JP3877833B2 - Comb type digital filter and signal extraction device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a signal extraction device that extracts a specific signal from a signal in which a plurality of signals are mixed, and a digital filter suitable for use in the signal extraction device, for example.
[0002]
[Prior art]
For example, it may be desired to extract only the singing voice from the signal in which the singing voice and the accompaniment sound are mixed. In this case, it is conceivable to extract only the singing voice by using a comb filter that combines the fundamental tone of the singing voice and its harmonics with peaks.
[0003]
As the above comb filter, for example, the one shown in FIG. 9 of Japanese Patent Laid-Open No. 6-4076 as the prior art or the one shown as the embodiment in FIG. It is done.
[0004]
FIG. 4A shows a basic configuration of the comb filter shown in FIG. 1 of the publication. This comb filter is a second-order digital low-pass filter and includes adders 2, 4, 6, multipliers 8, 10, 12 and delay circuits 14, 16. In particular, the delay circuits 14 and 16 delay the input signal over a plurality of sampling periods.
[0005]
The coefficient B supplied to the multipliers 8 and 10 corresponds to a parameter for determining the cut-off frequency of the low-pass filter. In the case of the comb filter, the pass bandwidth (width of the comb-like characteristic) W, in other words, For example, the upper and lower cutoff frequencies are determined (see FIG. 5). The coefficient P supplied to the multiplier 12 corresponds to a parameter for setting Q in the low-pass filter. In the case of a comb filter, this coefficient is set as described in JP-A-6-4076. By changing the shape, the shape of the passband can be changed. However, since it is not directly related to the present invention, the description is omitted assuming that it is set to a predetermined value. Further, by changing the number of delay stages of the delay circuits 14 and 16 (ie, changing the delay time), the peak positions Fp, 2Fp,.
[0006]
In addition, as shown in FIG. 4B, in the first-order digital low-pass filter constituted by the adders 18 and 20, the multiplier 22, and the delay circuit 24, the signal input by the delay circuit 24 over a plurality of sampling times. By selecting the number of delay stages so as to delay the signal, a digital low-pass filter having the same frequency characteristics as the low-pass filter shown in FIG.
[0007]
[Problems to be solved by the invention]
Even if only the singing voice is extracted from the signal in which the singing voice and the accompaniment sound are mixed using such a digital filter, it cannot be satisfactorily extracted. The cause is that the width W of the comb-like characteristics of the conventional comb filter is always the same as shown in FIG. That is, when a voice such as a singing voice is subjected to frequency modulation such as vibrato, the higher the harmonics, the wider the spectrum. Also, the pitch of the voice is not always constant and fluctuates, and the fluctuation of the higher harmonics increases the spectrum spread. Therefore, a conventional comb filter in which the width of each comb-like characteristic is constant in any comb cannot capture high-order harmonics.
[0008]
An object of the present invention is to provide a signal extraction device that can satisfactorily extract only a specific signal, for example, a singing voice, from a mixed signal, for example, a signal in which a singing voice and an accompaniment sound are mixed. It is another object of the present invention to provide a digital filter that can be used in such a signal extraction apparatus and can constitute a comb filter having a characteristic in which the range of comb-like characteristics is widened toward the high frequency range. Therefore, another object of the present invention is to provide a digital filter provided with coefficient multiplication means for performing coefficient calculation with frequency characteristics.
[0009]
[Means for Solving the Problems]
To achieve the above object, a comb-type digital filter according to the first aspect of the present invention includes a first digital high-pass filter whose gain increases as the frequency of the input signal increases, and the output of the first digital high-pass filter. First delay means for delaying the signal, and the output signal of the first delay means is fed back to the input side and output side of the first digital high-pass filter.
[0011]
According to a second aspect of the present invention, in the above comb digital filter, a waveform signal in which a plurality of types of signals are mixed is supplied to the digital high-pass filter, and a pitch of one signal among the plurality of types of signals is supplied. Pitch information input means for inputting information created by imitating information is provided, and control means for controlling the delay time of the first delay means according to the information created by imitating the pitch information is provided. .
