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Claims  |
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What is claimed is:
1. A sustainer for a musical instrument having a vibratory element
comprising:
(a) drive means responsive to a drive signal for applying a drive force to
a vibratory element of said instrument so that said drive force has a
predetermined phase relationship to said drive signal; and
(b) feedback means for accepting a pickup signal representing vibration of
a vibratory element of said instrument and having a predetermined phase
relationship to said vibration and providing said drive signal to said
drive means so that said drive force is substantially in phase with
vibration of said vibratory element.
2. A sustainer as claimed in claim 1 further comprising pickup means for
producing said pickup signal responsive to vibration of the vibratory
element of the instrument and providing said pickup signal to said
feedback means.
3. A sustainer as claimed in claim 2 wherein at least one of said pickup
means and said drive means has a non-zero phase transfer function and
wherein said feedback means has a phase transfer function substantially
inverse to the combined phase transfer function of said pickup means and
said drive means.
4. A sustainer as claimed in claim 1 or claim 3 further comprising
self-contained power supply means and means for mounting said power supply
means to the instrument, said feedback means including means for providing
power in said drive signal from said power supply means.
5. A sustainer for a musical instrument having a vibratory element, said
sustainer comprising feedback means for accepting a pickup signal
representing vibration of the vibratory element of the instrument and
converting said pickup signal to a drive signal so that for at least some
frequencies of said pickup signal said drive signal differs in phase from
said pickup signal and said phase difference varies with frequency, such
variation being towards a drive signal leading phase difference with
increasing frequency, and drive means for applying a drive force to the
vibratory element of the instrument responsive to said drive signal.
6. A sustainer as claimed in claim 5 wherein said drive means is operative
to apply said drive force to the vibratory element of the instrument so
that said drive force lags said drive signal for said at least some
frequencies.
7. A sustainer as claimed in claim 6, further comprising pickup means for
producing a pickup signal responsive to vibration of the vibratory element
of the instrument.
8. A sustainer as claimed in claim 7 wherein, for at least some frequency
said feedback means is operative to provide lead in said drive signal
relative to said pickup signal.
9. A sustainer as claimed in claim 8 further comprising self-contained
power supply means and means for mounting said power supply means to the
instrument, said feedback means including means for providing power in
said drive signal from said power supply.
10. A sustainer as claimed in claim 6 wherein said drive means includes an
inductive drive coil and means for applying said drive force to the
vibratory element of the instrument responsive to magnetic flux in said
coil, and said feedback means includes means for applying said drive
signal as a voltage across said coil.
11. A sustainer as claimed in claim 10 wherein said means for applying said
drive force responsive to said flux includes means for mounting said coil
to the instrument so that magnetic flux from said coil will impinge upon
the vibratory element of the instrument.
12. A sustainer as claimed in claim 11 wherein said mounting means includes
means for mounting said drive coil to an instrument having at least one
string as a vibratory element so that said drive coil is juxtaposed with
said a least one string.
13. A sustainer as claimed in claim 12 wherein said means for mounting said
drive coil to the instrument includes means for mounting said drive coil
to an instrument having a plurality of strings, and said means for
applying said drive force includes means for directing flux from said coil
to all of said plurality of strings.
14. A musical instrument comprising a sustainer as claimed in claim 13, a
structure, a plurality of strings mounted to said structure, and pickup
means for detecting vibratory motion of said strings and providing said
pickup signal to said feedback means.
15. A sustainer for a musical instrument having a vibratory element, said
sustainer comprising feedback means for accepting a pickup signal
representing vibration of at least one vibratory element of the instrument
and converting said pickup signal to a drive signal, drive means for
applying a drive force to the vibratory element of the instrument
responsive to said drive signal and control means for determining the
frequency content of said pickup signal and altering the phase transfer
function of the sustainer depending on said frequency content.
16. A sustainer as claimed in claim 15 wherein said control means includes
means for detecting a predominant frequency in said pickup signal having
the greatest amplitude and providing a signal representing said
predominant frequency and means for adjusting the phase transfer function
of at least one of said feedback means and said drive means in response to
said signal representing said predominant frequency.
