JP2019117224A - Tempo detector, tempo detecting method and program - Google Patents

Abstract

To provide a tempo detector capable of detecting a tempo of a stringed instrument.SOLUTION: A tempo detector comprises: a level acquisition section for acquiring a level per sample of a musical sound signal; a peak hold value calculation section for calculating a peak hold value in a present sample; a buffer section for storing the peak hold value from past one sample to past N samples when N is set to be 1 or more; an attack candidate detection section for detecting the present sample as an attack candidate when a value of a ratio between the peak hold value in the present sample and the peak hold value in the past N samples exceeds a prescribed value of 1 or more; and a BPM calculation section for calculating BPM being the number of beats per minute on the basis of an interval and a sampling frequency of the sample when the interval being a sample difference between the adjacent attack candidates satisfies a prescribed condition.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a tempo detection device, a tempo detection method, and a program for detecting a tempo from a tone signal.

  Patent Document 1 discloses a tempo display device that determines key depression and key release on a keyboard of an electronic piano or an electronic organ, and detects and displays a performance tempo from the key depression interval.

JP 2005-62697 A

  In the case of an electronic piano, it is easy to detect the moment the player presses the key with a sensor or the like, and as in Patent Document 1, the key depression and key release of the keyboard are determined, and the playing tempo is determined from the key depression interval. Detecting and displaying is not difficult. Also, since the striking sound of the drum is steeply attenuated, even when using a sound signal instead of the sensor, the moment the player strikes the drum and makes a sound (hereinafter referred to as the moment of attack) Is relatively easy to distinguish, and detection of tempo is also relatively easy.

  However, for example, in the case of a stringed musical instrument such as a bass guitar, it is difficult to arrange a sensor due to the structure of the musical instrument, so it is difficult to adopt the tempo detection method as disclosed in Patent Document 1. For example, even when a voice signal is used, since the tone of the plucked instrument differs in nature from the striking sound of the drum, it may be difficult to distinguish the moment of attack from the other. When the player flicks the string with a finger, the string vibration continues for a while, and usually the player often flicks the string before the vibration of the string completely stops, and the tempo detection criterion is used as a reference for tempo detection. It can not be.

  Therefore, it is an object of the present invention to provide a tempo detection device capable of detecting the tempo of a plucked instrument.

  The tempo detection device of the present invention includes a level acquisition unit, a peak hold value calculation unit, a buffer unit, an attack candidate detection unit, and a BPM calculation unit.

  The level acquisition unit acquires the level of each sample of the tone signal. The peak hold value calculator calculates a new peak hold level for the current sample when the level for the current sample is greater than the peak hold value attenuated by multiplying the peak hold value for the previous sample by a predetermined coefficient. Update as a value, otherwise keep the attenuated peak hold value as the peak hold value for the current sample. The buffer unit sets N as an integer of 1 or more, and stores peak hold values from one sample past to N samples past. The attack candidate detection unit detects the current sample as an attack candidate when the value of the ratio of the peak hold value in the current sample and the peak hold value in the past of N samples exceeds a predetermined value of 1 or more. When an interval which is a sample difference between adjacent attack candidates satisfies a predetermined condition, the BPM calculation unit calculates BPM which is the number of beats per minute based on the interval and the sampling frequency of the sample.

  According to the tempo detection device of the present invention, the tempo of a plucked instrument can be detected.

FIG. 1 is a schematic view of a tempo detection device of Example 1; FIG. 2 is a functional block diagram of the tempo detection device of the first embodiment. 6 is a flowchart showing the operation of the tempo detection device of the first embodiment. The flowchart which shows the details of operation of step S11C. The graph which shows the example of calculation of an example of an input signal, and a peak hold value. The graph which shows the example of calculation of an example of an input signal, and a peak hold value.

  Hereinafter, embodiments of the present invention will be described in detail. Note that components having the same function will be assigned the same reference numerals and redundant description will be omitted.

  Hereinafter, an outline of the tempo detection device of the first embodiment will be described with reference to FIG. As shown in the figure, the tempo detection device 1 of the present embodiment is configured to include a main body 11 and a clip 12, and the main body 11 includes a display unit 117 and various operation buttons. By holding the head portion of the bass guitar (for example, an electric bass) with the clip 12, the tempo detection device 1 can be attached to the bass guitar body.

