JP3947806B2 - Waveform synthesizer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a waveform synthesizer capable of faithfully reproducing an analog basic waveform by a digital synthesizer or the like.
[0002]
[Prior art]
Many devices have been proposed in the past for sampling an analog signal into a digital signal and reproducing the sampled digital signal at a corresponding pitch. In such a device, an analog signal is converted into a digital signal, stored, and the stored digital signal is reproduced when necessary, thereby reproducing an analog basic waveform by a digital synthesizer or the like. It is possible. When reproducing the sound of an analog synthesizer with a conventional PCM synthesizer, multi-sampling was performed in a plurality of ranges and interpolation processing was performed to reproduce at an arbitrary pitch. However, each sample data length is adjusted to one cycle of the sampled waveform. Therefore, it became shorter as it became a high range.
[0003]
However, this type of conventional device lacks fidelity when reproducing a digital signal. This is because when the sound is played at a pitch that is far from the sampled pitch, the waveform changes discontinuously or the timbre is different from the original timbre, and if the number of multisamples is increased, sampling will occur. This is because there is a problem of waveform discontinuity when the playback pitch is continuously variable, although the ratio of deviation from the pitch is reduced.
[Problems to be solved by the invention]
[0004]
Accordingly, an object of the present invention is to provide a waveform synthesizer that can faithfully reproduce an analog basic waveform by a digital synthesizer or the like.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a keyboard unit having a key group composed of a plurality of keys,
An analog signal generator for generating an analog signal of a predetermined shape at a specified frequency;
A sampling unit for sampling the analog signal;
A filter unit for filtering the sampling signal;
A table group provided for each of the plurality of keys, each of which can store a predetermined number of data, and data stored in a table corresponding to the pressed key are reproduced at a frequency corresponding to the key. A playback unit, and an overall control unit that performs overall control of the device,
The overall controller is
Designating the frequency of the analog generation unit so that the frequency of the analog signal is a frequency for a certain key, and storing the data obtained from the filter unit in a table corresponding to the key for all keys There is provided a waveform synthesizer characterized in that the waveform synthesizer performs the above.
[0006]
Further, when reproducing the data stored in the table corresponding to the pressed key, the reproducing unit is configured to cyclically read the data stored in the table at a frequency corresponding to the key. You can also. Further, a spectrum analysis unit for obtaining a frequency characteristic of the power spectrum of the signal from the sampling unit is further provided, and the filter unit performs filtering so that an attenuation amount at a specific frequency of the power spectrum becomes a predetermined value or more. The frequency characteristics may be changed and controlled.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0008]
(Constitution)
FIG. 1 is a configuration diagram of the waveform synthesizer 1. The waveform synthesizer 1 includes an analog signal generation unit 10, a sampling unit 20, an FFT unit 30, a variable filter unit 40, a table group of tables 1 (100a) to 128 (100n), and a plurality of keys ( A keyboard unit 50 having a key group (not shown) and a reproducing unit 60 that reads out and reproduces data in the table are provided. The overall operation of the apparatus is configured to be performed by the overall control unit 200.
[0009]
The analog signal generation unit 10 generates a SAW waveform that is an example of an analog basic waveform as shown in FIG. 1 at a specified frequency f, for example. The sampling unit 20 samples the analog signal at a frequency of, for example, fs = 44.1 (kHz) and supplies the sampled signal to the FFT unit 30 and the variable filter unit 40. The FFT unit 30 performs FFT processing on the obtained sampling data and calculates the frequency characteristic of the power spectrum, and the obtained result is given to the variable filter unit 40.
[0010]
The variable filter unit 40 is composed of a linear phase low-pass filter in order to suppress waveform ringing. Specifically, as shown in FIG. 2, a Gaussian filter is used, and the overall frequency characteristic is set so that attenuation of “−80 dB” or more can be performed at the Nyquist frequency (fs / 2: normalized frequency 0.5). In addition, it is possible to change and control the filtering characteristics by controlling movement in the A direction (low frequency side) or the B direction (high frequency side). Thus, the variable filter unit 40 changes and controls the filtering frequency characteristics so that the attenuation amount at the specific frequency (fs / 2) of the power spectrum obtained by the FFT unit 30 is attenuated by “−80 dB” or more. Can be done.
[0011]
Table 1 (100a) to table 128 (100n) are for 128 keys (not shown). That is, table 1 (100a) is for the key with key number “1”, table 2 (100b) is for the key with key number “2”,..., Table 128 (100n) is for the key with key number “128”. Is. As shown in FIG. 4, each table 1 (100a) to 128 (100n) can sequentially store data from the variable filter section 40 in an area “2048” in total from “0” to “2047”. It is configured. That is, each table 1 (100a) to 128 (100n) can store 2048 sample data.
[0012]
The keyboard unit 50 is provided with a key group including 128 keys (not shown). When a key pressing operation is performed, a key number corresponding to the pressed key is output to the reproducing unit 60. For example, when the first key is pressed, the reproduction unit 60 is notified of the key number “1”. The number of keys is not limited to 128, and the number of keys may be changed. In this case, the number of tables 100 may be changed according to the number of keys.
[0013]
The playback unit 60 includes a switch 65. The switch 65 operates to connect the table 100 corresponding to the key number obtained from the keyboard unit 50 to the reproducing unit 60. For example, when the reproducing unit 60 obtains the key number “1”, 2048 data items in the table 1 (100a) corresponding to the key number “1” are cyclically read out and reproduced in order to perform waveform synthesis. . Therefore, the data from the “0” th to the “2047” th of the table 100 may be cyclically reproduced without considering whether or not the read address of the reproduction data has reached the final address as in the prior art. . The reproduction frequency (readout frequency) is set for each key, that is, for each key number. As shown in FIG. 3, for example, when the key number is “1”, the frequency is f1 and the key number is “2”. In the case of the frequency f2,..., The key number “128”, the frequency f128.
