JPH0687198B2 - Tempo display - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tempo display device used in a sound reproducing device such as a tape recorder, a CD, a record, a television, a radio, and a karaoke machine.

2. Description of the Related Art As a device for extracting the tempo of music, there is a device related to an electronic musical instrument, particularly a keyboard.

This is not to extract the tempo from the music signal purely, but to physically detect the touch of a key on the keyboard (the moment when the player strikes the key) and extract the tempo from this switching information. there were.

Some electronic musical instruments and the like display the tempo of the music when it is automatically played.

Problems to be Solved by the Invention However, in the above-described configuration, the tempo is not purely extracted from the music signal, but the tempo is created from the synchronized clock when the automatic performance is performed, and the tempo is displayed. It didn't pass.

Further, as a device for extracting the rhythm of music, there is one that performs extraction by checking the sharpness of the rising edge of the amplitude of the music signal. This is to extract only the rhythm of music and display it. , The music tempo could not be extracted and displayed.

In view of the above problems, the present invention provides a tempo display device that enables tempo extraction and display in a normal music signal, which can be performed only in the performance by the electronic musical instrument and the automatic performance by the electronic musical instrument. is there.

Means for Solving the Problems In order to achieve the above object, the present invention provides an input terminal for inputting a music signal and a rhythm extraction for extracting a rhythm component in the music signal and outputting a certain signal when the rhythm is extracted. Means and the output signal of the rhythm extraction means, and if the time interval at which the input signal is input is not within a certain time, the input signal is calculated so as to ignore the time interval and the music tempo is calculated. And a tempo calculation means for gradually increasing the tempo to a predetermined value and outputting the extracted tempo,
Synchronous means for controlling the tempo calculating means so as to synchronize the tempo with the music by comparing and calculating the tempo signal output by the tempo calculating means and the rhythm extracted by the rhythm extracting means, and output from the tempo calculating means. It has a configuration including a display means for performing a display corresponding to the tempo signal.

Operation With this configuration, first, in the rhythm extraction means, the rising and falling slopes of the amplitude of the input signal are calculated, so that the rhythm of a musical instrument represented by a percussion instrument included in the input music signal is calculated. The signal is extracted, and the rhythm of music is extracted.

Next, the rhythm signal extracted by the rhythm extraction means is input to the tempo calculation means, and the tempo calculation means calculates the time interval of the input signal to determine the tempo of the input music signal. To be extracted.

Further, the tempo calculation means fades in the tempo display signal from the moment the rhythm is first extracted by the rhythm extraction means after the tempo is extracted (the value gradually increases from a small value to a certain value). While) display starts.

When the tempo display is started, the synchronization means temporally compares the rhythm signal extracted by the rhythm extraction means with the tempo signal output from the tempo display means, controls the tempo calculation means, and synchronizes with the music. Tempo synchronization control and tempo correction are performed, whereby accurate tempo display control is performed.

Further, the tempo signal output from the tempo calculation means is input to the display means, and the display means performs external display corresponding to this signal, and the tempo display synchronized with music is performed.

Embodiment One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a tempo display device according to an embodiment of the present invention.

In FIG. 1, 1 is an input terminal for inputting a signal, 2 is a band pass filter for passing only a signal in a certain band, 3, 4
Rectifies the input signal and then integrates the signals with different time constants to find the energy of the signal within a certain time. Is set to be larger than that in the rectifier circuit 3) 5 is an amplifier circuit that amplifies the level of the output signal of the rectifier circuit 3, and 6 is composed of a resistor and a capacitor that detect the rising edge of the signal. The differential path, 7 inputs two signals, compares the levels of those signals, and outputs a pulse signal when one signal is larger than the other signal, 11 indicates the first input signal A gate circuit that allows the signal to pass, but does not pass the signal that has been input within a certain period of time. 8 indicates the tempo by calculating the time interval of the signal that has been input. Extracting tempo calculation circuit, 9 synchronous circuit to synchronize the tempo and the extracted music signal by comparing calculating two signals inputted, 10 is a sound circuit that performs sound as a trigger input signal.

Further, a portion surrounded by a broken line is a rhythm extracting section that extracts a rhythm component in the input music signal.

FIG. 2 shows a signal waveform in each block in the rhythm extraction section of FIG.