[0013]
A comb type digital filter according to a third aspect of the present invention is the digital filter according to the first aspect, wherein the second digital high pass filter is the same as the first digital high pass filter supplied with the output signal of the first delay means. Second delay means for delaying the output signal of the second digital high-pass filter, the output signal of the second delay means being the input side of the first digital high-pass filter and the second digital high-pass filter. Each is fed back to the output side.
[0015]
According to a fourth aspect of the present invention, there is provided a signal extraction apparatus in which a comb-shaped digital filter according to the third aspect is supplied with a waveform signal in which a plurality of types of signals are mixed, and the pitch information of one signal among all types of undulation types is simulated. Pitch information input means for inputting the created information is provided, and control means for controlling the delay times of the first and second delay means according to the information created by imitating the pitch information is provided. .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1A, the signal extraction apparatus according to the present embodiment has filter calculation means, for example, a digital filter 2. This digital filter 2 is basically the one obtained by replacing the multiplier 22 of the digital filter shown in FIG.
[0018]
That is, the digital filter 2 has an adder 6, and an input signal is supplied to the first addition input side of the adder 6. The output side of the adder 6 is connected to the coefficient multiplication means 4. The output side of the coefficient multiplication means 4 is connected to the addition input side of the adder 8. The output side of the adder 8 is connected to the output terminal 10 and to the delay circuit 12. The delay circuit 12 has a plurality of delay stages, and the number of delay stages is variable as will be described later. The output of the delay circuit 12 is fed back to the second addition input side of the adder 6 and the subtraction input side of the adder 8.
[0019]
The digital filter 2 functions in the same manner as the comb-type digital filter shown in FIG. 4B when the coefficient multiplication means 4 is regarded as a normal multiplier. Therefore, the width of each comb-like characteristic (passband width) is determined by the coefficient B supplied to the coefficient multiplying means 4, and the frequency of each comb-like characteristic is adjusted by adjusting the number of delay stages of the delay circuit 12, that is, the delay time. The peak position on the axis has been determined.
[0020]
The coefficient multiplying means 4 is configured as shown in FIG. That is, the output of the adder 6 is input to the coefficient multiplying means 4, and the output is multiplied by the coefficient 1 / 2B by the multiplier 14. The output of the adder 6 is delayed by one sampling period by the delay circuit 16 and multiplied by the coefficient −1 / 2B by the multiplier 18. The outputs of the multipliers 14 and 18 are added by an adder 20 and supplied to the adder 8. The coefficients 1 / 2B and -1 / 2B are obtained by multiplying the coefficient B supplied from the filter coefficient supply means 28 described later by the coefficient 22 by the multiplier 22 and the coefficient -1/2 by the multiplier 24. It has gained.
[0021]
The coefficient multiplying means 4 itself is also configured as a digital high-pass filter, and the frequency characteristic of the coefficient multiplying means 4 increases as the frequency becomes higher, for example, as shown in FIG. Therefore, this coefficient multiplication means functions as a multiplier whose coefficient increases as the frequency of the input signal increases. As described with reference to FIG. 4B, since the width of each comb-like characteristic is determined by the coefficient supplied to the multiplier 22, it functions as a multiplier that increases as the frequency of the input signal increases. By using the coefficient multiplying means 4, the width of the comb frequency characteristic of the digital filter 2 becomes wider as the frequency of the input signal becomes higher as shown in FIG.
[0022]
The delay circuit 12 can arbitrarily set the delay time, and the delay time is set by the control means, for example, the delay time setting means 26. For example, pitch information of a signal supplied to the digital filter 2 is input to the delay time setting unit 26, and the delay time setting unit 26 sets the delay time in the delay circuit 12 in accordance with the pitch information.
[0023]
The delay circuit 12 basically delays the signal supplied to the delay circuit 12 by a delay time that is an integral multiple of the sampling period, such as a shift register that sequentially shifts in the sampling period. Furthermore, an interpolation calculation means for calculating the sampling data between the n-th sampling data and the (n + 1) -th sampling data by interpolation calculation is provided, and the delay time has a resolution finer than the sampling period according to the pitch information. Can be set.
[0024]
The coefficient B of the coefficient multiplication unit 4 is supplied to the coefficient multiplication unit 4 by a control unit, for example, a filter coefficient supply unit 28. The filter coefficient supply means 28 can change the value of the filter coefficient B, for example, according to the operation of the operation element 30.
