JP4360358B2 - Tempo detection device and tempo detection method - Google Patents

Description

  The present invention relates to a tempo detection device and a tempo detection method for detecting an input tempo of a beat signal based on a beat signal input intermittently.

  Conventionally, a tempo detection device that detects an input tempo of a signal that is intermittently input, such as a beat signal that is a signal indicating a time signature of music, and presents the tempo to a user is known (for example, Patent Documents 1 to 3). ). Such a tempo detection device is mounted on an audio device that reproduces music recorded on a recording medium, an electronic musical instrument played by a user, and the like, and widens the user's enjoyment of music.

  For example, in recent years, in a disco etc., a director called DJ can quickly feel the atmosphere of the dancer during the dance and provide tempo music that is comfortable for the dancer without interruption, thereby providing the stage effect during the dance. I try to increase it. At this time, the DJ needs to accurately grasp the tempo of the music being played using the audio device or the music to be played in the future so that the tempo of the music does not change suddenly. In this case, the tempo detection device mounted on the audio device generates a beat signal that is automatically detected and input from the music data being played back, or a beat signal that is manually input by the user according to the music tempo. Based on this, the tempo of the music is detected.

Japanese Patent Laid-Open No. 2001-243692 JP 2000-47664 A JP-A-8-179773

  Here, the input interval of the beat signal input to the tempo detection device is not constant and may change. For example, if the tempo of music that is a tempo detection target changes, the input interval of the beat signal that is input according to the tempo of the music naturally changes. In addition, an input interval may change due to an erroneous input of an unnecessary beat signal due to a user's erroneous operation or noise. When the change in the input interval is caused by the tempo change, it is necessary to quickly detect the tempo after the tempo change from the change in the input interval and present it to the user. On the other hand, when the change in the input interval is caused by an erroneous input, it is necessary to detect the tempo by ignoring the change in the input interval.

  However, the tempo detection device usually has a problem that it is difficult to determine whether the change in the input interval is due to a tempo change or an erroneous input. As a result, an inaccurate tempo affected by an erroneous input may be detected. Therefore, in order to reduce the influence of the erroneous input, a method of calculating the tempo based on the moving average value of the input intervals of the past several beat signals has been proposed. If the tempo is calculated based on this moving average value, the influence of a single erroneous input can be reduced. However, on the other hand, since the moving average value always includes a delay, there arises a problem that when a tempo change occurs, it cannot be quickly handled. In other words, the conventional method cannot quickly calculate an accurate tempo that is not affected by erroneous input.

  Therefore, an object of the present invention is to provide a tempo detection device and method that can quickly detect an accurate tempo.

  A tempo detection device according to the present invention is a tempo detection device that detects an input tempo of a beat signal based on a beat signal that is intermittently input, and includes a preset basic interval and a beat signal input interval. And the first determination means for determining whether or not both coincide with each other within a predetermined allowable range, and the input interval of the beat signal when the first determination means determines that both intervals do not match, Candidate interval setting means for setting as a candidate interval that is a candidate, second determination means for determining whether or not the set candidate interval and the input interval of the beat signal match within a predetermined allowable range, When it is determined that the beat signal is input at the candidate interval set by the determination unit, the basic interval update unit that sets the candidate interval as a new basic interval, and the beat based on the set basic interval The input tempo of the signal A tempo calculation unit configured to output, characterized in that it comprises a.

  In a preferred aspect, when the basic interval and the input interval of the beat signal are shifted within an allowable range that can be determined to match by the first determining means, the input interval of the beat signal is In accordance with the basic interval correction means for correcting the basic interval value, the tempo calculation means is based on means for storing at least the past three basic interval value change history and the basic interval change history. Tempo status determination means for determining whether or not the tempo has changed, and if it is determined that the tempo has changed, the tempo is calculated based on the latest basic interval, and it is determined that the tempo has not changed In this case, there is a calculating means for calculating the tempo based on the average value of the plurality of basic intervals stored in the change history. The tempo status judging means judges that the tempo has changed when the basic interval stored in the change history continuously increases or decreases, or is updated to a candidate interval. Is desirable.

