JP2005274782A - Electronic musical sound generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce electromagnetic wave disturbance without deteriorating musical sound. <P>SOLUTION: This device 1 is provided with a tone generator 5 which generates digital data indicating the musical sound, a buffer storage device 6 which temporarily records the digital data 6, a digital/ analog converter 7 which reads the recorded digital data stored in the buffer storage device 6 and generates an analog signal indicating the musical sound indicated by the recorded digital data, a first signal generator 2 which generates a first signal CK0 formed by a pulse train with fixed intervals and a second signal generator 3 which generates a second signal CK0m formed by a pulse train with fluctuated intervals. The tone generator 5 operates using the second signal CK0m as a clock signal. The digital to analog converter 7 operates using the first signal CK0 as the clock signal. Thus, the electromagnetic wave disturbance is reduced without deteriorating the musical sound. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electronic musical tone generator, and more particularly to an electronic musical tone generator that generates a musical tone waveform by calculation.

  An electronic device exemplified by an electronic musical sound generator and an electronic musical instrument emits EMI (Electro Magnetic Interference) by a current flowing inside. Such EMI is regulated to prevent adverse effects on other electronic devices. As a measure for reducing the EMI, it is known that a bypass capacitor, a choke coil, and a ferrite bead are mounted on the electronic device. It is desired to effectively reduce EMI noise at a lower cost.

  An SSCG (Spread Spectrum Clock Generator) technique that effectively reduces EMI is known. The SSCG technique is a technique that slightly fluctuates (frequency modulation) the frequency of the oscillation clock in the clock generator. The electric circuit can reduce EMI by using a clock whose frequency varies. Such an SSCG technique is disclosed in Japanese Patent Laid-Open Nos. 8-102660 and 8-32883. However, in the conventional electronic musical sound generator, the SSCG technology has not been used because of the fear that the slight frequency modulation will cause the sound quality to deteriorate. Electronic musical tone generators are desired to reduce EMI noise without degrading the musical tone to be generated.

  Japanese Patent Application Laid-Open No. 8-102660 discloses a signal modulation circuit capable of generating a highly accurate and variable frequency signal with a simple and inexpensive configuration. The signal modulation circuit selects a signal from a plurality of cascaded signal delay circuits that delay the original signal by almost the same time and one of the delayed signals output from the original signal or each of the signal delay circuits. A circuit and a signal selection control circuit for controlling selection of a signal by the signal selection circuit. This signal selection control circuit sequentially or within the range in which a maximum delay time corresponding to a phase difference of less than 360 ° is generated for one of the original signal or one of the delayed signals output from each signal delay circuit in order of increasing delay time. The signal selection circuit is configured to repeat the operation of selecting one or more jumps.

  Japanese Patent Laid-Open No. 8-32883 discloses an inexpensive high-frequency signal modulation circuit that does not require an intermediate frequency transformer and external parts, and that can be miniaturized and controlled by being incorporated into an IC chip. The high-frequency signal modulation circuit includes a reference oscillator, a fixed frequency divider, a voltage controlled oscillator, a first variable frequency divider that divides the output of the voltage controlled oscillator based on control data from an external control device, And a phase comparator that compares the inputs from the fixed frequency divider and feeds back to the voltage controlled oscillator, and oscillates the audio carrier by dividing the output of the fixed frequency divider by the control data from the external control device. A second variable frequency divider that performs switching, a video AM modulator that amplitude-modulates the output of the voltage controlled oscillator with a video signal, and an audio FM that frequency-modulates the output from the second variable frequency divider with an audio signal A modulator and a mixer circuit that mixes the frequencies f1 and f2 and outputs the mixed signal to the output terminal OUT are provided.

JP-A-8-102660 JP-A-8-32883

  An object of the present invention is to provide an electronic musical tone generator that reduces EMI noise without degrading musical tone to be generated.