In FIG. 2, (a) is an input signal, (b) is an output signal of the bandpass filter 2 (in this case, a low-frequency signal is passed), and (c) is a rectifier circuit 3. The signal output from the amplifier circuit 5, the output signal of the rectifying circuit 4, and the output signal of the differentiating circuit 6 are shown in FIG. Further, (f) shows the output signal of the comparison circuit 7, and (g) shows the output signal of the gate circuit 11.

The operation of this embodiment will be described below with reference to the drawings.

The signal (a) input to the input terminal 1 is input to the band pass filter 2 and the signal (b) of only a certain band is extracted (in this case, the case of extracting a low frequency signal is shown. ). As a result, the rhythm instrument signal of the input music signal can be emphasized. The output signal (b) of the bandpass filter 2 is input to the rectifier circuits 3 and 4 having different integration time constants in order to obtain the average energy of the input signal within a certain time.

Next, the output signal of the rectifier circuit 3 is input to the amplifier circuit 5,
The signal (c) is obtained by being amplified with a certain amplification degree. This is because the signal is attenuated in the next differentiating circuit 6, and this is compensated (if the differentiating circuit can compensate the signal attenuation, the amplifier circuit 5 is not necessary). The output signal (c) of the amplifier circuit 5 is input to the differentiating circuit 6 and the rising edge of the signal is detected (signal (e)). The signal (e) and the output signal (d) of the rectifier circuit 4 are input to the comparison circuit 7, and their amplitude levels are compared. If the signal (e) is larger than the signal (d), the pulse signal (h) is output. The signal (d) is a signal that slowly changes with a value proportional to the level of the signal input to the input terminal 1, and the signal (e) detects the sharp rising edge of the input signal. ) As a reference, it is possible to accurately extract a signal with a sharp rising edge (for example, a rhythm instrument sound) by following the fluctuating level of the input signal by comparing with the signal (e). Next, the output signal (f) of the comparison circuit 7 is the gate circuit.
It is input to 11, and at a certain time T, the input signal is gated and the signal (g) is output (here, the gate is
The first pulse that was input is passed through as is, then
It means that the signal input during the time T from that signal is not passed).

As described above, by providing the gate circuit, it is possible to prevent the abnormal occurrence of the pulse signal due to signals other than the rhythm musical instrument, noise, and slow fluctuation (beat) of the level of the rhythm musical instrument signal. By the above, the rhythm component contained in the music signal which is the input signal can be accurately extracted.

Next, the output signal (g) of the cage circuit 11 is input to the tempo calculation circuit 8, and the tempo is obtained from the time interval at which the signal is input.

Here, an example of an algorithm for obtaining the tempo in the tempo calculation circuit 8 will be described with reference to the flowchart of FIG. 3 and FIG.

FIG. 3 shows one of the tempo calculation algorithms, and there is a process of obtaining the minimum value of the time interval of the signal input to the tempo calculation circuit 8 within a certain time (in this case, 2 seconds). Repeat (4 times in this case),
In this method, the minimum values obtained by this processing are compared, and if there are a certain number of equal values (two in this case), the value is used as the tempo.

In FIG. 3, TMPMIN is the minimum value of the measured time interval T of the input signal, and MAX is the time interval T of the input signal,
Maximum value that can be taken, T is the value of the time interval of the input signal, TMIN is the minimum value that limits the value of T, TMAX is the maximum value that limits the value of T, and TINE extracts one TMPMIN. Time (2 seconds in this case), COUNT is the number of times TMPMIN is extracted (4 in this case, the initial value is 1), Ti (T1, T2, T3, T
4) is a buffer that stores the extracted TMPMIN.

First, the maximum possible value of T is set in TMPMIN, and the input signal pulse is awaited (steps 21 and 22). When a pulse is input, T becomes O (step 23), time counting is started, and the time is set to T (step 24). This time counting process is repeated until the next pulse arrives (step 25).

When the next pulse is input, the time counting is stopped, and T at that time is the time interval between the two first input signals.
Next, it is checked whether the value of T is larger than TMIN and smaller than TMAX (steps 26 and 27), and if not, the value of T extracted at that time is deleted and the next pulse comes again. Return to the process of waiting for (step 22). By this processing, it is possible to prevent extraction of an abnormally fast tempo or an abnormally slow tempo. When the value of T is included between TMIN and TMAX, T is compared with TMPMIN (step 28), and when T is smaller than TMPMIN, T is set to TMPMIN ( Step 29), and if not, proceed to the next process (step 30). As a result, the minimum time width between the input signals is extracted.

