JP6713400B2 - Musical sound signal conversion device, musical sound signal conversion method, and program - Google Patents

Description

The present invention relates to a tone signal conversion device, a tone signal conversion method, and a program for converting a tone signal.

A bit crusher (Non-Patent Document 1) is known as a type of effect for digital tone signals. The bit crusher is an effect that expresses various tones and sound qualities by intentionally reducing the fidelity (audio fidelity) of the digital tone signal to the original sound. The bit crusher deteriorates the original digital tone signal by reducing the quantization bit rate and the sampling rate. For example, at present, the quantization bit of a digital musical tone signal recorded on a music CD is 16 bits, and the sampling rate (sampling frequency) is 44.1 kHz. On the other hand, in the early video games, the quantization bit of the digital musical tone signal was 8 bits. Also, the sampling rate of the digital musical tone signals used in digital equipment in the 1970s was about 10 kHz.

As a typical usage of the bit crusher, there is a usage of reproducing a retro tone or sound quality by reducing a quantization bit and a sampling rate.

"Bitcrusher, From Wikipedia, the free encyclopedia", [online], 25 March 2016, [search on 20 September 2016], internet<URL:https://en.wikipedia.org/wiki/Bitcrusher>

DTM applications and the like having a bit crusher function exist conventionally. In these applications, the sampling rate can be degraded (also referred to as downsampling) by integrating a plurality of frames of the digital musical tone signal into one frame. For example, by integrating two consecutive frames of the original digital tone signal into one frame, the value of the sampling rate can be reduced to half. For example, the sampling rate can be degraded to 22.05 kHz by integrating two consecutive frames of the digital tone signal having the sampling rate of 44.1 kHz into one frame. In the following, the integration of N frames of the original digital tone signal into one frame is referred to as “thinning N frames”. In the above-mentioned application, for example, the original digital musical tone signal is thinned out by two frames, and the original digital musical tone signal is thinned out by three frames in the next step. For example, the sampling rate can be gradually deteriorated.

However, when the sampling rate is deteriorated by one stage from the state of “N frame thinning” to the state of “N+1 frame thinning”, and when N is sufficiently large, the boundary before and after the degradation can be easily heard at the moment when the degradation is executed. It appears as clear as possible. Even when the change in the opposite direction, that is, the state of "N+1 frame decimation" is improved by one step from "N frame decimation" to "N frame decimation", when N is sufficiently small, the boundary is similarly apparent.

For example, from a clear sound quality of a sampling rate of 44.1 kHz to a retro device-like sound quality of a sampling rate of 10.0 kHz, even if the musical tone signal is intended to be seamlessly deteriorated, deterioration of the musical tone signal is caused. Each time one step progresses, the listener clearly hears the joint (boundary). Therefore, it is not possible for the listener to perceive an effect in which the quality of a musical sound seamlessly traces back to the past.

Therefore, it is an object of the present invention to provide a musical tone signal conversion device that can seamlessly change the sampling rate of a musical tone signal.

The musical sound signal conversion apparatus of the present invention includes a signal acquisition unit, a first pseudo sampling unit, a second pseudo sampling unit, and a weighting addition unit. Note that N is a positive integer that can be set arbitrarily for pseudo sampling.

The signal acquisition unit acquires a digital musical tone signal. The first pseudo-sampling unit is a signal that expresses a waveform of a digital musical tone signal, while maintaining the sampling frequency of the digital musical tone signal, by using all the amplitude values of consecutive N frames of the digital musical tone signal as one type of amplitude value. Converted into a digitized signal. The second pseudo sampling unit is a signal that expresses the waveform of the digital musical tone signal while maintaining the sampling frequency of the digital musical tone signal with all the amplitude values of consecutive N+1 frames of the digital musical tone signal as one kind of amplitude value. Converted into a digitized signal. The weighted addition unit weights and adds the first pseudo sampling signal and the second pseudo sampling signal based on a weighting coefficient that can be arbitrarily set.

According to the tone signal converting apparatus of the present invention, the sampling rate of the tone signal can be changed seamlessly.

3 is a block diagram showing the configuration of the musical sound signal conversion apparatus according to the first embodiment. FIG. 3 is a flowchart showing the operation of the musical sound signal conversion apparatus according to the first embodiment. An example in which a musical tone signal pseudo-sampled in a state of 24 frame thinning-out and a musical tone signal pseudo-sampled in a state of 25 frame thinning-out generate a musical tone signal pseudo-sampled in a state of 24.5 frame thinning-out will be described. Fig.

Hereinafter, embodiments of the present invention will be described in detail. It should be noted that components having the same function are denoted by the same reference numerals, and redundant description will be omitted.

The configuration of the musical sound signal conversion apparatus according to the first embodiment will be described below with reference to FIG. As shown in FIG. 1, the musical sound signal conversion apparatus 1 of the present embodiment includes a signal acquisition unit 11, a pseudo sampling coefficient acquisition unit 12, a first pseudo sampling unit 13, and a second pseudo sampling unit 14. , A weighting addition unit 15 and a signal output unit 16.

