JPH0640267B2 - Digital filter device for tone signals - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a digital filter device used in an electronic musical instrument, a musical tone signal generator, or another musical tone signal processing device.

[Conventional technology]

The digital filter includes a finite impulse application filter (hereinafter referred to as FIR filter) and an infinite impulse response filter (hereinafter referred to as IIR filter). FI
The R filter has an advantage that it is relatively easy to set a filter coefficient for obtaining a desired filter characteristic and is easy to use. However, since the number of impulse responses is limited to the number of signal delay stages, the number of signal delay stages can be changed to an IIR filter. Compared to the above, the circuit configuration tends to be large and the scale tends to be large.

The basic structure of a conventional FIR filter is as shown in FIG. Here, x (n) is digital tone waveform sample value data at an arbitrary nth sample point, and is an input signal of the FIR filter. z ^-1 is a unit time delay element, and is composed of a delay circuit that sets a time delay of one sampling period. Therefore, x (n-1) is the digital tone waveform sample value data of the (n-1) th sample point, and x
(n-N + 1) is digital tone waveform sample value data at the (n-N + 1) th sample point. N is the duration of the impulse response and corresponds to the order of the FIR filter. h (0) to h (N-1) are Nth-order filter coefficients.
The operation sequence OP includes a multiplication element and an addition element. The triangular blocks to which the filter coefficients h (0) to h (N-1) are input are multiplication elements, and the data x (n) to x (n-N + 1) at each sample point delayed by the delay element The corresponding filter coefficients h (0) to h (N-1) are multiplied.
The block to which the + sign is added, to which the multiplication output is input, is an addition element, and the multiplication outputs are added together to obtain the output signal y (n).

Thus, the conventional FIR filter has only one operation sequence for one delay sequence.

[Problems to be solved by the invention]

Since the conventional digital filter has only one operation sequence for one delay sequence, only one filter characteristic can be realized for one digital filter. Further, in order to limit complicated characteristics such as multi-peak filter characteristics, it is necessary to considerably increase the number of delay stages, which complicates the circuit configuration.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a digital filter device for a musical tone signal, which can easily realize complicated filter characteristics and a plurality of filter characteristics with a simple configuration. .

[Means for solving problems]

The tone signal digital filter device according to the present invention comprises:
A digital tone signal is input and a plurality of stages of delay circuits for sequentially delaying, and output signals of each delay output stage of the delay circuit are commonly input to each series, and individual filter coefficient groups are individually input to each series. The output signals of the delay output stages are each multiplied by the filter coefficient of the order corresponding to each of the delay output stages, and a plurality of calculation sequences for individually performing the finite impulse response type filter calculation for each sequence are provided. It is characterized by that. This is shown in FIG. 1, which is as shown in FIG. 1. Each of the plurality (m) of operation sequences OP1 to OPm is configured similarly to the operation sequence OP of FIG. Filter coefficient set h given to OPm
_{, 1} (0) to h ₁ (N-1), ..., hm (0) to hm (N-1) are individual for each series.

[Action]

A plurality of operation sequences are provided, whereas only one sequence of delay circuits having a plurality of stages is provided. While the output signal of each delay output stage of the delay circuit is commonly input to each operation series, regarding the filter coefficient, an individual filter coefficient set is input for each operation queue. In each operation series,
Using a filter coefficient set unique to each, the output signal of each delay output stage is multiplied by the filter coefficient of the order corresponding to each delay output stage, and a unique finite impulse response type filter operation is individually performed for each sequence. Do each one.

Therefore, even if the delay circuit has only one series, it is possible to individually perform the filter operation for realizing the individual filter characteristic for each operation series. This makes it possible to easily realize a plurality of different filter characteristics. Further, by combining the filter characteristics of each operation series, complicated filter characteristics can be easily realized.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 shows an embodiment of an electronic musical instrument to which the digital filter device according to the present invention is applied. The keyboard 10 is provided with a plurality of keys for designating the pitch of a musical tone to be generated. The key detection circuit 11 detects a key pressed on the keyboard 10 and outputs a key code KC indicating the pressed key and a key-on signal KON indicating the key press or key release. The key touch detection device 12 detects a touch applied to the key pressed by the keyboard 10, and may detect either an initial touch or an after touch. The tone color selection device 13 comprises a group of operators for selecting the tone color of a musical tone to be generated.