[0025]
A notch filter 32 is provided in front of the digital filter 2. In the notch filter 32, the multiplier 34 multiplies the input signal by a predetermined coefficient. The input signal is delayed by a delay circuit 36 that delays a plurality of sampling times. The output of the delay circuit 36 is multiplied by a predetermined coefficient by a multiplier 38. The outputs of the multipliers 34 and 38 are added by an adder 40. This notch filter 32 is provided in order to sufficiently attenuate the valley of the frequency characteristic of the digital filter 2 shown in FIG.
[0026]
In this signal extraction device, the operator 30 is operated to set an appropriate filter coefficient B, for example, a mixed signal of singing voice and accompaniment sound is input as an input signal, and the pitch information of the singing voice is input to the delay time setting means 26. When input, the singing voice is frequency-modulated, and even if the spread of the higher order harmonic spectrum increases, the width of the comb-like characteristic of the digital filter 2 becomes wider as the frequency becomes higher, and the pitch of the singing voice is increased. Even if it fluctuates, since the peak frequency of each comb-like characteristic is changed accordingly, only the singing voice can be extracted well.
[0027]
For example, when the pitch information is obtained from a signal such as a CD that does not have the pitch information, the following may be performed, for example. While the user of the signal extraction device listens to the output of the CD in which the singing voice and the accompaniment sound are mixed, the pitch information is manually supplied to the delay time setting means 26 every time the pitch changes. In this case, it is difficult to change the pitch information corresponding to the pitch fluctuation of the singing voice in real time.
[0028]
Therefore, the CD output is temporarily stored in a memory of a computer such as a personal computer, and the pitch information is manually changed while listening to the reproduced one, and the change in the pitch information is synchronized with the reproduction of the performance. Remember. The change in the pitch information stored in this way is reproduced in synchronism with the performance, and the pitch information is supplied to the delay time setting means 26 based on this change, and the delay time is thus set. The result of signal extraction is stored again in the memory. The stored signal extraction result is reproduced again, and it is confirmed whether or not the pitch information is set appropriately. For the places where the pitch information is not properly set, the stored pitch information is manually changed. Such a work is repeated many times.
[0029]
Alternatively, the user sings while listening to the performance of the singing voice and the accompaniment sound, the user's singing voice is detected by the pitch detection device, and the detection result is supplied to the delay time setting means 26. At first, the pitch information is obtained in this way and stored in synchronism with the reproduction of the performance. Further, the delay time control based on the stored pitch information and the manual processing similar to the above are used in combination. If the stored pitch information is corrected, more accurate pitch information can be obtained.
[0030]
FIGS. 3A and 3B show a second embodiment. In this embodiment, the digital filter is configured as a second-order digital low-pass filter. That is, a signal is supplied from the notch filter 32 to the addition input of the adder 6a, and the output of the adder 6a is supplied to the coefficient multiplication means 4a. The output of the coefficient multiplication means 4a is supplied to the first addition input of the adder 8a. The output of the adder 8a is supplied to the delay circuit 12a. The output of the delay circuit 12a is supplied to the second addition input of the adder 8a. The output of the delay circuit 12a is further multiplied by a coefficient P by the multiplier 50, and the output of the multiplier 50 is supplied to the first subtraction input of the adder 6a.
[0031]
The output of the delay circuit 12a is further input to the coefficient multiplier 4b, and the output of the coefficient multiplier 4b is supplied to the first addition input of the adder 8b. The output of the adder 8b is used as the output of the digital filter 2a, delayed by the delay circuit 12b, supplied to the second addition input of the adder 8b, and further supplied to the second subtraction input of the adder 6a. Are also supplied.
[0032]
Similarly to the delay circuit 12 of the digital filter 2 in the first embodiment, the delay circuits 12a and 12b can set delay times for a plurality of sampling times, and the delay times are set by the delay time setting means 26. The The delay time setting means 26 determines the delay time based on the pitch information input thereto. Further, similarly to the delay circuit 12, the delay circuits 12a and 12b can set the delay time with a resolution finer than the sampling period in accordance with the pitch information. Further, the peak frequency of each comb-like characteristic is set by this delay time.