17. A sustainer as claimed in claim 16 wherein said drive means includes
means for applying said drive force to a plurality of vibratory elements
whereby when said pickup signal includes signals representing vibration of
a plurality of vibratory elements, all vibrating at different frequencies,
said sustainer will selectively reinforce the vibration of the vibratory
element having the greatest amplitude.
18. A sustainer as claimed in claim 16 wherein said control means includes
means for adjusting the phase transfer function of said feedback means in
response to said signal representing said predominant frequency.
19. A sustainer as claimed in claim 18 wherein said feedback means includes
an input connection for receiving said pickup signal, an output connection
for delivering said drive signal and a network having a pickup signal
infeed node connected to said input, an operational amplifier having
inverting and noninverting inputs and an output connected to said output
connection, a resistor connected between said pickup signal infeed node
and one said input of said operational amplifier, a capacitor having a
first side connected to said pickup signal infeed node and a second side
connected to the other one of said operational amplifier inputs, and a
variable value resistance element connected between said second side of
said capacitor and ground, said means for adjusting said phase transfer
function of said feedback means including means for varying the resistance
of said variable resistance element inversely to the predominant frequency
of said pickup signal.
20. A sustainer as claimed in claim 16 wherein said control means includes
means for adjusting the phase transfer function of said drive means in
response to said signal representing said predominant frequency.
21. A sustainer as claimed in claim 1 or claim 5 or claim 15 further
comprising alternate signal means for providing said drive signal
responsive to said pickup signal, the phase transfer function of said
alternate signal means being different from the phase transfer function of
said feedback means, and selector means for selectively actuating either
said feedback means or said alternate signal means.
22. A sustainer as claimed in claim 21 wherein said alternate signal means
includes lag network means for providing said drive signal so that said
drive signal lags said pickup signal and said lag increases with
frequency.
23. A sustainer as claimed in claim 22 wherein said alternate signal means
further includes straight-through means for providing said drive signal in
phase with said pickup signal, said selector means including means for
selectively actuating either said lag network means or said
straight-through means.
24. A sustainer as claimed in claim 1 or claim 5 or claim 15 further
comprising automatic gain control means for controlling said feedback
means to maintain said drive signal at a predetermined magnitude, and
means for adjusting said automatic gain control means to alter said
predetermined magnitude.
25. A sustainer as claimed in claim 24 wherein said feedback means includes
an output amplifier for producing said drive signal and means defining a
signal path leading to said output amplifier, said automatic gain control
means including a variable impedence connected in said signal path and
means for controlling said variable impedence responsive to the magnitude
of said drive signal.
26. A sustainer for a musical instrument of the type having a plurality of
strings extending in generally a lengthwise direction and disposed
side-by-side so as to define an array extending in lateral directions
transverse to said lengthwise direction, said sustainer comprising:
(a) means for providing a drive signal; and
(b) drive means responsive to said drive signal for applying drive forces
to the strings of the instrument at a drive location remote from the ends
of the strings so that the drive force applied to each said string is
substantially independent of lateral displacement of such string.
27. A sustainer as claimed in claim 26 wherein said drive means includes
means for providing a magnetic field varying in accordance with said drive
signal so that said varying magnetic field is substantially uniform
throughout the lateral range of motion of each string of the instrument at
said drive location.
28. A sustainer as claimed in claim 27, wherein said means for providing a
varying magnetic field includes a ferromagnetic element, means for
directing magnetic flux through said ferromagnetic element, and means for
mounting said ferromagnetic element to the instrument so that said
ferromagnetic element extends laterally across the entire width of said
array in proximity to said strings.
29. A sustainer as claimed in claim 28 wherein said means for providing
said varying magnetic field includes a coil juxtaposed with said
ferromagnetic element.
30. A sustainer as claimed in claim 29 wherein said coil encircles said
ferromagnetic element.
