US3916752A

US3916752A - Frequency conversion system for an electronic musical instrument

Info

Publication number: US3916752A
Application number: US175714A
Authority: US
Inventors: Kinji Kawamoto; Masahiko Tsunoo; Masuo Omura
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1968-10-21
Filing date: 1971-08-27
Publication date: 1975-11-04
Anticipated expiration: 1992-11-04

Abstract

A frequency conversion system for an electronic musical instrument. The system has a signal source, at least one frequency converter and an electro-acoustic transducer, and converts the fundamental frequency and overtones of each signal generated by said signal source into other frequencies so as to change said signal with said fundamental frequency and overtones into another signal having an inharmonicity function other than and having a natural tone quality, clearness and strength and also to change the pitch of said signal into another pitch which matches the natural pitch sensation recognized by human ears.

Description

O Umted States Patent 1191 1111 3,916,752 Kawamoto et al. Nov. 4, 1975 FREQUENCY CONVERSION SYSTEM FOR 3,004,460 10/1961 Wayne 84/1.0l AN ELECTRONIC MUSICAL INSTRUMENT 3,007,361 11/1961 Wayne 84/124 X 3,086,122 4/1963 Jones 34/DIG. 4 Inventorsr Kinji Kflwamfitoa y g 3,215,767 11/1965 Martin 84/1.24 Masahiko Tsunoo, Osaka;.Masuo 3,267,199 8/1966 Hurvitz 84/125 Omura, Hirakata, all of Japan 3,418,418 12/1968 Wilder 84/125 4 2 1 Assignw Matsushita Electric Industrial 33252:??? 31338 $323131: jijjiiiji....2;f. Osaka, Japan 3,598,893 8/1971 Uchiyama 84/124 x [22] Filed: Aug. 27, 1971 Primary Examiner.loseph W. Hartary [21] PP -Z 175,714 Assistant Examiner-U. Weldon Related s Application Data Attorney, Agent, or Firm-Wenderoth, Lind & Ponack 63 Continuation of Ser. No. 865 abandoned. Oct 1969 [57] ABSTRACT A frequency conversion system for an electronic musi [30] Foreign Application Priority Data cal instrument. The system has a signal source, at least Oct. 21, 1968 Japan 43-77565 one frequency Convener and an eleetre-aeeuetie transducer, and converts the fundamental frequency 52 us. c1. 84/1.19; 84/101; 84/125 and overtones of each Signal generated by Said Signal [51] Int. Cl. GIOH 3/00 Source into other frequencies 50 as to Change Said [58] Field 6rsea1-ch..... 8 1/101, 1.24, 1.25, DIG. 4; ml with Said fundamental frequency and Oveflones 331/45; 332/17 23 into another signal having an inharrnonicity function other than and having a natural tone quality, cleamess [56] References Cited and strength and also to change the pitch of said signal UNITED STATES PATENTS into another pitch which matches the natural pitch sensation recognized by human ears. 1,788,362 l/1931 Young 331/45 X 2,916,706 12/1959 Timperman 84/124 x 7 Claims, 18 Drawing Figures 1 98 r; zoo 3 TQNE FREQ. 7

GEN. cowv.

Hana 1' j U.S. Patent Nov. 4, 1975 Sheet 2 of3 3,916,752

2 3 4 5 FREQUENCY (BEFORE CONVERSION) FIG.|I

I INVENTORS KINJI KAWAMOTO 2 1 MASAHIKO TSUNOO MASUO OMURA ma ATTORNEYS FREQ- CONV.

259m w zutzmfix :11: w w 23 wzok rw l HHH PHIL FREQUENCY CONVERSION SYSTEM FOR AN ELECTRONIC MUSICAL INSTRUMENT This application is a continuation of application Ser. No. 865,030, filed Oct. 9, 1969, now abandoned.

FIELD OF THE INVENTION The present invention relates generally to the tone quality of an electronic musical instrument and more particularly relates to a frequency conversion system for getting a new signal the fundamental frequency and overtone frequencies of which are different in harmonicity and pitch from those of the original tone.

DESCRIPTION OF THE PRIOR ART A conventional electronic musical instrument has been said to be inferior in tone quality to a conventional musical instrument which utilizes mechanical vibration or acoustical vibration. The difference in tone character between an electronic musical instrument and a conventional musical instrument exists for the following reasons. The mechanical vibrations and the acoustical vibrations in a conventional musical instrument generally do not have exact harmonics; that is, the frequencies of the overtones of the vibration are not exactly positive integer multiples of the fundamental frequency of the vibration.

