U.S. patent number 3,920,905 [Application Number 05/441,031] was granted by the patent office on 1975-11-18 for production of non-frequency proportional vibrato.
This patent grant is currently assigned to CBS Inc.. Invention is credited to Paul H. Sharp.
United States Patent |
3,920,905 |
Sharp |
November 18, 1975 |
Production of non-frequency proportional vibrato
Abstract
Non-frequency proportional vibrato and like effects are achieved
by cooperation of a device such as a modulated analog shift
register that by itself produces frequency proportional modulation
and other components which dynamically shift the frequency or phase
of the processed signal. In one embodiment, the input signal is
offset downward in frequency by -.DELTA.f, processed by a modulated
bucket brigade device, and subsequently shifted back in frequency
by an amount +.DELTA.f. In another embodiment, the signal is passed
serially through a dynamic phase shifter and a modulated bucket
brigade delay line. By driving the phase shifter and the delay line
synchronously, the separately introduced modulation effects may be
partially cancelled. The output signal from each embodiment
exhibits vibrato or like modulation having non-frequency
proportional percentage frequency deviation characteristics.
Inventors: |
Sharp; Paul H. (Sierra Madre,
CA) |
Assignee: |
CBS Inc. (New York,
NY)
|
Family
ID: |
23751219 |
Appl.
No.: |
05/441,031 |
Filed: |
February 11, 1974 |
Current U.S.
Class: |
381/62; 84/706;
984/312 |
Current CPC
Class: |
G10H
1/045 (20130101) |
Current International
Class: |
G10H
1/045 (20060101); G10H 1/04 (20060101); G10H
001/04 () |
Field of
Search: |
;179/1J ;84/1.25 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cooper; William C.
Assistant Examiner: Kemeny; E. S.
Attorney, Agent or Firm: Flam & Flam
Claims
Intending to claim all novel, useful and unobvious features shown
or described, the applicant claims:
1. In apparatus for electronic superposition of vibrato upon
electrical impulses having a spectrum extending throughout a
substantial frequency range:
a. means forming an electrical input and and electrical output for
said apparatus;
b. a first modulator for superimposing vibrato upon said electrical
impulses with a depth of swing or frequency deviation substantially
proportional to the frequency of the impulses;
c. a second modulator for superimposing vibrato upon said
electrical impulses with a substantially constant frequency
deviation;
d. means serially connecting said modulators between said
electrical input and electrical output; and
e. common means for controlling said vibrato modulators in
synchronism at a selected vibrato rate whereby the frequency swing
of the superimposed vibrato of said modulators is algebraically
additive controllably to change the characteristics of the vibrato
spectrum from a linear frequency relationship.
2. The apparatus as set forth in claim 1 in which said modulators
are connected in opposition whereby frequency shift is
proportionately more greatly reduced at the lower spectrum.
3. The apparatus as set forth in claim 1 in which said first
modulator is an analog shift register having a clocking means and
in which said second modulator includes an impedance element that
is dynamically changed, said common means being a low frequency
oscillator in control both of said clocking means and said
dynamically changed impedance.
4. The apparatus as set forth in claim 1 in which said first
modulator is an analog shift register having a clocking means and
in which said second modulator comprises a series of networks each
including an impedance element dynamically changed, said common
means being a low frequency oscillator in control both of said
clocking means and all of the dynamically changed impedances of
said networks.
5. In apparatus for electronic superposition of vibrato upon
electrical impulses having a spectral range extending throughout a
substantial frequency range:
a. a modulator for superimposing vibrato upon said electrical
impulses with a depth of swing or frequency deviation substantially
proportional to the frequency of the impulses;
b. a first device for superimposing a substantially constant
frequency shift upon said electrical impulses;
c. a second device for superimposing a substantially constant
frequency shift upon said electrical impulses;
d. the frequency deviations imposed by said devices being
substantially equal and opposite; and,
e. means serially connecting the devices and modulator with the
modulator interposed between the devices whereby the
characteristics of the vibrato is not a direct linear function of
frequency.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the electronic production of
non-frequency-proportional vibrato.