  Another tempo detection method according to the present invention is a tempo detection method for detecting an input tempo of a beat signal based on a beat signal input intermittently, wherein a preset basic interval and a beat signal are detected. The first determination step for determining whether or not the input intervals of the beats coincide with each other within a predetermined allowable range, and the input interval of the beat signal when it is determined by the first determination step that the intervals are not the same. A candidate interval setting step that is set as a candidate interval that is a candidate for the basic interval, and a second determination step that determines whether or not the set candidate interval and the input interval of the beat signal match within a predetermined tolerance range; A basic interval update step for setting the candidate interval as a new basic interval when it is determined that the beat signal is input at the candidate interval set in the second determination step; and the set basic interval Characterized in that and a tempo calculation step for calculating an input tempo of the beat signal based.

  According to the present invention, when it is determined that a beat signal is input at a candidate interval, the candidate interval is set as a new basic interval. Therefore, the erroneous input that occurs once can be ignored, while the tempo change can be dealt with quickly. As a result, an accurate tempo can be detected quickly.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an audio apparatus 10 according to an embodiment of the present invention. The audio device 10 can reproduce music recorded on a recording medium. The audio apparatus 10 also has a tempo display function for detecting and displaying the tempo of the music based on the beat signal input by the user in accordance with the reproduced music.

  The playback unit 12 reads music data stored in a storage medium, such as an optical disk, a magnetic disk, or a magnetic tape, and outputs a sound corresponding to the music data. Various known configurations can be used as the configuration of the reproducing unit 12.

  The operation unit 14 is provided with various operators for operating the audio device 10. In this operation element, a tap button operated by the user according to the tempo of the music being reproduced is also provided. When it is desired to detect and display the music tempo, the user operates the tap button according to the music tempo. When the tap button is operated, a beat signal is output to the tempo detection unit 16.

  The tempo detection means calculates the tempo of the music based on the output interval of the beat signal. Here, the calculated tempo format is the number of beats per minute, so-called BPM (beat per minute). The tempo detection unit 16 manages two types of beat intervals as will be described in detail later. One is a basic interval that is the current beat interval, and one is a candidate interval that is a candidate for a new basic interval. These two intervals will be described in detail later.

  The tempo detected by the tempo detection means is displayed on the BPM display unit 24 provided on the display unit 18. As the display format, only the current BPM may be displayed, or the transition of the BPM may be displayed in a graph format.

  The control unit 20 controls each unit in accordance with an instruction from the user. An instruction from the user is input via the operation unit 14 described above. In response to this instruction, the control unit 20 instructs the playback unit 12 to play and stop music data, and instructs the tempo detection unit 16 to start and end tempo detection.

  FIG. 2 is a more detailed block diagram of the tempo detection unit 16. The tempo detection unit 16 includes a basic interval management unit 30, a candidate interval management unit 32, a comparison unit 34, a BPM calculation unit 40, and two timers 36 and 38 that are independent of each other. The basic interval management unit 30 manages a basic interval that is a beat interval (input interval of beat signals) at the present time. This basic interval is set based on the input interval of the beat signal input before that time. This basic interval is maintained at a constant value unless an update instruction is issued from a candidate interval manager 32 described later. The basic interval management unit 30 predicts the input timing of the next beat signal based on the basic interval, and outputs the basic signal to the comparison unit 34 in accordance with the timing.

  Here, the music to be detected for tempo is played by a person, and the operation of a tap button for detecting the tempo is also performed by the person. That is, a tempo is formed and detected by a person. For this reason, even if there is no significant change in the tempo, the input interval of the beat signal indicating the tempo must be slightly changed. In order to allow this variation, the basic interval management unit 30 sets an allowable range div in advance. As shown in FIG. 3, the basic signal is output earlier than the expected timing t by the allowable range div, and the output is stopped after the allowable range div has elapsed from the predicted timing t.