  Hereinafter, a functional block diagram of the main body 11 of the tempo detection device 1 will be described with reference to FIG. As shown in the figure, the main unit 11 includes a sample counter 111, a level acquisition unit 112, a peak hold value calculation unit 113, a buffer unit 114, an attack candidate detection unit 115, a BPM calculation unit 116, and a display unit. Including 117. It is assumed that digital or analog musical tone signals can be input to the tempo detection device 1. When the musical tone signal is a digital signal, a signal source (for example, an electric base) and the tempo detection device 1 are connected by wire or wirelessly to acquire a digital musical tone signal. When the musical tone signal is an analog signal, the main body 11 includes a piezo pickup or microphone, not shown, and an AD converter, and converts the analog signal acquired by the piezo pickup or microphone into a digital signal by the AD converter. The sampling rate of the acquired or converted digital signal is Fs.

  Hereinafter, the operation of the tempo detection device 1 will be described with reference to FIG. First, the sample counter 111 of the tempo detection device 1 sets the sample count value i to 0 (S11A). Next, the level acquisition unit 112 takes in the musical tone signal of the ith sample, and acquires the level (S11B). Next, the peak hold value calculator 113 calculates the peak hold value in the current (i-th) sample (S11C).

  Details of the operation of step S11C will be described with reference to FIG. First, the peak hold value calculation unit 113 obtains the absolute value a of the level in the current (i-th) sample (S11C-1). Next, the peak hold value calculation unit 113 multiplies the peak hold value d in the immediately preceding (i−1th) sample by a predetermined coefficient (for example, 0.9995) and attenuates it (d = d * 0.9995, S11 C -2). When there is no previous sample, the peak hold value d = 0 of the previous sample is set. The peak hold value calculator 113 compares the absolute value a of the level in the current sample with the attenuated peak hold value d, and in the case of d <a, adds the absolute value a of the level in the current sample to a new value. The peak hold value d is updated (d = a, S11C-3). For example, in the case of i = 0, since the immediately preceding sample does not exist, the peak hold value d of the immediately preceding sample is 0, so the absolute value a of the level of the first sample becomes the new peak hold value d. If d <a, the attenuated peak hold value d is maintained as the peak hold value for the current sample (S11C-4).

  5 and 6 show calculation examples of peak hold values. FIG. 5 is a graph showing the entire electric bass one-stroke tone signal, and FIG. 6 is a graph showing the first part of the stroke in an enlarged manner. As shown by the bold and square legends in FIGS. 5 and 6, the peak hold value is updated to the same value as the maximum value of the level (absolute value) of each sample each time the value is updated. After that, it decays slowly with the passage of time.

  Referring again to FIG. 3, the buffer unit 114 sets N as an integer of 1 or more, and stores peak hold values from one sample past to N samples past (S11D). N is a parameter that can be changed according to the musical instrument to be subjected to tempo detection. For example, in the case of electric bass, in the case of Fs = 10 kHz, it may be about N = 4. In the present embodiment, N = 4, and the buffer unit 114 stores peak hold values of 1 to 4 samples in the past, and erases the oldest peak hold value every time the peak hold value of a new sample is calculated. The new peak hold value is stored.

The attack candidate detection unit 115 obtains a value (ratio) of the ratio of the peak hold value in the current sample and the peak hold value in the past of N samples (4 samples in this embodiment) (S11E). The attack candidate detection unit 115 detects that the ratio of the peak hold value in the current sample to the peak hold value in the past of N samples exceeds a predetermined value (1.2 in the present embodiment) (ratio> 1). 2) Detect the current sample as an attack candidate. In FIG. 6, for example, a peak hold value in the sample f _n, the value of the ratio of the peak hold value in 4 samples past samples f _n-4, for more than 1.2, detecting the sample f _n as an attack candidates.

  For example, even if the second stroke (attack) generates a tone signal of the same level as the first stroke (attack), the peak hold value is attenuated with time as shown in FIG. The level of the second stroke (attack) satisfies ratio> 1.2 and can be easily detected. In order to increase the detection accuracy, the condition of the ratio for attack candidate detection or the coefficient used for attenuation may be adjusted.

  The BPM calculation unit 116 determines that the current sample level (absolute value) exceeds a predetermined minimum level (min_level) (level> min_level), and an interval which is a sample difference between adjacent attack candidates. If beat exceeds a predetermined minimum interval (min_interval) (interval> min_interval), BPM (Beat Per Minute), which is the number of beats per minute, based on the interval (interval) and the sampling frequency Fs of the sample Calculate (BPM = Fs * 60 / interval, S11H).