After that, by checking the value of TIME, it is checked whether or not 2 seconds have passed since the above processing was started (step 30), and if 2 seconds have not passed, the procedure returns to step 22 and the above processing is repeated and 2 seconds are repeated. TMPMIN to Ti (i is COUNT
Value) (step 31), check the value of COUNT,
It is checked whether the above process has been performed 4 times (step
32) (Here, the value of TIME is set to 2 seconds, because the tempo of music is about 1 second, and at least 2 seconds are required to extract the tempo at this time. Has been set). And if not done four times, COUN
The value of T is increased (step 32), and the process returns to the process of extracting the next TMPMIN (step 21). If it has been performed four times, the value of COUNT is decreased (step 34), and T1 to T
The values of 4 are compared (step 35). Here, if two of T1 to T4 are equal (for example, T1 = T2, T1
= T3, etc.) and determine that value as the tempo (step 3
6), end the tempo calculation process.

At this time, if there are no two equal items, T1 to T2
Set T3 to T2 and T4 to T3 (step 37), and return to the above process (step 21) for obtaining the next TMPMIN again (here, when comparing T1 to T4, The difference is Δt
In such a case, Δt = 0 is actually rare.
Therefore, it is not considered to be equal only when Δt = 0, and is considered equal when Δt is included in a range of some percentage of the value. Further, in this case, if they are considered equal, an accurate value can be obtained by setting the average value of the two values as the original value).

The tempo is extracted by the above processing, but this algorithm is based on the idea that the minimum value of the rhythm width of a rhythm in music is the tempo. This concept will be described with reference to FIG. FIG. 4 shows a rhythm part in a certain music, and the rhythm is assumed to be composed of quarter notes and eighth notes. Further, it is assumed that one bar is 2 seconds. Assuming that the rhythm shown in FIG. 4 is accurately extracted in the rhythm extraction section, the values extracted as T at the first measure are t1, t2, t3, t5, t6, and TM
The value extracted as PMIN is t5. Also, this value is 8
The value of a quarter note. Similarly, at the second measure, TMPMIN is t
7, t8 at the 3rd measure, t9 at the 4th measure, T1 = t
5, T2 = t7, T3 = t8, T4 = t9. In addition, the value is the value of an eighth note in both cases.

Therefore, in this case, the value of the eighth note is determined as the tempo. Actually, the value of the quarter note is the tempo of this music (rhythm), but since the eighth note is twice as fast as the quarter note, even if it is the tempo, it does not matter at all. This is because the tempo shown on the musical score and the tempo actually felt by the human are often different, and depending on the person, the tempo may be faster or slower.

Although the rhythm shown in FIG. 4 is very simple, it can be understood that the minimum unit of the rhythm of music can be extracted by using the above algorithm. That is, if the minimum unit of the rhythm of the input music is a quarter note, a quarter note, and if the minimum unit of the rhythm is an eighth note, the eighth note is the minimum unit of the rhythm.
If it is a 16th note, the 16th note is extracted as the tempo value. From the above, the above-mentioned algorithm allows the tempo of music (actually
It may be a multiple of one).

Next, when the tempo calculation circuit 8 extracts the tempo, the tempo calculation circuit 8 outputs a pulse signal (tempo signal) from the moment the input signal comes from the gate circuit 11 for the first time.
Is output to the synchronizing circuit 9 and the tone generating circuit 10. Pronunciation circuit 10
In, sound is produced in response to the input signal.

At this time, the sounding circuit 10 is controlled so as to increase from a small sound to a certain level and sound.
Here, the timing of starting sound generation (outputting the tempo signal from the tempo calculation circuit) becomes a problem, but as described above, the extracted tempo is the minimum unit of the rhythm of the music that is the input signal. Therefore, if the tempo display is started from the moment the rhythm is extracted, the music can be synchronized at that time. When the length of a quarter note is set to 1, the extracted tempo is the minimum unit of the rhythm of music and it is a multiple of 2, so the actual tempo is the tempo extracted at any moment of the rhythm. It is obvious because it is divisible by.

