JPH09114460A - Filter device of electronic musical instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a timbre variation which is close to that of an acoustic musical instrument by constituting a digital filter part by connecting plural digital filters in series. SOLUTION: The digital filter part 11 has secondary IIR filters A and B arranged in series. When a keyboard is pressed, the cutoff frequency of the filter A corresponding to the strength of the key depression is read out of a table memory 22 of a ROM 2. A CPU 1 calculates the control value of the filter A from the read cutoff frequency and the sharpness of resonance of the filter A and sends it to the filters A and B. The control value of the filter is determined according to the sent value and the sharpness of the filter B, which is then controlled with the control value. Consequently, the digital filter part 11 generates waveforms of a strong touch, an intermediate touch, a weak touch, etc., according to the strongest touch waveform generated by a musical sound signal generation part 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention stores a reference waveform as a digital signal (PCM waveform), reads out the waveform, and controls a digital filter in accordance with the strength of keystrokes, whereby each keystroke is controlled. The present invention relates to a digital filter device for an electronic musical instrument that generates musical tone waveforms according to strength.

[0002]

2. Description of the Related Art Generally, it is known that the sound of a piano changes its sound volume as well as its volume depending on the strength of keystrokes. There are the following tone color changing methods in a method of converting a piano sound into a digital signal and storing it (hereinafter referred to as a PCM method).

The first method is to have a plurality of waveforms with various keystroke strengths and switch the waveform data generated according to the keystroke strengths.

According to this method, if the number of waveforms of the musical instrument is increased, the tone color change of the piano can be reproduced with high fidelity, but for that purpose, a large amount of waveform data is required and a huge waveform memory is required. It becomes costly and there is a problem in practical use.

In addition, the waveform data is converted into various components (for example,
Frequency component, band component, striking component, actual sound component, etc.), and there is a method of changing the addition synthesis ratio of each component according to the strength of keystroke.

According to this method, since a plurality of digital control oscillators are required to generate one tone, the number of polys that can be simultaneously produced decreases. Further, even if the sounds can be produced at the same time, in order to obtain the same frequency characteristic change as that of the piano, it is necessary to decompose into more components, which is costly in terms of the waveform memory and the hardware configuration.

As another method, there is a method in which only the waveform data at the time of hitting is held, and the tone color is changed by changing the appearance of harmonics with a cutoff frequency variable digital filter.

This method saves memory, has a relatively simple structure, and is inexpensive, but the timbre change becomes a curve with a large degree of distortion as shown in FIG. 7, and especially, the change of low harmonics is an acoustic instrument. However, there is a problem in that the tone color change due to the strength of actual piano keystrokes cannot be expressed.

Filter control of a conventional electronic musical instrument that generates a musical tone waveform by using the third digital filter will be described below with reference to the drawings by taking a case of using a secondary IIR filter as an example.

FIG. 6 is a block diagram of a digital filter called a second-order IIR filter. The transfer function of the low-pass filter of the LCR resonance circuit in the design of such a general digital filter is represented by the following equation.

H (s) = ω ^ 2 / (s ^ 2 + (ω / Q) * s + ω ^ 2) (1)

Where ω is the resonance angular frequency (= 2 * π * F ₀ = 1 / √ (L *
C)) Q: Sharpness of resonance (= ω * L / R) R: Resistance value of coil capacitor

When the equation (1) is bitransformed and rearranged, H (z) = π ^ 2 * R ^ 2 (b ₀ + b ₁ * z (-1) + b ₂ * z (-2)) / (1 + a ₁ * z (-1) + a ₂ * z (-2)) ... (2)

However, b ₀ = 1 / (1 + π * R / Q + π ^ 2 * R ^ 2) b ₁ = 2 / (1 + π * R / Q + π ^ 2 * R ^ 2) b ₂ = 1 / (1 + π * R) / Q + π ^ 2 * R ^ 2)

A ₁ = -2 * (1-π ^ 2 * R ^ 2) /
(1 + π * R / Q + π ^ 2 * R ^ 2) a ₂ = (1-π * R / Q + π2 ^ 2) / (1 + π * R /
Q + π ^ 2 * R ^ 2)

A digital filter having the transfer function of the equation (2) is expressed by the following equation.

