JPH03188497A - Function generator - Google Patents

Abstract

PURPOSE:To obtain a natural effect by multiplying first and second triangular waves having pi/2 different phases, obtaining a modulating signal periodically fluctuating in positive and negative, and modulating a modulating means with the modulation signal. CONSTITUTION:The output of a multiplier 12 is multiplied by a constant D determining modulation depth in a multiplier 16, and supplied to the modulating means 6 as a modulation signal. The output of the multiplier 12 is in proportion to the waved-shape of that two times as many triangular waves as original frequencies are integrated. On the other hand, g.h is rewritten as (-H<2>t / T) + (4H<2>t<2> / T<2>). In the case they are compared, if H and T have a constant relation, it is clear that they are coincident with each other. Therefore, a period that a digital tone signal is written in the modulating means 6 is constant, and a digital system in which a read period is modulated with the modulation signal is adopted, so that the modulation signal is in proportion to that the triangular waves are integrated, that is differentiated is in proportion to the triangular waves, and the pitch of a tone signal changes in a shape of a triangu lar wave. Thus, a natural effect is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a function generator, and particularly to a function generator for generating a modulation signal for a modulator that adds effects such as a rotation sound effect or vibrato to a musical tone signal in an electronic musical instrument or the like. This invention relates to a function generator used for.

[Prior Art] Conventionally, the speed at which musical tone signals stored in a storage device are read out is modulated by a modulation signal, and the pitch of the musical tone signal is periodically changed up and down, thereby creating a rotating sound effect, a vibrato effect, etc. An effect adding device that adds an effect is known. Such an effect adding device includes B as a storage device.
There are analog systems using BDs and the like, and digital systems using a digital signal processing device (DSP).

An example of a digital method is, for example, Japanese Patent Application Laid-Open No. 58-1085.
It is disclosed in Publication No. 83. This is a storage device in which digital musical tone signals are sequentially stored at regular intervals, in which a readout signal for reading out digital musical tone signals is modulated by a modulation signal.

The waveform of the modulation signal is written to the modulation information memory.

A sine wave or the like is used as the waveform of the modulation signal.

[Problems to be Solved by the Invention] However, in such a system, the modulation waveform must be stored in the modulation information memory, which has the problem of complicating the circuit configuration. In particular, when it is desired to change the modulation state variously, various sine waves must be stored in the modulation information memory, which increases the capacity of the modulation information memory.

It is also possible to obtain the desired sine wave etc. by processing a triangular wave etc., which can be generated relatively easily, with a digital filter, but in the case of these waveforms with a relatively large period, filter calculation processing is necessary. The coefficient word length of is increased. instead of a sine wave.

If a triangular wave or a sawtooth wave is used as a modulation signal, the above problems can be solved. However, with digital systems, unlike analog systems, the write cycle to the storage device is constant, but only the read cycle is modulated by the modulation signal, so the effect of differentiating the modulation signal is applied, resulting in a triangular wave or sawtooth wave. When a waveform is used as a modulation signal, a new problem arises in that the pitch becomes a rectangular waveform and the effect of periodically changing up and down cannot be obtained.

The present invention has been made in view of the above points.

It is an object of the present invention to provide a device that can generate a function signal that can be generated with a simple configuration and that periodically changes up and down.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a first triangular wave generating means for generating a first triangular wave, and a first triangular wave generating means for generating a first triangular wave.
The second triangular wave generating means generates a jll12 triangular wave with a /2 phase shift, and the multiplication means multiplies the first triangular wave and the second triangular wave.

[Operation] According to the present invention, since the first and second triangular waves having different phases by π/2 are multiplied, a signal that periodically changes up and down, as will be explained in detail later, can be obtained.

[Example] This example uses a digital signal processing device to add effects such as chorus and vibrato.
The present invention is implemented in a low frequency oscillation means indicated by reference numeral 2 in the figure. In FIG. 1, this embodiment is shown in a block diagram.

It is actually implemented in software.

In FIG. 1, reference numeral 4 denotes an input terminal from which a digital tone signal is supplied to modulation means 6. In FIG. The modulation means 6 modulates the digital musical tone signal using the modulation signal from the low frequency oscillation means 2, adds effects such as chorus and vibrato, and outputs it from the output terminal 8.