Next, the synchronization circuit 9 includes a gate circuit 11 and a tempo calculation circuit 8
By inputting the output signals from the above, monitoring the deviation of these signals, and controlling the tempo calculation circuit 8, the tempo and music are synchronized and the tempo is corrected.

Here, the synchronization tempo and the necessity of correction will be described.

It is natural to think that the rhythm and tempo of music played by humans are not constant, but change from moment to moment,
On the contrary, it is difficult to play at a constant tempo. this is,
It can be seen from the fact that the automatic performance of electronic musical instruments and the performance of robots are mechanical and constant, which is not interesting.

Moreover, in actual music, the tempo is often changed intentionally. Furthermore, it can be said that the rhythm and the tempo are not constant, because of the influence of time fluctuations that occur during reproduction due to wow and flutter of a reproducing device such as a tape recorder or a record player. Therefore, it is necessary to synchronize with the temporal fluctuation of music and to correct the tempo itself. On the other hand, without this synchronization and tempo correction function, the tempo itself will be maintained, but the tempo will be out of sync with the music.

Regarding the method of synchronizing and the method of correcting the tempo, Part 5
It will be described with reference to the drawings.

In Fig. 5 (a) and (b), the waveform of the tempo is shown at the top, T is 1 tempo, and it is shown as a rectangular wave that becomes high level for 1 / 2T, and the rhythm is shown at the bottom with a certain width. The waveform is shown with a solid line, and the solid line shows the state before correction and the broken line shows the state after correction.

Further, FIG. 5 (a) shows the case where the tempo is ahead of the rhythm of music, and FIG. 5 (b) shows the case where it is behind. In both cases, the deviation between the tempo and the rhythm is X.

First, when the tempo signal is at high level,
When the rhythm signal becomes high, it is considered that the tempo is advancing (state shown in FIG. 5 (a)), from the moment the tempo signal becomes high, the time X at which the rhythm signal becomes high is measured, When the value of X is smaller than a certain value, the value X is added to the time 1 / 2T when the tempo signal is high level. As a result, the time of the entire tempo becomes T + X, and the deviation X between the tempo and the rhythm can be absorbed when the next tempo signal becomes high (state of broken line in FIG. 5A).

When the rhythm signal becomes high when the tempo signal is at low level, it is considered that the tempo is delayed (state as shown in FIG. 5B), and from the moment the rhythm signal becomes high. The time X when the tempo signal becomes high is measured, and when the value of X is smaller than a certain value, the value X is subtracted to the time 1 / 2T when the tempo signal is high level. As a result, the time of the entire tempo becomes T−X, and the deviation X between the tempo and the rhythm can be absorbed when the next tempo signal becomes high (state of broken line in FIG. 5B). still,
In the above-mentioned processing, the reason why X is limited is that it is processed depending on whether the value of X is the actual deviation on the score or the deviation caused by the loss of synchronization.

By repeating the above processing one after another, the tempo and the music can be synchronized.

The value X to be added to or subtracted from the tempo T is set to 1 / 2X or 1 / 4X to prevent abrupt change in tempo, which is more effective.

In addition, the above process is not performed one after another but by performing it when the tempo is advanced or the tempo is delayed several times in succession. In, it is possible to prevent a malfunction when an incorrect rhythm is extracted (this is because the efficiency of repeating the incorrect rhythm extraction is small).

The method of correcting the tempo is to extract the X obtained above (separately for the case where the tempo is advanced and for the case where the tempo is delayed) several times, and add the average value of these to the tempo (or
Method). That is, when the tempo is advanced, T = T + (X1 + X2 + ~ + XN) / N (X1, X2 ~ XN
Is each value of X), and if the tempo is delayed, T
= T- (X1 + X2 + to + XN) / N is calculated. Then, by repeating this process, it is possible to successively correct the deviation between the tempo and the actual rhythm.
It is possible to obtain a more accurate tempo.

In addition, there may be no rhythm (musical instrument signal extracting the rhythm) in the music between music pieces, and in such a case, it is impossible to synchronize with the music only by the above processing. Become. In particular, if there is no rhythm for a long time, the synchronization may be lost.

In order to prevent this, the synchronization circuit 9 also performs the following processing.

