CA1059804A

CA1059804A - Apparatus for automatic tuning of electronic musical instrument

Info

Publication number: CA1059804A
Application number: CA264,191A
Authority: CA
Inventors: Nobuaki Kondo
Original assignee: Kawai Musical Instrument Manufacturing Co Ltd
Current assignee: Kawai Musical Instrument Manufacturing Co Ltd
Priority date: 1975-10-27
Filing date: 1976-10-26
Publication date: 1979-08-07
Also published as: JPS5338612B2; AU1881476A; AU499346B2; DE2648472C3; JPS5252621A; DE2648472A1; DE2648472B2

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides an apparatus for tuning an electronic musical instrument comprising a voltage controlled oscillator and a key board for supplying control voltages to the voltage controlled oscillator, said apparatus comprising a calculation circuit for enabling an off-set voltage to be summoned with the control voltage from the keyboard, a tuning signal generating means and a phase locked loop operative in the presence of a tuning signal to vary the off-set voltage applied to the calculation circuit to lock the voltage controlled oscillator onto a reference frequency and operative in between tuning signals to maintain the off-set voltage at a constant value equal to that prevailing at the end of the preceding tuning signal.

Description

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This invention relates to an apparatus Eor automatie tuning of an electronic musical instrument using a voltage ~
eontrolled type oscillator. ~ -In a known method for tuning an electronic musical instrument, an oscillation tone is generated and an operator ; makes a manual adjustment while hearing the tone or the oscillation frequency is measured and is manually adjusted to be in eoincidenee ~ with a predetermined oseillation frequeney. Those methods are, -~ however, ineonvenient in that they require much trouble and are;~ lO diffieult far an amateur. ~
This invention seeks to provide an apparatus in which, ~ ;
tuning ean be carried out automa~ically by operation of a tuning switch. According to this invention, there is provided an ~-~
, .
apparatus for tuning an eleetronic musical instrument comprising ~. :
a voltage controlled oscillator and a key board for supplying ~-eontrol voltages to the voltage eontrolled oseillator, said i apparatus eomprising a ealeulation cireuit for enabling an i off-set voltage to be summoned with the eontrol voltage from the : . . .
`-~Y keyboard, a tuning signal generating means and a phase locked 20 loop operative in the presence of a tuning signal to vary the off-set voltage applied to the calculation circuit to lock the "~ voltage controlled oscillator onto a reference frequeney and operative in between tuning signals to maintain the off-set voltage at a eonstant value e~ual to that prevailing at the -. end of the preeeding tuning signal.
~he invention will now be deseribed further, by way : ::
:' of example, with referenee to the aceompanying drawings, in whieh~
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Fig. l is a bloek diagram showing one embodiment ~
. .
of this invention, ~ ~
i ~ , Figs. 2 and 3 are bloek diagrams showing respective portions o~ other embodiments, ~;
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Figs. 4 A-1....~-4, B~l....B-4 are diagrams for explaining operation of a phase eomparator shown in Fig. 3.

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Fig. 5 is a block diagram showing another embodiment of the inVention and Fig. 6 is a block diagram showing a portion of a urther embodiment of the invention.
:' :
: Referring to Fig. 1, numeral 1 denotes a voltage control-, ,:
led oscillator (hereinafter abbreviated to VCO) for generating a musical tone slgnal and an output terminal of the VCO 1 is connected to a speaker through a voltage controlled filter

2 (hereinafter termed VCF2) and a voltage controlled amplifier

3 hereinafter termed VCA 3).
Numeral 4 denotes a phase comparator, and an output signal thereof is fed back to the VCO 1 through a converter ~ ~
circuit in the form of a low-pass filter 5 for converting ~i the output signal of the phase comparator 4 into a voltage prop- ~ `
ortional thereto, a sample and hold circuit 6, a calculation ~ ;`
.,., :. ~ ~ .
circuit 7 and an anti-log amplifier 8. An output terminal of the VC0 1 is connected to an input t:erminal 4a of the phase , comparator 4 and another input terminal 4b of the phase comparator ~ 4 is connected to a reference oscillator 9. Numeral 10 ,;i 20 denotes ~ key signal generating circuit for generating a voltage ~- , `,'~ corresponding to a depres~ed key of a key board, which key `~

