JPH06266359A - Waveform generating device for electronic musical instrument - Google Patents

Abstract

PURPOSE:To reduce a reflected noise nearby an integer multiple of a sampling frequency by the waveform generating device for the electronic musical instrument which generates a musical sound waveform by using a waveform memory. CONSTITUTION:The gain nearby the integer multiple of the sampling frequency is decreased by correcting plural coefficients by which waveform amplitude values at sampling points at specified time intervals outputted from the waveform memory 5 are multiplied so that the sum of them is always a 'specified constant value'.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform generator used in an electronic musical instrument for generating a tone waveform by a waveform memory.

[0002]

2. Description of the Related Art As a waveform generator for an electronic musical instrument that uses a waveform memory to generate a musical tone waveform, Lagr is provided between waveform amplitude values of each sample point of the musical tone waveform stored in the waveform memory.
There is known one that interpolates by the angle interpolation method (Japanese Patent Publication No. 59-17838). In such a waveform generator for an electronic musical instrument, frequency information F corresponding to the frequency of the musical sound to be generated is output from the frequency information memory,
The frequency information F is accumulated by the accumulator, and the integer part I and the decimal part l of the accumulated value qF are output. The integer part I is supplied to the waveform memory after the count value (I + p) (p = 0, 1, 2, 3) of I, I + 1, I + 2, I + 3 is obtained by the counter. The waveform memory stores waveform amplitude values f _I (I = 0, 1, 1) of each sample point of a tone waveform of a desired tone color.
2, 3, ..., M) are stored, and the stored sample point waveform amplitude values f _{(I + p)} are sequentially read using the count value (I + p) from the counter as a read address. On the other hand, the fractional part 1 of the accumulated value qF is taken into the coefficient memory. This coefficient memory stores four coefficient values A _k (k = 0, 1, 2, 3) corresponding to the value of l, and stores the coefficient value A _k specified by the count value k by a predetermined counter. Output. Then, the coefficient values A _k are multiplied by the corresponding sample point waveform amplitude values f _{(I + p)} , respectively, and then the accumulated values are accumulated to obtain the distance between the sample point waveform amplitude values stored in the waveform memory. An interpolated tone waveform signal is formed.

Here, the aliasing component generated when the waveform memory is read so that a waveform of the fundamental frequency (pitch) f ₀ is obtained by the address signal that changes according to the sampling frequency f _S is nf _S ± f ₀ (n = 1, 2, ...). Here, when the amount of address change for each sampling time at the time of reading the waveform memory is not "1" (when the frequency information F ≠ 1), 1 is added to the reproduced waveform.
A frequency component of / 2f _S or more remains, which is generated as a folding component. In the pitch asynchronous sound source used in the electronic musical instrument described above, the waveform sampled at the sampling frequency f _S is read out in a state of being resampled by the pitch asynchronous non-uniform system frequency f _SYS , and therefore the aliasing component is generated during the resampling. Turns back to a lower frequency range, and noise is generated. The above-mentioned interpolation method in the electronic musical instrument waveform generator reduces the aliasing due to such resampling.

[0004]

By the way, in the above-described conventional waveform generator for electronic musical instruments, each coefficient value A
_{When 0} (l) to A ₃ (l) is obtained, quantization is performed to an appropriate number of bits according to the scale of the multiplier or the like. FIG. 5 (a),
(B) is a figure which shows the frequency characteristic and impulse response on the ideal conditions of interpolation in the above-mentioned waveform generator for electronic musical instruments. In FIG. 5A, the gain near the integral multiple of the sampling frequency f _S is “0”. This is because, as shown in FIG. 5B, the sum of the coefficient values A ₀ (l) to A ₃ (l) obtained from the calculation formula is “1”. However, in reality, as described above, since each coefficient value A ₀ (l) to A ₃ (l) is quantized into a finite number of bits, the least significant bit is moved up or down so that the coefficient value A The sum of ₀ (l) to A ₃ (l) does not become "1". Therefore, as shown in FIG. 6, the gain near the integral multiple of the sampling frequency f _S does not become “0”. Therefore, there is a problem that folding noise occurs.