For example, the fundamental frequency f and the frequencies of the harmonics f,, due to the vibration of a piano string can be represented as follows,

C /P where l is the free length of the string T is the tension thereof p is the density thereof S is the cross section thereof Q is Youngs modulus k is the radius of gyration about the neutral axis of the cross section n is the order of the harmonics (n=1, 2, 3,

We can define an inharmonicity function Y(n) as follows,

where Y(n) is a measure of inharmonicity and a ratio of n-th overtone frequency f, to the multiple n of the fundamental frequency f,. As b represented by Equation (5) is generally l0 -l0 so Y(n) becomes no less than 4 percent for a large n.

Equation (4) shows that the greater the order of harmonics, the greater the inharmonicity.

On the other hand, a sound or a signal of a conventional electronic musical instrument generated by an electronic oscillator circuit or a frequency divider circuit has exact harmonics, namely, frequencies of the overtones f are exactly positive integer multiples of the fundamental frequency f,. The inharmonicity function Y(n) for such a situation is as follows,

The conventional electronic musicalinstrument has another defect in that the pitch of the signal does not agree with the natural musical scale. Signals with an exact frequency ratio 2:1 do not sound as though they are at a one octave musical interval to the human ear, especially in a low or a high frequency range but there must be a frequency ratio greater than 2:1 for obtaining a l octave musical interval. In a conventional electronic musical instrument, the frequency ratio of two signals which are at a l octave musical interval is exactly 2:1 from the low frequency range to high frequency range.

As a result, a conventional electronic musical instrument has the defect that the pitch of the signal is not sufficiently high in the high frequency range and is not sufficiently low in the low frequency region.

When tone generators are used for every tone signal corresponding to every pitch of the natural musical scale, the defect mentioned-above is almost eliminated, although such a method is unnatural because the exact harmonics of each signal are not actually changed into the inexact harmonics of a conventional instrument. Moreover such construction is expensive, bulky and hard to maintain.

SUMMARY OF THE INVENTION It is a primary object of the present invention to pro vide a frequency conversion system for an electronic musical instrument, said frequency conversion system acting to improve the tone quality of a conventional electronic musical instrument with respect to naturalness, clearness and strength by converting an original signal into a new signal in which the inharmonicity function is other than 1.

It is another object of the invention to provide a frequency conversion system which converts an original signal of an electronic musical instrument into a new signal in such a way that the ratios of the frequencies of overtones to the fundamental frequency of the new signal are increased or decreased.

A further object of the present invention is to provide a frequency conversion system which improves the pitch of a conventional electronic musical instrument in the low and high pitch regions of the musical scale to reduce the pitch deviation from the natural pitch.

These objectives are achieved by employing a frequency conversion system for electronic musical instrument according to the present invention, which comprises a signal source, at least one frequency converter and an electro-acoustic transducer which are connected in series to each other in the described order. A signal from said signal source has the frequency and the pitch converted by said frequency converter and is transduced into a sound by said electro-acoustic transducer.

BRIEF DESCRIPTION OF THE DRAWINGS The objects and particulars of the present invention will be made clear from the following detailed description of the invention considered together with the accompanying drawings, wherein: I

FIG. 1 is a schematic block diagram of an embodiment of a frequency conversion system for an electronic musical instrument according to the present invention;

FIG. 2 is a diagram which depicts an example of the spectrum, i.e. the fundamental frequency and overtone frequencies, of an original signal and a signal which has had'the frequency converted;

FIG. 3 is a diagram of the inharmonicity function Y(n) vs. the order of harmonics;

FIG. 4 is a schematic block diagram of a second embodiment ofa frequency conversion system for an electronic musical instrument according to the present invention; I

FIG. Sis a schematic block diagram of a third embodiment ofa frequency conversion system for an electronic musical instrument according to the present invention;

FIG. 6 is a schematic block diagram of a fourth embodiment of a' frequency conversion system for an electronic'musical instrument according to the present invention; I I

FIG. 7 is a schematic block diagram of a fifth embodiment of a frequency conversion system for an electronic'musical instrument according to the present invention;