;- signal generatlng circuit 10 comprises a plurality of resistors ~i ;` 13-1.... 13-n which are connected in series one another and are ~; connected throughaconstant current circuit 12 to a power source 11, and a plurality of key switches 14-1.... 14-n each connected -~

between the junction of a respective pair of resistors 13~

13-n and a common termlnal 15. An output llne 16 led out therefrom ,~ is connected to a calculation input terminal of the calculation ~ `

`''~ circuit 7. ` `

~ 30 Numeral 17 denotes a gate circuit connected across , ~ ., a specific key switch 14-5. A control electrode of the gate circuit 17 and a control electrode of the sample hold circuit 6 .

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.
:: . .. . . .. . . . .

ss~a are connec-ted to an ou-tput terminal of a monostable multivibrator 19 arranged to be operated by operation of a tuning switch 18.
The calculation circuit 7 may either be an addition circuit of a subtraction circuit, but it will be explained with reference to a case where an addition circuit is used.
The circuit composed of the phase comparator 4, the low-pass ilter 5, the sample and hold circuit 6~ the calculation circuit 7, the anti-log amplifier 8 and the VCO 1 forms a phase- j ~ locked loop (PLL), and the operation of the apparatus will be -~ 10 explained hereinafter on the operational principle of the PLL.
If, the tuning switch 18 is manually closed, a pulse A is generated from the monostable multivibrator 19 and this pulse A not only opens the gate circuit 17 but also resets the -... . .! sample and hold circuit 6. Thus, the VCO 1 oscillates and its ;~ output signal is applied to the phase comparator 4 along with the reference signal of the oscillator 9, so that the two signals may be compared one with 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 -,:.~
conversion to a steady voltage~ This voltage is applied through .. ~
the sample and 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 which passes through the gate circuit 17. Further, the resultant signal `~ thereof is applied through the anti-log amplifier 8 to the VCO 1, ;l and because of the negative feedback the VCO 1 oscillates ~;
eventually at a frequency equal to the reference frequency from the referance oscillator 9. -~
.:-...... . .
When r the output signal A of the monostable multivibrator 19 drops, the gate circuit 17 is closed and the sample and hold circuit 6 holds the output of the filter 5. Thus, the voltage held in the sample hold circuit 6 is taken out so as to be applied .: ~