The present invention has been made under such a background, and an object thereof is to provide a waveform generator for an electronic musical instrument which can reduce the occurrence of aliasing noise in the vicinity of an integral multiple of the sampling frequency. .

[0006]

SUMMARY OF THE INVENTION A waveform generator for an electronic musical instrument according to the present invention has an address whose value sequentially changes in correspondence with the frequency of a musical tone to be generated and which is composed of an integer part and a decimal part of a plurality of pits. Address signal generating means for generating a signal, and a waveform memory storing the waveform amplitude value of each sample point for a desired tone waveform, based on the integer part of the address signal, the sampling point corresponding to the value of the integer part, and Waveform generating means for reading and outputting the waveform amplitude value of the total n (n is an integer of 3 or more) sample points of the sample points successively consecutive to this sample point, and the respective values that the fractional part of the address signal can take. Correspondingly, it includes a coefficient table in which n coefficients are stored, and n coefficients corresponding to the fractional value of the address signal generated from the address signal generator are From the table to output the coefficient, and a waveform amplitude value corresponding to n sample points output from the waveform generating means and n coefficients output from the coefficient generating means are respectively multiplied. In addition, in a waveform generator for an electronic musical instrument, which is provided with an interpolating means for adding and summing the respective multiplied values and outputting a waveform signal,
Each of the n coefficients stored in the coefficient table is set such that the sum of the n coefficients becomes the same "predetermined constant value" for each value that the fractional part of the address signal can take. It is characterized by that.

[0007]

According to the above construction, since the sum of the coefficients is always a "predetermined constant value", the gain in the vicinity of an integral multiple of the sampling frequency is lowered and the aliasing noise is reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a block diagram showing the configuration of an electronic musical instrument using a waveform generating apparatus for an electronic musical instrument according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a key-depression detection circuit, which is a key-on signal KO indicating that a key is depressed when each key of a keyboard (not shown) having a plurality of keys is depressed.
N and the key code KC corresponding to the key are output.
Reference numeral 2 denotes a frequency number memory, which stores a table in which the pitch of each key is associated with the frequency number F, and outputs the frequency number F corresponding to the key code KC output from the key depression detection circuit. An accumulator 3 receives a clock pulse φ ₁ and repeatedly accumulates a frequency number F at a predetermined time interval, and the accumulated value qF (q = 1, 2, 3).
Output the integer part I and the decimal part x. A counter 4 receives the clock pulse φ ₂ and takes in the integer part I of the accumulated value pF output from the accumulator 3 and outputs it as a count value (I + p) (p = 0, 1, 2, 3). The counter 4 changes the count value by I → (I + 1) → (I + 2) → (I +) every time the clock pulse φ ₄ is input.
Change to 3). Reference numeral 5 is a waveform memory, and waveform amplitude values f _I (I = 0, 1, 2, ...
m) is remembered. When the count value (I + p) is supplied from the counter 4, the waveform memory 5 receives this count value (I + p).
The stored waveform amplitude value f _{(I + p)} is sequentially read using _p) as a read address.

On the other hand, 6 is a counter, the count value by the clock pulses phi ₂ is input k (k = 0, 1,
2, 3) are reset and the clock pulse φ ₄ is input to change the count value k in the order of 0 → 1 → 2 → 3 and output. Reference numeral 7 is a coefficient memory, which takes in the decimal part x (0 ≦ x ≦ 1) of the accumulated value pF from the accumulator 3. The coefficient memory 7 stores four coefficient values A ₀ (x) to A ₃ (x) corresponding to the value of the fractional part x, and the count value k is supplied from the counter 6 as a read address signal and input. The coefficient value A _k (x) specified by the coefficient k corresponding to the fractional part x is output.