FIG. 8 is a diagram of the characteristic of frequency vs. pitch;

FIG. 9 is a schematic block diagram of a sixth embodiment of a frequency conversion system for an electronic musical instrument according to the present invention;

FIG. 10 is a schematic block diagram of a seventh embodiment of a frequency conversion system for an electronic musical instrument according to the present invention; I I

FIG. 11 is a diagram of the frequency conversion characteristic of the embodiment shown in FIG. 10;

FIG. 12 is a schematic block diagram of an example of a frequency converter which is used in a frequency conversion system for an electronic musical instrument according to the present invention;

FIG. 13 is a schematic block diagram of a multiplier which is used in the frequency converter shown in FIG. 12;

FIG. 14 is a schematic block diagram of another example of a frequency converter which is used in a frequency conversion system for an electronic musical instrument according to the present invention; and

FIGS. ISA-D is a diagram of a frequency spectrum for explaining the operation of the frequency converter shown in FIG. 14.

DETAILED DESCRIPTION FIG. 1 is a diagram ofa monophonic electronic musical instrument which can produce a new tone.

Referring to FIGS. 1, '2, and 3, in FIG. 1, a signal source 100 comprises a tone generator 98 and a pitch selector 1. The tone generator 98 produces a signal 6 which has fundamental and exact harmonics, i.e., a frequency spectrum f,,f ,f ,f,,, where the fundamental and harmonic frequencies are f Hz, f Hz, f Hz, ...,f,.Hz,...and

as shown by solid lines in FIG. 2. The fundamental frequency f is controlled by a pitch selector 1. A frequency converter 200 subtracts Afl-Iz from the signal 6 and produces a signal 7 having frequency components (fr-AflHz, (Zfl-AflHz, (3f,Af)Hz, (nf,Af)Hz,

. as shown by dotted lines in FIG. 2. The signal 7 is transduced into a sound by an electro-acoustic transducer 3.

The sound has such new tone qualities as naturalness, clearness and strength, and is a new tone which can not be obtained by a conventional electronic musical instrument. I

As for the signal 6, the inharmonicityfunction Y(n) Therefore the signal 6 does not have a naturalness of a tone produced by a conventional musical instrument. This relationship is shown by a solid line 10 in FIG. 3.

As for the signal 7, the inharmonicity function Y(n) can be represented as follows,

where (f Af) is a fundamental frequency and (nf -Af) is the frequency of the n-th harmonic. Equation (8) indicates that the ratios of the frequencies of overtones to the fundamental frequency increase with an increase in the frequency. Equation (8) is shown by a dotted line 11 in FIG. 3. The dotted line 11 shows that a signal 7 has an inharmonicity function somewhat similar to a piano tone, the inharmonicity function Y(n) of which is represented by Equation (4) and is shown by the curved line 12 in FIG. 3. The frequency Afis preferably a sub-audio frequency, for example, several Hz, for simulation of a piano tone.

When the frequency Af is less than 2 percent of the fundamental frequencyf, the converted signal 7 has an improved tone quality such as improved naturalness, clearness and strength. When Afis more than 2 percent and less than 4 percent of the fundamental frequency f, the tone quality of the converted signal 7 is further improved with respect to naturalness, clearness and I strength. When Afis more than 4 percent of the fundamental frequency f, the signal 7 has a tone quality that cannot be obtained either by a conventional electronic musical instrument or by the conventional musical instrument. I

As mentioned-above, a frequency conversion system according to the present invention can change a signal with exact harmonics into another signal with inexact harmonics such as those of the natural sound of a conventional musical instrument.

When the frequency converter 200 adds Af'I-Iz to the signal 6 in FIG. 1, the converted signal 7 becomes a signal with inexact harmonics and an inharmonicity function Y(n) represented by Equation (9).

Equation (9) shows that the ratios of the frequencies of overtones to the fundamental frequency decrease. Equation (9) is shown by curved line 13 in FIG. 3. This signal is a new one which a conventional electronic musical instrument cannot produce.

