KR100935769B1 - Varied characteristic compansated active noise cancelling with feedback control - Google Patents

Varied characteristic compansated active noise cancelling with feedback control Download PDF

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KR100935769B1
KR100935769B1 KR1020080041321A KR20080041321A KR100935769B1 KR 100935769 B1 KR100935769 B1 KR 100935769B1 KR 1020080041321 A KR1020080041321 A KR 1020080041321A KR 20080041321 A KR20080041321 A KR 20080041321A KR 100935769 B1 KR100935769 B1 KR 100935769B1
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signal
noise
coefficient
microphone
output
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KR1020080041321A
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Korean (ko)
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KR20090115450A (en
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민훈
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소리젠 주식회사
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Priority to PCT/KR2009/002331 priority patent/WO2009134107A2/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/10—Earpieces; Attachments therefor ; Earphones; Monophonic headphones
    • H04R1/1083—Reduction of ambient noise
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R5/00—Stereophonic arrangements
    • H04R5/033—Headphones for stereophonic communication

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Headphones And Earphones (AREA)
  • Circuit For Audible Band Transducer (AREA)

Abstract

Disclosed are an apparatus and method for actively controlling noise transmitted from the outside in consideration of frequency characteristics of noise propagated in the air and noise propagated through vibrations in various media in various portable devices using earphones.

In the state where the earphone is plugged into the ear, unlike the noise propagated into the air, the frequency characteristic of the noise is shifted through the process of propagating as vibration through the bone and flesh of the earphone body and the human body. An adaptive filter is applied to generate a noise canceling signal to remove noise, and to offset the residual signal generated after outputting the noise canceling signal to the lowest audible sound pressure level through feedback control. .

The present invention is an ADC for converting the analog signal input from each of the microphone and the earphone unit consisting of a noise collecting microphone for collecting noise propagated into the air, a microphone for the residual signal and a speaker unit DAC, which converts digital signal to analog signal for output to speaker unit, inverts phase of input noise signal by 180 ° and reduces variation characteristic correction filter and input residual signal which compensates for the variation of frequency characteristics. An adaptive signal processing unit and an amplifier for amplifying and outputting at an appropriate volume.

Active noise control, feedback control, frequency characteristic compensation, adaptive filter

Description

{Varied characteristic compansated active noise canceling with feedback control}

Electronics, Software Engineering, Acoustics, Voice Signal Processing

Speech signal processing, digital signal processing, digital filter algorithms, circuit technology, software engineering, acoustic engineering

The noise from the noise source is transmitted to the vibration of the air and vibrates the eardrum in the human ear so that the sound can be heard.

Active noise control technology researched and developed to date is based on the principle of canceling the original noise by inverting the phase of the noise propagating into the air by 180 ° and superimposing it with the original noise.

However, when the earphone is plugged in, the noise propagated into the air hits the earphone body and the bones and flesh of the human body. Some components of the noise are reflected or diffracted and disappear into the air. Some other components of the noise disappear from the earphone body and the human body. Absorbed or penetrated bones and flesh.

That is, the noise that vibrates the eardrum in the ear canal while the propagation path of noise propagated into the air is propagated through the vibrations of the earphone body and the bones and flesh of the human body. Unlike the noise, it is mutated and heard.

Therefore, in the present invention, it is possible to effectively cancel the noise by reflecting the frequency characteristic that is shifted to the original noise signal, and by inverting its phase by 180 ° to overlap the noise signal in the ear canal.

In reality, however, the superposition of the original noise signal and the noise canceling signal does not completely cancel the original noise signal, leaving a residual signal, and this residual signal also serves as a new noise source.

Therefore, the present invention can effectively cancel the noise by applying the adaptive filter to optimize the noise canceling signal to collect the residual signal to lower than the lowest audible sound pressure level that can not be heard by human hearing.

According to the present invention, the external noise is effectively canceled when listening to various portable devices using earphones or headphones, so only the audio signal to be listened to can be reproduced and listened to, and it is not necessary to listen at high volume in response to external noise. It can prevent noise-induced hearing loss and can listen to the portable device without increasing the volume, thereby reducing the power consumption of the portable device.

In addition, in a state where only external noise is canceled without listening to an audio signal, concentration of work and learning may be improved without being affected by the surrounding noise environment.

As shown in FIG. 1, the apparatus for implementing the present invention includes the earphone unit 100 and the circuit unit 200.