  The candidate interval management unit 32 manages a candidate interval that is a candidate for a new basic interval. This candidate interval is set when the basic interval does not match the input interval of the beat signal. Specifically, when a beat signal is input at an interval different from the basic interval, the different interval is set as a candidate interval. The candidate interval management unit 32 predicts the input timing of the next beat signal based on the candidate interval, and outputs the candidate signal to the comparison unit 34 in accordance with the timing. In addition, when a beat signal is input at a candidate interval twice in succession, an update instruction is output to the basic interval management unit 30 so as to set the candidate interval to a new basic interval. Also in this candidate interval management unit 32, the allowable range div is set, and the candidate signal is output by an amount equivalent to the div before and after the expected timing.

  The comparison unit compares the input timing of the beat signal input according to the tap button operation, the basic signal input from the basic interval management unit 30, and the candidate signal input from the candidate interval management unit 32. A comparison result signal corresponding to the comparison result is output. Based on the comparison result signal output from the comparison unit 34, the basic interval management unit 30 and the candidate interval management unit 32 determine whether or not the beat interval and the basic interval or the beat interval and the candidate interval match. And maintain or update the current basic or candidate interval.

  The first timer 36 is a timer used by the basic interval management unit 30. The first timer 36 performs time management according to an instruction from the basic interval management unit 30. Then, as necessary, the basic interval management unit 30 is notified of the value of the elapsed time, or an alarm is notified when a predetermined time has elapsed. The second timer 38 is a timer used by the candidate interval management unit 32 and notifies time management, elapsed time, and the like according to an instruction from the candidate interval management unit 32.

  The BPM calculation unit 40 calculates the BPM based on the basic interval managed by the basic interval management unit 30 and outputs the BPM to the display unit 18. The BPM calculation unit 40 switches the BPM calculation method according to the basic interval change history. This switching will be described in detail later.

  Next, a detailed configuration of the comparison unit 34 will be described. FIG. 4 is a diagram illustrating an example of the configuration of the comparison unit 34. As shown in FIG. 4, the comparison unit 34 includes a plurality of AND circuits and a NOR circuit. The comparison unit 34 receives a basic signal, a candidate signal, and a beat signal as input signals. Also, three types of output signals, A signal, B signal, and X signal, are output. Of the three types of output signals, the A signal is output to both the basic interval management unit 30 and the candidate interval management unit 32 (see FIG. 2). On the other hand, the B signal and the X signal are output only to the candidate interval management unit 32.

  FIG. 5 is a table showing the input / output relationship of the comparison unit 34. The upper three lines indicate the state of the input signal (beat signal, basic signal, candidate signal), and the lower three lines indicate the output signal (A signal, B Signal, X signal). In FIG. 5, “H” indicates a signal “High” state, that is, a signal is being output. “L” indicates that the signal is in the “Low” state, that is, the signal is not output. Furthermore, “x” indicates that either the “Low” state or the “High” state may be used.

  As can be seen from the table of FIG. 5, when the beat signal is in the “Low” state, that is, when no beat signal is input, the A signal, the B signal, and the X signal regardless of the state of the basic signal and the candidate signal. Neither signal is output.

  On the other hand, in the state where only the beat signal is input and the basic signal and the candidate signal are not input, only the X signal is output. Here, the beat signal is a signal output when the user operates the tap button. On the other hand, the basic signal is a signal output at an input timing of a beat signal that is expected based on a preset basic interval. The candidate signal is a signal that is output at an input timing that is expected based on a candidate interval that is a candidate for a new basic interval. The fact that the basic signal and the candidate signal are not inputted and only the beat signal is inputted means that the beat signal is inputted at a completely new interval which has never been obtained. In this case, an X signal is output. This X signal is output only to the candidate interval management unit 32.

  When the beat signal and the candidate signal are input simultaneously, the B signal is output regardless of whether or not the basic signal is input. In other words, the B signal is output when the candidate interval that is a new candidate for the basic interval matches the input interval of the beat signal. This B signal is output only to the candidate interval management unit 32.

  When the beat signal and the basic signal are input simultaneously and no candidate signal is input, the A signal is output. In other words, the A signal is output when the preset basic interval and the beat signal input interval (tap button operation interval by the user) match. This A signal is output to both the basic interval management unit 30 and the candidate interval management unit 32.