31. A sustainer as claimed in claim 30 herein said ferromagnetic element
includes a permanent magnet.
32. A sustainer as claimed in claim 30 wherein said means for providing a
varying magnetic field includes a second ferromagnetic element and a
second coil encircling said second ferromagnetic element said mounting
means including means for mounting said second ferromagnetic element to
the instrument so that said second ferromagnetic element extends laterally
across said array in proximity to said strings, said second coil being
wound in the opposite direction from the first said coil.
33. An instrument comprising a body, a plurality of strings mounted to said
body, a sustainer as claimed in claim 31, said permanent magnet of said
sustainer being mounted to said body, and a pickup incorporating a
permanent magnet mounted to said body, said permanent magnets being
mounted to said body so that flux from said permanent magnet of said
driver is codirectional with flux from the closest portion of said
permanent magnet of said pickup.
34. A sustainer as claimed in claim 29 wherein said means for mounting said
ferromagnetic element includes means for mounting said ferromagnetic
element to the instrument so that a surface of said ferromagnetic element
faces said strings and extends substantially parallel to the imaginary
surface defined by said strings when said strings are in an undisturbed
condition.
35. A sustainer as claimed in claim 27 wherein said means for providing a
varying magnetic field includes a coil and means for mounting said coil to
the instrument so that said coil encircles said strings.
36. A sustainer as claimed in claim 35 further comprising two ferromagnetic
elements, at least one of said ferromagnetic elements including a
permanent magnet, and means for mounting both said ferromagnetic elements
to the instrument so that said ferromagnetic elements are jutaposed with
one another above and below said strings and said ferromagnetic elements
are spaced apart from one another in the lengthwise direction of said
strings, said means for mounting said coil including means for mounting
said coil between said ferromagnetic elements. |
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Claims |
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Description |
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The present invention relates to a device for providing a sustained sound
from a musical instrument having a vibratory element such as a string.
BACKGROUND OF THE INVENTION
Musical instruments employing a vibrating mechanical element such as a
string to produce sound have been provide heretofore with transducers
commonly referred to as "pickups" for detecting the motion of the
vibrating element and producing an electronic signal representing this
vibration. This pickup signal may be amplified and converted to sound by a
loudspeaker. The sound produced from the pickup signal supplements or
replaces the sound produced by acoustical interaction of the string, the
instrument body and the air. Typically, the instrument body has little or
no acoustic response, so that the sound produced from the pickup signal
constitutes essentially the entire sound of the instrument. This is the
case in the common electric guitar, electric bass and the like.
The sound produced by instruments of this nature dies out progressively
after the string is excited. This is particularly so in the case of
instruments having little or no independent acoustic response. The sound
can be prolonged somewhat by operating the amplification and loudspeaker
system at extremely high power levels so that strong acoustic waves
representing the original vibration impinge upon the string. Such
"acoustic feedback" tends to sustain the vibration of the string, thereby
prolonging the note. However, this approach is effective only when the
sound produced by the amplification an loudspeaker system is
extraordinarily loud. Moreover, the acoustic feedback effect depends upon
the acoustic properties of the environment. Therefore, this effect will
produce different results in different concert halls
Various attempts have been made to provide a "sustainer" or device capable
of prolonging the notes independently of acoustic feedback from the
environment U.S. Pat. No. 4,245,540 discloses a sustainer incorporating a
loudspeaker mounted in close proximity to the strings. The amplified
signal from the pickup is passed to the loudspeaker, so that acoustic
vibrations produced by this loudspeaker will impinge directly upon the
strings. U.S. Pat. No. 4,697,491 discloses a sustainer for a tringed
instrument such as a guitar having a body and a neck projecting from the
body. An electromechanical transducer is mounted to the neck, remote from
the body. The pickup signal is passed to this electromechanical
transducer. The transducer vibrates the neck and these vibrations are fed
back into the strings. U.S. Pat. No. 3,813,473 discloses an instrument
having a "bridge" or string support linked to an electromagnet. An
electronic signal derived from the pickup signal is applied to this
electromagnet, so as to vibrate the bridge and, hence vibrate the strings.