FIG. 4 shows a second embodiment of a frequency conversion system for an electronic musical instrument according to the present invention. A signal source 100 is composed of a tone generator 98 and a pitch selector 1. The tone generator 98 the frequency of which is controlled by the pitch selector 1 produces a signal 6 which has fundamental and exact harmonics. A frequency converter 200 increases or decreases the frequencies of the signal 6 by Afl-Iz and puts out a signal 7. The signal 7 is transduced into a sound by an electro-acoustic transducer 3. Frequency Afl-Iz is also controlled by the pitch selector 1. Then, inharmonicity characteristic of the signal 7 is dependent on the pitch of the signal 7 and an optimum inharmonicity function for the signal 7 can be chosen as the pitch of the signal 7 ascends or descends.

FIG. shows the third embodiment of a frequency conversion system for an electronic musical instrument according to the present invention. Referring to FIG. 5, a signal source 100 comprises

tone generators

101, 102, 103, 104,. corresponding to the tones ofa musical scale and have fundamental frequencies f flog, f and their exact harmonics, respectively. The tone generatores 101, 102, 103, 104, are connected to

frequency converters

201, 202, 203, 204, respectively. The converting frequencies of the

frequency converters

201, 202, 203, 204, are Af Af Af Af respectively.

The output signals of the

frequency converters

201, 202, 203, 204, are connected to a keyswitch system 4 of a keyboard. Output signals selected by the keyswitch system 4 are filtered by a tone filter Sand transduced into sounds by an electro-acoustic transducer 3.

According to the embodiment shown in FIG. 5, any inharmonicity transition is obtainable along the musical scale by arranging the converting frequencies Af Af Af Af for desired inharmonicity transition. For example, when the converting frequencies Af Af Af Af are the same percentage of the fundamental frequencies of the corresponding tone generators, Equation (8) is the same for every tone generator and frequency converter; in other words, for every tone corresponding to a key of the keyswitch system 4. Therefore, a uniform inharmonicity characteristic is obtained over the whole musical scale.

FIG. 6 shows the fourth embodiment of a frequency conversion system for an electronic musical instrument according to the present invention. Referring to FIG. 6, a signal source 100 comprises tone generators 101, I02, I03, 104, corresponding to the musical scale and have fundamental frequencies f ,j" ,f ,f and their exact harmonics, respectively. Signals from the

tone generator

101, 102, 103, 104, are selected by a keyswitch system 4. Output signals from the keyswitch system 4 are gathered in one or more groups, for example, in three groups, and further fed to

frequency converters

201, 202, and 203 corresponding to the three groups. Output signals from the

frequency converter

201, 202 and 203 are fed to a tone filter 5 and transduced into sounds by electro-acoustic transducer 3. This embodiment requires fewer frequency converters than the embodiment shown in FIG. 5 and is more practical.

FIG. 7 shows a fifth embodiment of a frequency conversion system for an electronic musical instrument according to the present invention to obtain an inharmonicity characteristic in tones. Referring to FIG. 7, a signal source comprises

tone generators

101, 102, 103, 104, corresponding to the musical scale and having fundamental frequencies f ,f, ,f ,f and their exact harmonics, respectively. Signals from the

tone generators

101, 102, 103, 104, are selected by a keyswitch system 4 and fed through

resistors

301, 302, 303, 304, to a frequency range separator 400 comprising filters and separated into a plurality of groups, for example, into low frequency range signals, medium frequency range signals and high frequency range signals. Separated signals have the frequency converted by

frequency converters

201, 202, and 203 respectively which are then gathered by gathering means, i.e. resistors 501, 502 and 503, and further transduced into sounds by an electroacoustic transducer 3.

In the embodiments shown in FIG. 5, FIG. 6 and FIG. 7, pitches or fundamental frequencies of the

tone generators

101, 102, 103, 104, are preferably biased for compensation of any unwanted pitch deviatio caused by the frequency conversion.

A frequency conversion system for an electronic musical instrument according to the present invention has another function and effect which overcomes a defect of the conventional electronic musical instrument, i.e. a discrepancy between the musical scale produced by the conventional electronic musical instrument and a natural pitch sensation.-

FIG. 8 shows an example of the relation between the signal frequency and the pitch recognized by human ears. As shown in FIG. 8, the sensation of pitch change saturates in the low and high frequency regions and a greater frequency change is required for human ears to distinguish an equal pitch change in the low and high frequency ranges than is required to distinguish a corresponding change in the middle frequency region.