  Next, a simple flow of tempo detection by the tempo detection unit 16 will be described. FIG. 6 is a flowchart showing a basic flow of tempo detection by the tempo detection unit 16. When detecting the tempo, first, the basic interval management unit 30 sets the value of the basic interval (S10). This basic interval value setting process will be described in detail later. Subsequently, the basic interval management unit 30 predicts the input timing of the next beat signal based on the set basic interval, in other words, the timing at which the user operates the tap button. Then, at the obtained timing (precisely by an allowable range div), a basic signal is output (S12). At this point, since no candidate interval is set, the candidate interval management unit 32 does not output a candidate signal.

  Next, it is determined whether the input timing of the output basic signal and the beat signal to the comparison unit 34 coincide with each other (S14). This determination can be made based on the signal type output from the comparison unit 34. That is, when the beat signal and the basic signal are input to the comparison unit 34 at substantially the same timing, in other words, when the beat signal is input at a preset basic interval, the A signal is compared with the comparison unit 34. Is output from. When the A signal is output from the comparison unit 34, it is determined that the input timings of the basic signal and the beat signal match.

  Here, when the input timings of the basic signal and the beat signal coincide, it can be considered that the current basic interval represents the current BPM. Therefore, when the A signal is output, the BPM calculating unit 40 calculates the BPM based on the current basic interval (S26). The calculated BPM is output to the BPM display unit 24 and displayed. When the BPM is calculated, the tempo detection unit 16 performs input timing prediction, basic signal output, and the like again.

  On the other hand, if the input timings of the basic signal and the beat signal do not match, it can be considered that the tempo has been changed or that the beat signal has been input by mistake. In that case, an X signal is output from the comparison unit 34 to the candidate interval management unit 32. The candidate interval management unit 32 that has received the X signal sets a candidate interval that is a candidate for a new basic interval (S16). This candidate interval can be obtained by Tr = T1-T0, where T0 is the input timing of the previous beat signal, T1 is the current beat signal timing, and Tr is the candidate interval.

  If the candidate interval is set, the candidate interval management unit 32 predicts the input timing of the next beat signal based on the candidate interval and outputs the candidate signal at the input timing. Further, the basic interval management unit 30 predicts the input timing of the next beat signal based on the current basic interval, and outputs the basic signal at the input timing (S18).

  Subsequently, it is determined whether or not the input timing of the candidate signal and the basic signal to the comparison unit 34 coincides with the input timing of the beat signal to the comparison unit 34 (S20, S24). This determination can be made based on the type of signal output from the comparison unit 34. That is, when the candidate signal and the beat signal are input to the comparison unit 34 at substantially the same timing, in other words, when the beat signal is input at the candidate interval, the B signal is output from the comparison unit 34. The When this B signal is output to the candidate interval management unit 32, it is determined that the input timings of the candidate signal and the beat signal match. In this case, it is determined that the music tempo is changed and that beat signals are input at this candidate interval in the future. Therefore, when the input timings of the candidate signal and the beat signal coincide with each other, the candidate interval management unit 32 instructs the basic interval management unit 30 to change the basic interval value so that the candidate interval becomes a new basic interval. At the same time, the current candidate interval value is discarded (S22). Receiving the change instruction, the basic interval management unit 30 changes the value of the basic interval and outputs the changed value to the BPM calculation unit 40. The BPM calculating unit 40 calculates BPM based on the new basic interval and outputs it to the BPM display unit 24 (S26).

  On the other hand, if the input timings of the candidate signal and the beat signal do not match and the input timings of the basic signal and the beat signal match, the A signal is output from the comparison unit 34. When this A signal is received, it is determined that the previous beat signal is an erroneous input. Therefore, in this case, the candidate interval management unit 32 discards the current candidate interval. The basic interval management unit 30 predicts the input timing of the next beat signal while maintaining the current basic interval value (S12). The BPM calculation unit 40 calculates the BPM with the current basic interval value and outputs it to the BPM display unit 24 (S26).