2. Description of the Prior Art
Most musical sounds are enhanced by the addition of low frequency
modulation. Numerous techniques have been devised to introduce such
vibrato and tremolo effects in electronic musical instruments. Well
known among these is the use of a rotating speaker or acoustical
channel shown e.g., in the U.S. Pat. No. Re. 23,323 to Leslie.
The recent availability of integrated circuit analog shift
registers of the "bucket brigade" type provides another tool for
implementing vibrato. As taught in the recent U.S. Pat. No.
3,749,837 to Doughty, such effects can be achieved by passing the
musical signal through a shift register in which the shifting rate
is varied at a low frequency. The resultant periodic compression
and expansion of the wave passing through the shift register
results in frequency modulation of the delayed signal.
The vibrato modulation so produced is directly proportional to
frequency. Thus if the shifting rate of the bucket brigade delay
line is varied so as to introduce a modulation of .+-.2Hz for a
tone of 100Hz, when a 200Hz signal is passed through the shift
register, a modulation of .+-.4Hz will be introduced. For a signal
of 1000Hz, the modulation will be .+-.20Hz. In other words, the
vibrato frequency deviation is a constant percentage of the signal
frequency.
Another known system for producing frequency proportional vibrato
is disclosed in the U.S. Pat. No. 3,518,354 to Lubow. Here the
input signal simultaneously is recorded on opposite sides of an
electrostatic storage drum that is rotated at a rate which varies
above and below an average rate during each revolution. The signal
is recovered from the drum by a read electrode situated between the
record electrodes. The recovered signal is frequency modulated
above and below the input signal frequency as a result of the
varying drum rotation rate.
In practice, only a few conventional musical instruments, typically
the violin and the steel guitar, exhibit frequency proportional
vibrato. In most instruments, the vibrato is not proportional to
frequency. Thus in certain organ pipes there is little or no
vibrator at the pedal frequencies, a mild vibrato in the mid-range,
and considerable frequency deviation or "warble" at the highest
notes.
A principal object of the present invention is to implement
non-frequency proportional vibrator electronically. A further
object is to achieve such non-frequency proportional vibrato
through the cooperation of (a) a first device that by itself
produces frequency proportional modulation, and (b) other
components which dynamically shift the frequency or phase of the
signal processed by the first device.
SUMMARY OF THE INVENTION
In one embodiment these objectives are achieved by utilizing a low
frequency modulated analog shift register in conjunction with
circuits that dynamically shift the frequency of the signal
processed through the shift register. The input signal is shifted
downward in frequency by a constant amount -.DELTA.f prior to
introduction of frequency-proportional vibrator in the modulated
bucket brigade device. Subsequently the signal is shifted back in
frequency by an amount +.DELTA.f. The product is a vibrator having
a small percentage frequency deviation at low frequencies,
gradually increasing to a frequency deviation which at high
frequencies asymptotically approaches that of the modulated shift
register.
In another embodiment, a dynamic phase shifter is used to introduce
a low frequency modulation having generally non-linear percentage
frequency deviation characteristics. The signal also is modulated
by passage through the bucket brigade delay line, either before or
after processing by the dynamic phase shifter. By driving the phase
shifter and the modulated delay line synchronously, as from the
same low frequency oscillator, a partial cancellation or
subtraction may occur. The resultant signal exhibits a vibrator
which typically has a small percentage frequency deviation at low
frequencies, and rises along an S-shaped frequency deviation curve
with increasing frequency. Appropriate selection of the phase
shifter characteristics permits tailoring of the resultant vibrato
characteristics.
In alternative embodiments, the modulated shift register may be
replaced by some other device, such as a mechanical recording
medium that is driven at a varying rate, which by itself produces
frequency proportional vibrato.