  In the following, means for solving the problems will be described using the reference numerals used in the best modes and embodiments for carrying out the invention in parentheses. This reference numeral is added to clarify the correspondence between the description of the claims and the description of the best mode for carrying out the invention / example, and is described in the claims. It should not be used to interpret the technical scope of the invention.

  An electronic musical tone generator (1) according to the present invention includes a tone generator (5) for generating digital data indicating musical sounds, a buffer storage device (6) for temporarily recording the digital data, and a buffer storage device (6). A digital-analog converter (7) that reads recorded digital data stored in the digital signal and generates an analog signal indicating a musical tone indicated by the recorded digital data, and a first signal (CK0) formed by a pulse train having a constant interval And a second signal generator (3) for generating a second signal (CK0m) formed by a pulse train having a variable interval. The tone generator (5) operates using the second signal (CK0m) as a clock signal. The digital-analog converter (7) operates using the first signal (CK0) as a clock signal. According to such an electronic musical sound generator (1), it is possible to reduce electromagnetic interference without degrading musical sounds.

  The second signal generator (3) preferably generates the second signal (CK0m) by modulating the position of the pulse forming the first signal (CK0).

  The second signal (CK0m) is preferably periodic with a sampling period. At this time, the tone generator (5) records the digital data in the buffer storage device (6) for each sampling period. The digital-analog converter (7) reads the recorded digital data from the buffer storage device (6) at every sampling period based on the first signal (CK0).

  The first signal generator (2) generates a first signal (CK0) using the first vibrator. At this time, it is preferable that the second signal generator generates the second signal (CK0m) using a second vibrator different from the first vibrator.

  The digital-analog converter (7) reads the recorded digital data from the buffer storage device (6) at every sampling period based on the first signal (CK0). At this time, the second signal (CK0m) preferably has a sufficient number of pulses for the tone generator (5) to generate digital data during the sampling period.

  An electronic musical tone generator (1) according to the present invention divides a first signal (CK0) to generate a sampling period clock signal formed by a pulse train indicating a sampling period (11, 12, 14, 15). 21 and 22). At this time, the tone generator (5) preferably outputs digital data to the buffer storage device (6) for each sampling period based on the sampling period clock signal.

  The tone generator (5) is preferably a CPU that executes a computer program indicating a procedure for calculating a musical sound.

  The electronic musical instrument according to the present invention includes such an electronic musical tone generator (1) and a keyboard (55) having a plurality of keys. At this time, it is preferable that the tone generator (5) generates digital data based on a key that is pressed among a plurality of keys.

  According to the electronic musical sound generator according to the present invention, it is possible to reduce electromagnetic interference without degrading musical sounds.

  Embodiments of an electronic musical tone generator according to the present invention will be described with reference to the drawings. The electronic musical tone generator 1 includes a source oscillator 2, a spread spectrum clock generator 3, a tone generator 5, a buffer storage device 6, and a digital / analog converter 7, as shown in FIG. The source oscillator 2 includes a crystal as a vibrator. The source oscillator 2 generates a clock signal CK0 using a piezoelectric effect that oscillates when a voltage is applied to the vibrator. The clock signal CK0 is formed from a pulse train whose voltage changes. In the pulse train, the interval between two adjacent pulses is constant, and the number (frequency) of pulses generated per second is 36.864 MHz.

  The source oscillator 2 includes a 1/2 frequency divider 11, a 1/4 frequency divider 12, a 1/2 frequency divider 14, and a 1/48 frequency divider 15. The 1/2 divider 11 divides the clock signal CK0 by 1/2 to generate the clock signal CK1. That is, the clock signal CK1 forms a pulse whose voltage periodically changes at 18.432 MHz. The ¼ frequency divider 12 divides the clock signal CK1 by ¼ to generate the clock signal CK3. That is, the clock signal CK3 forms a pulse whose voltage periodically changes at 4.608 MHz. The 1/2 divider 14 divides the clock signal CK3 by 1/2 to generate the clock signal CK4. That is, the clock signal CK3 forms a pulse whose voltage periodically changes at 2.304 MHz. The 1/48 frequency divider 15 divides the clock signal CK4 by 1/48 to generate the clock signal CK9. That is, the clock signal CK9 forms a pulse whose voltage periodically changes at 48 kHz. Hereinafter, the interval between pulses whose voltage periodically changes at 48 kHz is referred to as a sampling period in this specification.