  If the input timing of the beat signal does not coincide with the input timing of either the basic signal or the candidate signal, the X signal is output again. When the X signal is output twice or more continuously, the input interval of the beat signal is disturbed. In this case, it cannot be determined whether the tempo has been changed or whether the beat signal has been input by mistake. Therefore, in this case, the candidate interval management unit 32 sets a new candidate interval again (S16). Then, the resetting of the candidate interval is repeated until either the candidate interval or the basic interval matches the input interval of the beat signal.

  Next, this tempo detection will be described using a specific example. 7A to 7E are timing charts of signal input to the comparison unit 34.

  In the nth and n + 1th beats of the beat signal, when the beat signal input interval matches the basic interval t0, in other words, the operation tempo of the user's tap button matches the basic interval t0. In this case, as shown in FIG. 6A, the output timing of the beat signal coincides with the output timing of the basic signal. At this time, the A signal is output from the comparison unit 34. At this time, no candidate signal is output because the candidate interval is not set. However, the A signal is output to the candidate interval management unit 32. When receiving the A signal, the candidate interval management unit 32 starts the second timer 38 and measures the time from the previous reception of the A signal to the reception of the next signal (A signal or X signal).

  Subsequently, when the beat signal is output at an interval different from that in the n + 2th shot, the timings of the basic signal and the beat signal are naturally shifted. In this case, an X signal is output from the output of the comparison unit 34. Upon receiving the X signal, the candidate interval management unit 32 newly sets a candidate interval t1. The candidate interval is obtained from the elapsed time of the second timer 38 from the previous reception of the A signal to the reception of the current X signal. And the candidate space | interval management part 32 outputs a candidate signal at the timing according to the said candidate space | interval t1. On the other hand, the basic interval management unit 30 outputs a basic signal at a timing based on the current basic interval t0. After that, the detected tempo differs depending on the timing at which the beat signal of the (n + 3) th beat is output.

  FIG. 7B illustrates a case where the input timings of the n + 3 strike signal and the candidate signal match. At this time, the comparison unit 34 outputs a B signal. That is, the X signal and the B signal are sequentially output from the comparison unit 34 in order. When the X signal and the B signal are sequentially output in sequence, the beat signal is output twice (n + 2, n + 3) at the candidate interval. In this case, it is determined that the operation tempo of the tap button, in other words, the tempo of the currently played music has been changed, and this candidate interval t1 is set as a new basic interval. Also, the current candidate interval is discarded. The BPM calculating unit 40 calculates BPM based on the changed basic interval (t1).

  Here, the new BPM is calculated immediately after the n + 3th shot. That is, if the beat signal is input for two strokes (n + 2, n + 3 strokes) after the tempo is changed, the BPM after the tempo change is calculated immediately. As a result, a new tempo (BPM) can be obtained very quickly after the tempo change.

  FIG. 7C shows a case where the input timings of the beat signal of the (n + 3) th hit, the candidate signal, and the basic signal match. In this case, similarly to FIG. 7B, it is recognized that the tempo has been changed, and the candidate interval is set as a new basic interval. That is, even if the input timings of the basic signal and the beat signal coincide with each other at the n + 3th shot, if the input timing of the candidate signal and the beat signal match, in other words, it continues at the candidate interval t1. If a beat signal is input twice (n + 2 strokes, n + 3 strokes), the candidate interval t1 is set as a new basic interval. Thereafter, BPM is calculated based on the new basic interval.

  FIG. 7D illustrates a case where the input timing of the n + 3 strike signal and the candidate signal do not match, and the input timing of the beat signal and the basic signal match. In this case, the A signal is output from the comparison unit 34 at the n + 3th shot. That is, the X signal (n + 2 stroke) and the A signal (n + 3 stroke) are sequentially output from the comparison unit 34. In this case, n + 2 strokes are determined to be erroneous input, and the current basic interval t0 is maintained. That is, the basic interval management unit 30 continues to output a basic signal based on the current basic interval t0. The BPM calculator 40 calculates BPM based on the current basic interval. The candidate interval management unit 32 discards the current candidate interval and stops outputting candidate signals until the X signal is output again.