BRIEF DESCRIPTION OF THE DRAWINGS
A detailed description of the invention will be made with reference
to the accompanying drawings wherein like numerals designate
corresponding elements in the several figures.
FIG. 1 is an electrical block diagram of an embodiment of the
invention in which the signal is shifted in frequency before and
after processing through an analog shift register.
FIG. 2 is a graph showing typical percentage frequency deviation
characteristics of the vibrator obtained using the circuit of FIG.
1.
FIG. 3 is an electrical block diagram of a frequency changing
device useful in the circuit of FIG. 1.
FIG. 4 is an electrical schematic diagram of a phase splitter
useful with the circuit of FIG. 3.
FIG. 5 is an electrical block diagram of another embodiment of the
present invention utilizing synchronously modulated phase shifter
and bucket brigade devices.
FIG. 6 is a graph showing typical percentage frequency deviation
characteristics of vibrato obtained using the circuit of FIG.
5.
FIG. 7 is an electrical schematic diagram of a dynamic phase
shifter applicable in the circuit of FIG. 5.
FIG. 8 is an electrical schematic diagram of a cascaded phase
shifter also useful in the circuit of FIG. 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following detailed description is of the best presently
contemplated modes of carrying out the invention. This description
is not to be taken in a limiting sense, but is made merely for the
purpose of illustrating the general principles of the invention
since the scope of the invention best is defined by the appended
claims.
Structural and operational characteristics attributed to forms of
the invention first described also shall be attributed to forms
later described, unless such characteristics obviously are
inapplicable or unless specific exception is made.
In the embodiment of FIG. 1, non-frequency proportional vibrato and
like effects are achieved by shifting the input signal by a
constant amount -.DELTA.f, processing the resultant signal through
a low frequency modulated analog shift register, and frequency
shifting the output signal by a corresponding amount +.DELTA.f. As
illustrated by the typical curve 8 of FIG. 2, the resultant output
signal will exhibit a vibrato effect which is proportionately less
at lower input signal frequencies and greater at higher
frequencies, in contrast with the constant percentage frequency
deviation vibrator (see curve 9 of FIG. 2) obtained using only the
modulated bucket brigade delay line.
In the circuit 10 of FIG. 1, an input audio frequency signal is
supplied via line 11 to a frequency changing device 12 which shifts
the input signal downward in frequency by an amount -.DELTA.f.
Preferably the shift -.DELTA.f is constant over the entire input
signal frequency range. For example, the device 12 may shift the
frequency downward by .DELTA.f=100 Hz. In such instance, an input
signal of 300 Hz on the line 11 will result in an output of 200 Hz
on a line 13 from the device 12. An input signal of 4000 Hz will be
decreased in frequency to 3900 Hz by the device 12.
The signal on the line 13 is supplied via a low pass filter 14 and
a line 15 to a low frequency modulated analog shift register 16.
This bucket brigade device periodically samples the amplitude of
the input signal on the line 15 and shifts this amplitude value
from stage to stage to the register output line 17. The shift rate,
and hence the delay time through the register 16 is established by
a clock 18. The clock 18 is modulated at a low frequency by a
modulator 19. Thus the clock 18 and the modulator 19 cooperate to
vary the effective delay time through the bucket brigade 16 at a
low frequency, vibrato or chorus rate.
The signal on the line 17 is supplied via another low pass filter
20 and a line 21 to a second frequency changing device 22. Here the
signal is shifted upward in frequency by an amount +.DELTA.f. The
resultant output signal is supplied via a line 23. The following
Table I illustrates operation of the circuit 10 for a value
.DELTA.f = 100 Hz, and with the clock 18 and modulator 19 selected
so that the bucket brigade device 16 by itself introduces a 2
percent frequency modulation of a signal supplied to that
device.