The earphone unit 100 includes a first microphone 110 that picks up noise Na (t) propagated into the air and a noise signal Na '(t) whose phase, amplitude, delay, frequency characteristics, etc. are changed during transmission from the outside. And a second microphone 120 for collecting a signal added with the sum signal O (t) output from the speaker unit 130 in the ear canal, and a speaker unit 130 for outputting the sum signal.

As shown in FIG. 2, the first microphone 110 is disposed in a direction opposite to the speaker unit 130 so as to be suitable for picking up noise transmitted from the surroundings, and the second microphone 120 is arranged as a speaker unit ( Located in front of the 130 is disposed in a form suitable for collecting the sum signal O (t) output from the speaker unit 130 and the noise signal Na '(t) transmitted from the outside into the ear canal.

At this time, in order to minimize the sum signal O (t) output from the speaker unit 130 affecting the input of the first microphone 110, air flow is provided between the speaker unit 130 and the first microphone 110. The blocking wall 150 is installed to block the sum signal O (t) output from the speaker unit 130 to prevent propagation to the first microphone 110 through air.

In addition, the vibration is reduced to minimize the signal transmitted to the first microphone 110 by the vibration generated by the summation signal O (t) output from the speaker unit 130 through the earphone body 140 and the blocking wall 150. It is to isolate the first microphone 110 with a damping material (吸 振 材) or a suction module (160).

In addition, the sound absorbing material or sound absorbing module 170 for blocking non-voice signals such as wind and contact incident from the outside has a structure that surrounds the first microphone 110 on the outside of the earphone body 140.

As shown in FIG. 6, when observing the frequency spectrum in each frequency band, the noise signal Na (t) propagated into the air and the noise signal Na '(t) in the ear canal according to the degree of wearing of the earphone have different frequency characteristics. It can be seen that.

That is, the noise signal Na '(t) propagated by vibration through the earphone body 140 and human bones and flesh has a low amplitude in the low frequency band and a small amplitude in the high frequency band compared to the noise signal Na (t) propagated in the air. Losing character.

In addition, as shown in FIG. 6, when the frequency spectrum envelope is compared in each case, the amplitude of the low frequency and high frequency bands is different depending on the degree of wearing of the earphone when the earphone is loosely worn and when the earphone is worn in close contact. You can see that it appears.

7 to 13 illustrate the frequency spectrum of the measured original sound and the frequency spectrum of each case of detaching the earphone.

As shown in FIG. 1, the noise signal Na (t) propagated into the air collected by the first microphone 110 is input to the first filter 210.

The first filter 210 passes only signals in a band where the energy of the noise signal Na (t) is concentrated among the audible frequency bands ranging from 20 Hz to 20 KHz.

The noise signal filtered by the first filter 210 is a digital signal Na (e.g., a digital signal Na (easy to process the signal in a digital system) through a first analog-to-digital converter (ADC) 220 that converts an analog signal into a digital signal. n) is input to the variation characteristic correction filter 230.

The second microphone 120 has a variation in phase, delay, amplitude, frequency characteristics, etc. in the process where external noise Na (t) generated from the outside is transmitted to the vibration through the medium such as the earphone body 140 and human bones and flesh. The noise signal Na '(t) and the summation signal O (n) output from the speaker unit 130 are added in the ear canal, a limited space from the auricle to the eardrum, as shown in FIG. Diffraction, reflection, resonance, superposition, and the like generated by the characteristic H ear (t) and the signal Nm (t) mutated by the characteristic H SPK (t) of the speaker unit 130 are collected and the second filter ( 240).

In the analog system, this is expressed as a formula based on the time axis.

Nm (t) = [O (t) * H SPK (t) + Na '(t)] * H ear (t)

H ear (t) is the acoustic transfer function in the ear canal

H SPK (t) is the transfer function of the speaker unit

Na '(t) is the mutated noise signal in the analog domain

The second filter 240 is a digital system through a second ADC 250 for converting the analog signal of the audible frequency band passed through the other signals except the audible frequency band from 20 Hz to 20 KHz into a digital signal. The signal is converted into a digital signal Nm (n) that is easily processed and input to the adaptive signal processor 260.

