JPH10173489A - Adaptive filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically obtain optimal noise suppression and S/N improvement according to an input signal level by varying the response characteristics of an adaptive filter based on the input signal or on S/N of the adaptive filter. SOLUTION: A function for switching an adaptive following-up speed and the delay time of a delay circuit according to the received signal of a receiver is added to an adaptive filter 1. An input signal y(n) is inputted to the adaptive filter 1, and this input signal y(n) is inputted to a delay circuit 3. A difference (error) signal between the output of the adaptive filter 1 and the output of the delay circuit 3 is obtained by a subtracting circuit 5. This error signal is multiplied by a prescribed coefficient by a multiplying circuit 4, and supplied to the adaptive filter 1. An MPU 2 adjusts the delay time of the delay circuit 3 or the coefficient of the multiplying circuit 4 according to a received signal intensity (level) from a receiving circuit 6, and the adaptive operation (response) characteristics of the adaptive filter 1 is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an adaptive filter, and more particularly to an adaptive filter capable of effectively suppressing noise and improving S / N.

[0002]

2. Description of the Related Art In recent years, adaptive filters whose application fields have been remarkably expanded have been used not only in the data communication field of wired / wireless communication but also in the field of voice communication for suppressing noise and interference. Is coming.

[0003] In a radio device, particularly a receiver, in the voice communication field, an adaptive filter is used to maintain an optimum state for a received signal whose state changes every moment. However, since the following characteristic of the adaptive filter is changed depending on the input level and the S / N, when the S / N is deteriorated or the interference becomes extremely large, the processing capability is greatly reduced.

The principle of operation of a noise suppression filter using an adaptive filter for noise suppression will be described below. First, an adaptive filter input signal (received signal) y for noise suppression by a receiver
(N) is a sine wave s (n) of 1 kHz and random noise d.
It is assumed that the superposed signal y (n) of (n) = s (n) + d (n). A signal y obtained by delaying the input signal (received signal) y (n) by a delay time T as a reference signal of the adaptive filter.
(NT) is used. Here, assuming that the delay time T is 10 ms, the sine wave waveform of the periodic signal s (n) included in each of the input signal y (n) and the reference signal y (n-T) having a time difference has a difference of 10 periods. , A filter that suppresses the random noise d (n) is formed by forming a filter that minimizes the error between the two signals. The periodic signal s ( n) will be obtained.

When only an irregular signal such as noise is present in the input signal y (n), the input signal (received signal) y (n)
There is no correlation between the signal and the signal y (n-T) delayed by the delay time T, and the filter output decreases in an attempt to reduce the error.

[0006]

When the S / N is significantly deteriorated or when there is interference, the adaptive filter as described above has a signal y delayed from the input signal (received signal) y (n) by a delay time T. Since the correlation detected between (n-T) is low, the level of the periodic signal is lowered, and the S / N improvement is deteriorated. As described above, the adaptive performance of the adaptive filter for the purpose of noise suppression to the periodic signal is good when the S / N that does not require the S / N improvement is high, and the S / N that requires the S / N improvement is improved. Worse when low. On the other hand, if the response characteristic of the adaptive filter is set so that the S / N improvement is high when the S / N is low, the periodic signal is more emphasized and output when the S / N is high. For a periodic signal that is good, it is good, but for a combined signal of a quasi-periodic signal and a non-periodic signal like human voice, the adaptive filter suppresses the consonants of the voice that is a non-periodic signal and outputs The sound quality is deteriorated as compared with the case where no adaptive filter is passed. If the response characteristic of the adaptive filter is set to suppress sound quality degradation when the S / N is high, the degree of improvement of the S / N is low when the S / N is low, and the periodic signal is output without much emphasis. Therefore, the degree of S / N improvement is deteriorated.