[0033]
As shown in FIG. 3B, the coefficient multiplication means 4a and 4b function as a digital high-pass filter with the same configuration as the coefficient multiplication means 4 in the first embodiment. However, the coefficients supplied to the multipliers 22 and 24 are 1/3 and −1/3, and only this point is different. This value can be set to ½ and −½ as in the first embodiment, but is experimentally set to this value.
[0034]
The coefficient B supplied to the coefficient multiplying means 4a and 4b determines the width of each comb-like characteristic as in the first embodiment. The coefficient P supplied to the multiplier 50 corresponds to a parameter for setting Q in the low-pass filter as described with reference to FIG. As described in the publication, the shape of the passband can be changed by changing this value.
[0035]
These coefficients B and P correspond to the operation of the operator 30, and the filter coefficient supply means 28a supplies the coefficient B to the coefficient multiplication means 4a and 4b and the coefficient P to the multiplier 50, respectively.
[0036]
Also in the second embodiment, as in the first embodiment, the width of each comb-like characteristic becomes wider as the frequency becomes higher, and the peak of each comb-like characteristic according to the fluctuation of the pitch information. The frequency of changes. Therefore, as in the first embodiment, only the singing voice can be accurately extracted from the mixed signal of the singing voice and the accompaniment sound.
[0037]
In the above embodiment, the comb filter is used as the digital filter. However, other filters such as a low-pass filter and a high-pass filter may be used.
[0039]
【The invention's effect】
As described above, according to the first or third aspect of the invention, the width of the comb-like characteristics of the comb-type digital filter changes according to the frequency change of the signal input to the digital filter. Even if the spectrum changes as the higher-order harmonics become higher, the input signal can be extracted well.
[0040]
According to the second or fourth aspect of the invention, the information created by imitating the pitch information input by the pitch information input means is changed according to the desired signal in the mixed signal, so that the pitch information at that time is imitated. The peak position of the comb-like characteristics changes according to the information created in the above. In addition, when the frequency of the desired signal moves to a higher frequency, the width of the comb-like characteristic also changes. Therefore, from the mixed waveform of a plurality of waveform signals, it is possible to satisfactorily extract a waveform whose spectrum is broadened and pitch is fluctuated as the higher-order harmonics are obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram of a signal extraction device according to a first embodiment of the present invention and a block diagram of coefficient multiplication means used in the device.
FIG. 2 is a frequency characteristic diagram of the signal extraction device and a frequency characteristic diagram of coefficient multiplication means.
FIG. 3 is a block diagram of a signal extraction device according to a second embodiment of the present invention and a block diagram of coefficient multiplication means used in the device.
FIG. 4 is a block diagram of a conventional digital filter.
FIG. 5 is a frequency characteristic diagram of a conventional digital filter.
[Explanation of symbols]
2 Digital filter 4 Coefficient multiplying means 12 Delay circuit

Claims (4)

A first digital high-pass filter whose gain increases as the frequency of the input signal increases;
First delay means for delaying the output signal of the first digital high-pass filter, and the output signal of the first delay means is fed back to the input side and output side of the first digital high-pass filter. Comb type digital filter. 2. The comb digital filter according to claim 1, wherein a waveform signal obtained by mixing a plurality of types of signals is supplied to the digital high-pass filter, and information created by imitating pitch information of one of the plurality of types of signals is generated. A signal extraction apparatus provided with pitch information input means for input, and provided with control means for controlling the delay time of the first delay means in accordance with information created by imitating the pitch information . The comb-type digital filter according to claim 1,
A second digital high-pass filter having the same configuration as the first digital high-pass filter to which the output signal of the first delay means is supplied;
Second delay means for delaying the output signal of the second digital high-pass filter;
And a digital filter in which the output signal of the second delay means is fed back to the input side of the first digital high-pass filter and the output side of the second digital high-pass filter. 5. A pitch information input means for supplying a waveform signal obtained by mixing a plurality of types of signals to the comb digital filter according to claim 3, and inputting information created by imitating pitch information of one of the plurality of types of signals. And a control means for controlling the delay times of the first and second delay means according to the information created by imitating the pitch information .

Images