JP2959018B2 - LFO generator for electronic musical instruments - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic musical instrument, and more particularly, to an LFO for adding a periodic modulation to volume, tone, pitch, etc.
The present invention relates to an LFO generator that generates a signal (low-frequency oscillation signal).

[Prior art and its problems] There are known conventional LFO generators that generate a triangular wave using an up / down counter and those that have an LFO waveform memory such as a sine wave and periodically read data from the memory. ing. The former up-down counter type LFO
Although the generator is simple in configuration, the LFO waveform generated changes abruptly at the minimum value of the maximum value.
There is a disadvantage that the musical tone to which the effect is added becomes an unnatural and mechanical sound. On the other hand, the latter
Although the LFO generator can generate a desired LFO waveform depending on the data in the memory, the storage capacity is sacrificed and the circuit scale is increased.

[Object of the Invention] Accordingly, an object of the present invention is to provide an L signal which can generate a naturally smooth LFO waveform with a relatively simple configuration.
To provide a FO generator.

[Constitution of the Invention] In order to achieve the above object, according to the present invention, a counting means for receiving a rate signal indicating a change in an LFO signal and counting the LFO signal, and a target value for the rising and falling directions of the LFO signal are determined. Target data storage means for storing target data to be indicated,
Setting rate data storage means for storing set rate data of the LFO signal; comparison means for comparing the LFO signal from the counting means with a target value stored in the target data storage means; and a comparison signal from the comparison means. A direction control means for controlling the rising and falling directions of the LFO signal based on the change rate of the LFO signal by the direction control means by changing a set rate from the set rate data storage means according to a predetermined recurrence formula; An LFO generator for an electronic musical instrument, characterized by having a rate changing means for generating, as the rate signal, a signal whose value changes smoothly at the time of (1).

In this configuration, the rate changing means functions as a kind of rate filter, and when the direction of the LFO signal is switched, the rate signal input as a difference value to the counting means is not suddenly switched as in the conventional up / down counter method. , Gradually change. In response to this smooth rate change, a smooth change occurs in the LFO signal. Further, since a memory for storing the LFO waveform is not required unlike the waveform reading method, an LFO generator can be realized with a relatively small circuit scale.

In one configuration example, one set rate data is stored in the set rate storage means, and a direction signal indicating the direction of the LFO signal generated by the direction control means is input to the rate change means. In the rate changing means, there is provided switching means for alternately generating positive, negative and set rate data by a direction signal from one set rate data of the set rate storage means. The data is used by the recurrence calculation means in the rate changing means. As a result, when the set rate data is positive, the rate signal output changes toward the positive value to remove, and when the set rate data is negative, the rate signal output becomes negative. The rate signal gradually changes with the value as the convergence value. By this repetition, periodically from positive to negative,
A rate signal that changes from negative to positive is generated, and a periodic change having the difference as a difference occurs in the LFO signal.

Further, in order to enhance the accuracy of the reproduction of the rate signal, the first rate signal after the direction switching in the recurrence calculating means is responsive to the comparison signal indicating the arrival of the target value from the comparing means. The calculation may be performed only from such setting data.

In another configuration example, the set rate storage means stores a positive set rate data output when the direction signal from the direction control means is in the upward direction and a negative set rate data output when the direction signal is in the downward direction. Stored with data. In this case, the rate changing means does not need the above-mentioned switching means, and the output of the set rate storing means is directly input to the recurrence calculating means.

Still another configuration example is a combination of the above-described configuration examples. Two set rate data are stored in the set rate storage means, both of which have positive values, and the switching means in the rate change means switches the LFO signal. The set rate data is selectively inverted depending on the direction. In this case, the stored 2
By giving different magnitudes to the two set rate data, an asymmetric LFO waveform can be obtained.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In the embodiment shown in FIGS. 1 to 4, the LFO waveform signal is generated based on set rate data which is a set value of the slope and target data indicating the maximum and minimum values. According to the present invention, the rate signal as the difference value of the LFO waveform signal does not use the set rate data as it is,
It is generated by changing the set rate data according to a predetermined recurrence formula. In this embodiment, the recurrence formula is given by R _n = (R _n-1 + R _c ) / 2 (1) (n = 1, 2,...). Here, R _n represents the rate signal used in the n-th LFO waveform signal calculation after the LFO waveform has turned the maximum or minimum value, and R _c is the change direction (up, down) of the LFO waveform after the return. Represents the set rate set for. When the equation (1) is modified, R _n −R _c = (R _n−1 −R _c ) / 2 Therefore, R _n = R _c − (R _c −R ₀ ) / 2 ⁿ (2). Here, _R0 is a set rate set for the change direction (fall, rise) of the LFO waveform before the return.
Therefore, the sequence R of the rate signal after the LFO waveform is folded back
_1, R _2, ...... would gradually approaches the set rate R _c of the set rate R _c after folding as convergent value. For example, when R ₀ = 1 and R _c = −1, R ₁ = 0, R ₂ = −1 / 2, R ₃
= −3 / 4, R ₄ = −7 / 8, R ₅ = −15 / 16, R ₆ = −31 / 32, and as shown in FIG. 5, the LFO waveform that changes smoothly at the time of folding is can get. In FIG. 5 (a), the dotted line shows the return of the LFO waveform obtained from the conventional LFO generator of the up-down counter system, and the solid line shows the return waveform of the smooth LFO obtained by the present invention.

