sensitivity control 111 is coupled to resistor 33 and to the
line 66 which controls the tuning of the musical apparatus of the
present invention. As discussed previously, the tuning controls
modify the frequency of oscillation of the oscillators 29a-f. Since
control unit 110 feeds back a portion of the voltage across
resistor 33, variation of this voltage will also cause a
concommitant change in the tuning voltage to thus produce the
desired vibrato effect in response to a variation of the skin
pressure on the touch plates. The amount of tremolo or vibrato is
controlled by sensitivity control 111.
Similarly, control unit 110 may be coupled to choppers 102a-f and
to stretching and shaping circuits 53a-f, 57a-f to provide for
special effects modulation.
Further control of the audio output of the musical apparatus of the
present invention is provided by the use of a filtering circuit at
the output of amplifier 60 and the input of loudspeaker 61.
Filtering means 112, as illustrated in FIG. 7, includes four filter
components designated 112a through 112d each having a richness
control 113 and timbre control 114. The richness controls in the
preferred embodiment are ganged together. FIG. 7A shows a typical
filter 112a which includes a plurality of .pi. sections each having
an inductor and two capacitors. The timbre control 114 ties to
ground the capacitors of two .pi. sections and bridges across the
inductors of these .pi. sections to provide input and output
terminals which are respectively coupled to the amplifier 60 and
loudspeaker 61. However, the input terminal has series connected to
it a potentiometer 113 which is actually the richness control. In
practice, potentiometer 113 has a maximum impedance substantially
equal to the characteristic impedance of the filter 112a. Since the
output terminal of the filter is not terminated there will be a
mismatch at the output and a variation of richness control 113 from
its characteristic impedance value causes a mismatch in the input
to provide reflections. This provides additional richness in the
output signal of loudspeaker 61. Additional variation in timbre is
achieved by moving the ganged switch 114.
Although four filters 112a-d are shown in FIG. 7, additional
filters may be used and ganged as desired to produce different
sound effects.
Furthermore in addition to the use of filters between amplifier 60
and loudspeaker 61 the same type of filters may be used at the
several inputs to amplifier 60 to individually change the
characteristic of the audio frequency signal output from the
balanced modulators 51a-f.
FIG. 8 shows a modification of the stringing arrangement of FIG. 1.
Here the string 116 is coupled directly to two rubber grommets 117a
and 118a. Tension may be provided by a cylindrical wedge (not
shown) in either of the grommets. This construction may be
desirable for some applications over the spring type construction
shown in FIG. 1 where a spring 19 is used.
It is apparent from the foregoing description that many different
types of sound effects which may be produced by the present
invention involve the manipulation of several control knobs. Thus,
the present invention contemplates the use of matrix cards or
similar type devices for presetting the controls.
Thus, the present invention provides an improved electronic musical
apparatus where the fingerboard of the stringed instrument is
actually simulated by capacitive-type touch switches allowing
greater ease of playing. This also provides more accurate frequency
output of the instrument and allows for greater versatility and
production of different types of sound effects from the instrument
so modified. In addition, the use of strings merely for modifying
the amplitude and rise and fall time etc. of the output frequencies
again allows a greater versatility in the sound quality of the
instrument.
* * * * *