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Description  |
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FIELD OF THE INVENTION
This invention relates to an apparatus for the automatic tuning of an
electronic musical instrument using a voltage controlled type oscillator.
BACKGROUND
Hitherto, for tuning an electronic musical instrument, such a means has
been employed in which an oscillation tone is generated and an operator
effects a manual adjustment while listening to the tone or an oscillation
frequency is measured and is manually adjusted to be in conincidence with
a predetermined oscillation frequency. These means are, however,
disadvantageous in that they require much trouble and are difficult for an
amateur.
SUMMARY OF THE INVENTION
An object of this invention is to provide an apparatus in which for
removing such disadvantages tuning can be carried out automatically by
operation of a tuning switch.
The apparatus in accordance with the invention comprises a phase
comparator, a converter circuit for converting an output signal of the
phase comparator into a voltage at a level corresponding thereto, a sample
hold circuit, a calculation circuit and a voltage controlled type
oscillator for generating a musical tone signal connected in series, and
an output terminal of the voltage controlled type oscillator connected to
an input terminal of the phase comparator and another input terminal of
the phase comparator formed as an input terminal for a standard signal,
and an output terminal of a key signal generating circuit for generating a
voltage corresponding to a depressed key connected to a calculation input
terminal of the foregoing calculation circuit, the key signal generating
circuit being provided with a gate circuit which generates a key signal
corresponding to a specific key, and control electrodes of the gate
circuit and the sample hold circuit connected to an output terminal of a
monostable multi-vibrator which is operated by operation of a tuning
switch.
Embodying examples of this invention will next be explained with reference
to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram showing one embodiment according to this
invention.
FIGS. 2 and 3 are block diagrams showing respective portions of other
embodiments thereof.
FIGS. 4 A-1 . . . A-4, B-1 . . . B-4 are diagrams for explaining the
operation of a phase comparator shown in FIG. 3.
FIG. 5 is a block diagram of another embodiment example of this invention.
DETAILED DESCRIPTION
Referring to FIG. 1, numeral 1 denotes a voltage controlled type oscillator
for generating a musical tone signal (called hereinafter VCO 1) and an
output terminal of VCO 1 is connected to a speaker through a voltage
controlled type filter 2 (called hereinafter VCF 2) and a voltage
controlled type amplifier 3 (called hereinafter VCA 3).
Numeral 4 denotes a phase comparator, and an output terminal thereof is
connected to a control electrode of VCO 1 through a converter circuit 5
for converting an output signal of the phase comparator 4 into a voltage
at a level corresponding thereto, e.g., a low-pass filter 5, a sample hold
circuit 6, a calculation circuit 7 and an anti-log amplifier 8. An output
terminal of VCO 1 is connected to an input terminal 4a of the phase
comparator 4 and another input terminal 4b of the phase comparator 4 is
connected to a standard signal oscillator 9. Numeral 10 denotes a key
signal generating circuit for generating a voltage corresponding to a key
which is depressed, the key signal generating circuit 10 comprising a
plurality of resistances 13-1 . . . 13-n which are connected in series
with one another and are connected through a constant current circuit 12
to a power source 11, and a plurality of key switches 14-1 . . . 14-n
connected at respective end terminals to respective connecting points of
resistances 13-1 . . . 13-n, the other end terminals of the key switches
14-1 . . . 14-n being connected together to form a common terminal 15, an
output terminal 16 from circuit 10 being connected to a calculation input
terminal of the calculation circuit 7.
Numeral 17 denotes a gate circuit connected in parallel with a specific key
switch 14-5, and a control electrode of the gate circuit 17 and a control
electrode of the sample hold circuit 6 are connected to an output terminal
of a monostable multi-vibrator 19 arranged to be operated by operation of
a tuning switch 18.
The calculation circuit 7 may be either an addition circuit or a
subtraction circuit, but it will be described with reference to the case
where the addition circuit is used.