TABLE I ______________________________________ FREQUENCY FREQUENCY
OF OUTPUT SIGNAL OF INPUT USING ONLY "BUCKET BRIGADE" WITH SIGNAL
"BUCKET BRIGADE" FREQUENCY SHIFTED INPUT AND OUTPUT
______________________________________ 100 Hz 100 Hz .+-. 2 Hz 100
Hz .+-. 0 Hz 200 200 .+-. 4 200 Hz .+-. 2 Hz 400 400 .+-. 8 400
.+-. 6 1,000 1,000 .+-. 20 1,000 .+-. 18 2,000 2,000 .+-. 40 2,000
.+-. 38 4,000 4,000 .+-. 80 4,000 .+-. 78
______________________________________
The middle column of Table I indicates the type of frequency
proportional vibrato which is achieved using only a modulated shift
register, such as disclosed in the above mentioned U.S. Pat. No.
3,749,837 to Doughty. An input signal of 100 Hz will have a
modulation of .+-.2 Hz, while a signal at 2000 Hz will have a
modulation of .+-.40 Hz. In contrast, using the inventive system of
FIG. 1 a non-frequency proportional vibrato is obtained. Thus with
the typical values given above, an input signal on the line 11 of
100 Hz will have no frequency deviation introduced. An input at 200
Hz will result in a signal output on the line 23 of 200 Hz .+-.2
Hz. This modulation is one percent of the input frequency, which is
half of the percentage frequency deviation that would be introduced
using only the bucket brigade device 16. An input signal of 2000 Hz
is modulated by .+-. 38 Hz which approaches two percent modulation.
It is readily apparent that different non-frequency proportional
effects can be achieved using the circuit of FIG. 1 with different
values of .DELTA.f and/or different effective modulation
frequencies through the bucket brigade device 16.
The analog shift register 16 advantageously, but not necessarily,
may be implemented using a conventional integrated circuit bucket
brigade delay line such as the ITT Intermetall type TCA 350 or the
Amperex type M31 device. The operation of such bucket brigade delay
lines is described, e.g., in the article entitled "Bucket-brigade
Electronics-- New Possibilities for Delay, Time-Axis Conversion,
and Scanning" by Sangster and Teer, Journal of Solid-State
Circuits, Volume SC-4, No. 3, June 1969 and in the article "Bucket
Brigade Devices Pass from Principle to Prototype" in the Feb. 28,
1972 issue of Electronics magazine. The low pass filter 14 is used
to insure that the signal supplied to the bucket brigade device 16
contains no components at or near the shift frequency of that
device. Thus typically the filter 14 will pass signals in the audio
range of up to say 20,000 Hz but will attenuate frequency
components above that range. The low pass filter 20 is used to
eliminate from the output signal any components which might be
introduced by the device 16 at the bucket brigade shift
frequency.
Each frequency changing device 12 and 22 may be of the type
disclosed in the U.S. Pat. Nos. 3,251,924 or 3,372,225 to Donald J.
Leslie. Such a frequency changing device 12a is shown in FIGS. 3
and 4, and utilizes a rotary capacitor 25 having four equiangularly
arrayed stationary plates 26, 27, 28 and 29 driven respectively by
signals differing in phase by 0.degree., 90.degree., 180.degree.
and 270.degree. with respect to each other. These signals are
supplied by a phase splitter 30 (FIG. 4) receiving an input via a
line 31. The capacitor 25 also includes a rotor plate 32
eccentrically mounted with respect to the center of the plates 26
through 29. A motor 33 rotates the plate 32 at a constant rate.
The output from the capacitor 25, present on a line 34 from the
rotor plate 32, will differ in frequency from the input signal on
the line 31 by an amount established by the rate and direction of
rotation of the plate 32. If the plate 32 is rotated
counterclockwise as viewed in FIG. 3, a negative frequency shift is
obtained, as preferred for the changing device 12. Clockwise
rotation of the plate 32 results in a positive frequency shift, as
preferred for the changing device 22. The rate of rotation
establishes the amount of frequency change. Thus when the motor 33
rotates the plate 32 at 100 revolutions per second, a frequency
shift .DELTA.f of 100 Hz results.