FIG. 9 shows a sixth embodiment of a frequency conversion system for an electronic musical instrument according to the present invention for correcting the pitch imperfection of a conventional electronic musical instrument. Referring to FIG. 9, a tone generator 99 of a conventional electronic musical instrument generates tone signals which correspond to the musical scale. Generally, the tone generator 99 is composed of twelve oscillators corresponding to the respective tones of the chromatic musical scale and twelve chains of frequency dividers corresponding to said twelve oscillators. For example, when the tone generator 99 comprises oscillators and frequency dividers each of which divides the frequency of an input signal by a factor of two, the one octave musical intervals of the output signals are in the exact frequency ratio of 2:1.

The signals from the tone generator 99 are fed to a frequency converter 200 through a keyswitch 4 and a tone filter 5 and are transduced into sounds by an electro-acoustic transducer 3. The tone generator 99, the keyswitch system 4 and the tone filter 5 compose a signal source 100. The frequency converter 200 decreases the frequency fHz of the input signal by Afl-Iz and produces a signal with a frequency (f-AflHz. The percent-' age of frequency change 1 from the original pitch corresponding to the fundamental frequency fHz of said tone generator 99 is represented as follows:

1,: Af/fx 100 1 becomes great as the frequency fHz decreases, i.e., the pitch reduction becomes great as the frequency fHz decreases. Therefore, a tone in the low frequency range has a sufficiently low pitch and the pitch imperfection is improved in the low frequency range. Because the inharmonicity characteristic is also improved, the tone quality is improved.

FIG 10.'shows a seventh embodiment of a frequency conversion system for an electronic musical instrument according to the present invention for correcting the pitch imperfection ofa conventional electronic musical instrument. Referring to FIG. 10, a signal source 100 comprises a tone generator 99, a keyswitch system 4 and a tone filter 5. The tone generator 99 of a conventional electronic musical instrument generates tone signals having frequencies which correspond to the musical scale. The signal from the tone generator 99 is fed to a frequency range separator 40 through the keyswitch system 4 and the tone filter 5, so as to be separated into a plurality of frequency-band-limited signals, for example, into four signals the range of frequencies of which are (F,-F (F -F (F -F and (F.,-F respectively, where F, F F F F as shown in FIG. 10. At least one signal from the frequency range separator 400, for example, three signals, are fed to sub-frequency converters, for example, 205, 206 and 207, respectively.

Signals from the

sub-frequency converters

205, 206 and 207 and the remainder of the frequency-bandlimited signal which is not fed to any sub-frequency converter are gathered together through

resistors

501, 502, 503 and 504 and further transduced into sounds by an electro-acoustic transducer 3.

The frequency range separator 400, the

subfrequency converters

205, 206 and 207 and

resistors

501, 502, 503 and 504 compose a frequency converter 210.

When the converting frequencies of the

subfrequency converters

205, 206 and 207 are Afl-Iz, Af'I-Iz and AfHz, respectively, and are in the relation,

the pitch defect is improved not only in the low frequency range (F,-F but also in the high frequency range (F -F.,) and F,-F A negative converting frequency corresponds to a frequency decrement and a positive converting frequency corresponds to a frequency increment.

FIg. 11 shows an example of the frequency conversion characteristic achieved by the embodiment shown in FIG. 10.

Tone quality is also improved by the inharmonicity characteristic which is obtained. In the embodiments shown in FIG. 9 and FIG. 10, it is best if the tone generator 99 is biased to change the frequency for compensation of unwanted pitch deviation caused by frequency conversion.

When a magnetic tape recorder or a record player for playing record discs is used as a signal source in FIG. 1, FIG. 4, FIG. 9 and FIG. 10, the harmonicity characteristic or the pitch of the signals recorded on the tape or the disc is changed and the tone quality and the pitch imperfection are improved.

When a conventional musical instrument such as a violin, a clarinet or a trumpet and an acoustic-electric transducer such as a microphone are used as a signal source 100 in FIG. 1, FIG. 4, FIG. 5, FIG. 9 and FIG. 10, the inharmonicity characteristic of the musical instrument can be changed and a new tone having better tone quality than the original tone quality can be obtained. Some conventional musical instruments having pitch imperfection can be improved. It is also possible to obtain an entirely new tone quality by converting frequencies of signals of conventional musical instruments.

As mentioned-above, the scope of the present invention is not limited to a particular kind of signal source 100. It is only necessary that the signal source 100 generate an audio frequency signal.