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to the calculation circuit 7, so that the VC0 1 continues to oscillate at the tuned reference frequency.
This reference signal input terminal 4b of the phase J comparator 4 is connected to a reference signal oscillator in the embodiment shown in Fig. 1 alternative, however, the terminal 4b may be connected to an output terminal of an ~
oscillator of a corresponding frequency in another electronic :
musical instrument, whereby tuning to the said other musical instrument can be effected.
In a further modification, shown in Fig. 2, the stand-ard signal oscillator 9 is replaced by a monostable multi~
`; vibrator 9', and an output terminal of the ~C0 1 is branched so , . . .
` as to be connected to an input terminal 9a of the monostable multivibrator 9'. If, in this case, the frequency which is to ` ~ be tuned is high, a frequency divider 21 is interposed in a :i.l `' circuit connecting between the output terminal of the VC0 1and the input terminals 4a, ~b. Thus, the loop is locked when ~ ~-the output pulse width o the VC0 1 and an output pulse width ~ -. .
of the monostable multivibrator 9' become equal one to another.
~ 20 As shown in Fig. 3, the phase comparator 4 in Fig. 2 `~ comprises two flip-flop circuits 22,23 and a charge pump 24, and the flip-flop circuits 22,23 comprise a D-FF of the type ~r. that when the data terminal D is "H", the output is "H" by the change of the input terminal T from "~l" to "L", and when the 'r' data terminal D is "L", the output is "L" by the input terminal T being "L".
. If, now, the oscillation frequency of the YC0 1 is higher than the standard frequency, the output of the frequency ~; divider 21 becomes as shown in Fig. 4 A 1, and the output of the monostable multi-vibrator 9' is as shown in Fig. 4 A-2. Accord-~- ingly, 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 :, :, . . ............................... .. .
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the input terminal PD of the charye pump 24 is applied with "H", and the same is inverted by the invertor 24a. The input `~ terminal PU is applied with "~", Thus, the output of the diode ~ 24b is pulled in hy "L" of the anode of the diode 24c~ and the - output of the output terminal 24d of the charge pump 24 becomes rapidly to be "L". This "L" is applied through the low-pass : .:
filter S to the sample hold circuit 6, and the sampling con-denser is discharged and the oscillation frequency of the VCO
:
is lowered. ~ ~ -. . . .
If the oscillation frequency of the VCO 1 is lower than the standard frequency, the output of the frequency divid r ~ 21 becomes as shown in Fig. 4 B-l. The output of the monostable }l 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"l and the same is inverted by the invertor 24a and the anode of the diode 2]b 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 becomes rapidly to be "H". This ~-~output is applied through the low-pass filter 5 to the sampling I ~
condenser of the sample hold circuit 6 for charging the~same, ~ -~` whereby the oscillation frequency of the VCO is heightened.
~5 Thus, it is repeated that the oscillation~frequency -~ of the VCO is lowered and if lowered in excess the same is : :, i. :
;~~ heightened, and the oscillation frequency closes to the standard `1 value as nearest as possible, c~` In this case, the low-pass filter 5 is a direct current in its input, so that the same does not especially act on the loop. The same acts only for removing unnecessary signals at the time of excess degree response operation and others.

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~591511~4 Fig. S shows another embodiment. In this embodiment the two input terminals 4a, 4b of the phase comparator 4 are connected throuqh a logic circuit 26 to a light emitting element 27, The light emitting element 27 is a diode and the logic circuit 26 is an Exclusive OR circuit with invert~d output i.e. ~-a coincidence circuit. The cathode of diode 27 is connected to ~i an output terminal of the logic circuit 26 and the anode thereof is connected through a resistor 28 to a power source terminal 29. The output signal of the logic circuit 26 is "1" when the output pulse oE the frequency divider 21 and the output pulse ; of the monostable multivibrator 9' coincide and the output signal thereof is "O" when the two pulses are not coincident, ~ -thus during non-coincidence an electric current flows from the power source 29 through the light emitting diode 27, so that ~ the diode 27 lights up. When a "1" output is produced the ,;,i,, diode 27 goes out. ~
`~ When tuning is effected in essentially the same -~ -;~ manner as in the foregoing case of Fi~. 1 by pushing of the . tuning switch 18, as long~as the two pulse signals applied to i, 20 the two input terminals 4a4b of the phase comparator 4 are part- -~
:, . .. .
ly different in phase, the diode 27 ~oes on and off, and when ~ the two pulses are completely coincident in phase, the same `~_ completely goes out, and thereby it is indicated that the oscillation frequency of the VCO 1 has reached the predetermined ~' value. '~

In the embodiment of Fig. 5, the tuning switch 18 is ~`~ of a changeover type and bistable multivibrator 30 is provided ~....................................................................... ::
instead of the monostable multivibrator 19 so that an output ~:' signal obtained while the tuning switch 18 is pushed as shown ~- 30 by dotted lines may serve to open the gate circuit 17 and `~
release holding of the sample hold circuit 6 and when the tuning switch 18 is released from being pushed the gate circuit : '.. ,: -,:
~ 6 -:

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. .