Y (n) = a ₁ * Y (n-1) + a ₂ * Y (n-2) + π ^ 2 * R ^ 2 * (b ₀ * x (n) + b ₁ * x (n-1) ) + B ₂ * x (n-2)) (3)

R in the equation (3) is R = F _S / F _c F _S = system sampling frequency F _c = digital filter cutoff frequency

As described above, the transfer function of the second-order IIR filter illustrated in FIG. 6 is expressed by equation (3), and the frequency characteristic of the filter is as illustrated in FIG. 7 when Q = 1, for example. .

However, such a conventional secondary II
The R filter is different from the frequency characteristic of the acoustic instrument, and cannot accurately represent the sound of the acoustic instrument.

[0021]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a digital filter device for an electronic musical instrument using a digital filter, which makes it possible to change the tone color close to that of an acoustic musical instrument. The purpose is to do.

[0022]

According to the present invention, a musical tone waveform serving as a reference is stored as a digital signal (PCM waveform), and the digital filter unit 11 is controlled according to the strength of keystroke to serve as the reference. In the electronic musical instrument that generates a musical tone signal according to the strength of keystroke from musical tone waveform data, the digital filter unit 11 is configured by connecting a plurality of digital filters in series.

Further, the control value of each filter constituting the digital filter unit 11 is configured to be determined according to the specific value and / or the control value of the filter connected before.

[0024]

According to the present invention, the digital filter unit 11 obtains the difference between the frequency characteristic of the strongest hit and the change in the frequency characteristic corresponding to the strength of each keystroke, and uses the control value obtained by linearly approximating the difference value.
(EN) A filter device capable of expressing a timbre change according to the strength of keystrokes of an acoustic musical instrument by controlling the.

Therefore, the digital filter of the present invention is
A plurality of digital filters are arranged in series, and each filter is controlled according to a different sharpness of resonance and a cutoff frequency of a digital filter connected in advance.

As a result, it is possible to provide an electronic musical instrument having a simple structure, a small memory capacity, a low price, and capable of expressing a timbre change close to that of an acoustic musical instrument.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the basic concept of the filter device of the present invention will be described. In this embodiment, the digital filter unit 11 is assumed to be composed of two second-order IIR filters.

FIG. 3 shows a change in the strength of keystrokes and changes in frequency characteristics of an acoustic keyboard instrument (for example, a piano). Therefore, based on the frequency characteristics at the time of the strongest hit, the difference between the strong hit, the medium hit, the weak hit, etc. is taken, and the levels of the fundamental tones are matched, with the vertical decibel (db) and horizontal hertz (Hz) axes. It is as shown in FIG.

However, since it is difficult to make a filter capable of expressing the change of FIG. 4 in real time with the current technology, the present invention performs control by approximating each curve of FIG. 4 by the straight line illustrated in FIG. Use a filter.

That is, since the trend of the curve of FIG. 4 is close to a straight line, linear approximation of the curve of FIG. 4 by the method of least squares is expressed as shown in FIG.

Therefore, the electronic musical instrument of the present invention has, for example, the strongest striking waveform data as the reference musical tone data, and the digital filter section 11 has the function of performing the inverse characteristic movement of the linear approximation shown in FIG. On the other hand, a strong hit, a medium hit, and a weak hit are generated by controlling the data of the strongest hit waveform by the digital filter unit 11, and a tone color change of a piano is simulated by an electronic musical instrument.

However, since the desired frequency characteristic cannot be obtained by the conventional filter as described above, the second embodiment IIR filter is connected in series in the present embodiment as illustrated in FIG. In, the parameter value of each filter is controlled by the following values.