Reference numeral 8 denotes a multiplier which receives the waveform amplitude value f _{(I + p)} which is the output of the waveform memory 5 and the coefficient value A _k (x) which is the output of the coefficient memory 7 and multiplies them. The waveform signal A _k (x) · f _{(I + p)} is output. An accumulator 9 is cleared by inputting the clock pulse φ ₂ and outputs the waveform signal A _k (x) · f _{(I + p)} output from the multiplier 8 by inputting the clock pulse φ _3. Accumulate and output. A latch circuit 10 latches and outputs the waveform signal ₃ Σ _{p, k = 0} A _k (x) · f _{(I + p)} output from the accumulator 9 when the clock pulse φ ₁ is input. An envelope waveform generator 11 receives the key-on signal KON and generates an envelope waveform EV. 1
Reference numeral 2 denotes a multiplier, which multiplies the output signal of the latch circuit 10 by the envelope waveform EV and outputs it to the sound system 13. The sound system 13 produces the tone waveform output from the multiplier 12. Here, as shown in FIG.
Clock pulse φ ₁ is time t ₁ , clock pulse φ ₂ is time t ₂ , clock pulse φ ₃ is time t ₃ , t ₄ , t ₅ , t ₆ ,
The clock pulse φ ₄ is generated at the times t ₄ , t ₅ and t ₆ .

Before describing the operation of the electronic musical instrument having the above-described structure, first, a method of calculating coefficients stored in the coefficient memory 7 will be described with reference to the flowchart of FIG.

In step S1, first, 0 is set as the decimal part x. Next, in step S2, the four coefficient values A ₀ (x) -corresponding to the fractional part x are calculated by the following equation.
Find A ₃ (x). A ₀ (x) =-x (x-1) (x-2) / 6 (1) A ₁ (x) = (x + 1) (x-1) (x-2) / 2 (2) A _{2 (x) = - (x} + 1) x (x-2) / 2 ... (3) a 3 (x) = (x + 1) x (x-1) / 6 ... (4) for example, the value of the fraction x If 0, coefficient value A
₀ (0) = 0, A ₁ (0) = 1, A ₂ (0) = 0, A
₃ (0) = 0.

Next, in step S3, the calculated coefficient values A ₀ (x) to A ₃ (x) are quantized into an m-bit length. In this case, the fractions are rounded off. Next, the process proceeds to step S4, and the sum sum of the four coefficient values A ₀ (x) to A ₃ (x) is sum.
To calculate. Here, for example, when the value of the decimal part x is 0,
The total value sum is sum = A ₀ (0) + A ₁ (0) + A ₂ (0) + A ₃ (0) = 0 + 1 + 0 + 0 = 1. Then, the process proceeds to step S5, and it is determined whether or not the value of the total value sum is 1. When the value of the decimal part x is 0, the value of the total value sum is 1, so the process proceeds to step S7. Then, in step S7, in the coefficient memory 7,
The calculated four coefficient values A ₀ (0) to A ₃ (0) are written to the address corresponding to the value of the decimal part x at this time. Next, in step S8, it is determined whether the value of the fractional part x is 1 or more. If the value of the fractional part x is 0, the result of this determination is "NO", so the flow proceeds to step S9. Then, in step S9, a constant value Δx that is the resolution of the decimal part x is added to the value of the decimal part x, and the process returns to step S2.

Thereafter, steps S2 to S9 are repeatedly executed until the fractional part x becomes 1, and the coefficient value A ₀ (corresponding to the value of the fractional part x at that time is incremented while the fractional part x is incremented by Δx. x) to A ₃ (x) are sequentially obtained. In the execution of steps S2 to S9, if the determination result of step S5 is "NO", that is, if the total value sum is not 1, the process proceeds to step S6. Then, step S6
In the above, in the four coefficient values A ₀ (x) to A ₃ (x), the one having the largest absolute value is added with the value obtained by subtracting the total value sum from 1 so that the total value sum becomes 1. To do. For example, the total value sum is smaller than 1 by the value d, and the coefficient value A
_If the absolute value of the coefficient value A ₂ (x) among ₀ (x) to A ₃ (x) is the maximum, the value d is added to the coefficient value A ₂ (x). As a result, the total value sum of the coefficient values A ₀ (x) to A ₃ (x) is increased by the value d to be 1. Then, when the determination result of step S8 is “YES”, that is, when the value of the decimal part x is 1, the process is ended. The coefficient values A ₀ (x) to A ₃ (x) (0 ≦ x ≦ 1) calculated for each value of the decimal part x as described above are written in the coefficient memory 7. As a result, the sum of the set of coefficient values A ₀ (x) to A ₃ (x) stored corresponding to each value of x is “1”.