A circuit composed of the phase comparator 4, the low-pass filter 5, the
sample hold circuit 6, the calculation circuit 7, the anti-log circuit 8
and the VCO 1 forms a phase-locked loop (PLL), and the operation of the
apparatus will be explained hereinafter with respect to the operational
principle of the PLL.
If the tuning switch 18 is pushed to closed position, a pulse A is
generated from the monostable multi-vibrator 19 and this pulse A not only
opens the gate circuit 17 but also releases the sample hold circuit 6 from
its holding state. Thus, the VCO 1 oscillates and its output signal is
applied to the phase comparator 4 along with the standard signal of the
oscillator 9 applied thereto, so that the two signals may be compared to
one another in phase or frequency. If a difference therebetween in phase
or in frequency is detected, a difference signal is supplied to the
low-pass filter 5 for being converted into a voltage signal of a magnitude
corresponding thereto. This voltage signal is applied through the sample
hold circuit 6 to the calculation circuit 7, and there is carried out in
this calculation circuit 7 an addition thereof to an output voltage of the
specific key-switch 14-5 through the gate circuit 17. The resultant signal
thereof is applied through the anti-log amplifier 8 to the VCO 1, and, the
the VCO 1 oscillates in such a condition that the oscillation frequency
thereof has been made equal to the input frequency of the standard signal
input terminal 4b of the phase comparator 4.
If, thereafter, the output signal A of the monstable multi-vibrator 19
vanishes, the gate circuit 17 is closed and the sample hold circuit 6 is
brought into its hold condition. Thus, the voltage at that time held in
the sample hold circuit 6 is thereafter taken out so as to be applied to
the calculation circuit 7, so that the VCO 1 under goes an oscillation as
already has been tuned to the standard signal.
The standard signal input terminal 4b of the phase comparator 4 is
connected to the standard signal oscillator 9 in the embodiment shown in
FIG. 1, but such a modification can be considered that the same may be
connected to an output terminal of an oscillator of a corresponding
frequency in another electronic musical instrument, whereby to the other
musical instrument can be effected.
A modification can also be considered, as shown in FIG. 2, in which the
standard oscillator 9 is replaced by a monostable multi-vibrator 9' , and
an output terminal of the VCO 1 is diverged so as to be connected to an
input terminal 9a of the monostable multi-vibrator 9' . If, in this case,
the frequency which is to be tuned is high, a frequency divider 21 is
interposed in a circuit connected between the output terminal of the VCO 1
and the input terminals 4a, 4b. Thus, the loop is locked when the output
pulse width of the VCO 1 and the output pulse width of the monostable
multi-vibrator 9' become equal one to another.
As shown in FIG. 3, the phase comparator 4 comprises two flip-flop circuits
22,23 and a charge pump 24. The flip-flop circuits 22,23 comprise a D-type
flip-flop in which when the data terminal D is "H," the output is "H" by
change of the input terminal T from "H" to "L," and when the data terminal
D is "L," the output is "L" by the input terminal T being "L."
If, now, the oscillation frequency of the VCO 1 is higher than the standard
frequency, the output of the frequency divider 21 is as shown in FIG. 4
A-1, and the output of the monostable multi-vibrator 9' is as shown in
FIG. 4 A-2. Accordingly, it will be clear that the output signals of the
output terminals F22, F23 are as shown in FIGS. 4 A-3, A-4. Accordingly,
the input terminal PD of the charge pump 24 is applied with "H," and the
same is inverted by the invertor 24a. The input terminal PU is applied
with "L." Thus, the output of the diode 24b is pulled in by "L" of the
anode of the diode 24c, and the output of the output terminal 24d of the
charge pump 24 rapidly becomes "L." This "L" is applied through the
low-pass filter 5 to the sample hold circuit 6, and the sampling condenser
is discharged and the oscillation frequency of the VCO is lowered.
If the oscillation frequency of the VCO1 is lower than the standard
frequency, the output of the frequency divider 21 becomes as shown in FIG.
4 B-1. The output of the monostable multi-vibrator 9' becomes as shown in
FIG. 4 B-2. Accordingly, it will be clear that the output signals of the
output terminals F22, F23 are as shown in FIGS. 4 B-3, B-4.