The tone generator 14 generates a digital musical tone signal based on the key code KC and the key-on signal KON given from the key depression detection circuit 11, and is assumed to be a single tone generation type for simplification of description. Any tone signal generation method in the tone generator 14 may be used. For example, a method of sequentially reading tone waveform sample value data stored in a waveform memory according to address data that changes corresponding to the pitch of a tone to be generated (memory reading method), or the address data as phase angle parameter data. A method for obtaining musical tone waveform sample value data by performing a predetermined frequency modulation calculation (FM method), or a method for performing a predetermined amplitude modulation calculation using the above address data as phase angle parameter data to obtain musical tone waveform sample value data ( Any known method such as AM method) may be used. When the memory reading method is adopted, the number of tone waveforms stored in the waveform memory is 1.
Although only the periodic waveform may be used, a plural-period waveform is preferable because the sound quality can be improved. A method of storing a plurality of periodic waveforms in a waveform memory and reading them out is, for example, a method of storing all the waveforms from the start to the end of sounding and reading out once as shown in JP-A-52-121313, or As shown in Japanese Patent Application Laid-Open No. 58-142396, a method of storing a plurality of periodic waveforms of an attack portion and one or a plurality of periodic waveforms of a sustain portion, reading the waveform of the attack portion once and then repeatedly reading the waveform of the continuous portion, or JP-A-60-14
Various methods are known, such as a method in which a plurality of discretely sampled waveforms are stored as shown in No. 7793, the waveforms to be read are sequentially switched in time and designated, and the designated waveforms are repeatedly read. However, these may be appropriately adopted.

The digital tone signal generated by the tone generator 14 is input to the digital filter circuit 15. The digital tone waveform sample value data output from the digital filter circuit 15 is the digital / analog converter 1
At 6, it is converted into an analog tone signal and is sounded via the sound system 17.

The digital filter circuit 15 performs a filter operation on the digital musical tone signal output from the tone generator 14 according to the filter characteristic set therein, and performs tone color setting and other control. This filter characteristic is set according to various tone color setting / control factors. For example, the output TC of the tone color selection device 13 is set to the digital filter circuit 15 in order to set the filter characteristics according to the tone color type selected by the tone color selection device 13.
And the output TD of the key touch detection device 12 for performing the filter characteristic setting according to the key touch,
The key code KC is used to set the filter characteristic according to the pitch (or range), and the key-on signal KON is used to set the filter characteristic according to the passage of time after the key is pressed. The outputs of the manipulators 18 for setting the filter characteristics are respectively the digital filter circuit 1
Given to 5.

A concrete example of the digital filter circuit 15 is as shown in FIG. The digital tone signal output from the tone generator 14 is input and a plurality of stages of delay circuits 19 for sequentially delaying, and the output signals of each delay output stage of the delay circuit 19 are commonly input to each series, and also for each series. individual filter coefficient set _{h 1 (0) ~h 1 (} N-1), ..., hm (0) ~hm
(N-1) is input respectively, and the output signal of each delay output stage is multiplied by the filter coefficient of the order corresponding to each delay output stage, and the finite impulse response type filter operation is individually performed for each series. Of the operation sequence OP1 to OPm. Each of the operation series OP1 to OPm for performing the finite impulse response type filter operation is the operation series OP1 to Om in FIG.
It is constructed similarly to Pm. Filter coefficient generation circuit 2
0 is an individual filter coefficient set h ₁ (0) to h ₁ (N−1), ..., Hm for each series according to various tone color setting / control factors.
(0) to hm (N-1) respectively, the output TC of the tone color selection device 13, the output TD of the key touch detection device 12,
The key code KC, the key-on signal KON, the output of the operator 18 and the like are input as tone color setting / control factor data, and individual filter coefficient sets for each series are generated based on these.

The outputs of the operation sequences OP1 to OPm are input to the output circuit 21, respectively, and on the other hand, they are combined by the adder 22 and then input to the output circuit 21. The output circuit 21 selects and combines the outputs of the operation sequences OP1 to OPm and the output of the adder 22 and outputs the selected output. The tone color selection signal TC and the output of the selection switch 24 are given to the output control circuit 23, and a signal for controlling selection / synthesis is output from the output control circuit 23 according to the selected tone color type or operation of the selection switch 24. The selection / combination in the output circuit 21 is controlled by the output of the output control circuit 23.

The individual outputs of the respective operation sequences OP1 to OPm correspond to those obtained by filtering the common input musical tone signal with a plurality of different filter characteristics. Therefore, a plurality of m different filter characteristics can be realized only by using the delay circuit 19 of one series. The output circuit 21 can appropriately select these m output signals having different filter characteristics.

The output of the adder 22 corresponds to the one obtained by filtering the input musical tone signal according to one complicated filter characteristic that is a combination of the filter characteristics in each of the operation sequences OP1 to OPm. For example, each operation sequence OP1 to OP4 realizes a single-peak formant filter characteristic having a different center frequency,
By combining these, as shown in FIG. 4, it is possible to realize a complex filter characteristic including a multimodal formant. In order to realize a complicated filter characteristic consisting of multi-peak formants with a single-series digital filter, the number of delay stages must be considerably increased, and the setting of the filter coefficient is troublesome. There is no such thing. The output of the adder 22 can be appropriately selected by the output circuit 21.