As described above, in the conventional adaptive filter,
When the received signal strength is weak, it is desirable that the effect of noise suppression is large. However, when the received signal strength is strong, the S / N can be reduced by performing the noise suppression processing even though there is no need for noise suppression.
However, the sound quality was degraded when it was good, making it difficult to hear. Therefore, a human had to operate the receiver to operate the adaptive filter in accordance with the received signal strength changing every moment, which was complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an adaptive filter capable of automatically obtaining an optimal noise suppression and S / N improvement effect according to an input signal level.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an adaptive filter according to the present invention is an adaptive filter for suppressing a noise component contained in an input signal. The adaptive filter is configured to vary a response characteristic of the adaptive filter on the basis of the adaptive filter.

According to another aspect of the present invention, there is provided an adaptive filter for suppressing a noise component included in an input signal, wherein a response characteristic of the adaptive filter is determined based on an average value level of the input signal of the adaptive filter. It is configured to be variable.

Further, the adaptive filter according to another aspect of the present invention varies its response characteristic based on a difference signal between an output signal thereof, an input signal and a delay signal obtained by delaying the input signal by a predetermined time, and varies the response characteristic. In an adaptive filter that suppresses a noise component included in an input signal, when the input signal is high, the following speed of the adaptive filter is set to be slow, or the delay time is set short, and when the input signal is low, the adaptive filter It is configured to set the following speed faster or set the delay time longer.

An adaptive filter according to another aspect of the present invention comprises:
An adaptive filter that varies its response characteristic and suppresses a noise component included in the input signal based on a difference signal between the output signal and the input signal and a delay signal obtained by delaying the input signal for a predetermined time. When the average value level of the input signal is high, the following speed of the adaptive filter is set to be slow, or the delay time is set short, and when the average value level of the input signal is low, the following speed of the adaptive filter is set fast. , The delay time is set to be long.

Here, the operation of the adaptive filter is turned ON / OFF.
The input signal is a received signal received by an antenna or a signal obtained from an S meter or RSSI provided in a receiver, and an output from the adaptive filter is output as a sound from a speaker. . Further, there is provided switching means for switching between the difference signal and the zero level signal and supplying the signal to the adaptive filter.

[0014]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the adaptive filter according to the present invention. In this embodiment, an adaptive filter is provided with a function of switching the adaptive following speed and the delay time of the delay circuit according to the received signal strength of the receiver, and adapts according to the received signal strength (input signal level) of the receiver. The adaptive following speed of the filter and the delay time of the delay circuit are controlled.

Referring to FIG. 1, adaptive filter 1 includes:
The input signal y (n) is input, and this input signal is also input to the delay circuit 3. A difference (error) signal between the output of the adaptive filter 1 and the output of the delay circuit 3 is obtained by the subtraction circuit 5. The error signal is multiplied by a predetermined coefficient in a multiplication circuit 4 and supplied to the adaptive filter 1. The MPU 2 has a receiving circuit 6
The adaptive operation (response) characteristic of the adaptive filter is varied by adjusting the delay time of the delay circuit 3 and the coefficient of the multiplication circuit 4 in accordance with the received signal strength (level) from the adaptive filter.

More specifically, the MPU 2 receives the received signal received by the receiving circuit 6, obtains an average value of the received signal strength, and when it is determined that the average received signal strength is strong, the multiplication circuit 4 Are set to lower the adaptive following speed of the adaptive filter 1 and the delay time T of the delay circuit 3 is set shorter. As described above, when the adaptive following speed is set to be low, the change speed of the response characteristic of the filter formed by the adaptive operation of the adaptive filter 1 becomes slow,
Changes in tone and distortion due to changes in the response characteristics of the filter are reduced. When the delay time T of the delay circuit 3 is set short, the input signal is passed as it is. That is, when T = 0,
The signal y (n-T) that has passed through the delay circuit 3 is y (n-T)
= Y (n-0), and the input signal of the adaptive filter 1 and the adaptive filter reference signal become the same, so that the input signal is passed as it is. With such control, the adaptive filter is configured with a filter having characteristics suitable for all the input signals, so that it is possible to obtain an output in which sound quality deterioration is minimized. However, the S / N improvement is not high because the periodic signal is not emphasized, but when the received signal strength is strong, an output with little deterioration in sound quality can be obtained even if the S / N improvement is not so good.