The

frequency converters

200, 201, 202, 203, 204,

.. and

sub-frequency converter

205, 206, 207 can be realized as follows.

FIG. 12 shows an example of a frequency converter. Referring to FIG. 12, an audio frequency signal A sin 21rft, such as the output signal of anelectronic musical instrument, is applied to an input terminal 601 and is split by a constant phase splitter 603 into two signals X and X having a phase difference from each other of -n'/2 radians and respectively supplied to

leads

605 and 606. Signals X and X, from the

leads

605 and 606 are fed to

multipliers

609 and 610 respectively and are gathered by gathering means, i.e. resistors 611 and 612, and supplied to an output terminal 613. An oscillator 602 generates a pair of frequency converting signals Y and Y having a phase difference of 11/2 radians from each other and supplies them to leads 607 and 608. Signals Y and Y from the leads 607and 608 are fed to the

multipliers

609 and 610 respectively. The signals X X Y and Y, can be represented as follows.

X A sin (Z'rrft 4-4)) Y B sin(21rAft +d1) I, B sin(21rAft 1r/2 41) Output signals Z and Z from the

multipliers

609 and 610 can be represented as follows.

2 x AB sin(21rft i 17/2 an sin(211-Aft i 1r/2 l The signals Z and Z are gathered together and a signal /(Z,+Z as represented by Equation (18) appears at the output terminal 613.

The signal V2(Z1+Z2) at the output terminal 613 is a signal the frequency of which is the sum of or the difference between the two frequencies from the input terminals 601 and the oscillator 602. Whether the frequency of the signal %(Z +Z becomes the sum or the difference of the two frequencies depends on the phase dif ference between the two output signals from the phase splitter 603 and the phase difference between the two output signals from the oscillator 602.

FIG. 13 shows an embodiment of the

multipliers

609 and 610. A signal X applied to a terminal 614 is modulated in an amplitude modulator 616 by a modulating signal Y applied to a terminal 617. The signal X is also fed to a phase inverter 615. Output signals from the amplitude modulator 616 and the phase inverter 615 are gathered together by gathering means, i.e. resistors 618 and 619, and appear at an output terminal 620. The output signal from the amplitude modulator 616 has a carrier signal X and its two side bands. When the carrier signal X is cancelled by a phase inverted signal from the phase inverter 615 at the output terminal 620, only two side-bands appear at the terminal 620. The two side-bands correspond to a signal XY, namely, a product of the signal X and the signal Y. The

multipliers

609 and 610 and the amplitude modulator 616 should be linear.

An embodiment of a frequency converter which can be used as the

frequency converter

200, 201, 202, 203, 204, is shown in FIG. 14. A modulator 623 modulates an audio frequency signal{f which is applied to a terminal 621, by a modulating signal f which has a frequency higher than {f,,} and which is supplied to another terminal 622. The modulator 623 produces at least two side bands fl{j",,} and f +{fl,} as shown in FIG. 15(a) and (b). A band pass filter 624 passes only the lower side band f {f,,} as shown in FIG. 15(c). Another modulator 626 modulates the filtered lower side band f {f by another modulating signal )1. (=fg-Aj) and produces at least two side bands f f +{f and f +f {fi,} as shown in FIG. 15(d). The lower side band f '-f +{f is passed by another band pass filter 627 and appears at an output terminal 628. The output signalf f +{f,,} is {fi Afthe frequency of which is lower than that of the signal 2} by a small frequency Af. The

balanced modulators

623 and 627 can be linear modulators such as multipliers using a Hall effect or nonlinear modulators such as ring modulators.

While particular embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that numerous modifications and variations can be made in the form and construction thereof without departing from the fundamental principles of the invention.

We claim:

l. A frequency conversion system for an electronic musical instrument comprising;

a signal source composed of at least one biased tone generator which is detuned from a normal musical scale by a predetermined frequency difference AfHz in a predetermined direction for generating a first tone signal having a first fundamental frequency component which is biased from said normal musical scale by said frequency difference AfHz in said direction and which also has exact harmonic components the frequencies of which are a positive integer multiple of the frequency of said first fundamental frequency;

at least one frequency converter connected to said signal source for changing all the frequency components of said first tone signal in a direction the opposite of said predetermined direction by a converting frequency equal to said predetermined frequency difference AjHz in order to produce a converted tone signal having frequency components consisting of a second fundamental frequency component and inexact harmonics thereof, each of said second fundamental frequency component and said inexact harmonics having a changed frequency which differs from said first fundamental frequency component and said exact harmonics of said first tone signal by said converting frequency AjHz of said frequency converter; and

an electro-acoustic transducer connected to said at least one frequency converter.