The operation of the musical sound signal converting apparatus 1 of the present embodiment will be described below with reference to FIGS. The signal acquisition unit 11 acquires a digital musical tone signal (S11). The pseudo sampling coefficient acquisition unit 12 acquires the pseudo sampling coefficient N, which is a positive integer that can be arbitrarily set for pseudo sampling (S12). The pseudo sampling coefficient N is determined, for example, based on the value manually input by the user. Next, the first pseudo-sampling unit 13 is a signal that expresses the waveform of the digital musical tone signal while maintaining the sampling frequency of the digital musical tone signal, by setting all the amplitude values of consecutive N frames of the digital musical tone signal as one type of amplitude value. The signal is converted into the first pseudo sampled signal (S13).

For example, in the example of FIG. 3, N=24 is set by the user. Therefore, the first pseudo sampling section 13 converts all the amplitude values of the continuous 24 frames of the original digital musical tone signal into a first pseudo sampling signal which is a signal expressing its waveform as one kind of amplitude value (S13). .. However, it is assumed that the first pseudo sampling signal remains at the original sampling rate. For example, if the original digital tone signal has a sampling rate of 44.1 kHz, the first pseudo-sampling signal retains the sampling rate of 44.1 kHz, and all the amplitude values of consecutive 24 frames become one kind of amplitude value. It is assumed that the waveform of the signal is expressed by replacing it. As described above, in the present specification, performing pseudo sampling in order to perceive the sampling rate of the original digital musical tone signal as if the sampling rate had deteriorated while maintaining the sampling rate of the original digital tone signal is referred to as pseudo sampling in this specification. ..

Next, the second pseudo-sampling unit 14 is a signal that expresses the waveform of the digital musical tone signal while maintaining the sampling frequency of the digital musical tone signal with all the amplitude values of consecutive N+1 frames of the digital musical tone signal as one type of amplitude value. The second pseudo sampled signal is converted (S14).

For example, in the example of FIG. 3, since N=24 is set by the user, the second pseudo-sampling unit 14 sets all the amplitude values of the 25 consecutive frames of the original digital musical tone signal as one type of amplitude value and its waveform. Is converted into a second pseudo sampling signal which is a signal expressing (S14). As before, it is assumed that the second pseudo sampled signal remains at the original sampling rate.

Next, the weighting addition unit 15 weights and adds the first pseudo sampling signal and the second pseudo sampling signal based on a weighting coefficient that can be arbitrarily set (S15). The weighting factor is typically determined based on values manually entered by the user. The weighting coefficient for the first pseudo sampled signal is r _{1, the} weighting coefficient for the second pseudo sampled signal is r _2, and r ₁ +r ₂ =1.

For example, in the example of FIG. 3, the weighting coefficient r ₁ for the first pseudo sampled signal is set to 0.5 by the user. Since the weighting coefficient r ₂ =1−r ₁ for the second pseudo sampled signal, r ₂ is also set to 0.5. Therefore, in the example of FIG. 3, both the first pseudo sampling signal and the second pseudo sampling signal are multiplied by the weighting coefficient 0.5, and the two weighted signals are added.

For example, if the sampling interval of the original digital tone signal is s ₀ , then the pseudo sampling interval of the first pseudo sampling signal in the example of FIG. 3 is 24 s ₀ . Similarly, the pseudo sampling interval of the second pseudo sampling signal is 25s ₀ . Therefore, when weighting and adding the first pseudo sampling signal and the second pseudo sampling signal, it is necessary to represent the signal with a sampling interval of 25s ₀ -24s ₀ =s ₀ in the signal after the addition. That is, it is necessary to maintain the sampling rate of the original digital tone signal.

As described above, since the first and second pseudo sampling signals are only pseudo sampled while maintaining the sampling rate of the original digital musical tone signal, a fine sampling rate is required by weighted addition. Even in the case, the signal after the weighted addition can be correctly expressed.

Next, the signal output unit 16 outputs the digital tone signal weighted and added in step S15 (S16).

For example, in the example of FIG. 3, since the output signal is a signal obtained by evenly mixing the pseudo sampling signal obtained by thinning out 24 frames and the pseudo sampling signal obtained by thinning out 25 frames, the pseudo signal obtained by thinning out “24.5 frames” is output. It can be expressed as a sampled signal. By adjusting the weighting coefficient r ₁ , the output signal can be various pseudo sampling signals such as 24.1 frame thinning, 24.2 frame thinning, and so on. Therefore, it is possible to realize a bit crusher that seamlessly changes the digital musical tone signal in a unit that is more subdivided than the conventional sampling by thinning out integer frames, and that does not cause a sense of discomfort.