U.S. Pat. No. 4,484,508 describes a generally similar sustainer having an
electromechanical transducer adapted to shake the instrument body
responsive to the pickup signal, and also having a circuit for
progressively reducing the amplitude of the signal so as to provide a
controlled fadeout. The fadeout circuit is arranged to provide a quicker
fadeout for higher frequency signals.
U.S. Pat. Nos. 4,137,811 and 4,181,058 provide a sustain action utilizing
magnetic interaction between a static magnetic field and electrical
currents passing through the strings themselves. Thus, a magnet is mounted
adjacent the strings, and both the strings and frets of the instrument are
electrically conductive. Circuitry is provided for directing an
alternating current feedback signal representing the pickup signal through
the strings via the frets. The alternating current in each string
interacts with the static magnetic field to produce an alternating
magneto-motive drive force on the string. U.S. Pat. No. 4,236,433
discloses a sustainer employing an electromagnetically actuated tensioning
device for each string, each such tensioning device being connected to a
feedback circuit. The signal from a pickup associated with each string is
applied through the feedback circuit to the tensioning device, so that the
tensioning device will periodically stretch and release the string. The
'433 patent also discloses an alternative arrangement wherein an
electromagnet or "driver" is juxtaposed with each string so that flux from
the electromagnet will impinge directly upon the string. Each such
electromagnet is provided with a drive signal representing the signal from
a pickup associated with the same string. Thus, variations in magnetic
flux of the electromagnet will cause variations in the flux impinging upon
the strings. This varying flux tends to excited the string in vibration,
provided the string itself is ferromagnetic. U.S. Pat. No. 4,075,921
discloses a generally similar approach, employing a magnetic pickup and a
magnetic driver arranged to directly excite a ferromagnetic string. The
sustainer may be a hand held, battery-powered device incorporating both a
pickup and a driver, and arranged so that the pickup and driver can be
aligned with one string of the instrument. Alternately, the sustainer may
be built into the instrument and may be provided with separate pickups and
drivers for the various strings. U.S. Pat. No. 3,742,113 likewise employs
a magnetic pickup and magnetic driver directly associated with each
string, with a feedback and amplification circuit connected between the
pickup and the driver. The ' 113 patent emphasizes that the feedback
circuit or amplifier should have "zero phase shift" so as to provide a
driving force "in phase with the string's fundamental frequency of
oscillation as transduced by the pickup" so as to reinforce the
fundamental mode vibration of the string.
The aforementioned '921, '433 and '113 patents utilize pickups and drivers
having a separate ferromagnetic pole piece disposed beneath each string,
so as to provide a substantially concentrated magnetic field from each
pole piece at normal, undistorted position of the associated string.
Separate coils may be provided for each pole piece. U.S. Pat. Nos.
4,580,481 and 4,535,668 disclose a pickup having a unitary, oblong coil
and ferromagnetic core extending laterally across the string array.
Movable permanent magnets are also provided. By repositioning the
permanent magnets, the field direction can be varied s as to provide
different phase relationships among the signals induced in the coil by the
various strings. U.S. Pat. No. 3,983,777 suggests a pickup having a
uniform magnetic field strength across the lateral extent of the string
array to suppress variations in pickup response caused by lateral movement
of the strings. Other unitary pickups having a single coil and a single
ferromagnetic pole piece extending across the string array are shown in
U.S. Pat. Nos. 4,364,295 and 4,151,776.
Despite the extensive efforts of the art heretofore, there have been
substantial, unmet needs for further improvement. The sustainers available
heretofore generally have been inefficient, in that they require
substantial electrical power to the drive coil in order to produce an
appreciable sustain effect. This high power consumption poses a
significant problem where the sustainer draws its power from a battery
mounted on the instrument.
Moreover, application of high power to an electromagnetic drive coil in a
sustainer tends to produce substantial electromagnetic emissions.