Next, the operation of the electronic musical instrument using the waveform interpolation circuit according to this embodiment will be described. In this embodiment, except for the coefficient memory 7, the construction is described in JP-B-59-178.
Since it is similar to that described in Japanese Patent No. 38, the detailed description is omitted. When a certain key is pressed, the frequency number F corresponding to the key is read from the frequency number memory 2,
It is supplied to the accumulator 3. When the clock pulse φ ₁ is input, the accumulator 3 accumulates the frequency number F, and outputs the integer part I of the accumulated value pF to the counter 4 and the decimal part x to the coefficient memory 7. The counter 4 takes in the integer part I when the clock pulse φ ₂ is input, and changes the count value from I to I + 3 every time the clock pulse φ ₄ is input. This count value I, (I + 1), (I + 2),
(I + 3) is input to the waveform memory 5 as an address signal, and the waveform amplitude values f _I , f _{( I + 1)} , f are input from the waveform memory 5.
_{(I + 2)} and f _{(I + 3)} are sequentially read. In sync with this,
The counter 6 changes the count value k from 0 to 3 every time the clock pulse φ ₄ is input. According to the flow shown in FIG. 3, the coefficient memory 7 has four coefficient values A ₀ (x) and A ₁ (corresponding to the value of the decimal part x among the coefficient values stored in the coefficient memory 7 in advance. x), A ₂ (x), A
₃ (x) is sequentially output in synchronization with the change of the count value k.
Then, the multiplier 8 calculates the waveform amplitude value f _I and the coefficient value A
₀ (x), f _{(I + 1)} and A ₁ (x), f _{(I + 2)} and A ₂ (x),
And f _{(I + 3)} and A ₃ (x) are respectively multiplied, and the multiplication result A _k
Output (x) · f _{(I + p)} to the accumulator 9. The multiplication result A _k (x) · f _{(I + p)} is accumulated by the accumulator 9, and the waveform signal ₃ Σ _{p, k = 0} A _k (x) which is the accumulation result is accumulated.
・ F _{(I + p)} is clock pulse φ ₁ by the latch circuit 10.
It is latched every time. Then, the multiplier 12 multiplies the envelope waveform EV output from the envelope waveform generator 11 and supplies it to the sound system 13 to be sounded as a musical tone.

As described above, the frequency characteristic of the waveform signal output from the latch circuit 10 in the interpolated state has the characteristic shown in FIG. 5 (a). In the characteristic of the conventional interpolation circuit shown in FIG. 6, the value around the integral multiple of the sampling frequency f _S is not completely “0”, but in the case of the present invention, it is always “0”. Further, in FIG. 4, the sampling frequency f
The frequency characteristics around _S are shown. The dotted line in this figure is a constraint condition (correction condition) when quantizing coefficient values as in the past.
Shows the frequency characteristic in the case of not providing, and the solid line shows the frequency characteristic in the case of providing the constraint condition as in the present application. As shown in this figure, when there is no constraint condition (correction condition), the attenuation is not complete around the sampling frequency f _S , but when there is a constraint condition, it is completely attenuated.