FIG. 4 shows a phase splitter 30 which may be used in the frequency
changing device 12a of FIG. 3. In this circuit, the input signal on
the line 31 is directed to the base of a transistor 37 the
collector of which is connected to a positive voltage source via a
resistor 38 and the emitter of which is connected to ground via a
resistor 39. Driven by the emitter and collector of the transistor
37 is a symmetric pair of capacitor-resistor networks 40, 41 which
provide the appropriately phased signals at the capacitor plates 26
through 29.
Frequency changing devices other than that shown in FIGS. 3 and 4
may be used in the circuit 10 of FIG. 1. For example, a single
sideband modulation-demodulation system could be used. The input
signal is used to modulate a carrier at a certain frequency. The
modulated carrier is passed through a single sideband filter and
then demodulated. By utilizing a demodulation carrier frequency
separated by .DELTA.f from that of the modulation carrier, the
resultant signal will be shifted in frequency by a like amount
.DELTA.f with respect to the original audio input.
In the illustrated circuit 10 (FIG. 1) the input frequency changing
device 12 introduces a negative frequency shift -.DELTA.f and the
output device 22 introduces a positive frequency shift +.DELTA.f.
This arrangement generally is preferred since it results in a lower
vibrato rate at the lower input frequencies and a greater vibrato
effect at higher frequencies. However, for certain unusual vibrato
effects it may be desirable to interchange these devices, so that
an upward frequency shift is introduced prior to passage through
the shift register 16, with a compensating downward shift in
frequency being introduced into the output signal. Unusual chorus
effects may be achieved by using different values of .DELTA.f in
the two frequency changing devices 12 and 22.
In the embodiment 40 of FIG. 5, non-frequency proportional vibrato
effects are obtained by using a dynamic phase shifter 41 in
conjunction with a modulated bucket brigade device 16'. A common
low frequency oscillator 42 is used synchronously to modulate both
the shift register clock 18' and the phase shifter 41 in opposite
senses. With this arrangement, phase shift vibrato modulation
introduced by the phase shifter 41 (see the typical curve 43 of
FIG. 6) subtractively cancels out some of the constant frequency
deviation vibrato (see curve 9' of FIG. 6) produced by the bucket
brigade device itself. The resultant vibrato modulation (curve 44
of FIG. 6) exhibits non-linear percentage frequency deviation
characteristics that cannot be obtained using phase-shifters alone,
and which can be tailored to desired values.
The input signal supplied on a line 46 (FIG. 5) is dynamically
shifted in phase by the device 41. This causes frequency modulation
of the input signal by an amount dependent on the rate of change of
the phase shift. For example, a phase shift of +180.degree. in
one-twelfth of a second is equivalent to adding 6 Hz to the
frequency of the input signal. In typical phase shift circuits the
net phase shift is a non-linear function of frequency. Thus, if the
circuit employs a resistance-reactance bridge, the phase shift may
exhibit a characteristic S-curve, as shown, e.g., in the U.S. Pat.
No. 3,146,292 to Bonham.
The phase shift modulated signal from the device 41 is supplied via
a line 47 and a low pass filter 14' to the analog shift register
16'. As noted above, this bucket brigade delay line device 16' is
modulated synchronously with the phase shifter 41, so that the
frequency modulation introduced by the bucket brigade 16' will
partly cancel or "buck-out" the modulation produced by the phase
shifter 41. The resultant signal from the device 16' is supplied
via a low pass filter 20' to the output line 48. In an alternative
configuration, the phase shifter 41 may be omitted and a like phase
shifter 41' (shown in phantom in FIG. 5) placed in the output line
48. Similar results are achieved.
The constant amplitude phase shifter circuit 41a shown in FIG. 7
and described on page 63 of the January, 1971 issue of EEE
Magazine, is useful as the device 41 or 41'. The circuit produces
an output voltage on the line 47a equal in magnitude to the input
voltage on the line 46a but shifted in phase. The input signal is
supplied via a capacitor 51 to one input terminal 52a of an
operational amplifier 52, and via a resistor 53 to the other
complementary input terminal 52b of the amplifier. A feedback
resistor 54 connects the output line 47a to the amplifier input
terminal 51b. For unity gain the resistors 53 and 54 are of equal
value.
