JPH088464B2 - Tone adjustment circuit for electronic musical instruments - Google Patents

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to a tone color adjusting circuit for an electronic musical instrument. “Prior Art” With the progress of integrated circuit technology, digital filters have been used instead of analog filters for tone color adjustment in electronic musical instruments. For example, the primary low-pass filter including the resistance element 11 (resistance value R) and the capacitor 12 (capacitance value C) as shown in FIG. 7 can be replaced with a digital filter having the configuration shown in FIG. In FIG. 8, a digital signal to be filtered is input to one input terminal of the subtractor 1. The output signal of the subtractor 1 is input to the multiplier 2 and a predetermined multiplication coefficient α
Is multiplied. The output of the multiplier 2 is integrated by the integrator composed of the adder 3a and the one sampling period delay circuit 3b, and the output of the delay circuit 3b is input to the other input terminal of the subtractor 1. According to such a configuration, the transfer function H between the input and the output
As (z), Then, the multiplication coefficient α given to the multiplier 2 is selected to be 1 / (CR), whereby a digital low-pass filter equivalent to the analog low-pass filter shown in FIG. 7 is realized. [Problems to be Solved by the Invention] By the way, an analog filter is not always configured by an analog element having ideal characteristics. For example, each analog element has a distortion factor, such as dielectric distortion in the case of a capacitor, non-linearity of resistance value in the case of a resistance element, and amplification distortion of an operational amplifier in the case of an analog filter using an operational amplifier. There is. In this way, when the tone signal is filtered by the analog filter having a distortion factor inside, a tone signal including a complicated harmonic component is obtained, and a rich sound quality is obtained. However, in the case of a digital filter, the ideal frequency characteristic according to the desired transfer function can be obtained, but when this is used as a tone adjustment filter, the rich frequency due to the distortion obtained in the case of an analog filter is obtained. There was a problem that the sound quality could not be obtained. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tone color adjusting circuit for an electronic musical instrument using a digital filter in which the distortion of an analog filter is taken into consideration and rich sound quality is obtained. "Means for Solving the Problem" The present invention interconnects digital signal processing means for performing signal processing corresponding to various operators in correspondence with a desired filter arithmetic expression or an arithmetic expression equivalent to this filter arithmetic expression. A digital filter having one or a plurality of feedback loops configured by the above, and at least one of the feedback loops is provided with a non-linear conversion means for performing a desired non-linear conversion on a signal transmitted through the feedback loop. It is characterized by having done. [Operation] According to the above configuration, the harmonic component is added to the signal of the feedback loop by inserting the non-linear conversion means in the feedback loop. Therefore, an output signal including a harmonic component can be obtained in addition to a signal obtained by applying a desired filter arithmetic expression to the input signal. [Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a block diagram showing a configuration of a tone color adjusting circuit of an electronic musical instrument according to a first embodiment of the present invention. Adder 3a and 1
A ROM (read only memory) 3y storing a non-linear function table is inserted between the sampling cycle delay circuit 3b and the sampling cycle delay circuit 3b. When the output x of the adder 3a is given as an address, the value y corresponding thereto is read from the ROM 3y and given to the delay circuit 3b. As the table contents of the non-linear function, for example, as shown in FIG.
A value y of y = −x ² for input value x in the range of 1 ≦ x ≦ 0
However, when the range is 0 ≦ x ≦ 1, the values y satisfying y = x ² are stored. Since the other components are exactly the same as those in FIG. 8 described above, corresponding parts are designated by the same reference numerals and the description thereof will be omitted. According to such a configuration, the output x of the adder 3a is
After the non-linear conversion shown in FIG. 2 is performed by y, it is fed back to the adder 3a via the delay circuit 3b and accumulated. As a result, for example, an operation similar to that in the case where the capacitor 12 in FIG. 7 has a dielectric distortion and the voltage value does not always rise in proportion to the accumulated charge amount, a digital filter of FIG. Obtained in. Further, since the ROM3y as the non-linear element is inserted, the transmission amount frequency characteristic as the primary low-pass filter is disturbed. Therefore, the adder 3a outputs an output signal including a signal in which the input signal is band-limited by the transmission amount frequency characteristic corresponding to the above equation (1) and many harmonic components.

Second Embodiment FIG. 3 is a block diagram showing a configuration of a tone color adjusting circuit of an electronic musical instrument according to a second embodiment of the present invention. This digital filter differs from the configuration shown in FIG. 1 in that the ROM 3y storing a non-linear function is inserted between the delay circuit 3b and the subtractor 1 rather than between the adder 3a and the delay circuit 3b. According to such a configuration, for example, the operation is similar when the resistance 11 in FIG. 7 is non-linear and the relationship between the voltage difference between the input voltage and the charging voltage of the capacitor 11 and the current flowing into the capacitor 11 is non-linear. The motion is obtained. Then, similarly to the first embodiment, an output signal containing a large amount of harmonic components can be obtained as a filter output. The above description corresponds to the case where each element forming the analog filter has a non-linear characteristic that causes distortion, and the non-linear conversion means for simulating the non-linear characteristic (in the case of the above first and second embodiments). Is an example with ROM3y). However, in the case of an analog filter having a complicated structure to some extent, the cause of distortion is often unclear. However, the point is that it is only necessary to obtain a digital filter capable of performing distortion-containing filtering as a result, so it is not always necessary to clarify the location of the cause of distortion in the target analog filter. There is no. In this case, prepare a digital filter that can obtain an appropriate transmission frequency characteristic and insert ROMs for nonlinear conversion at appropriate places in this digital filter to limit impulse response or transmission frequency characteristic. By doing so, a digital filter equivalent to an analog filter having distortion can be realized.