  The spread spectrum clock generator 3 includes a multistage delay circuit 16, a signal selection circuit 17, a switch 18, a counter 19, a 1/8 frequency divider 21, and a 1/96 frequency divider 22. The multistage delay circuit 16 includes a plurality of delay circuits not shown in the figure that are not less than 2 and not more than 767. The plurality of delay circuits are connected in series. The first delay circuit among the plurality of delay circuits generates a clock signal obtained by delaying the clock signal CK0 generated by the source oscillator 2. Among the plurality of delay circuits, the second and subsequent delay circuits generate a clock signal obtained by delaying the clock signal generated by the preceding delay circuit.

  The switch 18 outputs either the clock signal CK3 or the clock signal CK9 to the counter 19 as a reset signal. That is, the reset signal forms a pulse whose voltage periodically changes at 4.608 MHz, or a pulse whose voltage changes periodically at 48 kHz. The counter 19 counts pulses indicated by the clock signal CK0m output from the signal selection circuit 17. The counter 19 further resets the pulse count of the clock signal CK0m in response to the pulse of the reset signal output from the switch 18, and selectively outputs the clock signal CK0 output from the source oscillator 2. 17 is instructed.

  The signal selection circuit 17 associates the number of pulses with a plurality of delay circuits of the multistage delay circuit 16. The signal selection circuit 17 selects a delay circuit corresponding to the number of pulses counted by the counter 19 from the plurality of delay circuits, and outputs a pulse of the clock signal output from the delay circuit as the clock signal CK0m. At this time, the clock signal CK0m is formed by a pulse train in which the interval between two adjacent pulses varies. At this time, the average value of the frequency at which the pulse is generated is 36.864 MHz. Note that the clock signal CK0 output from the source oscillator 2 is also input to the signal selection circuit 17, and the pulse of the clock signal CK0 is output as the clock signal CK0m in the period indicated by the pulse of the reset signal output from the switch 18.

  The 1/8 frequency divider 21 divides the clock signal CK0m by 1/8 to generate the clock signal CK3m. That is, the clock signal CK3m forms a pulse whose voltage periodically changes at 4.608 MHz when the reset signal forms a pulse of 4.608 MHz. The clock signal CK3m is formed by a pulse train in which the interval between two adjacent pulses varies when the reset signal forms a 48 kHz pulse, and the average value of the frequencies generated by the pulse is 4. 608 MHz.

  The 1/96 frequency divider 22 divides the clock signal CK3m by 1/96 to generate the clock signal CK9m. The clock signal CK9m always forms a pulse whose voltage periodically changes at 48 kHz regardless of whether the reset signal forms a pulse of 4.608 MHz or 48 kHz.

  The tone generator 5 includes a plurality of electric circuits. The tone generator 5 uses the clock signal CK0m, the clock signal CK3m, and the clock signal CK9m as clock signals, and synchronizes the processes sequentially executed by the plurality of electric circuits to generate digital data indicating musical sounds. The digital data indicates the displacement of the waveform of the musical sound to be generated for each sampling period. The tone generator 5 outputs the digital data to the buffer storage device 6 every sampling period indicated by the clock signal CK9m.

  The buffer storage device 6 is a FIFO storage device, and temporarily records the digital data output from the tone generator 5. The buffer storage device 6 can also be composed of only one stage memory for storing L / R digital data for one sampling period. The digital-analog converter 7 reads the digital data from the buffer storage device 6 at every sampling period indicated by the clock signal CK9, and generates an analog signal. The analog signal is an electric signal whose voltage changes with time, and the voltage indicates a waveform of a musical sound indicated by digital data output from the tone generator 5. The analog signal is formed of a left analog signal and a right analog signal. That is, the buffer storage device 6 corrects the difference in operation time between the tone generator 5 and the digital / analog converter 7.