- ~LC35~8~4 17 may be opened and the sample and hold circuit 6 may be brought into its hold condition. Accordingly, the tuning can be achieved by releasinq the tuning switch 18 when the diode ~ 27 goes out completely.
The sample and hold circuit 6 is composed of a circuit :, .
; including a chanqe storage capacitor, so that when the circuit 6 is reset, the output voltages of the low-pass filter 5 is ~ passed to the condenser. When set, the sample and hold circuit .~ 10 holds the prevailing voltage from the low-pass filter 5 and its ~' output remains at that voltage. However, it is possible for ~;
the capacitor to discharge little by littIe with a long lapse of time and the held voltage may vary, and thus the instrument ~, goes out of tune. Accordingly, it becomes necessary for the ~
~` tuning switch to be pushed frequently. ; ` -The embodiment where the reference signal is applled from another electronic musical lnstrument, instead of applic- ~-ation from the reference si~nal oscillator 9, and where the . ::~ .. , - .
reference signal oscillator 9 is replaced by a monostable` multi~
~`' 20 vibrator 9' as shown in Fig. 3, may be modified by the provision of an indicating device as shown in Fig. 5, or by replacement ,. ..... . .
; of the tuning switch 18 and the monostable multivibrator 19 by the tuning switcb 18' and bistable muleivibrator 30 as shown ;

The inventlon thus enables tuning to be automatically oarried out for a short time only~by operating of a tuning switch and can be carried out simply by anybody. ;~

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for tuning an electronic musical instrument comprising a voltage controlled oscillator and a key board for supplying control voltages to the voltage controlled oscillator, said apparatus comprising a calculation circuit for enabling an off-set voltage to be summoned with the control voltage from the keyboard, a tuning signal generating means and a phase locked loop operative in the presence of a tuning signal to vary the off-set voltage applied to the calculation circuit to lock the voltage controlled oscillator onto a reference frequency and operative in between tuning signals to maintain the off-set voltage at a constant value equal to that prevailing at the end of the preceding tuning signal.

2. Apparatus for automatically tuning an electronic musical instrument, comprising a phase comparator, a converter circuit for converting the output signal of the phase comparator into a voltage proportional thereto, a sample and hold circuit, a calculation circuit and a voltage controlled oscillator for generating a musical tone signal connected in series wherein an output terminal of the voltage controlled type oscillator is connected to an input terminal of the phase comparator, another input terminal of the phase comparator is formed into an input terminal for a reference signal, and an output terminal of a key signal generating circuit for generating a voltage corresponding to a key depressed is connected to an input terminal of the 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 of the sample hold circuit being connected to an output terminal of a multivibrator which is operable by a tuning switch.

3. An apparatus for automatic tuning of an electronic musical instrument as claimed in claim 2, in which the converter circuit is composed of a low-pass filter.

4. An apparatus for automatic tuning as claimed in claim 2 or 3, in which the phase comparator is composed of two flip-flop circuits.

5. An apparatus for automatic tuning as claimed in claim 2 or 3, in which the phase comparator is composed of two flip-flop circuits and a charge pump.

6. An apparatus for automatic tuning as claimed in claim 1 or 2, in which the reference signal is derived from a reference signal oscillator.

7. An apparatus for automatic tuning as claimed in claim 1 or 2, in which the reference signal is derived from another electronic musical instrument.

8. An apparatus for automatic tuning as claimed in claim 2, in which an output terminal of the voltage controlled oscillator is connected to an input terminal of the phase comparator and also is connected to the reference signal input terminal of the same through a monostable multivibrator.

9. An apparatus for automatic tuning as claimed in claim 8, in which a single common circuit for connecting the output terminal of the voltage controlled oscillator to one input terminal of the phase comparator and the monostable multivibrator is provided with a frequency divider interposed therein.

10. An apparatus for automatic tuning as claimed in claim 2, in which the two input terminals of the phase comparator are connected to a light emitting element through a logic circuit.