Next, when the MPU 2 judges that the received signal strength is weak, the MPU 2 changes the coefficient of the multiplication circuit 4 to set the adaptive following speed of the adaptive filter 1 to a high value.
Set a longer delay time. When the adaptive tracking speed is set to be high, the change speed of the response characteristic of the filter formed by the adaptive operation of the adaptive filter becomes steep, so that it is easy to follow the change of the periodic signal. If the delay time of the delay circuit 3 is set to be long, the correlation of the irregular signal becomes low, so that the periodic signal is emphasized. With these controls, the adaptive filter forms a filter that emphasizes and passes the periodic signal, so that an output with a high S / N improvement can be obtained. However, although the deterioration of the sound quality is not small because the periodic signal is emphasized, when the received signal strength is weak, the irregular noise is reduced even if the sound quality is changed, and the S / N improvement is increased. , Listening becomes easier.

In the description of the above embodiment, the reason why the average value of the received signal strength is used as the reference signal for controlling the adaptive operation (response operation) of the adaptive filter is that the received signal strength such as pop noise and multipath is used for the received signal. This is to prevent the MPU 2 from excessively controlling the adaptive following speed of the adaptive filter 1 in the DSP and the delay time of the delay circuit when. If the adaptive tracking speed of the adaptive filter 1 in the DSP and the delay time of the delay circuit 3 are sensitively controlled using the received signal strength obtained from the receiving circuit 6 as it is, the S / N improvement is improved when the S / N is low. In this way, the response characteristics of the adaptive filter are set, and when the S / N is high, the periodic signal is more emphasized and output. Therefore, although it is good for a periodic signal such as a sine wave, for a combination signal of a quasi-periodic signal and an aperiodic signal such as a human voice, the adaptive filter removes the consonant of the aperiodic signal. Since the output is suppressed, the sound quality is deteriorated as compared with the case where the signal is not passed through the adaptive filter. In order to avoid this deterioration in sound quality, the MPU 2 calculates an average value as preprocessing.

FIG. 2 shows that a panel switch 30 for adaptive control of the adaptive filter shown in FIG. 1 is installed on the panel surface of the receiver, and the MPU 20 of the receiver determines the strength of the received signal to determine the adaptive following speed and the delay circuit. The operability is improved by giving information such as the delay time of the above to the adaptive filter and controlling it.

Referring to FIG. 2, a received signal received by antenna ANT is converted into an RF signal by RF circuit 40, mixed with a local signal from local circuit 60 by mixing circuit 50, and an IF signal is output. Is done. This IF signal is
IF processing is performed by the F circuit 50 and detected by the detection circuit 80.
It is sent to the DSP 10. The DSP 10 has an adaptive filter 11 and a following speed / delay time setting circuit 12 for setting the following speed / delay time of the adaptive filter 11.

The IF signal from the IF circuit 70 is
0, and the received signal strength determination circuit 21 of the MPU 20
, The received signal strength is determined, and the following speed and delay time of the adaptive filter 11 as described with reference to FIG. 1 are appropriately set based on the determination result.

The panel switch 30 is provided on the panel surface of the receiver, and is a switch for controlling ON / OFF of the operation of the adaptive filter 11 in the DSP 10. An ON / OFF instruction signal from this switch is output from the MPU 20. ON / OFF of the operation of the adaptive filter is controlled.

Thus, the output signal from the adaptive filter 11 of the adaptively controlled DSP 10 is output as a sound from the speaker SP.

FIG. 3 is a block diagram showing the configuration of another embodiment of the present invention. In this embodiment, a noise suppression filter for turning on / off the adaptive operation of the adaptive filter is formed. There is provided a changeover switch 7 for switching between supplying an error signal to be supplied to the adaptive filter 1 and supplying a zero-level signal to the adaptive filter 1.