As shown in FIG. 4, in this embodiment shows a case of performing the sampling at a sampling frequency f _S of 50kH _Z. Therefore, the bandwidth of _{40kH Z (2 / 4f S ~3} / 4f S) the attenuation is large, 40KH
In less than _Z bands _{(1 / 4f S ~2 / 4f} S) attenuation decreases. _{Therefore, 1 / 4f S ~2 / 3f} S such frequency components is not too large, it is appropriate to store the waveform having a fundamental pitch of 0~5kH _Z. In general, in the musical instrument, the number the basic pitch of the tone to be generated is 10H _Z ~2k
Since it is in the range of H _Z , it meets the above conditions. Therefore, by using the interpolation circuit according to the present embodiment, the noise around the turn-around of the basic pitch of the musical tone is effectively removed.

In the above embodiment, each coefficient value A
_{The case} where the sum of ₀ (x) to A ₃ (x) is always set to “1” for any value of the decimal part x has been described, but the present invention is not limited to this. The sum of the coefficient values A ₀ (x) to A ₃ (x) may be set to be always the same for any value of the decimal part x.
For example, in each of the equations (1) to (4), the coefficient values A ₀ (x) to A ₃ (x) are calculated by multiplying the right side by the same value, for example, “0.8”. May be. In this case, the sum of the coefficient values A ₀ (x) to A ₃ (x) is always “0.8”.

In the above embodiment, the case where the interpolation processing is performed by using the waveform amplitude values of four sample points and four coefficients has been described. However, the present invention is not limited to this, and the waveform amplitude values of three sample points and three coefficients are used. The same can be applied to the case where the interpolation processing using one coefficient or the interpolation processing using the waveform amplitude value of 5 sample points or more and the coefficient of 5 or more is performed.

[0020]

As described above, according to the waveform generating apparatus for an electronic musical instrument of the present invention, a plurality of coefficient values used for the interpolation of a musical tone waveform are "constant values" whose sums are always the same value. Since it is prepared in such a state as to be corrected, the gain in the vicinity of an integral multiple of the sampling frequency is reduced, and the aliasing noise is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an electronic musical instrument using a waveform generating device for an electronic musical instrument according to an embodiment of the present invention.

FIG. 2 is a timing chart of clock pulses used in the embodiment.

FIG. 3 is a flowchart showing a coefficient calculation process of the waveform generator for an electronic musical instrument according to the embodiment.

FIG. 4 is a diagram showing a gain in the vicinity of a sampling frequency with and without a constraint condition when quantizing a coefficient.

5A is a diagram showing frequency characteristics of a waveform interpolation circuit under ideal conditions, and FIG. 5B is a diagram showing impulse responses of a conventional waveform interpolation circuit under ideal conditions.

FIG. 6 is a diagram showing frequency characteristics of a conventional waveform interpolation circuit.

[Explanation of symbols]

2 ... Frequency number memory, 3, 9 ... Accumulator, 5 ... Waveform memory, 7 ... Coefficient memory, 8 ... Multiplier.

Claims (1)

[Claims] 1. An address signal generating means for generating an address signal whose value sequentially changes corresponding to a frequency of a musical tone to be generated and which is composed of an integer part and a decimal part of a plurality of bits, and a desired musical tone waveform. Including a waveform memory that stores the waveform amplitude value of each sample point, and based on the integer part of the address signal, the total of the sample points corresponding to the value of the integer part and the sample points successively succeeding this sample point (n is n Three
(The above integer) Corresponding to each of the values that can be taken by the fractional part of the address signal, the waveform generating means for reading out and outputting the waveform amplitude value for the sampling points,
Each includes a coefficient table that stores n coefficients,
Coefficient generating means for reading out n coefficients corresponding to the value of the fractional part of the address signal generated from the address signal generating section and outputting the coefficient, and a waveform for n sample points output from the waveform generating means. An electronic musical instrument provided with an interpolating means for multiplying corresponding amplitude values and n coefficients output from the coefficient generating means, and for adding and synthesizing the respective multiplied values to output a waveform signal. In the waveform generator, each of the n coefficients stored in the coefficient table has the same “predetermined constant value” for each value that the sum of the n coefficients can have in the decimal part of the address signal. A waveform generator for an electronic musical instrument, characterized by being set as follows.