The low frequency oscillation means 2 has a first triangular wave generation means lO. This first triangular wave generating means 10 uses an accumulator to accumulate rate information determined by a rate setting means (not shown), and overflows the bit width of the register of this accumulator, as shown in FIG. 2(a). As shown, a sawtooth wave whose positive and negative peak values are +H1-H is generated. Note that the frequency of this sawtooth wave is determined by rate information.

Then, the absolute value of this sawtooth wave is taken, and as shown in FIG. 2(c), a triangular wave that changes from 0 to +H1+H to O and has one frequency the same as the sawtooth wave in FIG. 2(a) is generated. By subtracting H/2 from this triangular wave, the positive and negative peak values are respectively 10 H/2. -H/2, a triangular wave having the same frequency as the sawtooth wave shown in FIG. 2(a) is generated. This is the output of the first triangular wave generating means lO.
is supplied to the 1 multiplier 12 as a triangular wave.

This low frequency oscillation means 2 also has a second triangular wave generation means 14. The second triangular wave generating means 14 inputs the sawtooth wave shown in FIG. 2(a) from the first triangular wave generating means 10, adds H/2 to this, and generates a signal as shown in FIG. 2(b). Then, a sawtooth wave whose phase is delayed by π/2 from that of the sawtooth wave shown in FIG. 3(a) is generated. The absolute value of this is taken as shown in the same figure (d), and a triangular wave varying from 0 to +H is generated. By subtracting H/2 from this triangular wave, a triangular wave varying from -H/2 to +H/2 is generated as shown in FIG. This is supplied to the 1 multiplier 12 as a second triangular wave which is the output of the second triangular wave generating means 14.

That is, the phases of the first and second triangular waves supplied to the first multiplier 12 differ by π/2, but the positive and negative peak values are 10H/2 and -H/2, respectively, and the one frequency is as shown in FIG. It becomes a triangular wave, which is the same as the sawtooth wave in a). Therefore, as shown in FIG. 2(g), the output of the multiplier 12 changes to positive and negative at twice the frequency of the first and second triangular waves, and the positive and negative peak values are +
)l''716, -H'/16, resulting in a quadratic curve wave.

This will be explained in detail with reference to FIG.

FIG. 3(a) shows the waveform of one cycle T of the first triangular wave, and FIG. 3(b) shows the corresponding second triangular wave. As is clear from this, the value a of the first 1/4 period of the first triangular wave is expressed as a = 2Ht/T. However, t is time. Similarly, the value of the first 174 cycles of the second triangular wave is b = (H/2)-
(2Ht/T), the output y of the multiplier 12 multiplied by a and b is y=a
・b −(2Ht/T)((H/2)−(2Ht/T))～−
H"(2t/T-1/4)"◆H"/16. This is illustrated as axb in Fig. 3(c), which is 2 with a positive peak value H"/16 at T/8. It becomes a curved wave.

Similarly, the value C of the second 174 cycles of the first triangular wave is expressed as c = (H/2) - (2Ht/T), and the value C of the second 1/4 cycle of the second triangular wave is d is d So-2) 1t/T. The output y of the multiplier 12 multiplied by c and d is y=c
@d Zero ((H/2)-(2Ht/T))・(-2Ht/T)
-H"(2t/T-1/4)"-H"/16. If this is illustrated, it becomes cxd in Figure 3 (C), and T/8
It becomes a quadratic curve wave having a negative peak value -H''/16.

Similarly, the value C of the third 1/4 period of the first triangular wave is expressed as e−2)1t/T, and the value f of the third 1/4 period of the second triangular wave is f -(-H/2) ten (2Ht/T). The output y of the multiplier 12 multiplied by e and f is y=e
・f −(−2Ht/T)・(−(11/2)◆(2Ht/T
))-H”(2t/T-1/4)”+H! /16. To illustrate this, as shown by exf in FIG. 3(C), it becomes a quadratic curve wave having a positive peak value H''/16 at T/8.

Similarly, the value g of the fourth 1/4 period of the first triangular wave is expressed as g - (-H/2) + (2Ht/T), and the value g of the fourth 174 period of the second triangular wave is The value is 0g expressed as h-2Ht/T, and the output y of the multiplier 12 multiplied by h is y=g・h=((-H/2)+(2Ht/T))・(2)1t/ T
)-H"(2t/T-1/4)"-H"/16.