  That is, in this embodiment, even if the beat signal is input only once at an interval different from the basic interval, the basic interval is not changed, in other words, the reference value for BPM calculation is not changed. As a result, even if the user mistakenly operates the tap button at the wrong timing, the erroneous operation is not reflected in the BPM value. Therefore, it is possible to recognize a more reliable BPM that is not affected by an erroneous operation.

    In FIG. 7E, after the input timing of the beat signal and the basic signal does not match at the n + 2 stroke, the input timing of the beat signal, the candidate signal, and the basic signal also does not match at the n + 3 stroke. The case is illustrated. In this case, the current reference interval t0 is maintained again and a new candidate interval is set. That is, when the X signal is output at the n + 2th shot, t1 is set as the candidate interval, and the basic interval is maintained at t0. Subsequently, also in the n + 3th shot, when the X signal is output, a new candidate interval t2 is set, and the basic interval t0 is maintained as it is. If the candidate signal and the beat signal coincide with each other at the n + 4th stroke, that is, if the beat signal at the n + 4th stroke is input at timing a in FIG. 7E, the candidate interval is set as a new basic interval. The On the other hand, if the basic signal and the beat signal coincide with each other at the n + 4th beat, that is, if the beat signal at the n + 4th beat is input at timing b in FIG. 7E, the candidate interval is discarded and at the present time. The basic interval is maintained. Even in the n + 4th shot, if the input timings of the beat signal, the basic signal, and the candidate signal do not match, the candidate interval is set again. During this time, BPM is calculated based on the basic interval at that time.

  In other words, in this embodiment, even if the input interval of the beat signal is changed, the BPM is not changed until it is clear whether the cause of the change is due to a tempo change or an erroneous hit. As a result, it is possible to obtain a highly reliable BPM that is not affected by an erroneous hit.

  Next, the initial value setting of the basic interval will be described with reference to FIG. FIG. 8 is an example of a timing chart immediately after inputting the beat signal. The initial value of the basic interval may be set in advance by the user, or may be obtained based on the actually input beat signal. FIG. 8 shows how the initial value of the basic interval is obtained based on the actually input beat signal.

  In this case, in the initial stage, both the basic interval and the candidate interval are not set. Therefore, when the user operates the tap button and inputs the first beat signal, neither the basic signal nor the candidate signal is output. Therefore, the X signal is always output from the comparison unit 34 at the time of the first hit. If the X signal is output, the candidate interval management unit 32 tries to set the candidate interval. However, the candidate interval cannot be set because there is no beat signal input history before the first shot at the time immediately after the input of the first beat signal.

  Therefore, the candidate signal and the basic signal are not set even at the time of inputting the second beat signal, and the X signal is always output even at the second shot. Upon receiving this X signal output, the candidate interval setting unit tries to set the candidate interval again. At this time, the candidate interval t0 can be obtained based on the difference between the input timing of the second stroke and the input timing of the first stroke. Therefore, the candidate interval management unit 32 outputs a candidate signal based on the candidate interval t0. If this candidate signal matches the input timing of the third beat signal, the B signal is output. If the B signal is output, the current candidate interval t0 is set as the initial value of the basic interval. After the fourth shot, a basic signal is output based on this basic interval t0.

  By the way, in the above description, the basic interval value is assumed to be constant unless there is an update instruction from the candidate interval management unit 32 for easy understanding. However, in practice, the basic interval is appropriately corrected within a minute range. This correction will be described. FIG. 9 is a timing chart showing how the basic interval value is corrected. As described above, the basic interval management unit 30 predicts the input timing of the next beat signal based on the basic interval. Then, the basic signal is output with a margin of the allowable range div before and after the expected timing (see FIG. 3).