When the deviation X between the tempo signal and the rhythm signal shown above is greater than a certain value, it is considered that the tempo and the rhythm of the music are out of synchronization, the tempo calculation circuit 8 is controlled, and the output of the tempo signal is stopped. Then, the tempo calculation circuit 8 controls to output the pulse signal to the synchronization circuit 9 and the tone generation circuit 10 again from the moment the input signal comes from the gate circuit for the first time. At this time, the sounding circuit 10 starts sounding from a small sound to a certain level. By doing so, even if the tempos of the songs are out of sync with each other, it is possible to correct the out-of-sync without feeling unnatural.

If this process is performed when the value of X is larger than a certain value and occurs several times in succession, it is possible to prevent a malfunction when the rhythm extracting section extracts an incorrect rhythm. This is because the probability of repeatedly performing erroneous rhythm extraction is small.

By the processing of the synchronization circuit 9 as described above, the tempo calculation circuit 8 is controlled and the tempo can be synchronized and the tempo can be corrected.

As described above, according to this embodiment, it is possible to accurately extract the tempo of a normal music signal and display the tempo in synchronization with music.

It should be noted that the tempo extraction algorithm of the tempo calculation circuit 8 in this embodiment is one embodiment, and there are a number of signals having the same value within a certain time interval of the signals input to the tempo calculation circuit 8. In this case, the tempo can be accurately extracted even if an algorithm that uses the value as the tempo is used. This algorithm can be regarded as the minimum unit of rhythm of music as described above, but this minimum unit of rhythm tends to appear frequently in music. On the contrary,
Rhythms that often appear in music (the rhythm here is
It refers to the time interval between the rhythm signal and the rhythm signal), which can be regarded as the tempo because it is the center of the rhythm of the music.

In addition, when the signals having the same time interval of the input signals are continuously input a certain number of times, the tempo can be accurately extracted by using an algorithm that uses the value as the tempo. This is also based on the same principle as the algorithm described above.

Furthermore, by combining the three algorithms described above, it is possible to improve the effect on tempo extraction.

Further, the sounding circuit 10 described in the present embodiment is configured to automatically change the sounding level in proportion to the amplitude level of the music signal input to the input terminal 1, thereby making it more harmonious with music. The tempo can be displayed.

Effects of the Invention The present invention provides an input terminal for inputting a music signal, a rhythm extraction means for extracting a rhythm component in the music signal and outputting a certain signal at the time of extracting the rhythm, and an output signal of the rhythm extraction means. Input and extract the tempo of music by calculating the signal, and according to the tempo, fade out a signal at the start of display (output the signal gradually increasing from a small value to a certain value) And a synchronization means for controlling the tempo calculation means so as to synchronize the tempo with the music by comparing and calculating the tempo signal output by the tempo calculation means and the rhythm extracted by the rhythm extraction means. Extraction of the tempo of a normal music signal by providing a display means for performing a display corresponding to the tempo signal output from the tempo calculation means The extracted tempo can be displayed in synchronization with the music.

In addition, when the display of the tempo signal is started, the tempo can be displayed more naturally by fading it in (increasing the signal from a small value to a certain value).

[Brief description of drawings]

FIG. 1 is a block diagram of a tempo display device according to an embodiment of the present invention, FIG. 2 is a waveform diagram of signals corresponding to each block of a rhythm extraction section in this embodiment, and FIG. 3 is a tempo calculation in this embodiment. FIG. 4 is a flowchart showing the tempo calculation algorithm of the circuit, FIG. 4 is a principle diagram showing the tempo calculation algorithm of the tempo calculation circuit in this embodiment, and FIG. 5 is a timing showing the principle of synchronization in the synchronization circuit in this embodiment. It is a chart. 1 ... Input terminal, 2 ... Band pass filter, 3,4 ... Rectifier circuit, 5 ... Amplification circuit, 6 ... Differentiation circuit, 7 ... Comparison circuit, 8 ... Tempo operation circuit, 9 ... Synchronization Circuit, 10 ...
Sounding circuit, 11 ... Gate circuit.