  The electronic musical sound generator 1 further includes a left amplifier 31, a left speaker 32, a right amplifier 33, and a right speaker 34. The left amplifier 31 amplifies the left analog signal generated by the digital-analog converter 7. The left speaker 32 converts the left analog signal amplified by the left amplifier 31 into sound. The right amplifier 33 amplifies the right analog signal generated by the digital-analog converter 7. The right speaker 34 converts the right analog signal amplified by the right amplifier 32 into sound.

  Such an electronic musical sound generator 1 is mounted on an electronic musical instrument, a mobile phone, a karaoke device, and a personal computer that generate musical sounds.

  FIG. 2 shows the tone generator 5 mounted on the electronic musical instrument in detail. The tone generator 5 includes an MPU 41 which is an electric circuit, a key touch detection circuit 42, an assignment memory 43, an F number accumulator 44, a waveform memory 45, a sample point interpolation circuit 46, a digital filter 47, an envelope generator 48 and a multiplier. 49, a series accumulator 51, an effect adder 52, and a parallel-serial converter 53.

  The electronic musical instrument further includes a panel 54 and a keyboard 55. The key touch detection circuit 42 detects a key that has been pressed out of a plurality of keys included in the keyboard 51 and measures the key pressing speed of the key. The MPU 41 collects the keys of the keyboard 51 and the keystroke speed detected by the key touch detection circuit 42, and collects input information input to the panel 54 by the user. The input information indicates a musical sound sequence and an effect type.

  The assignment memory 43 records an F number, a filter type, an envelope type, a sequence, and an effect in association with information output from the MPU 41. The assignment memory 43 outputs information corresponding to the information output from the MPU 41 to the F number accumulator 44, the digital filter 47, the envelope generator 48, the sequence accumulator 51, and the effect adder 52.

  The F number accumulator 44 calculates an address based on the F number output from the assignment memory 43. The address indicates the phase of the waveform of the musical sound arranged at the time for each sampling period. The F number accumulator 44 further calculates an integer address indicating the integer part of the address and a decimal address indicating the decimal part of the address.

  The waveform memory 45 records a displacement for one period of a waveform indicating a musical sound. That is, the waveform memory 45 records the displacement of each phase of the waveform indicating the musical sound in association with the integer address. The waveform memory 45 outputs a waveform displacement corresponding to the integer address calculated by the F number accumulator 44. The sample point interpolation circuit 46 interpolates based on the waveform displacement output from the waveform memory 45 and the decimal address calculated by the F number accumulator 44, and converts the waveform of the musical sound to be arranged at the time of each sampling period. Displacement is calculated to generate a musical sound waveform.

  The digital filter 47 filters the tone waveform generated by the sample point interpolation circuit 46 based on the type of filter output from the assignment memory 43. The envelope generator 48 calculates a value to be multiplied by the musical sound waveform based on the type of envelope output from the assignment memory 43, and generates an envelope. The multiplier 49 multiplies the musical sound generated by the digital filter 47 by the value generated by the envelope generator 48 and adds an envelope to the musical sound generated by the digital filter 47.

  The series accumulator 51 distributes and accumulates the digital data of one tone of music multiplied by the multiplier 49 into one of the three series. The effect adder 52 adds an effect to the musical sound generated by the series accumulator 51 based on the type of effect output from the assignment memory 43. The parallel-serial converter 53 performs parallel-serial conversion on the digital data indicating the musical sound generated by the effect adder 52 and causes the buffer storage device 6 to record the digital data.