Now, in certain n-th shot, beat signal, and is input earlier than expected timing T _n in a range not exceeding the allowable range div. At this time, the basic interval management unit 30 predicts the input timing of the n + 1 beat signal based on the current basic interval t0 based on the input timing of the nth beat signal as a reference. A basic signal is output based on the timing T _{n + 1} . At this time, it is assumed that the beat signal of the (n + 1) th stroke is input after the expected timing _{Tn + 1} within a range that does not exceed the allowable range div. At this time, the basic interval management unit 30 corrects the interval t1 from the nth stroke input to the (n + 1) th stroke input as the basic interval. Then, the predicted timing T _{n + 2} of the n + 2 stroke is predicted based on the interval t1 with reference to the input timing of the beat signal of the n + 1 stroke. Also in the n + 2 stroke, when the predicted timing T _{n + 2} and the actual input timing are shifted within the allowable range div, the basic interval value is expressed as (n + 2 stroke input timing−n + 1 stroke). Input value) is corrected.

  That is, the value of the basic interval is always corrected when the actual beat signal input timing and the expected timing based on the basic interval deviate within a range that does not exceed the allowable range div.

The basic interval management unit 30 appropriately corrects and changes the value of the basic interval for the past m times t _n , t _n−1 , t _n−2 ... T _{n− (m−1).} And remember. The BPM calculating unit 40 calculates the BPM based on the basic intervals t _n , t _n−1 , t _n−2 ... T _{n− (m−1)} for the past m times. In calculating this BPM, the calculation method is changed according to the fluctuation state of the basic intervals t _n , t _n−1 , t _n−2 ... T _{n− (m−1)} for the past m times. Yes.

That is, the BPM calculating unit 40 compares the values of the basic intervals for the past m times before calculating the BPM. Then, when the basic interval is gradually shortened (t _n <t _n-1 <t _n-2 ... <T _{n- (m-1)} ), or when the basic interval is gradually increased (t _n > T _n-1 > t _n-2 ...> T _{n− (m−1)} ), it is determined that the tempo is changing. In this case, based on the latest basic interval t _n, calculating the BPM. That is, BPM = 60 / t _n (the unit of t _n is sec). In this way, when a tempo change is predicted, the BPM that more strongly reflects the latest tempo state can be obtained by calculating the BPM based only on the latest basic interval. As a result, BPM with higher reliability can be obtained.

Also, when a new base distance on the basis of the candidate interval is re-set, based on the latest basic interval t _n, calculating the BPM. That is, when a new basic interval is reset based on the candidate interval, in other words, when there is an obvious tempo change, the BPM is calculated based only on the latest basic interval. As a result, a more accurate BPM that is not affected before the tempo change can be obtained.

On the other hand, when the past m times the basic interval _{t n,} the variation situation of _{n- t n-1, t n} -2 ··· t (m-1) is, none of the above, the tempo stable Calculating the average value of the basic intervals t _n , t _n−1 , t _n−2 ... T _{n− (m−1)} for the past m times when the basic interval has not changed. BPM is calculated based on the average value. That is, BPM = 60 / {(t _n , t _n−1 , t _n−2 ... T _{n− (m−1)} ) / m}. By calculating the BPM based on the average of the past three times, it is possible to reduce the influence of noise and human inaccuracy. In addition, it is desirable that m is an appropriate number at 3 times or more. When m is set to twice, in most cases, (t _n <t _n-1 ) or (t _n > t _n-1 ), it is always determined that the tempo is changing. On the other hand, if m is a very large number, the basic interval is gradually shortened or gradually increased, and it is always determined that the tempo is stable.

  Thus, a BPM with higher reliability can be obtained by changing the BPM calculation method according to the fluctuation state of the basic interval.

  As described above, in this embodiment, it is determined that the tempo is changed only when the beat signal indicating the tempo is continuously input twice or more at a candidate interval different from the basic interval. By determining that the tempo is changed only when two or more times are continuously performed, it is possible to clearly determine whether the variation in the input interval of the beat signal is due to an erroneous input or due to a tempo change. As a result, an accurate BPM can be obtained without being affected by an erroneous input. When the tempo is changed, the BPM after the tempo change can be obtained quickly. Further, in the present embodiment, the BPM calculation method is switched in accordance with the value fluctuation state of the basic interval for the past several times, in other words, according to the fluctuation state of the input interval of the beat signal. Therefore, BPM with higher reliability can be obtained.