That is, Q of digital filter A = 0.25 Cutoff frequency of digital filter A = ω Q of digital filter B = 0.5 Cutoff frequency of digital filter B = 2 * Cutoff frequency of digital filter A ... (4)

In this way, by controlling the cutoff frequency of the digital filter B according to the cutoff frequency of the digital filter A, it is possible to obtain a filter which changes the tone color like an acoustic piano.

Further, according to the present invention, it is possible to provide an electronic musical instrument having a simple structure, a small memory, a low price, and capable of expressing a change in tone color close to that of an acoustic musical instrument.

Next, the overall structure of the electronic musical instrument using the filter of the present invention will be described. FIG. 1 is a block diagram showing a configuration of a main part of an electronic musical instrument to which the musical sound generating apparatus according to the present invention is applied.

In the figure, a CPU 1 controls each section of the electronic musical instrument according to a control program stored in a program memory section 21 of a ROM 2.

The ROM 2 is the program memory unit 21.
In addition to the table memory unit 22, the tone color data memory unit 2
3 are provided. The table memory unit 22 stores the cutoff frequency of the digital filter A corresponding to the strength of keystroke.

Further, the tone color data memory section 23 stores the strongest hitting frequency number, waveform number, envelope waveform number, mode data and the like which are data for generating a tone signal, and each data is a tone color. Specified by a pointer.

The tone color pointer is changed according to a panel operation or a keyboard operation, each data designated by the changed tone color pointer is read from the tone color data memory section 23, and a predetermined calculation is performed by the CPU 1. And is supplied to the musical sound generating section 7.

The RAM 3 is a ROM under the control of the CPU 1.
The data area for transferring and storing the necessary data stored in 2 and the data necessary for sound emission corresponding to the states of the keys and switches of the keyboard section 4, the touch sensor 5 and the panel switch section 6 are set. It includes a plurality of registers and an assigner memory for storing data for allocating the tone signal generator 8 to unused channels.

The keyboard section 4 is composed of a keyboard having a plurality of keys, and includes a key scan circuit for detecting the pressed state of each key.

The touch sensor 5 detects the strength (speed) of the key touch according to the signal from the keyboard section 4. The data indicating the pressed state of each key and the touch data indicating the strength of key touch are sent to the CPU 1.

The panel switch section 6 includes various switches such as a power switch, a mode designating switch, a melody selecting switch, a rhythm selecting switch, and the like. The set state of each switch is detected by a panel scan circuit included therein.

The musical tone generating section 7 comprises a musical tone signal generating section 8 and a digital filter section 11, generates musical tone waveform data, adds musical tone waveform data and envelope data, and outputs it as a musical tone signal.

The tone signal generator 8 which constitutes the tone generator 7 reads tone waveform data and envelope data from the waveform memory 9 and the envelope generator 10 in response to the tone generation start command from the CPU 1, and envelopes the tone waveform data with the envelope. Is added and output as a tone signal.

For this reason, a waveform memory 9 and an envelope generator 10 are connected to the musical tone signal generator 8, and the waveform memory 9 performs waveform processing such as looping, resampling, and cutting on the strongest hitting source waveform data. The waveform data subjected to is stored.

The digital filter unit 11 controls the strongest hitting tone signal sent from the tone signal generating unit 8 to give a tone color change close to that of a piano. For this reason, the digital filter unit 11 of the present invention is configured such that a plurality of second-order IIR filters are arranged in series as described above, and the sharpness of each resonance and the cutoff frequency of the filter are controlled. There is.

The tone signal output from the digital filter unit 11 is analog-converted by the D / A converter 12 and then supplied to an amplifier (not shown). After being subjected to predetermined amplification, it is supplied to the speaker 13.

The waveform memory 9 is a part of the ROM 2 and stores musical tone waveform data corresponding to a tone color and a tone range. Also, the envelope generator 10 includes a keyboard unit 4
A musical tone waveform envelope is generated based on the output of performance data from the.

The digital tone signal output from the digital filter section 11 is supplied to the D / A converter 12.
The input digital musical tone signal is converted into an analog musical tone signal by the D / A converter 12, and the converted analog musical tone signal is amplified by an amplifier (not shown) and supplied to the speaker 13.