2. A frequency conversion system for an electronic musical instrument as claimed in claim 1, wherein:

said signal source consists essentially of twelve master oscillators and twelve chains of frequency dividers corresponding to said twelve master oscillators and being coupled thereto, said twelve master oscillators being biased to bias the frequency from the normal chromatic musical scale in an upward direction; and said frequency converter connected .to said signal source changes the frequency of an output signal from said signal source in a downward direction by said converting frequency for compensating a pitch discrepancy from a natural pitch sensation of the human ear.

3. A frequency conversion system for an electronic musical instrument as claimed in claim 1, wherein said tone generator has a pitch selector which controls both the frequency of said tone generator and said converting frequency.

4. A frequency conversion system for an electronic musical instrument as claimed in claim 1, wherein there is-a plurality of tone generators corresponding in number to the respective tones of the musical scale, and there is a plurality of frequency converters corresponding in number to the number of said tone generators, respectively.

5. A frequency conversion system for an electronic musical instrument as claimed in claim 1 further comprising a key switch system, and in which there is a plurality of tone generators corresponding in number to the respective tones of the musical scale, said key switch system being connected to said tone generator for selecting tone signals from among said plurality of tone generators and gathering said selected tone signals into a plurality of groups each of which has successive tone signals of the musical scale, said frequency conversion system having a plurality of frequency converters corresponding in number to said plurality of groups of tone signals, said key switch system being connected to said frequency converters for feeding said gathered tone signals to the respective frequency converters.

6. A frequency conversion system for an electronic musical instrument comprising;

a signal source composed of at least one biased tone generator generating a first tone signal having a first fundamental frequency component which is biased from a normal musical scale by a predetermined frequency difference AfHz in a predetermined direction and further having exact harmonic components the frequencies of which are a positive integer multiple of the frequency of said first fundamental frequency; at least one frequency converter composed of a constant phase splitter connected to said tone generator for splitting said first tone signal into a pair of signals having a phase difference of 17/2 radians, an oscillator for generating a pair of frequency converting signals having said predetermined frequency difference afHz and a phase difference of 1r/2 radians, a first multiplier coupled to said phase splitter and said oscillator for multiplying one output signal from said phase splitter by one of said frequency converting signals from said oscillator, a second multiplier coupled to said phase splitter and said oscillator for multiplying the other output signal from said phase splitter by the other of said frequency converting signals from said oscillator, and gathering means coupled to said multipliers for gathering'the output signals from said first and second multipliers, said frequency converter changing all the frequency components of said first tone signal in a direction the opposite of said predetermined direction by said predetermined frequency difference Afl-lz in order to produce a converted tone signal having frequency components consisting a second fundamental frequency component and inexact harmonics thereof, said second fundamental frequency component and said inexact harmonics having a changed frequency which differs from said first fundamental frequency component and said exact harmonics of said first tone signal by the converting frequency of said frequency converter, respectively; and

7. A frequency conversion system for an electronic musical instrument comprising;

a signal source composed of at least one biased tone generator which is detuned from a normal musical scale by a predetermined frequency difference Afl-lz in a predetermined direction for generating a first tone signal having a first fundamental frequency component which is biased from said normal musical scale by said frequency difference Afl-lz in a predetermined direction and further having exact harmonic components the frequencies of which are positive integer multiples of the frequency of said first fundamental frequency compo- 'nent;

at least one frequency converter composed of a modulator connected to said tone generator for modulating said first tone signal by a modulating signal having a frequency fcHz which is higher than twice the frequencies of said exact harmonic components, a first filter coupled to said first modulator for passing only one side band of the modulated signal from said modulator, a further modulator coupled to said first filter for modulating the output signal from said filter by another modulating signal having frequency fcHz which differs by said predetermined frequency difference Afl-lz from said frequency fcHz, and a second filter coupled to said further modulator for passing only the lower side band of the modulated signal from said further modulator; and

i an electro-acoustic transducer connected to said second filter of said frequency converter.