 The details will be described below.

FIG. 4 is a block diagram of an electronic musical instrument having the above-described LFO generation function. The key assigner 2 scans the key switch circuit and generates a key code KC of a key being pressed and a key-on signal KH for starting sound generation. The envelope generation circuit 3 receives the key-on signal KH and starts generating an envelope waveform E. Frequency information generating circuit 4 receives key code KC from key assigner 2 and generates frequency information FI corresponding thereto. The waveform generation circuit 5 receives the frequency information FI, accumulates it, generates waveform phase data, and generates waveform data based on the phase data. The generated waveform data is multiplied by the envelope signal E from the envelope generating circuit 3 and output as a musical sound waveform W. Here, the LFO waveform signal LW from the LFO generating circuit 6 acts on the frequency information FI or the envelope E to give a fluctuation effect on the volume, tone and pitch of the musical sound. Next, when the key is released, a key-off signal KF is generated from the key assigner 2, and the envelope generation circuit 3 sets the envelope that has advanced to decay and sustain (only the sustained sound) after the start of the attack, to the release state. When the release is completed, the envelope generating circuit 3 sends an envelope end signal EF to the key assigner 2. Upon receiving the envelope end signal EF, the key assigner 2 enters the sound ending state. The waveform generation circuit 5 resets the phase by the key-on signal KN so that the phase starts at the same phase when the attack starts. Although the function of the block has been mainly described above, a polyphonic configuration can be realized by performing time-division processing using a shift register or the like. The sound system 7 performs D / A conversion on the generated digital musical sound waveform signal W and emits the sound via an amplifier and a speaker.

FIG. 2 is a detailed block diagram of the LFO generation circuit 6.
LFO waveform change direction (up, down) in rate memory 8
The set rate data is stored as a positive value representing the gradient set for each of the above, and the target data representing the target values (maximum value, minimum value) for each of them in the direction of change of the LFO waveform is stored in the level memory 9. You. Both memories are addressed by the direction signal / D from the up / down control circuit 13 for controlling the changing direction of the LFO waveform signal, and output the corresponding setting data. Set rate output R of rate memory 8
Is input to the rate change circuit 10 according to the present invention, where it is filtered according to the recurrence formula described above, and the LFO
A change rate signal R 'is generated as a difference value of the waveform signal. This change rate signal R 'is input to the LFO counter 11. The LFO counter 11 updates the value of the LFO waveform signal by adding / subtracting the change rate signal R 'to / from the current value of the LFO waveform. The updated value LW ₀ of the LFO waveform is compared with the target value L from the level memory 9 in the comparison circuit 12. When the value LW _{0 of the} LFO waveform reaches the target value L, the comparison circuit 12 outputs a comparison signal RH of “1”.
Is output. In detail, the comparison circuit 12 determines (a) / D = 0 (during rising) and LW ₀ ≧ L or (b) according to the direction of the LFO waveform indicated by the direction signal / D from the up / down control circuit 13. When / D = 1 (during falling) and LW ₀ ≦ L, the comparison signal RH of “1” is output. The output comparison signal RH is input to a rate changing circuit 10 described later in detail, and is also input to an up / down control circuit 13 for switching the direction of the LFO waveform.

The up / down control circuit 13 is configured as shown in FIG. First, when the key-on signal KN from the key assigner 2 becomes “1”, the clock φ is input to the FF 18 by the OR gate 15 and the AND gate 16. At this time, since KH = "1" is input to the NOR gate 17, FF18 is reset to "0". In addition, the inverter 1
9. “0” indicating that the direction signal / D rises via the AND gate 20
Becomes Thereafter, after the KN signal becomes “0”, the NOR gate 17 functions as an inverter that inverts the output of the FF18, and the AND gate 20 functions as a gate that passes the output of the FF18 as the / D signal. Under this state, when the comparison signal RH of “1” indicating the arrival of the target value from the comparison circuit 12 is input to the OR gate 15, the / D signal changes from 0 to 1 according to the state of FF18.
→ Inversion is repeated, such as 0.