[Third Embodiment] FIG. 4 is a block diagram showing a configuration of a tone color adjusting circuit of an electronic musical instrument according to a third embodiment of the present invention. The tone color adjusting circuit of this electronic musical instrument is a known secondary digital low-pass filter in which a ROM3y storing a non-linear function is inserted. In the figure, 21,23,26,27,30 are multipliers, and f in the multiplier 23, -1 / Q in the multiplier 26, and -1 in the multiplier 30 are multiplication coefficients.
Further, 22, 24, 28 are adders, and 25, 29 are one sampling period delay circuits. According to this configuration, the output signal of the delay circuit 29 is non-linearly converted by being passed through the ROM 3y and input to the multiplier 30, so that it can be obtained when there is no ROM 3y.
Disturbance is added to the transmission amount frequency characteristic of the next low-pass filter. As a result, the output signal containing many harmonic components is output from the adder 28.

Fourth Embodiment Special tone color processing can be performed by using a limiter as the non-linear conversion means. FIG. 5 shows a configuration example of the limiter. In this figure, D _{0 to} D ₁₅ represent each bit of a 16-bit input digital signal, D ₁₅ is the MSB (most significant bit), and D ₀ is the LSB (least significant bit). D ₁₅ is a sign bit, and 16 bits D _{0 to} D ₁₅ represent a numerical value in the range of −1024 to +1023 in 2's complement format. The upper 2 bits D ₁₅ and D ₁₄ are directly output as the MSB (Q ₁₅ ) and the 14th bit (Q ₁₄ ) of the output digital signal. The lower 14 bits D _{0 to} D ₁₃ are input to one input terminal of each of the OR gates OR _{0 to} OR ₁₃ . The AND gate ANa receives the 15th bit D ₁₅ at the positive logic input terminal and the 14th bit D ₁₄ at the negative logic input terminal, and outputs the result of the AND operation D _15
14 is input to the other input terminals of the OR gates OR ₀ to OR ₁₃ . O
The outputs of the R gates OR _{0 to} OR ₁₃ are input to the positive logic input terminals of the AND gates AN _{0 to} AN ₁₃ , respectively. The AND gate ANb receives the 14th bit D ₁₄ at the positive logic input terminal and the first at the negative logic input terminal.
5-bit D ₁₅ is input and the result of AND operation ₁₅ and D ₁₄ is
It is input to the negative logic input terminal of each of AND gates AN _{0 to} AN ₁₃ . Then, the _0th to 13th bit outputs Q _{0 to} Q ₁₃ are obtained from the AND gates AN _{0 to} AN ₁₃ . With such a configuration, the limiter characteristic shown in FIG. 6 is realized. And, such a limiter is shown in FIGS.
If you use it instead of ROM3y in the figure or Figure 4,
The amplitude of the signal passing through the insertion position is limited, and special tone color processing is performed. [Advantages of the Invention] As described above, according to the present invention, the digital signal processing means for performing signal processing corresponding to various operators can correspond to a desired filter arithmetic expression or an arithmetic expression equivalent to this filter arithmetic expression. And a digital filter having one or more feedback loops configured by interconnecting each other, and for at least one of the feedback loops,
Since the non-linear conversion means for performing a desired non-linear conversion is inserted in the signal transmitted through the feedback loop, distortion components due to the non-linear conversion means are cumulatively generated, and a tone color processing means having a distortion like an analog filter is realized. be able to. As a result, it is possible to obtain an effect that an electronic musical instrument can generate a musical sound with extremely rich sound quality.

[Brief description of drawings]

1 is a block diagram showing a configuration of a tone color adjusting circuit of an electronic musical instrument according to a first embodiment of the present invention, FIG. 2 is a diagram illustrating a non-linear function used in the same embodiment, and FIG. 2 is a block diagram showing a configuration of a tone color adjusting circuit of an electronic musical instrument according to a second embodiment, FIG. 4 is a block diagram showing a configuration of a tone color adjusting circuit of an electronic musical instrument according to a third embodiment of the present invention, and FIG.
FIG. 7 is a circuit diagram showing a configuration example of a limiter used in the fourth embodiment of the present invention, FIG. 6 is a diagram showing input / output characteristics of the limiter of FIG. 5, and FIG. 7 is a circuit showing a primary analog low-pass filter. FIGS. 8 and 9 are block diagrams showing the structure of a first-order digital low-pass filter corresponding to the structure of FIG. 3y ... ROM (non-linear conversion means), 1 ... subtractor, 2 ...
Multiplier, 3a ... Adder, 3b ... 1 sampling cycle delay circuit.

Claims (1)

[Claims] 1. A digital signal processing means for performing signal processing corresponding to various operators, which is constructed by interconnecting digital signal processing means corresponding to a desired filter arithmetic expression or an arithmetic expression equivalent to this filter arithmetic expression, or An electronic musical instrument comprising a digital filter having a plurality of feedback loops, and at least one of the feedback loops is provided with a non-linear conversion means for performing a desired non-linear conversion on a signal transmitted through the feedback loops. Tone adjustment circuit.