The shift characteristic correction filter 230 receives information such as phase difference, delay level, amplitude variation, frequency characteristic, etc. from the shifted noise signal Na '(n) from the adaptive signal processor 260 and propagates into the air. The phase and delay, amplitude and frequency characteristics of n) are corrected and the feedback control generates an anti-noise signal O 1 (n).

As shown in FIG. 3, the shift characteristic correction filter 230 collects through the first microphone 110 by applying the phase coefficient Pm (n) provided from the adaptive signal processor 260 to the phase correction unit 231. The phase of Na (n) is corrected by correcting the phase of the external noise signal Na (n) propagated into the air and applying the delay coefficient Dm (n), which is also provided from the adaptive signal processor 260, to the delay compensator 232. Compensating for the delay of the signal corrected by the signal, and applying the amplitude coefficient Am (n) provided from the adaptive signal processor 260 to the amplitude corrector 233 to adjust the phase and delay of Na (n). The amplitude is corrected, and the frequency spectrum coefficient Fm (n) provided from the adaptive signal processor 260 is also applied to the band pass filter bank 234 and the amplifier 235 for each band so that the phase of Na (n) and Delay and amplitude corrected signals may have different amplitudes for each frequency band. Processing phase and delay and the amplitude and the frequency characteristic is the phase of the corrected signal 180 ° turn in which the noise cancellation signal O 1 generates and outputs a (n) of Na (n) is added, and all in an adder 236, these signals do.

The noise cancellation signal Na (n) propagated into the air and the noise cancellation signal O 1 (n) generated through the variation characteristic correction filter 230 have the following relationship.

O 1 (n) = Na (n) * H PDAF (n)

H PDAF (n) is the transfer function of the mutation characteristic correction filter

The signal Nm (n) collected by the second microphone 120 is characterized by the speaker unit 130 after adding the distorted external noise Na '(n) and the sum signal O (n) output from the speaker unit 130. Acoustical characteristics of H SPK (n) and ear canal are mutated by H ear (n).

In the digital system, this is expressed as an equation.

Nm (n) = [O (n) * H SPK (n) + Na '(n)] * H ear (n)

H ear (n) is the acoustic transfer function in the ear canal

H SPK (n) is the transfer function of the speaker unit

Na '(n) is the mutated noise signal in the digital domain

The speaker unit 130 applies the noise canceling signal O 1 (n) generated by the shift characteristic correction filter 230 to the adaptive filter 265 and the optimized noise canceling signal O 2 (n) and the audio signal s generated by the adaptive filter 265. The signal O (n) obtained by adding the (n) is output, and in the ear canal, a sound shifted by the transfer function H SPK (n) according to the characteristics of the speaker unit 130 is heard.

If this is expressed in parallel with the above equation is as follows.

O (n) = O 2 (n) + s (n)

Nm (n) = [O (n) * H SPK (n) + Na '(n)] * H ear (n)

= {[O 2 (n) + s (n)] * H SPK (n) + Na '(n)} * H ear (n)

As shown in FIG. 4, in the signal Nm (n) input to the adaptive signal processor 260, s (n) is adjusted by the amplifier 2661 to an appropriate value and subtracted through the subtractor 2660. In the subtracted signal, the amplifier 2665 outputs a signal that is time-advanced or delay compensated by the time preceding / delay section 266 by the optimized noise canceling signal O 2 (n) passing through the adaptive filter 265. After adjusting the volume, the signal subtracted through the subtractor 2664 finally cancels the desired noise and becomes the remaining residual signal e (n).

If this is expressed as an expression, it is as follows.

e (n) = Nm (n)-A 1 * s (n)-A 2 * O 2 (n) * H T (n)

A 1 and A 2 are the amplification degrees of each amplifier

H T (n) is the time leading / delay function of O 2 (n)

The adaptive filter 265 cancels the noise from the noise canceling signal O 1 (n) received from the variation characteristic correction filter 230 and the lowest audible sound pressure level at which a human cannot hear the remaining signal e (n) (healthy person). As the smallest sound that can be heard, it produces an optimized noise canceling signal O 2 (n) for minimization below 2 x 10 -5 N / m 2 or 10 -6 W / Cm 2 ) for 1 KHz pure sound.

To this end, Linear Feedback Control or Linear Feedforward Contel is adapted to minimize the residual signal e (n) by applying LMS (Least Mean Square) algorithm or various algorithms that have been improved or modified. ).