Electromagnetic fields radiated rom the drive coils impinge upon the
pickup and induce unwanted signals. Although the pickups used in
electronic musical instruments typically incorporate features for
suppressing the effect of stray electromagnetic radiation, these measures
are not always perfectly effective. Radiation from the driver can be
suppressed to some degree by shielding, but such shielding adds weight,
bulk and cost. Thus, there has been a substantial need heretofore for an
efficient sustainer capable of providing a powerful sustaining effect with
only a modest power input to the driver. There has been a further need for
a sustainer which would permit the musician to adjust the action of the
sustainer to provide varied artistic effects.
SUMMARY OF THE INVENTION
The present invention addresses these needs.
A sustainer according to one aspect of the present invention is adapted for
use with a musical instrument having at least one vibratory element, which
may be a string or the like. The sustainer includes drive means for
applying a drive force to a vibratory element of the instrument responsive
to the drive signal so that the drive force bears a predetermined phase
relationship to the drive signal. Feedback means are provided for
accepting a pickup signal representing vibration of the vibratory element
of the instrument and having a predetermined phase relationship to the
vibration. The feedback means are arranged to provide a drive signal to
the drive means such that the drive force applied by the drive means will
be substantially in phase with the vibration of the vibratory element. The
sustainer may further include a pickup for providing the pickup signal in
response to the vibration of the string.
One or both of the pickup means and the drive means typically will have a
non-zero phase shift. That is, the pickup signal produced by the pickup
means may lag or lead the actual movement of the vibratory element,
whereas the drive force applied by the drive means may lag or lead the
drive signal. The feedback means preferably is arranged to provide a phase
shift which is substantially inverse to the combined phase shift of the
pickup means and the drive means, taken together. Thus, the combined
overall phase shift of the entire sustainer will be approximately zero and
the drive force will be applied i phase with the vibratory motion of the
string itself, i.e., in phase with the sustainers according to this aspect
of the invention can provide a powerful, sustaining action to prolong the
fundamental mode vibration of a string or other vibratory element with
only modest power input to the driver. Such sustainers according to the
invention can provide sustaining action suitable for prolonged, continuous
use, as in a concert environment, while employing only small,
self-contained batteries as a power supply. Although the present invention
is not limited by any theory of operation, it is believed that the
enhanced results achieved arise at least in part from better phase
matching of the force applied to the vibratory element and the actual,
fundamental mode vibration of the vibratory element.
The feedback means may be arranged so that for at least some frequencies of
the pickup signal, the drive signal differs in phase from the pickup
signal and this phase difference varies with frequency. Most desirably,
such variation in the phase difference between the pickup and drive
signals is towards a drive signal leading phase difference with increasing
frequency. Preferably, the feedback means is operative to provide the
drive signal so that for at least some frequencies, the drive signal leads
the pickup signal.
Control means may be provided for determining the frequency content of the
pickup signal and altering the phase transfer function of the feedback
means, the phase transfer function of the drive means or both depending
upon this frequency content. Thus, the control means may include means for
adjusting the phase transfer function of the feedback means towards a
drive signal leading condition as the predominant or highest amplitude
frequency of the pickup signal increases.
The drive means may include an inductive coil and means for applying he
drive force to the vibratory element responsive to magnetic flux produced
by the coil. The force applied by drive means employing an inductive coil
tends to lag behind the drive signal or voltage applied to the coil.
Moreover, this lag increases with the frequency of the signal. Thus, the
phase difference and variation in phase difference with frequency provided
by the feedback means according to this aspect of the present invention
come for the characteristics of the drive means. Where the pickup signal
provided by typical electromagnetic pickups tends to lag behind the actual
motion of the vibratory element or string, and where this lag likewise
increases with frequency the phase difference and the variation in phase
difference with frequency provided in the feedback means of the preferred
sustainers are believed to compensate for the characteristics of the
pickup as well. The net result is to provide a drive force substantially
in phase with the fundamental motion of the vibratory element.