FIG. 1 is a detailed block diagram of the rate changing circuit 10. The plurality of circuits 21 are provided for selectively inverting the positive set rate R from the rate memory 8 in accordance with the direction of the LFO waveform indicated by the signal / D. ), The set rate R is passed as it is, and the signal / D
Is "1" (falling), a 2's complement of the set rate R is generated (note that the 2's complement circuit 21 can be omitted if the set rate of the rate memory 8 in the descending direction is set to a negative value). . The selection circuit 23 selects data to be taken into the flip-flop (FF) 24, that is, the value of R _n-1 in the above equation (1), and selects the key-on signal KN or the comparison signal RH.
Is "1", the set rate (data corresponding to _R0 in equation (2)) which is the output of the two's complement circuit 21 is selected by the "1" selection signal given from the OR gate 22, In other normal times, the previous change rate R '(= R _n-1 ) which is the output of the shift circuit 26 is selected. Equivalent to R _n-1 in equation (1)
The output of FF24 and the 2's complement circuit corresponding to R _c in equation (1) are
Is added by an adder 25, and the result of the addition is shifted by a shift circuit 26.
, The change rate R _n according to equation (1)
Is obtained. The output of the shift circuit 26 is the difference value R of the LFO waveform.
Is sent to the LFO counter 11.

The operation will be described below. First, the LFO counter 11 is initialized to "0" by the key-on signal KN from the key assigner 2, and the up / down control circuit 13 sets the / D signal to "0" (rising). I do. Further, in the rate change circuit 10, FF24
The value R (0) of the set rate when / D is "0" is fetched, and the adder 25 and the shift circuit 26 set the first change rate R ₁ (= R ') as R ₁ = (R ( 0) + R (0)) / 2 = R (0). Subsequent change rates R ₂ , R ₃ ... Are similarly calculated. As a result, the LFO signal waveform output from the LFO counter 11 rises with a slope of R (0) and eventually reaches the target value L (0). The arrival of this target value is determined by the comparison circuit 12.
And the comparison signal output RH becomes "1". As a result, the set rate R (0) when / D selected by the selection circuit 23 is "0" is taken into the FF 24 of the rate change circuit 10. Further, the direction signal / D of the up / down control circuit 13 is switched to "1" indicating that the direction is falling by the comparison signal of "1".

Thereby, the change rate calculation after the return to the LFO waveform in the rate change circuit 10 is started. That is, first change rate R ₁ after the transition to the falling is calculated by _{R 1 = (R (0)} -R (1)) / 2. Here, -R (1) is a negative set rate (two's complement of the set rate R (1) of the rate memory 8) with respect to the falling of the LFO waveform generated according to / D = 1 in the two's complement circuit 21. Thereafter, in the same manner, the n-th change rate R _n after the transition to the lowered being calculated by R _n = (R _n-1) -R (1)) / 2, gradually value -R (1) It approaches the value (see Fig. 5).

As a result, the LFO signal waveform decreases, and when it reaches the negative target value (minimum value) L (1), the comparison circuit 12 again generates the comparison signal RH of “1”. As a result, the set rate -R (1) for the falling is set in the FF 24 of the rate changing circuit 6 through the selecting circuit 23, and subsequently, it is switched to "0" (during the rising) from the up / down control circuit 13. According to the changed direction signal / D, the calculation of the change rate in the ascending mode starts. That is, in the rise _{mode, R 1 = (- R (} 1) + R (0)) / 2 R n = (R n-1 + R (0)) / 2 by changing rate feel more alert operation. R (0) indicates a set rate value in the ascending direction given from the rate memory 8 via the inactive two's complement circuit 21.

By this repetition, a folded LFO waveform as illustrated in FIG. 5 is generated.

FIG. 6 shows another configuration example of the rate changing circuit. This rate change circuit 10M, according recurrence formula represented by _{R n = αR n-1 +} (1 + α) R c (3), calculates a change rate R _n.
Here, α is a convergence speed coefficient that satisfies 0 ≦ α ≦ 1.