This allows the generation of noise canceling signals O 2 (n) optimized to attenuate the noise heard in the ear canal, ie the residual signal e (n) below the lowest audible sound pressure level inaudible to humans.

The optimized noise canceling signal O 2 (n) is expressed by the following equation.

O 2 (n) = O 1 (n) * H AP (n) + e (n)

H AP (n) is the transfer function of the adaptive filter

Assuming s (n) is '0', O (n) is equal to O 2 (n).

Under the above assumption, the process of adding various signals in the ear canal is as follows.

Nm (n) = [O 2 (n) * H SPK (n) + Na '(n)] * H ear (n) = e (n)

= {[O 1 (n) * H AP (n) + e (n)] * H SPK (n) + Na '(n)} * H ear (n) = e (n)

Here, to simplify the equation, assuming that each of the transfer functions H AP (n), H SPK (n), and H ear (n) are all '1', the equation can be expressed as follows.

e (n) = [O 1 (n) + e (n)] + Na '(n)

e (n)-e (n) = 0 = O 1 (n) + Na '(n)

That is, as can be seen in the above equation, it can be seen that the noise canceling signal O 1 (n) and the mutated noise signal Na (n) are added to be '0'.

However, in reality, e (n) does not become '0' by the transfer function H SPK (n) of the speaker unit 130 and the transfer function H ear (n) according to the acoustic characteristics of the ear canal.

For this reason, the transfer function H AP (n) of the adaptive filter 265 is left by the transfer function H SPK (n) of the speaker unit 130 and the transfer function H ear (n) according to the acoustic characteristics of the ear canal. It should be set such that the residual signal e (n) becomes '0'.

In addition, since the mutated noise signal Na '(n) continuously changes with time, the residual signal e (n) directly affected by this also changes continuously with time, so that the adaptive filter 265 continues with time. The noise canceling signal O 2 (n), which is optimized so that the changing residual signal e (n) is equal to '0' or below the lowest audible sound pressure level, must also be continuously generated over time, and the transfer function of the adaptive filter 265 H AP (n) should be made so that an optimized noise canceling signal O 2 (n) can be generated by adapting to the change of the residual signal e (n).

In the adaptive signal processor 260, the phase coefficient Pm (n) for correcting the phase, delay, amplitude, and frequency characteristics of the noise canceling signal O 1 (n) so that the variation characteristic correction filter 230 can perform feedback control. , Delay coefficient Dm (n), amplitude coefficient Am (n), frequency characteristic coefficient Fm (n) and the like are generated and provided to the variation characteristic correction filter 230.

For this purpose, if the amplification degree of the amplifier 2661 for the audio signal s (n) and the amplifier 2665 for the noise canceling signal O 2 (n) is set to '0', the subtractor 2660 and the noise for the audio signal s (n) The residual signal e (n) output through the subtractor 2664 for the cancellation signal O 2 (n) becomes equal to Nm (n).

If this is expressed as an expression, it is as follows.

e (n) = Nm (n)-0 * s (n)-0 * O 2 (n) * H T (n) = Nm (n)

The phase coefficient Pm (n) is calculated from the residual signal e (n) through the phase difference detector 261, and the delay coefficient Dm (n) is calculated through the delay coefficient detector 262.

In addition, the amplitude variation amount Am (n) of the specified section is calculated through the section amplitude variation detection unit 263, and the spectrum Fm (n) for each frequency band, which is a frequency characteristic coefficient, is calculated by the frequency spectrum analyzer 264 for each band. do.

The optimized noise canceling signal O 2 (n) and the audio signal s (n) output from the adaptive signal processor 260 are added by the adder 270 to generate a sum signal O (n).

The sum signal O (n) thus made is converted into an analog signal through a digital to analog converter (DAC) 280 that converts a digital signal into an analog signal, and thus the amplification degree is adjusted in the termination amplifier 290 to the speaker unit 130. Is output.

Looking at the summation signal O (n) in the ear canal and Nm (n) collected by the second microphone in an environment where there is no noise, the following relationship is observed.

Nm (n) = O (n) * H ear (n) * H SPK (n)

In the presence of noise, the sum signal O (n) in the ear canal and the residual noise signal Nm (n) overlap and the remaining signal e (n) remains as follows.

e (n) = Nm (n) + Na '(n)

= [O (n) * H ear (n) * H SPK (n)] + Na '(n)

The present invention is not limited to the above-described embodiment, and of course, modifications may be made by those skilled in the art within the spirit of the present invention.

