JP3088838B2 - Music detection circuit and audio signal input device using the circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a music detection circuit and an audio signal input device using the music detection circuit.
When recording using a tape recorder, or when recording and recording using a video camera or the like, detecting whether music is included in the audio signal to be recorded, and further detecting music Recording of the audio signal input,
It is possible to record up to the frequency band in which the music is included.

[0002]

2. Description of the Related Art FIG. 6 is a view for explaining a conventional technique for preventing the influence of ambient wind noise or the like at the time of recording and recording with a video camera or the like, particularly at the time of recording.
Is a wind noise detection circuit, 12 is a frequency characteristic conversion circuit, 13 is a signal switch (switch), an input signal (Tin) detected by a voice detection device such as a microphone is a wind noise detection circuit 11, and a wind noise is detected. At a certain time (that is, when a low frequency band wind noise component as shown in FIG. 7 enters the input signal), the wind noise is detected and the switch 13 is switched from the dotted line position to the solid line position, The input signal is converted to a frequency characteristic conversion circuit 12 (this frequency characteristic conversion circuit
Has a characteristic of cutting low frequency components as indicated by Y), and cuts out low frequency components and outputs (Tout). Note that the switch 13 is normally at the position shown by the dotted line in FIG. 6, and the input signal becomes the output signal (Tout) as it is. In other words, normally, the input signal is output through a circuit having a flat frequency characteristic as shown by Z in FIG.

[0003]

In the prior art as described above, when recording or wind noise comes in, the low frequency range is cut off by a frequency characteristic conversion circuit (filter), so that good sound quality and good sound quality can be obtained. However, in other cases, since the frequency characteristics are flat (the switch 13 is at the position indicated by the dotted line), depending on the recording target, a low and high frequency range is recorded and reproduced. There are many cases. For example, when recording outside a room, low and high noises from a car or the like are recorded mixed with the voice of the person to be recorded, and when reproduced, the sound is unpleasant. In contrast,
When music such as a concert is recorded, it is preferable that the frequency characteristics be flat because a sufficient tone can be obtained. Therefore, when recording music, it is preferable to make the frequency characteristics flat, and otherwise to cut out the region other than the middle region of the human voice. In view of the above situation, the present invention detects whether or not music is included in a recording target, in other words, determines whether or not the recording target is music. This is for the purpose of widening the recording band by flattening the frequency characteristics when the sound is included, and thereby performing good recording of music such as a concert.

[0004]

(1) A plurality of bandpass filters for dividing an input signal into a plurality of frequency bands, a detection circuit for detecting the presence / absence of output of each bandpass filter, and a detection circuit for each detection circuit An output signal is input, and a determination circuit is provided for determining whether or not the output signal is periodically repeated for each output signal from each band-pass filter. (2) a circuit system for guiding the input signal to an audio signal processing device via a filter, and a circuit for directing the input signal to the audio signal processing device And a switching means for switching between the two circuit systems to selectively guide the input signal to the audio signal processing device; and a music detection circuit according to (1), The switching means is switched by an output signal of a circuit.

[0005]

The input signal is divided into several frequency bands using a plurality of bandpass filters (hereinafter referred to as BPF), and the presence or absence of the output signal of each BPF is detected. When the output is detected with periodicity, it is determined that the input signal is music including bass drums and bass. Also,
When recording the input signal, when it is determined that music is contained, the frequency characteristic is flattened and the frequency region of the music is also set as the recording region.

[0006]

FIG. 1 is a diagram for explaining an embodiment of a music detection circuit according to the present invention. In the drawing, reference numeral 1 denotes a BPF group, 2 denotes a sound presence / absence detection circuit, and 3 denotes music judgment. Circuit, 4 is a frequency characteristic conversion circuit (filter), 5 is a signal switch (switch), 6 is an audio signal processing device (recording device), and BPF
The group 1 includes, for example, bandpasses (ie, frequencies f _L , f _O , f, respectively) as shown by 1a, 1b, 1c in FIG.
Passing through _M) bandpass filter 1a having a characteristic,
1b and 1c, the input signal (Tin) passes through these BP F1a, 1b and 1c, and is then guided to a detection circuit 2 for detecting the presence or absence of sound.

[0007] The presence / absence detection circuit 2 includes a BP F1a,
The output signals of 1b and 1c are converted into DC component detection circuits 2a ₁ and 2a
b ₁ , 2c ₁ , and comparison circuits 2a ₂ , 2b ₂ , 2c ₂ for comparing the DC components of the respective DC component detection circuits with the reference value SL. Is detected only. However, these comparison circuits 2a ₂ , 2b ₂ , 2c ₂ are not always necessary, and the detection circuit 2 determines in real time whether there is a signal of a predetermined level or more in the output of each BPF. Anything that can be determined can be used.

The detection accuracy can be improved as the number of BPFs increases, and FIG. 1 shows an example in which three BPFs are used. If it is composed of one BPF having a frequency characteristic as shown in FIG. 3, when a signal as shown in FIG. At (1) and at (3) in FIG. 4B, it is determined that there is an input signal, and the frequency f
There is a possibility that the sound of _{H and} the sound of frequency f _L may be erroneously determined to be the same sound.