Accordingly, the input terminal PD of the charge pump 24 is applied with
"L," and the same is inverted by the invertor 24a and the anode of the
diode 21b is applied with "H." Additionally, the input terminal PU is
applied with "H." Thus, the "H" of the anode of the diode 21b is pulled in
by the diode 21c and the output terminal 24d rapidly becomes "H." This
output is applied through the low-pass filter 5 to the sampling condenser
of the sample hold circuit 6 for the charging the same, whereby the
oscillation frequency of the VCO is increased.
Thus, it is repeated that the oscillation frequency of the VCO is lowered
and if lowered in excess the same is increased, and the oscillation
frequency closes to the standard value as near as possible.
In this case, the low-pass filter 5 has direct current in its input, so
that the same does not especially act on the loop. The filter acts only
for removing unnecessary signals at the time of excess degree response
operation and the like.
FIG. 5 shows another embodiment in which the two input terminals 4a, 4b of
the phase comparator 4 are connected through a logical circuit 26 to a
luminous element 27. The luminous element 27 comprises a luminous diode
and the logical circuit 26 comprises an Ex-NOR circuit. The cathode of the
luminous diode 27 is connected to the output terminal of the Ex-NOR
circuit 26 and the anode thereof is connected through a resistance 28 to a
power source 29. Thus, the output signal of the Ex-NOR circuit 26 is "1"
when an output pulse of the frequency divider 21 and an output pulse of
the monostable multi-vibrator 9' coincide one with another, and the output
signal thereof is "0" when the two pulses are not coincident so that for
the output "0" at the time of non-coincidence an electric current flows
from the power source 29 through the luminous diode 27, so that the
luminous diode 27 goes on. With the output "1" at the time of the
coincidence, the luminous diode 27 is de-energized, so that it goes out.
Thus, if tuning is being effected in almost the same manner as in the
foregoing case of FIG. 1 by pushing of the tuning switch 18, as long as
the two pulse signals applied to the two input terminals 4a, 4b of the
phase comparator 4 are partly different in phase, the luminous diode 27
goes on and off, and when the two pulses are completely coincident in
phase, the diode goes completely out, and thereby it is indicated that the
oscillation frequency of the VCO 1 has reached a predetermined value.
In the embodiment of FIG. 5, the tuning switch 18 is of a changeover type
and a bistable multi-vibrator 30 is provided instead of the monostable
multi-vibrator 19 so that an output signal obtained while the tuning
switch 18 is pushed (as shown by dotted lines) may serve to open the gate
circuit 17 and release holding of the sample hold circuit 6 whereas when
the tuning switch 18 is released the gate circuit 17 may be opened and the
sample hold circuit 6 may be brought into its hold condition. Accordingly,
the tuning can be achieved by releasing the tuning switch 18 when the
luminous diode 27 goes out completely.
The sample hold circuit 6 is composed of a circuit including a holding
condenser, so that when the hold of the circuit 6 is released, the output
voltage corresponding thereto is sent out therefrom and when the circuit 6
is brought into its hold condition the output voltage of the low-pass
filter 5, at the moment when the loop is locked, is charged therein, so
that voltage corresponding thereto is sent out and this output is
continued. However, the holding condenser often discharges little by
little over a long lapse of time and the hold voltage is varied, and,
thus, it comes to be out of tune. Accordingly, it becomes necessary for
the tuning switch to be pushed frequently.
Any of such modifications can be considered also in this embodiment in
which the standard signal is applied from another electronic musical
instrument, instead of application from the standard signal oscillator 9,
the standard signal oscillator 9 is replaced by a monostable
multi-vibrator 9' as shown in FIG. 3, such an indicating device as shown
in FIG. 5 is provided, or the tuning switch 18 and the monostable
multi-vibrator 19 are replaced by the tuning switch 18' and bistable
multi-vibrator 30 as shown in FIG. 5.
Thus, according to this invention, tuning can be automatically effected in
a short time merely by operating a tuning switch and can be carried out
simply even by unskilled personnel.
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