Any mode of selection / combination in the output circuit 21 may be used. For example, the selection is performed according to either the first mode or the second mode. In the first mode, the individual outputs of the operation sequences OP1 to OPm are selected and output in parallel, and the second output is selected. In the mode of 1, the output of the adder 22 can be selectively output. Further, it is also possible to select a plurality of arbitrary outputs from the individual outputs of the respective operation sequences OP1 to OPm, combine them, and output them. Furthermore, arbitrary 2 (or 3 or more) outputs may be selected from the individual outputs of the operation sequences OP1 to OPm, and these may be interpolated and combined according to an appropriate interpolation function and output. May be.

FIG. 5 shows an example of the case where the output circuit 21 is composed of an interpolation circuit. The individual outputs of the operation sequences OP1 to OPm are input to the selection circuit 25, and a signal from the output control circuit 23 selects any two outputs from the individual outputs of the operation sequences OP1 to OPm. One of the selected outputs is indicated by F1 and the other is indicated by F2. The signal of F1 is multiplied by the multiplier 26
Then, the F2 signal is input to the multiplier 27, respectively. The interpolation function IP1 is input to the multiplier 26, and the interpolation function IP2 is input to 27. The interpolation functions IP1 and IP2 are related to the filter coefficient generation circuit 20. The output TC of the tone color selection device 13, the output TD of the key touch detection device 12, the key code KC, the passage of time after the key-on signal KON is generated, and the operator. The output of 18 may be generated according to each tone color setting / control factor. In the multipliers 26 and 27, F
The signals of 1 and F2 are level-controlled at a ratio according to the interpolation functions IP1 and IP2, and these are added and synthesized by the adder 28. An example of the interpolation functions IP1 and IP2 is shown in FIG. The parameter on the horizontal axis is the tone color setting / control factor described above. As an example, the filter characteristic applied to the signal selected as F1 is as shown in FIG.
The filter characteristic applied to the signal selected as 2 is the 7th
If it is as shown in FIG. 6B, the signal that has passed through both filter characteristics is processed by the interpolation function I corresponding to the current value of the parameter.
Interpolation will be performed at a ratio according to the values of P1 and IP2.
A signal similar to the signal filtered according to the filter characteristic obtained by substantially interpolating both filter characteristics can be obtained.

In the above embodiment, the order in each of the operation sequences OP1 to OPm is the total N from the 0th order to the N−1th order, but it is not necessary that all the sequences have the same order N, and may be appropriately different.

Of course, the present invention can be applied not only to a single-tone generating type electronic musical instrument or musical tone generating device, but also to a multiple-tone generating type electronic musical instrument or musical tone generating device.

〔The invention's effect〕

As described above, according to the present invention, since a plurality of operation series are provided for one series of delay circuits, even if the delay circuit is only one series, individual filter characteristics are realized for each operation series. Each filter operation can be performed, so that a plurality of different filter characteristics can be realized with a simple configuration, and complex filter characteristics can be easily realized by combining the filter characteristics of each operation sequence. It has the excellent effect of being able to

[Brief description of drawings]

1 is a block diagram showing an outline of a digital filter device according to the present invention, FIG. 2 is a block diagram showing an embodiment of an electronic musical instrument to which the digital filter device according to the present invention is applied, and FIG. 3 is FIG. FIG. 4 is a block diagram showing an example of a digital filter circuit in FIG. 4, FIG. 4 is a diagram showing an example of filter characteristics realized by combining filter characteristics of a plurality of operation sequences, and FIG. 5 is an interpolation circuit of the output circuit in FIG. 6 is a block diagram showing an example of an interpolation function, FIG. 6 is a diagram showing an example of an interpolation function, and FIGS. 7A and 7B are diagrams showing an example of filter characteristics corresponding to two signals to be interpolated. FIG. 8 is a block diagram showing the basic configuration of a finite impulse filter. 10: keyboard, 11: key depression detecting circuit, 12: key touch detecting device, 13: tone color selecting device, 14: tone generator, 15: digital filter circuit, 19: delay circuit,
OP, OP1 to OPm; operation series, 20; filter coefficient generation circuit, 21; output circuit.

Claims (1)

[Claims] 1. A plurality of stages of delay circuits for inputting a digital musical tone signal and sequentially delaying the same, and inputting an output signal of each delay output stage of the delay circuit in common for each series, and an individual filter for each series. A plurality of operations for inputting each coefficient set, multiplying the output signal of each delay output stage by the filter coefficient of the order corresponding to each delay output stage, and individually performing the finite impulse response type filter calculation for each series. A digital filter device for a musical tone signal, characterized by comprising a series.