<Additional notes>
The device of the present invention is, for example, as a single hardware entity, an input unit to which a keyboard or the like can be connected, an output unit to which a liquid crystal display or the like can be connected, and a communication device (for example, a communication cable) capable of communicating with the outside of the hardware entity. Connectable communication unit, CPU (Central Processing Unit, cache memory or register may be provided), RAM or ROM that is a memory, external storage device that is a hard disk, and their input unit, output unit, communication unit , A CPU, a RAM, a ROM, and a bus connected so that data can be exchanged among external storage devices. If necessary, the hardware entity may be provided with a device (drive) capable of reading and writing a recording medium such as a CD-ROM. A physical entity having such hardware resources includes a general-purpose computer.

The external storage device of the hardware entity stores a program necessary to realize the above-described functions and data necessary for the processing of this program (not limited to the external storage device, for example, the program is read). It may be stored in a ROM that is a dedicated storage device). In addition, data and the like obtained by the processing of these programs are appropriately stored in the RAM, the external storage device, or the like.

In the hardware entity, each program stored in an external storage device (or ROM, etc.) and the data necessary for the processing of each program are read into the memory as needed, and interpreted and executed/processed by the CPU as appropriate. .. As a result, the CPU realizes a predetermined function (each constituent element represented by the above,... Unit,... Means, etc.).

The present invention is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the present invention. Further, the processes described in the above embodiments may be executed not only in time series in the order described, but also in parallel or individually according to the processing capability of the device that executes the processes or the need. ..

As described above, when the processing functions of the hardware entity (the apparatus of the present invention) described in the above embodiments are realized by a computer, the processing contents of the functions that the hardware entity should have are described by a program. Then, by executing this program on the computer, the processing functions of the hardware entity are realized on the computer.

The program describing the processing contents can be recorded in a computer-readable recording medium. The computer-readable recording medium may be, for example, a magnetic recording device, an optical disc, a magneto-optical recording medium, a semiconductor memory, or the like. Specifically, for example, a hard disk device, a flexible disk, a magnetic tape or the like is used as a magnetic recording device, and a DVD (Digital Versatile Disc), a DVD-RAM (Random Access Memory), or a CD-ROM (Compact Disc Read Only) is used as an optical disc. Memory), CD-R (Recordable)/RW (ReWritable), etc., as a magneto-optical recording medium, MO (Magneto-Optical disc), etc., as semiconductor memory, EEP-ROM (Electronically Erasable and Programmable-Read Only Memory), etc. Can be used.

The distribution of this program is performed by, for example, selling, transferring, or lending a portable recording medium such as a DVD or a CD-ROM in which the program is recorded. Further, the program may be stored in a storage device of the server computer and transferred from the server computer to another computer via a network to distribute the program.

A computer that executes such a program first stores, for example, the program recorded in a portable recording medium or the program transferred from the server computer in its own storage device. Then, when executing the processing, this computer reads the program stored in its own recording medium and executes the processing according to the read program. As another execution form of this program, a computer may directly read the program from a portable recording medium and execute processing according to the program, and the program is transferred from the server computer to this computer. Each time, the processing according to the received program may be sequentially executed. In addition, a configuration in which the above-described processing is executed by a so-called ASP (Application Service Provider) type service that realizes a processing function only by the execution instruction and result acquisition without transferring the program from the server computer to this computer May be Note that the program in this embodiment includes information that is used for processing by an electronic computer and that conforms to the program (such as data that is not a direct command to a computer but has the property of defining computer processing).

Further, in this embodiment, the hardware entity is configured by executing a predetermined program on the computer, but at least a part of these processing contents may be implemented by hardware.

Claims (3)

Let N be a positive integer that can be set arbitrarily for pseudo sampling, and
A signal acquisition unit that acquires a digital tone signal,
Converting the amplitude values of consecutive N frames of the digital musical tone signal into one type of amplitude value and converting the waveform into a first pseudo-sampling signal which is a signal expressing the waveform while maintaining the sampling frequency of the digital musical tone signal; 1 pseudo sampling unit,
A second pseudo-sampling signal that is a signal that expresses its waveform with all the amplitude values of consecutive N+1 frames of the digital tone signal as one type of amplitude value while maintaining the sampling frequency of the digital tone signal. 2 pseudo sampling unit,
A musical tone signal conversion apparatus including a weighting addition unit for performing weighted addition of the first pseudo sampled signal and the second pseudo sampled signal based on a weighting coefficient that can be arbitrarily set. A tone signal conversion method executed by a tone signal conversion device, comprising:
Let N be a positive integer that can be set arbitrarily for pseudo sampling, and
Acquiring a digital tone signal,
A step of converting the amplitude values of consecutive N frames of the digital tone signal into a first pseudo-sampled signal which is a signal expressing the waveform thereof as one type of amplitude value while maintaining the sampling frequency of the digital tone signal. When,
A step of converting the amplitude values of consecutive N+1 frames of the digital tone signal into a second pseudo-sampling signal which is a signal expressing the waveform thereof as one type of amplitude value while maintaining the sampling frequency of the digital tone signal. When,
A tone signal conversion method comprising the step of weighting and adding the first pseudo sampled signal and the second pseudo sampled signal based on a weighting coefficient that can be set arbitrarily. A program for causing a computer to function as the musical tone signal conversion apparatus according to claim 1.

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