JPH0690639B2 - Pitch extractor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pitch extraction device for audio signals such as various musical sounds and voices.

2. Description of the Related Art In recent years, various pitch extraction techniques have been proposed along with the progress of digital technology, and there are techniques for obtaining the autocorrelation of time waveforms, cepstrum techniques, etc., but integral pitch extraction is a technique that does not require a multiplier. There is technology (for example, the Acoustical Society of Japan / Speech Study Group Material / Material No. S82-05 (1982-
4) PP30-40).

Hereinafter, the pitch extraction device described above will be described with reference to the drawings.

FIG. 3 shows the structure of a conventional pitch extracting device. In FIG. 3, 101 is a high-pass filter, 102 is a low-pass filter, 103 is an AD (analog / digital) converter, 104 is an integrator, and 105 is a judgment unit.

The operation of the pitch extracting device configured as described above will be described below.

An audio signal input from a microphone or the like is subjected to antialiasing filtering that satisfies the sampling theorem by passing through a lowpass filter 102 after a direct current component is removed by a highpass filter 101.

Next, the AD converter 103 performs analog-to-digital conversion to obtain digital data. The digital data output from the AD converter 103 is integrated by the integrator 104 and then the integrated result is output to the determination unit 105. Judgment unit 105
Will calculate the pitch by detecting the minimum value in the integration result and counting the number of samples between the minimum values. That is, the digital data of the audio signal as shown in FIG. 4a, that is, the output of the AD converter 103 is the integrator 1
It is converted by 04 into the integration result as shown in FIG. The determination unit 105 detects the minimum value as an absolute value as indicated by A, B, and C with respect to the integration result of FIG. 4c, and pitches the number of samples N _A , N _B , and N _C between the minimum values. It will be obtained as a cycle. In order to convert the pitch period Ni pieces into a so-called pitch i, the sampling frequency s [Hz] is used. Can be asked as

In order to facilitate detection of the minimum value, the result of moving average (smoothing) of the integration result of the integrator 104 is used as the fourth result.
As shown in FIG. B, if the moving average processing result is input to the determination unit 105, the influence of the harmonic component on the pitch period detection can be removed.

Problem to be Solved by the Invention However, in the above-described configuration, there is a problem that the integration result diverges in the positive or negative direction because there is a frequency component lower than the pitch period.

In view of the above problems, the present invention provides a pitch extraction device capable of preventing the divergence of integration results with a simple configuration.

Means for Solving the Problems In order to achieve this object, the pitch extraction device of the present invention is
AD that converts band-limited acoustic signals into digital data
The converter, the integrator for cumulatively adding the digital data output from the AD converter, and the integrator are reset each time the cumulative result passes the preset threshold twice, and each reset interval is used as the pitch period. It is composed of a control determination unit for detecting.

Operation The present invention allows a band-limited acoustic signal to be generated by this configuration.
Converted to digital data by AD converter. AD
The digital data output from the converter is sequentially cumulatively added by the integrator reset to the initial value O, and the result is sequentially output. The control determination unit detects a time interval until the cumulative result output from the integrator once exceeds the threshold value θ and then becomes equal to or less than the threshold value θ with respect to a predetermined threshold value θ, and sets this as a pitch cycle. Output and reset to integrator O. By repeating the above-mentioned operation, the pitch periods detected sequentially are output from the control determination unit.

Example Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a pitch extracting device according to an embodiment of the present invention.

In FIG. 1, 10 is an integrator and 11 is a control determination unit.

Incidentally, 101 is a high-pass filter, 102 is a low-pass filter, and 103 is a converter, which have the same configurations as those of the conventional example.

The operation of the pitch extracting device configured as described above will be described below.

First, the acoustic signal input to the high-pass filter 101 is subjected to high-pass filtering that removes frequency components (for example, 5 cHz or less) considerably lower than the pitch frequency, and then input to the low-pass filter 102. The high-pass filtered acoustic signal input to the low-pass filter 102 is s / 2 [H] with respect to the sampling frequency s [Hz] so that the so-called sampling theorem is satisfied.
z] Low-pass filtering is performed so that only the values below are passed. In the present embodiment, it is desirable to remove the influence of high frequency components by performing low pass filtering having a cutoff frequency of c << s / 2.

The acoustic signal that has passed through the high-pass filter 101 and the low-pass filter 102 becomes digital data that is AD-converted by the AD converter 103 at the sampling frequency of s [Hz] as a band-limited acoustic signal. Digital data output from the AD converter 103 is sequentially accumulated and added by the integrator 10. Here, it is assumed that the integrator 10 is reset to the initial value zero.

The control determination unit 11 holds a predetermined threshold value θ as a determination reference value and compares it with the cumulative result output from the integrator 10. As a result of the comparison, after detecting that the cumulative result exceeds the threshold value θ for the first time, the integrator 10 is reset at the same time when the cumulative result becomes equal to or less than the threshold value. On the other hand, the control determination unit 11 counts the number of digital data from resetting the integrator 10 to the next resetting, and outputs the count value as a pitch cycle detection value.

The relationship between the above data is shown in FIG.

When the pitch period is to be a time value, 1 / s is multiplied by the detected value, and when it is desired to be the pitch frequency, s is divided by the detected value.

Further, in the above, regarding the comparison with the threshold value θ in the control determination unit 11, the case where the cumulative result is a positive value has been described. Should be changed appropriately.

As described above, according to this embodiment, the control determination unit 11 resets the integrator 10 each time the pitch period is detected, so that the accumulated result can be prevented from diverging in the positive or negative direction. Further, unlike the conventional case, the threshold θ can be eliminated without requiring a complicated determination unit for determining the minimum value or the maximum value.
The determination can be made by comparison with. Also,
The cutoff frequency c of the low-pass filter 102 is set to c <<
By setting s / 2, a smooth cumulative result can be obtained.

EFFECTS OF THE INVENTION The present invention sequentially accumulates digital data obtained by converting a band-limited acoustic signal by an AD converter by an integrator, and adds the result in a control determination unit to a predetermined threshold θ.
Since the pitch period is detected by comparing and determining with, the cumulative result of the integrator is reset to zero, so that the cumulative result can be prevented from diverging in the positive or negative direction.

[Brief description of drawings]

FIG. 1 is a block diagram of a pitch extracting device according to an embodiment of the present invention, FIG. 2 is an exemplary waveform diagram of each data according to the pitch extracting device, and FIG. 3 is a block diagram of a conventional pitch extracting device. FIG. 4 is a signal waveform diagram of each part. 10 ... integrator, 11 ... control determination unit, 101 ... high-pass filter, 102 ... low-pass filter, 103 ... AD converter, 104 ... integrator, 105 ... determination unit.

Claims (1)

[Claims] 1. An AD converter for converting a band-limited acoustic signal into digital data, an integrator for sequentially cumulatively adding the digital data output from the AD converter, and a cumulative addition result output from the integrator. And a predetermined threshold value, and a control determination unit that resets the integrator in accordance with the comparison result, the control determination unit being configured to perform the integrator every time the cumulative addition result passes the threshold value twice. A pitch extracting device, wherein the reset interval is instructed to, and each of the reset intervals is detected as a pitch cycle.