  Note that the tone generator 5 can also be configured by a CPU. At this time, the CPU operates by executing the installed computer program. That is, the computer program includes an MPU 41, a key touch detection circuit 42, an assignment memory 43, an F number accumulator 44, a waveform memory 45, a sample point interpolation circuit 46, a digital filter 47, an envelope generator 48, and a multiplier 49. It is formed of a plurality of computer programs each indicating a plurality of operations executed by the series accumulator 51, the effect adder 52, and the parallel-serial converter 53.

  FIG. 3 shows a clock signal CK0m generated by the spread spectrum clock generator 3 when the multistage delay circuit 16 includes a six-stage delay circuit. As shown in FIG. 3, the clock signal CK0 generated by the source oscillator 2 is periodically formed with pulses. The first delay circuit of the plurality of delay circuits delays the clock signal CK0 by a time sufficiently shorter than the pulse interval of the clock signal CK0 to generate the clock signal CK0d1. That is, the pulse of the clock signal CK0d1 is formed with a slight delay in time after the pulse of the clock signal CK0 is formed. The i-th delay circuit (i = 2, 3, 4, 5, 6) of the plurality of delay circuits is the clock signal CK0d (i−1) generated by the (i−1) -th delay circuit. ) Is slightly delayed in time to generate the clock signal CK0di. At this time, the pulse of the clock signal CK0d6 generated by the final delay circuit among the plurality of delay circuits is delayed from the pulse of the clock signal CK0 by approximately 3% of the pulse interval of the clock signal CK0. doing.

  The pulses formed in the clock signal CK0m are formed simultaneously with one of the pulses of the clock signals CK0d1 to CK0d6 and the clock signal CK0. At this time, the clock signal CK0m is formed by a pulse train in which the interval between two adjacent pulses varies, and the average value of the frequency at which the pulse is generated coincides with the frequency at which the pulse of the clock signal CK0 is generated. 36.864 MHz.

  The electric circuits 2 to 53 mounted on the electronic musical tone generator 1 are formed of gates that turn on / off certain electric signals. Such a gate emits an electromagnetic wave in a band of an integral multiple of the frequency of the pulse when supplying a clock signal composed of pulses with a constant interval, and an electromagnetic wave in the band when supplying a clock signal composed of pulses with a variable interval. Power is reduced to a fraction. For this reason, the electronic musical tone generator 1 can reduce the intensity of the radiated electromagnetic wave as compared to when the tone generator 5 uses the clock signal CK0 as a clock signal. Further, the number of gates included in the tone generator 5 accounts for 95% or more of the total number of gates included in the electronic musical tone generator 1. For this reason, the electronic musical tone generator 1 can reduce the intensity of the radiated electromagnetic wave to a predetermined amount by replacing only the clock signal supplied to the tone generator 5 with the clock signal CK0m.

  The electronic musical sound generator 1 uses the clock signal CK0 having a constant pulse interval to generate an analog signal indicating the waveform of the musical sound as the voltage changes with time. For this reason, the electronic musical tone generator 1 is preferable because it is difficult for noise to be added to the musical tone, and an appropriate musical tone can be generated.

  In another embodiment of the electronic musical tone generator according to the present invention, the spread spectrum clock generator 3 in the above-described embodiment is replaced with another SSCG. The SSCG includes a vibrator having a lower accuracy than the vibrator (crystal) used by the source oscillator 2. Examples of such a vibrator include a CR oscillator and a ceramic oscillator. In other words, the SSCG does not use the clock signal CK 0 generated from the source oscillator 2, and generates a variable clock signal whose pulse interval varies greatly from the source oscillator 2. The fluctuation clock signal is formed with a sufficient number of pulses during the sampling period so that the tone generator 5 can generate digital data indicating the musical sound produced during the sampling period. The tone generator 5 is further supplied with a clock signal CK9m in which a pulse is formed for each sampling period.