  In the present embodiment, the beat signal indicating the tempo is generated and output when the user manually operates the tap button. However, a beat signal may be automatically generated and output from audio data of music to be reproduced. That is, if a low frequency signal is output from audio data, a beat signal may be automatically output. For the output of the beat signal, the technique described in Patent Document 1 can be applied.

  In the present embodiment, the tempo detection unit 16 installed in the audio device 10 is described as an example. However, as long as the device requires tempo detection, it can naturally be applied to other devices such as an electronic musical instrument.

  In the present embodiment, as a condition for updating the basic interval to the value of the candidate interval, it is assumed that the input of the beat signal at the candidate interval is continuous twice. However, the number of beats is not particularly limited as long as the beat signal input at the candidate interval is continuous. However, if this number is increased too much, the response to the tempo change (update of the value of the basic interval) is delayed, so it is desirable that the number of times is not problematic for the user.

1 is a block diagram illustrating a schematic configuration of an audio apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of a tempo detection part. It is a figure which shows the tolerance | permissible_range div of a basic signal and a candidate signal. It is a figure which shows the structure of a comparison part. It is a table | surface which shows the input / output relationship of a comparison part. It is a flowchart which shows the flow of tempo detection. It is a timing chart which shows an example of the signal input / output in a comparison part. It is a timing chart which shows an example of the signal input / output in a comparison part. It is a timing chart which shows an example of the signal input / output in a comparison part. It is a timing chart which shows an example of the signal input / output in a comparison part. It is a timing chart which shows an example of the signal input / output in a comparison part. It is a timing chart explaining the mode of the initial value setting of a basic interval. It is a timing chart explaining the mode of correction of a basic interval.

Explanation of symbols

  10 audio devices, 12 playback units, 14 operation units, 16 tempo detection units, 18 display units, 20 control units, 24 BPM display units, 30 basic interval management units, 32 candidate interval management units, 34 comparison units, 36, 38 timers 40 BPM calculator.

Claims (3)

A tempo detection device for detecting an input tempo of a beat signal based on a beat signal input intermittently,
First determination means for determining whether or not the preset basic interval and the input interval of the beat signal match within a predetermined allowable range;
Candidate interval setting means for setting the input interval of the beat signal as a candidate interval that is a candidate for a new basic interval when the first determination means determines that both intervals do not match;
Second determination means for determining whether or not the set candidate interval and the input interval of the beat signal match within a predetermined allowable range;
A basic interval update unit that sets the candidate interval as a new basic interval when it is determined that a beat signal is input at the candidate interval set by the second determination unit;
Tempo calculation means for calculating the input tempo of the beat signal based on the set basic interval;
A tempo detection device comprising: The tempo detection device according to claim 1, further comprising:
When the basic interval deviates from the input interval of the beat signal within an allowable range that can be determined to match by the first determining means, the value of the basic interval is set according to the input interval of the beat signal. Having a basic interval correction means for correcting,
Tempo calculation means
Means for storing a change history of at least three basic interval values;
Based on the change history of the basic interval, tempo situation determination means for determining whether or not the tempo has changed,
When it is determined that the tempo has changed, the tempo is calculated based on the latest basic interval, and when it is determined that the tempo has not changed, the average value of the plurality of basic intervals stored in the change history Calculating means for calculating the tempo based on
I have a,
The tempo status determination means determines that the tempo has changed when the basic interval stored in the change history continuously increases or decreases, or when it is updated to the candidate interval,
A tempo detection device characterized by the above.   A tempo detection method for detecting an input tempo of a beat signal based on a beat signal input intermittently,
  A first determination step of determining whether or not the preset basic interval and the input interval of the beat signal match within a predetermined allowable range;
  A candidate interval setting step for setting the input interval of the beat signal when it is determined by the first determination step that the intervals do not match, as a candidate interval that is a candidate for a new basic interval;
  A second determination step of determining whether or not the set candidate interval and the input interval of the beat signal match within a predetermined allowable range;
  A basic interval update step for setting the candidate interval as a new basic interval when it is determined that the beat signal is input at the candidate interval set in the second determination step;
  A tempo calculation step for calculating the input tempo of the beat signal based on the set basic interval;
  A tempo detection method comprising:

Images