Claims (13)

[Claims] 1. An input terminal for inputting a music signal, rhythm extraction means for extracting a rhythm component from the music signal, and outputting a certain signal at the time when the rhythm component is extracted, and an output of the rhythm extraction means. When a signal is input and the time interval at which the input signal is input is not within a certain time period, the tempo of the music is extracted by calculating the input signal so that the time interval is ignored, and the tempo is adjusted according to that tempo. Synchronize music and tempo by comparing and calculating the tempo calculation means for gradually increasing the signal to a predetermined value and outputting the tempo signal output by the tempo calculation means and the rhythm extracted by the rhythm extraction means. Synchronization means for controlling the tempo calculation means so as to obtain a display, and display means for performing a display corresponding to the tempo signal output from the tempo calculation means. Tempo display apparatus comprising. 2. The rhythm extracting means extracts a rhythm signal of an instrument mainly responsible for a rhythm part such as a percussion instrument in a music signal by calculating a rising or falling slope of the amplitude of the input signal. The tempo display device according to claim 1, wherein the tempo display device has the following structure. 3. The tempo calculation means is configured to monitor the time interval of an input signal for a certain period of time and detect the minimum time interval within that time as the tempo of the music. The tempo display device according to the first section. 4. The tempo calculation means monitors the time interval of an input signal for a certain period of time, and detects the time interval as the tempo of the music when the same time interval continuously exists a certain number of times. The tempo display device according to claim 1, wherein the tempo display device has the following structure. 5. The tempo calculation means monitors a time interval of an input signal for a certain fixed time, and when the same time interval exists a certain number of times within the fixed time, the detected time interval is detected as the tempo of the music. The tempo display device according to claim 1, wherein the tempo display device is configured as described above. 6. The tempo calculation means gradually fades in the tempo signal (from a small value to a certain value) from the moment the rhythm is first extracted by the rhythm extraction means after detecting the tempo. The tempo display device according to claim 1, wherein the tempo display device is configured so as to start the display by (largely). 7. The synchronizing means obtains the difference between the time when the tempo signal is output from the tempo calculating means and the time when the rhythm is first extracted by the rhythm extracting means after the tempo signal is output, When the difference is smaller than a certain time, the difference is added to the tempo obtained by the tempo extraction means to control the tempo calculation means so as to synchronize the music signal with the tempo. The tempo display device according to claim 1. 8. The synchronizing means comprises a time when the rhythm is extracted by the rhythm extracting means and a time after the rhythm is extracted,
Synchronize the music signal with the tempo by first finding the difference from the time at which the tempo signal was output from the tempo calculator, and subtracting the difference from the tempo found by the tempo extractor The tempo display device according to claim 1, wherein the tempo display means is configured to control the tempo calculation means. 9. The synchronizing means obtains the difference between the time when the tempo signal is output from the tempo calculating means and the time when the rhythm is first extracted by the rhythm extracting means after the tempo signal is output. When the difference is smaller than a certain time, the tempo calculating means is controlled so as to correct the tempo by obtaining an average for the number of times of the difference and adding the average value to the tempo obtained by the tempo extracting means. The tempo display device according to claim 1, which is configured as described above. 10. The synchronizing means calculates the difference between the time when the rhythm is extracted by the rhythm extracting means and the time when the tempo signal is first output from the tempo calculating means after the rhythm is extracted, and the difference is calculated. If the time is smaller than a certain time, the tempo calculation means is controlled so as to correct the tempo by obtaining an average for the number of times of difference and subtracting the average value to the tempo obtained by the tempo extraction means. The tempo display device according to claim 1, wherein the tempo display device has the following structure. 11. The synchronizing means includes a difference between a time when the tempo signal is output from the tempo calculating means and a time when the rhythm is first extracted by the rhythm extracting means after the tempo signal is output, and the rhythm. If the difference between the time when the rhythm is extracted by the extraction means and the time when the tempo signal is output from the tempo calculation means for the first time after the rhythm is extracted, and the difference is larger than the certain time,
When the tempo display is stopped when it is detected a certain number of times consecutively, and thereafter, the tempo signal is faded in (from a small value to a certain constant value) from the moment when the rhythm is extracted by the rhythm extracting means for the first time. The tempo display device according to claim 1, wherein the tempo calculation means is configured to control the tempo calculation means so that the display is started again. 12. The display on the display means is sound or light,
The tempo display device according to claim 1, wherein the tempo display device is configured to perform vibrations and images. 13. The tempo display device according to claim 1, wherein the display means is configured to control the display level in accordance with the amplitude level of the music signal input to the input terminal.