To illustrate this, as shown by gxh in FIG. 3(C), it becomes a quadratic curve wave having a negative peak value -)1''/16 at T/8.

The same thing holds true for each of the other periods of the first triangular wave. Therefore, the output of the multiplier 12 is a quadratic curve whose positive and negative peak values are 10"/16 and -I2/16, which periodically changes in positive and negative directions at twice the frequency of the first and second triangular waves. It becomes a wave.

The output of this multiplier 12 is multiplied by a constant that determines the modulation depth in a 1 multiplier 16, and is supplied to the modulation means 6 as a modulation signal.

Furthermore, the output of the 1 multiplier 12 is proportional to a waveform obtained by integrating a triangular wave with twice the original frequency.

For example, when a triangular wave rises from -H/2 to H/2, the value is (-H/2) ÷ (2Ht/T). Integrating this, we get (-Ht/2)◆(Ht2 /T). On the other hand, if we rewrite gh as /, we get (-H”t/T)◆
(4H"t2/T") 0 Comparing both, H,
It is clear that if there is a certain relationship between T and T, then both will match. Therefore, by using a digital method in which the writing period of the digital musical tone signal to the modulating means 6 is constant and only the reading period is modulated by the modulating signal,
Even if the effect of differentiating the modulation signal is applied, the modulation signal is proportional to the integral of the triangular wave, and the differentiated signal is proportional to the triangular wave, so the pitch of the musical tone signal changes in the shape of a triangular wave, which is natural. effect can be obtained.

FIG. 4 is an example of a flowchart when the above-mentioned low frequency oscillation means 2 is configured by software. First, the counter C1 is preset to O (step S2), and each time the rate information r is input, the counter C1 is The value of the counter C1 is incremented by the rate information r (step S4), and the amplitude is limited in step S6.7 so that the value of the counter C1 does not exceed ±H, thereby generating the sawtooth wave shown in FIG. 2(a). let The waveform on the negative side of the count value of counter C1 is folded back,
The value is stored in register R1, and the triangular wave shown in FIG. Generate the triangular wave shown in figure (e) (step 5
I2), step S4, 6.7.8.9.1O112 corresponds to the first triangular wave generating means 10.

Following step S12, H/2 is added to the value of counter C1 and stored in register R3 (step 5I4).
, the amplitude is limited in step S16.17 so that the value in register R3 does not exceed ±H, and is stored in register R3 to generate the sawtooth wave shown in FIG. 2(b). The waveform on the negative side of the value stored in register R3 is folded back and stored in register R4 to generate the triangular wave shown in FIG. H/2 is subtracted and stored in register R5 to generate a triangular wave shown in FIG. 2(f) (step 522), steps S14.16.17.18.
1g.

20 and 22 correspond to the second triangular wave generating means 14.

Next, the values stored in registers R2 and R5 are multiplied by the modulation depth coefficient, and the result is supplied to the modulation means 6° as a modulation signal (
Step 524), this step S24 is performed by the multiplier 12.
It corresponds to 16. Then, the process returns to step S4. Although the amplitude is limited in step S6.7 and step S16.17, registers and adders are only prepared for the necessary number of bits during the addition operation in step S4.14.
If the overflow due to addition is ignored, the amplitude is automatically limited, and these steps S6, 7 and S16.17
There is no need to provide one.

[Effects of the Invention] As described above, according to the present invention, the first and second triangular waves whose phases differ by π/2 are multiplied to obtain a modulation signal that periodically fluctuates between positive and negative. By modulating the modulation means with a modulation signal, natural effects can be obtained. Moreover, triangular waves like this can be obtained with various frequencies relatively easily using software.
There is no need to increase the scale of the hardware configuration.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of an effect adding device implementing a function generating device according to the present invention, FIG. 2 is a timing diagram of each part of the same embodiment, and FIG. 3 is a diagram explaining the principle of generation of a function signal.
FIG. 4 is a flowchart of the same embodiment. lO: first triangular wave generating means, 12: multiplier, I4: second triangular wave generating means. ! IP+1 1!1 Mature 21!

Claims (1)

[Claims] (1) A first triangular wave generating means that generates a first triangular wave, a second triangular wave generating means that generates a second triangular wave whose phase is shifted by π/2 from the first triangular wave, and a second triangular wave generating means that generates a first triangular wave. and a multiplier for multiplying a second triangular wave by a second triangular wave.