The speaker 13 converts an analog musical tone signal as an electric signal sent from the amplifier into an acoustic signal. That is, a tone is emitted according to the generated tone signal.

According to this structure, when the keyboard is pressed,
The touch sensor 5 detects the strength of keystrokes, and the cutoff frequency of the filter corresponding to the strength of keystrokes is read from the table memory 22.

Based on the read cutoff frequency and the sharpness (= 0.25) of the digital filter A, the CPU
Reference numeral 1 calculates the control value of the digital filter A and sends it to the digital filter A, and also sends the calculated result to the digital filter B connected subsequently.

The control value of the digital filter B is determined based on the sent value and the sharpness (= 0.5) of the digital filter B, and the digital filter B is controlled by the control value.

As a result, based on the strongest hit waveform generated by the tone signal generator 8, the digital filter 11 generates a strong hit, a medium hit, a weak hit, and the like.

FIG. 8 uses the digital filter of the present invention,
The cutoff frequency of the digital filter A is 500 Hz,
It is a figure which shows the frequency characteristic at 1 KHz, 2 KHz, 4 KHz, and 8 KHz.

As shown in the figure, according to the present invention, unlike the distorted curve shown in FIG. 7, a value close to the inverse characteristic value of the linear approximation shown in FIG. 5 can be obtained especially in the low frequency band. Therefore, it is possible to obtain a tone color change close to that of an acoustic instrument.

In this embodiment, the digital filter is set to 2
Although the case where the number of connected digital filters is one has been described as an example, the present invention does not limit the number of connected digital filters to two.

As the control value of the digital filter,
Q1 = 0.25, Q2 = 0.5, cutoff frequency of digital filter B = 2 * cutoff frequency of digital filter A has been described as an example, but these control values are experimentally optimum control values. Should be determined and used.

[0061]

As described above in detail, according to the filter of the present invention, the memory can be saved with a simple structure and at a low price,
It is possible to provide an electronic musical instrument capable of expressing a tone color change of a more acoustic musical instrument.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing an overall configuration of an electronic musical instrument of the present invention.

FIG. 2 is a diagram illustrating a configuration of a filter of the electronic musical instrument of the present invention.

FIG. 3 is a diagram illustrating a change in frequency characteristic of a waveform according to a keystroke strength.

FIG. 4 is a diagram illustrating a difference in frequency characteristic of waveforms according to strength of each keystroke when the strongest stroke is used as a reference.

FIG. 5 is a diagram illustrating a case where a difference in frequency characteristics of waveforms corresponding to the strength of each keystroke based on the strongest keystroke is linearly approximated.

FIG. 6 is a diagram illustrating a configuration of a conventional second-order IIR filter.

FIG. 7 is a diagram illustrating frequency characteristics at each cutoff frequency when Q = 1 in the conventional second-order IIR filter.

FIG. 8 is a diagram illustrating frequency characteristics at each cutoff frequency of an electronic musical instrument using the filter of the present invention.

[Explanation of symbols]

 1 CPU 2 ROM 3 RAM 4 Keyboard part 5 Touch sensor 6 Panel switch part 7 Musical sound generation part 8 Musical sound signal generation part 9 Waveform memory (waveform storage means) 10 Envelope generator 11 Digital filter part 12 D / A converter 13 Speaker 21 Program memory 22 Table memory 23 Tone color data memory A, B Digital filter

Claims (2)

[Claims] 1. A reference tone waveform is a digital signal (P
CM waveform), the digital filter unit is controlled in accordance with the strength of keystrokes to generate a tone signal in accordance with the strength of keystrokes from the reference tone waveform data. The filter unit of an electronic musical instrument, wherein the filter unit is configured by connecting a plurality of digital filters in series. 2. The control value of each filter constituting the digital filter unit is determined according to a specific value and / or a control value of a filter connected in advance. Filter device for electronic musical instruments.