The feedback means most preferably includes a network having an input for
receiving a pickup signal, an output for delivering the drive signal and a
variable value component connected between the input and output. The
network may be arranged so that adjustment of the variable valuable
component alters the phase transfer function of the network, i.e., the
relationship between phase shift through the network and frequency. The
control means may include means for monitoring the frequency of the pickup
signal and adjusting the value of the variable value component response to
the frequency of the pickup signal so as to alter the phase transfer
function of the network. The pickup signal is typically a complex signal,
incorporating components at various frequencies. Desirably, the means for
monitoring the frequency of the pickup signal is arranged to detect the
predominant frequency in the pickup signal, having the greatest amplitude,
and to provide a signal representing this predominant frequency. The means
for adjusting the value of the variable value component desirably includes
means for adjusting this value dependent upon the signal representing the
predominant frequency. This arrangement provides a selective sustain
effect, in that the sustainer is adjusted to provide the optimum phase
transfer function for the reinforcement of particular frequencies having
the greatest amplitude.
A further aspect of the present invention provides a sustainer for a
musical instrument of the type having a plurality of taut, flexible
strings extending in a lengthwise direction and disposed side-by-side in
an array. The sustainer according to this aspect of the invention includes
means for providing a drive signal and drive means for applying drive
forces to the strings responsive to the drive signal so that the drive
force applied to each string is substantially independent of lateral
displacement of the string. Therefore, the response of the sustainer is
substantially unaffected by lateral bending of the strings.
Preferably, the drive means includes means for providing a magnetic field
varying in accordance with the drive signal so that the varying magnetic
field is substantially uniform throughout the range of lateral motion of
each string. The means for providing a varying magnetic field may include
a ferromagnetic element, means such as a coil juxtaposed with this element
for directing magnetic flux through the ferromagnetic element and means
for mounting the ferromagnetic element so that it extends laterally across
the string array. The surface of the ferromagnetic element facing toward
the strings may be substantially parallel to an imaginary surface defined
by the strings when in their normal, undistorted position. The
ferromagnetic element employed in this arrangement preferably includes a
permanent magnet.
In an alternate arrangement, the coil encircles the strings. A pair of
ferromagnetic elements such as permanent magnets may be spaced apart from
one another in the lengthwise direction of the strings and disposed above
and below the string array, with the coil encircling the strings between
these elements.
These and other objects, features and advantages of the present invention
will be more readily understood from the detailed description of the
preferred embodiment set forth below, taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic perspective view of a sustainer in accordance with
one embodiment of the present invention, in conjunction with a musical
instrument.
FIGS. 2 and 3 are fragmentary, schematic sectional views taken along lines
2--2 and 3--3 respectively in FIG. 1.
FIG. 4 is a functional block diagram of the sustainer and instrument shown
in FIG. 1.
FIG. 5 is a schematic circuit diagram showing a portion of the sustainer of
FIGS. 1-4.
FIG. 6 is a graph of certain variables associated the sustainer of FIGS.
1-5.
FIG. 7 is a fragmentary schematic circuit diagram depicting a portion of a
sustainer according to a further embodiment of the invention.
FIG. 8 is a schematic, fragmentary perspective view depicting a portion of
a sustainer in accordance with another alternate embodiment of the
invention.
FIG. 9 is a fragmentary, schematic sectional view taken along lines 9--9 in
FIG. 8.
FIG. 10 is a fragmentary perspective view similar to FIG. 8 but depicting a
sustainer in accordance with another embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A conventional electric guitar 20 has a structure including a body 22 and
an elongated neck 24 projecting from the body. A conventional tailstock 26
and bridge 28 are secured to body 22, whereas a headstock 30 is secured to
the end of neck 24 remote from head 22. Frets 25 are arranged along neck
24. Six ferromagnetic, typically steel strings 32 are held under tension
by tailstock 26 and headstock 30, and engaged with bridge 28 so that each
string extends generally in the same, longitudinal direction from the
tailstock to the headstock, the strings being disposed side-by-side above
the neck 24 and body 22. The strings thus define an array having a
widthwise direction transverse | | |