[0014]
FIG. 3 is an explanatory diagram of a table 300 referred to by the overall control unit 200. The table 300 registers a key number and a frequency (also a frequency at the time of reproduction) in association with each other. For example, in the case of the key number “1”, the frequency is “f1”, and the frequency is designated to the analog signal generation unit 10 so that an analog signal is generated at this frequency f1.
[0015]
(Operation)
First, the data construction operation in the table 100 will be described with reference to FIG. When the overall control unit 200 designates the frequency “f1” corresponding to the key number “1” to the analog signal generation unit 10, the SAW waveform of the frequency f1 is generated. This is filtered by the variable filter unit 140, and 2048 pieces of the data are stored in the table 1 (100a). At this time, the frequency characteristic of the filter is moved and controlled so that the value at “fs / 2” of the power spectrum obtained by the FFT unit 30 is taken into account so that it is attenuated by “−80 dB” or more.
[0016]
Similarly, next, when the overall control unit 200 designates the frequency “f2” corresponding to the key number “2” to the analog signal generation unit 10, a SAW waveform of the frequency f2 is generated. This is filtered by the variable filter unit 140, and 2048 pieces of the data are stored in the table 2 (100b). Such operation is repeated, and finally, when the overall control unit 200 designates the frequency “f128” corresponding to the key number “128” to the analog signal generation unit 10, a SAW waveform of the frequency f128 is generated. This is filtered by the variable filter unit 140, and 2048 pieces of the data are stored in the table 128 (100n). Thus, 2048 pieces of data for each key are stored in a table corresponding to each of the plurality of keys.
[0017]
FIG. 5 is an explanatory diagram schematically showing waveform data stored in each of the table 1 (100a) to the table 128 (100n). Actually, the waveform data of the adjacent tables have a strong correlation and do not change suddenly but are only slightly changed, and the change of the stored waveform data for each table is extremely gradual.
[0018]
Next, the reproduction operation will be described. The switch 65 operates to connect the table 100 corresponding to the key number obtained from the keyboard unit 50 to the reproducing unit 60. For example, when the reproducing unit 60 obtains the key number “1”, the 2048 data items in the table 1 (100a) corresponding to the key number “1” are cyclically sequentially and the frequency corresponding to the key number “1”. The waveform is synthesized by reproducing at f1. Similarly, when the reproducing unit 60 obtains the key number “2”, the 2048 data items in the table 2 (100b) corresponding to the key number “2” are cyclically and sequentially turned into the key number “2”. The waveform is synthesized by reproducing at the frequency f2.
[0019]
As described above, according to the embodiment of the present invention, the overall control unit 200 corresponds the data obtained from the variable filter unit 40 to the key so that the frequency of the analog signal is a frequency for a certain key. By performing the processing to be stored in the table 100 for all keys, data related to the key can be stored in the table 100 corresponding to the key. Moreover, at the time of reproduction, it is only necessary to cyclically reproduce the data of the table 100 corresponding to the key at the frequency corresponding to the key, thereby providing a waveform synthesis apparatus that can faithfully reproduce the analog basic waveform by a digital synthesizer or the like. I can do it. Further, the waveform change with respect to the pitch change is very smooth, the aliasing noise is extremely small, and the calculation load at the time of waveform reproduction is extremely small.
[0020]
Although the embodiments of the present invention have been described above, various modifications and changes can be made to the above-described embodiments without departing from the gist of the present invention. In the waveform synthesizer 1 shown in FIG. 1, the components other than the keyboard unit 50 can be realized by hardware such as a dedicated LSI as much as possible, and the CPU (or DSP) can perform the function as much as possible. It can also be realized by executing an operation program. Furthermore, a series of operations may be performed by an algorithm program without using each table. For example, the waveform synthesizer 1 of FIG. 1 can be realized by a single PC (personal computer) having a keyboard unit 50. Further, the analog waveform may be a waveform other than the SAW waveform.
【The invention's effect】
As described above, according to the present invention, it is possible to provide a waveform synthesizing apparatus that can faithfully reproduce an analog basic waveform by a digital synthesizer or the like.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a waveform synthesizer 1. FIG.
FIG. 2 is an explanatory diagram of filtering characteristics and the like of the variable filter unit 40;
FIG. 3 is an explanatory diagram of a table 300. FIG.
4 is an explanatory diagram of a table 100. FIG.
FIG. 5 is an explanatory diagram of waveform data stored in tables 100a to 100n.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Waveform synthesis apparatus 10 Analog signal generation part 20 Sampling part 30 FFT part 40 Variable filter part 50 Keyboard part 100a Table 100b Table 100n Table 200 Overall control part 300 Table

Claims (1)

A keyboard part having a key group composed of a plurality of keys;
An analog signal generator for generating an analog signal of a predetermined shape at a specified frequency;
A sampling unit for sampling the analog signal;
A filter unit for filtering the sampling signal;
A table group provided for each of the plurality of keys, each of which can store a predetermined number of data, and data stored in a table corresponding to the pressed key are reproduced at a frequency corresponding to the key. A playback unit, and an overall control unit that performs overall control of the device,
The overall control unit
Designating the frequency of the analog generation unit so that the frequency of the analog signal is a frequency for a certain key, and storing the data obtained from the filter unit in a table corresponding to the key for all keys A waveform synthesizer characterized in that the waveform synthesizer is applied to the waveform synthesizer.

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