By transforming equation (3), thus _{R n -R c = α (R} n-1 -R c), the ^{_{R n = R c + α n}} (R 0 -R c) (4). Therefore, the rate sequence of _{R 0, R 1, R 2} ...... R n is
Converges at a rate that follows from the values of R ₀ in convergence rate coefficient towards the value of R _c alpha. For _{example, R 0 = 2, R 1} = -1, α = 3/4 a Taking as an _{example, R 1 = 5/4,} R 2 = 11/16, R 3 = 17/64, R 4 = -1
3/256, R ₅ = −295 / 1024..., And a folded waveform of the LFO as shown by the solid line in FIG. 7 is obtained. The dotted line is based on a conventional up / down counter. When the convergence speed coefficient α is halved, Expression (3) is equivalent to Expression (1). As the convergence speed coefficient α approaches 1, the return of the LFO waveform becomes gentler.

In the rate changing circuit 10M in FIG. 6, a two's complement circuit 2
1, OR gate 22, selection circuit 23 and FF24 are the same as corresponding elements in FIG. The convergence speed coefficient α is given by the lower bits of the data in the rate memory 8. On the other hand, the set rate is given by the upper bits of the rate memory data, and this is input to the two's complement circuit 21. In order to perform the recurrence equation operation shown in the equation (3), the subtractor 30 outputs the two's complement circuit 21 from the output R _n-1 of the FF 24
Subtracted set rate output R _c of the subtractor 30 by the multiplier 31
Is multiplied by the convergence speed coefficient α, and the output of the two's complement circuit 21 is added to the multiplied output of the multiplier 31 by the adder 32. The output of the adder 32 is input to the LFO counter 11 as the difference value of the LFO waveform signal, and is output to the FF 24 via the selection circuit 23.
Is returned to.

This concludes the description of the embodiments, but various modifications are possible within the scope of the present invention. For example, the rate change circuits 10 and 10M shown in FIGS.
Each time the target value (return point) is reached, the FF is set at the set rate before the return by the comparison signal RH of "1".
24 is reset, but at this point, the rate changing circuit 10 has generated a change rate sufficiently close to the set rate before the return, so that this resetting means is unnecessary if desired. The purpose of the rate change circuit is to change the set rate at the turning point of the LFO waveform,
O It is to smooth the rate change so that the slope of the waveform does not change suddenly, so it is not limited to the above-mentioned recurrence formula, but to generate a change rate signal by other appropriate recurrence formula operation Is also good. For example, (W _c and W _i are weighting factors, and R _n-ki is a change rate of a sample point in the past by ki from sample point n). The change rate R _n can be calculated according to a recurrence formula as shown.

[Effects of the Invention] As described above in detail, according to the present invention, basically, an up-down counter method of generating an LFO waveform based on a set rate and a set target value is used, but the set rate is not changed. Since the set rate is changed in accordance with a predetermined recurrence formula in the rate changing means functioning as a rate filter instead of being input to the counting means and then input to the counting means, an advantage that the folded portion of the LFO waveform becomes smoother There is. Therefore, a sudden change in the LFO waveform as in the conventional up / down counter method can be removed, and an LFO waveform memory as in the conventional waveform reading LFO generator is unnecessary.

[Brief description of the drawings]

FIG. 1 is a block diagram of a rate changing circuit used in the LFO generating circuit of this embodiment, FIG. 2 is a block diagram of an LFO generating circuit according to the embodiment, and FIG. 3 is an up / down diagram of FIG. FIG. 4 is a block diagram of an electronic musical instrument incorporating the LFO generating circuit shown in FIG. 2, FIG. 5 is a diagram illustrating an LFO waveform generated by the embodiment, and FIG. 6 is a rate. FIG. 7 is a block diagram showing a modification of the change circuit, and FIG. 7 is a diagram illustrating a folded portion of the LFO waveform obtained when the rate change circuit of FIG. 6 is used. 6 LFO generation circuit, 8 rate memory, 9 level memory, 10 rate change circuit, 11 LFO counter, 12 comparison circuit, 13 up / down control circuit.

Claims (1)

(57) [Claims] 1. A counting means for receiving a rate signal indicating a variation of an LFO signal and counting the LFO signal; a target data storage means for storing target data indicating a target value for the rising and falling directions of the LFO signal; Setting rate data storing means for storing setting rate data of a signal; comparing means for comparing the LFO signal from the counting means with a target value stored in the target data storing means; based on a comparison signal from the comparing means Direction control means for controlling the rising and falling directions of the LFO signal, and changing the set rate from the set rate data storage means according to a predetermined recurrence formula.
An LFO generator for an electronic musical instrument, comprising: rate changing means for generating, as the rate signal, a signal whose value changes smoothly when the direction of the O signal is switched.