  The tone generator 5 executes a tone generation process for calculating a displacement for each sampling period of the waveform of the tone to be generated for each sampling period, and causes the buffer storage device 6 to record the displacement in response to a pulse of the clock signal CK9m. . At this time, the tone generator 5 stops the tone generation process, delays the tone generation process, or invalidates the generated tone and executes the tone generation process again, thereby performing the tone generation process for each sampling period. Running to. According to such an operation, the buffer storage device 6 functions only with one-stage memory for storing L / R digital data for one sampling period, and the storage capacity of the digital data in the buffer storage device 6 overflows. Is preferably prevented.

  The electronic musical sound generating apparatus according to the present embodiment can reduce the intensity of the electromagnetic wave to be radiated as compared to when the tone generator 5 uses the clock signal CK0 as a clock signal. The electronic musical sound generator further uses the clock signal CK0 having a constant pulse interval to generate an analog signal that indicates the waveform of the musical sound as the voltage changes with time. For this reason, the electronic musical sound generator is preferable because it is difficult for noise to be added to the musical sound, and an appropriate musical sound can be generated.

FIG. 1 is a block diagram showing an embodiment of an electronic musical tone generator according to the present invention. FIG. 2 is a block diagram showing the tone generator. FIG. 3 is a time chart showing a clock signal.

Explanation of symbols

1: Electronic musical sound generator 2: Source oscillator 3: SSCG
5: Tone generator 6: Buffer storage device 7: Digital / analog converter CK0 to CK9: Clock signal CK0m to CK9m: Clock signal 11: 1/2 divider 12: 1/4 divider 14: 1/2 divider 15: 1/48 frequency divider 16: Multistage delay circuit 17: Signal selection circuit 18: Switch 19: Counter 21: 1/4 frequency divider 22: 1/96 frequency divider 31: Left amplifier 32: Left speaker 33 : Right amplifier 34: Right speaker 41: MPU
42: Key touch detection circuit 43: Assignment memory 44: F number accumulator 45: Waveform memory 46: Sample point interpolator 47: Digital filter 48: Envelope generator 49: Multiplier 51: Sequence accumulator 52: Effect Adder 53: Parallel serial converter 54: Panel 55: Keyboard CK0d1 to CK0dn: Clock signal

Claims (8)

A tone generator that generates digital data representing musical sounds;
A buffer storage device for temporarily recording the digital data;
A digital-to-analog converter that reads recorded digital data stored in the buffer storage device and generates an analog signal indicating a musical sound indicated by the recorded digital data;
A first signal generator for generating a first signal formed by a pulse train having a constant interval;
A second signal generator for generating a second signal formed by a pulse train having a variable interval;
The tone generator operates using the second signal as a clock signal,
The digital-to-analog converter is an electronic musical tone generator that operates using the first signal as a clock signal. In claim 1,
The electronic signal generating apparatus, wherein the second signal generator generates the second signal by modulating a position of a pulse forming the first signal. In claim 2,
The second signal is periodic with a sampling period;
The tone generator records the digital data in the buffer storage device for each sampling period,
The digital-to-analog converter reads the recorded digital data from the buffer storage device every sampling period based on the first signal. In claim 1,
The first signal generator generates the first signal using a first vibrator,
The electronic signal generator according to claim 1, wherein the second signal generator generates the second signal using a second vibrator different from the first vibrator. In claim 4,
The digital-analog converter reads the recorded digital data from the buffer storage device at every sampling period based on the first signal,
An electronic musical sound generating device, wherein the second signal is formed with a sufficient number of pulses for the tone generator to generate the digital data during the sampling period. In claim 5,
A frequency divider that divides the first signal to generate a sampling period clock signal formed by a pulse train indicating the sampling period;
The tone generator outputs the digital data to the buffer storage device at each sampling period based on the sampling period clock signal. In any one of Claims 1-6,
The electronic tone generator, wherein the tone generator is a CPU that executes a computer program indicating a procedure for calculating the tone. An electronic musical sound generator according to any one of claims 1 to 7,
A keyboard having a plurality of keys,
The tone generator is further an electronic musical instrument that generates the digital data based on a key that is pressed among the plurality of keys.

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