A variable resistor 55 is connectd between the amplifier input
terminal 51a and ground. As the value of this resistor is varied
from a very high value (open circuit) to a very low value (short
circuit), the phase shift introduced by the circuit 41a varies
concomitantly between 0.degree. and 180.degree.. A resistance
variation over a smaller range will correspondingly reduce the
range of phase shift variation.
The resistance value of the resistor 55 is varied at the low
frequency rate established by the oscillator 42. This may be
accomplished in any conventional manner. Thus in the circuit of
FIG. 7, a light-sensitive resistor 55 is illuminated by the
changing intensity of a lamp 56 driven by the oscillator 42. The
shape of the vibrato percentage frequency deviation curve 44 (FIG.
6) can be altered by appropriate selection of the phase shift
characteristics introduced by the dynamic phase shifter 41. For
example, the linear region 43' of the curve 43 may be displaced
upward in frequency by increasing the total effective phase shift
introduced by the phase shifter 41. This will cause a corresponding
change in the frequency deviation versus frequency characteristics
(curve 44) of the circuit 40.
Such tailoring of the vibrato characteristics can be achieved e.g.,
by employing cascaded phase shift networks as the phase shifter 41.
Such cascaded phase shift vibrato circuits are known per se, as
described in the U.S. Pat. No. 3,418,418 to Wilder.
A useful cascaded phase shift network 41b is shown in FIG. 8. Each
stage consists of a transistor 58 receiving an input signal at its
base. The transistor output signals across the collector and
emitter resistors 59, 60 are of opposite phase. These are fed to a
common terminal 61 respectively via a capacitor 62 and a variable
resistor 63. Variation of the resistance 63 causes a concomitant
phase change at the output terminal 61. The resistance change
conveniently is achieved by using a light sensitive resistor
illuminated by a lamp 56' driven by the low frequency oscillator
42. The output terminal 61 is connected to the base of the
transistor 58' associated with the next like, cascaded phase shift
circuit. The net phase shift introduced to a signal between the
input terminal 46b and the output terminal 47b will be the sum of
the individual phase shifts introduced by each of the cascaded
networks.
For producing vibrato effects, the frequency of the modulator 19
(FIG. 1) or the oscillator 42 (FIG. 5) preferably is in the range
of from about 3 Hz to about 10 Hz. However, the invention is not so
limited. Chorus-like effect are produced by using a lower
frequency, which may be less than 1 Hz. Other unique effects are
produced with frequencies above 10 Hz.
Although the systems of FIGS. 1 and 5 each utilize a bucket brigade
analog shift register, the invention is not so restricted. This
component may be replaced in either system with another device that
by itself produces frequency proportional vibrato. For example, the
present invention may be implemented by processing the input signal
first through a frequency changing device 12 like that of FIG. 1,
than through a variable speed storage disc of the type shown in
U.S. Pat. No. 3,518,354, and finally through another frequency
changing device 22 (FIG. 1). As another example, a dynamic phase
shifter like that of FIG. 7 or 8 may be combined with a device
which itself produces frequency proportional modulation, in a
manner analogous to that shown herein in FIG. 5.
Other variations will be apparent to those skilled in the art. For
example, in the circuit of FIG. 5, the relative phase of the drive
signals to the bucket brigade device and the dynamic phase shifter
may be altered to introduce different amounts of vibrato addition
or subtraction as a function of frequency. Further, amplitude
modulation effects easily may be imparted to the inventive system,
as for example by making the resistors 53 and 54 in the dynamic
phase shift circuit of FIG. 7 of different values .
* * * * *