Claims

1. A frequency conversion system for an electronic musical instrument comprising; a signAl source composed of at least one biased tone generator which is detuned from a normal musical scale by a predetermined frequency difference Delta fHz in a predetermined direction for generating a first tone signal having a first fundamental frequency component which is biased from said normal musical scale by said frequency difference Delta fHz in said direction and which also has exact harmonic components the frequencies of which are a positive integer multiple of the frequency of said first fundamental frequency; at least one frequency converter connected to said signal source for changing all the frequency components of said first tone signal in a direction the opposite of said predetermined direction by a converting frequency equal to said predetermined frequency difference Delta fHz in order to produce a converted tone signal having frequency components consisting of a second fundamental frequency component and inexact harmonics thereof, each of said second fundamental frequency component and said inexact harmonics having a changed frequency which differs from said first fundamental frequency component and said exact harmonics of said first tone signal by said converting frequency Delta fHz of said frequency converter; and an electro-acoustic transducer connected to said at least one frequency converter.

2. A frequency conversion system for an electronic musical instrument as claimed in claim 1, wherein: said signal source consists essentially of twelve master oscillators and twelve chains of frequency dividers corresponding to said twelve master oscillators and being coupled thereto, said twelve master oscillators being biased to bias the frequency from the normal chromatic musical scale in an upward direction; and said frequency converter connected to said signal source changes the frequency of an output signal from said signal source in a downward direction by said converting frequency for compensating a pitch discrepancy from a natural pitch sensation of the human ear.

4. A frequency conversion system for an electronic musical instrument as claimed in claim 1, wherein there is a plurality of tone generators corresponding in number to the respective tones of the musical scale, and there is a plurality of frequency converters corresponding in number to the number of said tone generators, respectively.

6. A frequency conversion system for an electronic musical instrument comprising; a signal source composed of at least one biased tone generator generating a first tone signal having a first fundamental frequency component which is biased from a normal musical scale by a predetermined frequency difference Delta fHz in a predetermined direction and further having exact harmonic components the frequencies of which are a positive integer multiple of the frequency of said first fundamental frequency; at least one frequency converter composed of a constant phase splitter connected to Said tone generator for splitting said first tone signal into a pair of signals having a phase difference of pi /2 radians, an oscillator for generating a pair of frequency converting signals having said predetermined frequency difference Alpha fHz and a phase difference of pi /2 radians, a first multiplier coupled to said phase splitter and said oscillator for multiplying one output signal from said phase splitter by one of said frequency converting signals from said oscillator, a second multiplier coupled to said phase splitter and said oscillator for multiplying the other output signal from said phase splitter by the other of said frequency converting signals from said oscillator, and gathering means coupled to said multipliers for gathering the output signals from said first and second multipliers, said frequency converter changing all the frequency components of said first tone signal in a direction the opposite of said predetermined direction by said predetermined frequency difference Delta fHz in order to produce a converted tone signal having frequency components consisting a second fundamental frequency component and inexact harmonics thereof, said second fundamental frequency component and said inexact harmonics having a changed frequency which differs from said first fundamental frequency component and said exact harmonics of said first tone signal by the converting frequency of said frequency converter, respectively; and an electro-acoustic transducer connected to said at least one frequency converter.

7. A frequency conversion system for an electronic musical instrument comprising; a signal source composed of at least one biased tone generator which is detuned from a normal musical scale by a predetermined frequency difference Delta fHz in a predetermined direction for generating a first tone signal having a first fundamental frequency component which is biased from said normal musical scale by said frequency difference Delta fHz in a predetermined direction and further having exact harmonic components the frequencies of which are positive integer multiples of the frequency of said first fundamental frequency component; at least one frequency converter composed of a modulator connected to said tone generator for modulating said first tone signal by a modulating signal having a frequency fcHz which is higher than twice the frequencies of said exact harmonic components, a first filter coupled to said first modulator for passing only one side band of the modulated signal from said modulator, a further modulator coupled to said first filter for modulating the output signal from said filter by another modulating signal having frequency f''cHz which differs by said predetermined frequency difference Delta fHz from said frequency fcHz, and a second filter coupled to said further modulator for passing only the lower side band of the modulated signal from said further modulator; and an electro-acoustic transducer connected to said second filter of said frequency converter.