In addition to the above-described embodiments, the present invention can be easily applied to an adaptive filter having a function of fixing the characteristics of the adaptive filter by setting the adaptive operation to ON when the received signal strength is strong and to OFF when the received signal strength is weak. In this case, ON / OF of the adaptive operation
By the synergistic effect with the effect by F, the deterioration of sound quality can be suppressed more stably, and the S / N improvement effect can be improved.

Also, an adaptive filter having a beat canceling function for canceling a beat (periodic signal) from an input signal (received signal) of the adaptive filter by adding a periodic signal with an opposite phase to the input signal of the adaptive filter. Is also applicable. In this case, by controlling the degree of beat cancellation, it is possible to reduce the suppression of vowels (influence of humans) of the voice, which is a quasi-periodic signal, and to suppress deterioration in sound quality after the beat is canceled.

In the above-described embodiment, when the signal received by the receiver is subjected to AGC and limiter processing as an input of the adaptive filter, a signal obtained by an S meter or RSSI can be used.

[0028]

As described above, according to the adaptive filter of the present invention, the noise suppression effect is enhanced when the noise suppression effect is desired, and the noise suppression effect is improved when the noise suppression effect is not desired. All functions of weakening and suppressing deterioration of the reception (communication) sound quality can be performed automatically. If a receiver having this function is used, it is only necessary to control ON / OFF of an adaptive filter for suppressing noise, and operability is significantly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an adaptive filter according to the present invention.

FIG. 2 is a block diagram showing another embodiment of the adaptive filter according to the present invention.

FIG. 3 is a block diagram showing still another embodiment of the adaptive filter according to the present invention.

[Explanation of symbols]

 Reference Signs List 1,11 Adaptive filter 2,20 MPU 3 Delay circuit 4 Multiplying circuit 5 Subtraction circuit 6 Receiving circuit 7 Changeover switch 10 DSP 12 Tracking speed / delay time setting circuit 21 Received signal strength judgment circuit 22 Adaptive filter ON / OFF judgment circuit 30 Panel Switch 40 RF circuit 50 Mixing circuit 60 Local oscillation circuit 70 IF circuit 80 Detection circuit

Claims (9)

[Claims] 1. An adaptive filter for suppressing a noise component included in an input signal, wherein a response characteristic of the adaptive filter is varied based on an input signal of the adaptive filter. 2. An adaptive filter for suppressing a noise component included in an input signal, wherein a response characteristic of the adaptive filter is varied based on an average value level of the input signal of the adaptive filter. 3. A response component is varied based on a difference signal between the output signal and an input signal and a delay signal obtained by delaying the input signal for a predetermined time to suppress a noise component included in the input signal. In the adaptive filter, when the input signal is high, the following speed of the adaptive filter is set to be slow, or the delay time is set short, and when the input signal is low, the following speed of the adaptive filter is set to be fast, or An adaptive filter characterized by setting a long time. 4. A response characteristic is varied based on a difference signal between the output signal and an input signal and a delay signal obtained by delaying the input signal for a predetermined time to suppress a noise component included in the input signal. In the adaptive filter, when the average value level of the input signal is high, the following speed of the adaptive filter is set to be slow or the delay time is set short, and when the average value level of the input signal is low, the following speed of the adaptive filter is low. An adaptive filter, wherein is set earlier or the delay time is set longer. 5. An adaptive filter for suppressing a noise component contained in an input signal, wherein a response characteristic of the adaptive filter is varied based on an S / N of an input signal of the adaptive filter. 6. The adaptive filter according to claim 1, further comprising control means for ON / OFF-controlling the operation of said adaptive filter. 7. The adaptive filter according to claim 1, wherein the input signal is a received signal received by an antenna, and an output from the adaptive filter is output as a sound from a speaker. 8. The adaptive filter according to claim 1, wherein the input signal is a signal obtained from an S meter or RSSI provided in a receiver, and an output from the adaptive filter is output as a sound from a speaker. 9. The adaptive filter according to claim 1, further comprising switch means for switching between the difference signal and the zero level signal and supplying the signal to the adaptive filter.