In FIG. 6, for example, a peak hold value in the sample f _m, the value of the ratio of the peak hold value in 4 samples past samples f _m-4, for more than 1.2, the sample f _m is detected as an attack candidate but sample difference of adjacent attack candidate is (sample _{f m} and sample _{f n} of sample difference) interval is, because not exceeding min_interval, flow does not proceed to S11H, described later (interval> 3 * Fs)? Proceed to the judgment of The min_interval may be, for example, 0.1 seconds, ie, 0.1 * Fs samples. By adding such a determination flow, it is possible to prevent noise and the like at the rise of the level of the tone signal from affecting the BPM calculation.

  The display unit 117 displays the calculated BPM, for example, in the form of numerical values and waveforms as shown in FIG. 1 (S11K, S11L). After that, the BPM calculation unit 116 resets the interval to 0 (S11M), and the process proceeds to step S11G described later.

  Hereinafter, exception processing in the BPM calculation unit 116 will be described. As described above, since the tempo detection device 1 of this embodiment is assumed to be attached to the head of a bass guitar and used, the device needs to be small, and the display unit 117 also has a small screen. It is required to Therefore, when displaying the calculated BPM on the display unit 117, it is necessary to devise an easy-to-understand display. Therefore, in the tempo detection device 1 of the present embodiment, a range is provided in the BPM displayed on the display unit 117. In the tempo detection device 1 of the present embodiment, the range of BPM to be displayed is 80 to 160 BPM. For example, when the BPM calculated in step S11H is smaller than the preset minimum BPM (min_BPM = 80) (BPM <min_BPM), the BPM calculation unit 116 multiplies the calculated BPM by 2 (S11I), and the minimum again The comparison with the BPM is performed (BPM <min_BPM?), And 2 is repeatedly multiplied until the BPM multiplied by 2 becomes equal to or larger than the minimum BPM (S11I).

  Further, for example, when the BPM calculated in step S11H is larger than the preset maximum BPM (max_BPM = 160) (BPM> max_BPM), the BPM calculation unit 116 divides the calculated BPM by 2 (S11 J), The comparison with the maximum BPM is performed again (BPM> max_BPM?), And division is further repeated by 2 until the BPM divided by 2 is equal to or smaller than the maximum BPM (S11J).

If the performer understands the specifications of the above-described tempo detection device 1 in advance, for example, if the performer performs at a tempo exceeding max_BPM, the performer appropriately doubles the numerical value displayed on the display unit 117. , or four times, or by, for example, be converted into 2 ^x times, it is possible to check the tempo of its own performance. Similarly, when the performer performs at a tempo slower than min_BPM, the performer appropriately converts the numerical value displayed on the display unit 117 into a half, a quarter, or a half ^x , etc. You can check your own playing tempo.

  Referring back to FIG. 3, the operation of the tempo detection device 1 in the case where the ratio, level, interval, etc. do not satisfy predetermined conditions after execution of step S11E will be described. In this case, for example, an interval exceeds three times the sampling frequency Fs (ie, it can be considered that the attack candidate does not exist or the attack candidate exists but the attack candidate can not be regarded as an attack). If the interval exceeds 3 seconds, the BPM value or the waveform displayed on the display unit 117 is turned off (S11F). Otherwise, the BPM value or the waveform displayed on the display unit 117 is displayed. The interval is maintained, the sample count value (i) is incremented by 1 (S11 G), and if the sample count value i is the last sample count value of the tone signal (i = Nsample), the processing is ended. To (end). On the other hand, if the sample count value i is not the last sample count value of the musical tone signal (i ≠ Nsample), the process returns to step S11B to fetch the musical tone signal of the sample of the sample count value i incremented by 1 and acquire its level. (S11B). Hereinafter, step S11C and subsequent steps are performed in the same manner as described above.

According to the tempo detection device 1 of the present embodiment, the calculation of the peak hold value is made easy, so it is possible to accurately detect the tempo in an instrument such as a plucked string instrument that makes it difficult to distinguish the moment of attack from the other. it can. Moreover, since it was decided to view the display of the BPM outside the display range as appropriate 2 ^x times, also with 1/2 ^x times, even not to the amount of information overload when the display screen is small, the proper tempo performer It can be displayed.

<Supplementary Note>
The apparatus according to the present invention is, for example, 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 as a single hardware entity, or a communication device (for example, communication cable) capable of communicating outside the hardware entity. Communication unit that can be connected, CPU (central processing unit, cache memory, registers, etc. may be provided), RAM or ROM that is memory, external storage device that is hard disk, input unit for these, output unit, communication unit , CPU, RAM, ROM, and a bus connected so as to enable exchange of data between 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. Examples of physical entities provided with such hardware resources include general purpose computers.