Thus, in the present invention, a plurality of BPFs are provided, and the pass band of each BPF is narrowed.
For example, when a signal as shown in FIG. 4A is input, only the BP F1b passes the signal of the frequency f _O and the other B.P.
Since the P.F.1a and 1c do not pass through, a signal appears with a periodicity in the output of this B.P.F.1b ((1) and (3) in FIG. 4 (A)). ,
It can be determined that a sound of this frequency (for example, a sound of a bass drum) is included. When a signal as shown in FIG. 4B is input, an output signal of frequency f _H appears at the output of BP.F1c in (1) of FIG. 4B. Since this signal has no periodicity, it is determined that the signal is not music. Also, in (3) of FIG. 4B, a signal of frequency f _L appears at the output of BP F1a, but since this signal also has no periodicity, it is determined that this signal is not music.

More specifically, 1a is a frequency f _L
B.P.F passing signals, 1b is B.P.F passing a signal of a frequency f _O, 1c in B.P.F passing a signal of a frequency f _H, the pass band is narrow The more you become,
The frequency of the signal passing through each BPF can be detected with high accuracy. Here, taking as an example the simplest example having periodicity, that is, a case where a rhythm is carved at a constant period, in (A) and (B) of FIG.
It is assumed that the process proceeds in a certain time, which is the order of (3). For example,
When there is the sound of the bass drum frequency f _O in the input signal, since repeated at a constant period the sound with the bass drum, as this signal is shown in (A) in FIG. 4, B.P.
Since it appears in the output of F1b at regular intervals and does not become as shown in FIG. 4B, it can be determined from this that there is music in the input signal. Note that, in the above example, the case of a fixed cycle has been described, but in actual music, for example, the sound of a bass drum has periodicity, but is rarely repeated at a fixed cycle. Therefore, even intervals appearing discontinuity in f _O, and the like is determined that there is periodicity in the case of a half of an integral multiple of the minimum interval, the determination conditions for determining the periodicity circuit 3 May be used to determine the periodicity. Note that this condition is merely an example, and more accurate conditions can be determined by giving more conditions. The output of the BPPF is supplied to a detection circuit 2 at the next stage, where the presence or absence of a signal is detected for each BPPF. Is not limited to the circuit shown in the figure, as long as it can be detected as described above.

As described above, the signal detected for each BPF is input to the determination circuit 3, and the period of each detected signal is determined by using a microcomputer or the like as to whether or not the signal has an output. Is detected. When a periodicity appears in the output of a certain BPF in the determination circuit 3, for example,
As shown in (A) in FIG. 4, when the output of B.P.F1b appeared at a fixed period, the input signal is determined to be music containing the frequency f _O, the switch 5 through (TH ) (Dotted line). When the switch 5 is switched to the TH side, the frequency characteristic becomes a flat characteristic as shown by Z in FIG. 5, and is applied to music including sound in a low frequency range from a low frequency range to a high frequency range. And good recording is possible.

Reference numeral 6 denotes an audio signal processing device (recording device) such as a tape recorder. For example, when a human voice is being recorded, the switch 5 passes an audio signal as shown by a solid line in FIG. Filter 4 that cuts the low and high frequencies
Connected to the side. In other words, when a signal as shown in FIG. 4B or a signal such as the wind noise shown in FIG. 7 is input, the output of BPF has no periodicity. The determination circuit 3 determines that the input signal is not music, and sets the switch 5 to the FL side (solid line position). This FL
The frequency characteristic on the side is a characteristic as indicated by x in FIG. 5 by the filter 4, that is, a characteristic in which the low and high frequencies of the audio signal are cut off, and therefore, the switch 5 is set to the filter 4 side. At times, more clear recordings can be made through the middle range of human voices. In the above description, low and high frequencies are cut except for music having low frequencies. However, this is only an example, and cutting of only low frequencies may be performed.

[0013]

As is apparent from the above description, according to the present invention, it is possible to easily determine whether or not a recording target is music requiring a low frequency component, for example, a concert. If it is determined to be music, the frequency response of the signal input to the recording device is flattened, otherwise the low and high frequencies are cut, making noise and wind noise less audible and the voice of humans Can be automatically made to sound clear, and recording of good sound quality can be performed for more recording targets.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of a music detection circuit and an audio signal input device using the circuit according to the present invention.

FIG. 2 is a diagram showing a frequency characteristic of BPF shown in FIG. 1;

FIG. 3 is a diagram for explaining an operation when one BPF having a wide pass band is used.

FIG. 4 is a diagram for explaining the operation of the present invention.

FIG. 5 is a frequency characteristic diagram for explaining the prior art and the present invention.

FIG. 6 is a diagram illustrating an example of a conventional wind noise control device.

FIG. 7 is a diagram showing a frequency distribution of wind noise.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... BPF group, 2 ... Sound presence / absence detection circuit, 3 ... Period determination circuit, 4 ... Signal switch, 5 ... Frequency characteristic conversion circuit,
6: Recording device, 11: Wind noise detection circuit, 12: Frequency characteristic conversion circuit.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ identification code FI H03G 5/02 G10L 7/04 B (58) Field surveyed (Int.Cl. ⁷ , DB name) G10L 11/00-21 / 06 G10H 1/00 101 G11B 20/02 H03G 5/02 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A plurality of bandpass filters for dividing an input signal into a plurality of frequency bands, a detection circuit for detecting the presence or absence of an output of each bandpass filter, and an output signal of each detection circuit, A determination circuit for determining whether or not the output signal is repeated with a periodicity for each output signal from the band-pass filter, and when the input / output signal is music, A music detection circuit characterized by determining. 2. A circuit system for guiding the input signal to an audio signal processing device via a filter, a circuit system for directing the input signal to the audio signal processing device, and switching between the two circuit systems to convert the input signal. A sound, comprising: switching means for selectively leading to the audio signal processing device; and the music detection circuit according to claim 1, wherein the switching means is switched by an output signal of the music detection circuit. Signal input device.