  The external storage device of the hardware entity stores a program necessary for realizing the above-mentioned function, data required for processing the program, and the like (not limited to the external storage device, for example, the program is read) It may be stored in the ROM which is a dedicated storage device). In addition, data and the like obtained by the processing of these programs are appropriately stored in a RAM, an external storage device, and the like.

  In the hardware entity, each program stored in the external storage device (or ROM etc.) and data necessary for processing of each program are read into the memory as necessary, and interpreted and processed appropriately by the CPU . As a result, the CPU realizes predetermined functions (each component requirement expressed as the above-mentioned,...

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. Further, the processing described in the above embodiment may be performed not only in chronological order according to the order of description but also may be performed in parallel or individually depending on the processing capability of the device that executes the processing or the necessity. .

  As described above, when the processing function in the hardware entity (the apparatus of the present invention) described in the above embodiment is implemented by a computer, the processing content of the function that the hardware entity should have is described by a program. Then, by executing this program on a computer, the processing function of the hardware entity is realized on the computer.

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

  Further, this program is distributed, for example, by selling, transferring, lending, etc. a portable recording medium such as a DVD, a CD-ROM or the like recording the program. Furthermore, this program may be stored in a storage device of a server computer, and the program may be distributed by transferring the program from the server computer to another computer via a network.

  For example, a computer that executes such a program first temporarily stores a program recorded on a portable recording medium or a program transferred from a server computer in its own storage device. Then, at the time of execution of the process, the computer reads the program stored in its own recording medium and executes the process according to the read program. Further, as another execution form of this program, the computer may read the program directly from the portable recording medium and execute processing according to the program, and further, the program is transferred from the server computer to this computer Each time, processing according to the received program may be executed sequentially. In addition, a configuration in which the above-described processing is executed by a so-called ASP (Application Service Provider) type service that realizes processing functions only by executing instructions and acquiring results from the server computer without transferring the program to the computer It may be Note that the program in the present embodiment includes information provided for processing by a computer that conforms to the program (such as data that is not a direct command to the computer but has a property that defines the processing of the computer).

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

Claims (5)

A level acquisition unit for acquiring the level of each sample of the tone signal;
Update the level in the current sample as the new peak hold value if the level in the current sample is greater than the peak hold value attenuated by multiplying the peak hold value in the previous sample by a predetermined factor A peak hold value calculation unit that maintains the attenuated peak hold value as the peak hold value in the current sample otherwise;
A buffer unit for storing the peak hold value from 1 sample past to N sample past samples, where N is an integer of 1 or more;
An attack candidate detection unit that detects the current sample as an attack candidate when the value of the ratio of the peak hold value in the current sample and the peak hold value in the past N samples exceeds a predetermined value of 1 or more;
A BPM calculation unit that calculates BPM, which is the number of beats per minute, based on the interval and the sampling frequency of the sample when an interval that is a sample difference between adjacent attack candidates satisfies a predetermined condition;
Tempo detection device including. The tempo detection device according to claim 1, wherein
The BPM calculation unit
When the BPM is smaller than a preset minimum BPM, the BPM is repeatedly multiplied by 2 until it is equal to or larger than the minimum BPM, and the BPM is larger than the preset maximum BPM In this case, the tempo detection device repeatedly divides the BPM by 2 until it is equal to or smaller than the maximum BPM. A level acquisition step of acquiring the level of each sample of the tone signal;
Update the level in the current sample as the new peak hold value if the level in the current sample is greater than the peak hold value attenuated by multiplying the peak hold value in the previous sample by a predetermined factor A peak hold value calculating step of maintaining the attenuated peak hold value as the peak hold value in the current sample otherwise
A current sample is detected as an attack candidate when N is an integer of 1 or more and the ratio of the peak hold value in the current sample to the peak hold value in the past N samples exceeds a predetermined value of 1 or more. Attack candidate detection step;
A BPM calculation step of calculating BPM, which is the number of beats per minute, based on the interval and the sampling frequency of the sample, when an interval which is a sample difference between adjacent attack candidates satisfies a predetermined condition;
Tempo detection method including: The tempo detection method according to claim 3, wherein
The BPM calculation step is
When the BPM is smaller than a preset minimum BPM, the BPM is repeatedly multiplied by 2 until it is equal to or larger than the minimum BPM, and the BPM is larger than the preset maximum BPM In this case, the tempo is repeatedly divided by 2 until it is equal to or smaller than the maximum BPM.   A program that causes a computer to function as the tempo detection device according to claim 1 or 2.

Images