The present invention can also be embodied as computer readable codes on a computer readable recording medium, and the computer readable recording medium is any type in which data that can be read by a computer system is stored. Recording device.

Examples of computer-readable recording media include ROM, RAM, flash memory, CD-ROM, magnetic tape, hard disk, floppy disk, optical data storage device, USB bus-based disk, and the like. For example, it is implemented in the form of transmission over the Internet).

The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

In addition, the present invention can be implemented as a digital or analog circuit, including the integrated implementation as any type of logic circuit including a semiconductor chip, code that can be read by a microprocessor, a microcontroller, a digital signal processing processor, etc. It is stored and implemented as.

1 is a block diagram of a system according to the present invention.

2 is a block diagram of an earphone unit according to the present invention.

3 is a detailed block diagram of the variation characteristic correction filter of FIG. 1.

4 is a detailed block diagram of the adaptive signal processor of FIG. 1.

5 is a flowchart illustrating a frequency characteristic compensation type active noise cancellation method having a feedback characteristic according to the present invention.

6 is a view comparing the envelope of the frequency spectrum according to the detached state of the measurement sound source and the earphone.

7 is a diagram showing a frequency spectrum of a measurement sound source.

8 is a diagram showing a frequency spectrum of a measurement sound source measured in the ear canal without the earphone.

FIG. 9 is a combined view for comparing the drawing of FIG. 7 with the drawing of FIG. 8.

10 is a diagram showing the frequency spectrum of the measurement sound source measured in the ear canal with the earphones loosely worn.

FIG. 11 is a diagram summarizing to compare the drawing of FIG. 7 and the drawing of FIG. 10.

FIG. 12 is a diagram showing a frequency spectrum of a measurement sound source measured in the ear canal with the earphone fully worn.

FIG. 13 is a diagram summarizing to compare the drawing of FIG. 7 and the drawing of FIG. 12.

14 is a view showing the structure of the human ear. (Source encyber.com)

Claims (7)

In the active noise control method, Generating a noise canceling signal of a reverse phase in which noise signals propagated into the air are corrected by reflecting characteristics shifted due to phase difference, delay, amplitude variation, and frequency characteristic variation in the ear canal; Generating a noise canceling signal optimized to adapt to the minimization of the residual signal in order to minimize the residual signal remaining after the noise cancelation with the generated noise canceling signal below a minimum audible sound pressure level; Adding the generated optimized noise canceling signal to an audio signal; And outputting the added signal to the speaker unit to remove the distorted noise signal in the ear canal by the optimized noise canceling signal output to the speaker unit. The method of claim 1, Outputting an optimized noise canceling signal added to the audio signal to a speaker unit; Canceling the mutated noise signal in the ear canal and collecting the remaining sound with the output optimized noise canceling signal; Detecting noise of the sound signals collected in the ear canal and separating the remaining signals from other signals; Calculating a phase coefficient, a delay coefficient, an interval amplitude variation coefficient, and a frequency characteristic coefficient for each band from the separated residual signal; Active noise control method, characterized in that for generating a noise canceling signal of the reverse phase by reflecting the characteristic of the noise signal mutated by the various characteristic coefficients calculated. The method of claim 1, And a feedback control for reflecting the shifted characteristic of the noise signal displaced from the noise signal propagated into the air collected by the ear canal in the generation of the noise canceling signal having the reverse phase characteristic. In an active noise control device, An earphone unit including a first microphone for collecting noise signals propagated into the air, a second microphone for collecting sound signals in the ear canal, and a speaker unit for outputting sound signals; A first filter for extracting only a signal of a desired band among noise signals propagated into the air output from the first microphone of the earphone unit and a first ADC for converting the extracted analog signal into a digital signal; A second filter for extracting only an audio frequency signal from an acoustic signal output from the second microphone of the earphone unit and a second ADC for converting the extracted analog signal into a digital signal; Compute and output the phase coefficient, delay coefficient, interval amplitude variation coefficient and band-specific frequency characteristic coefficient of the mutated noise signal from the signal output from the second ADC, and separate the residual signal from the signal output from the second ADC An adaptive signal processor for detecting and outputting an optimized noise canceling signal in response to the residual signal; The adaptive signal processor is provided with a phase coefficient, a delay coefficient, an interval amplitude variation coefficient, and a frequency characteristic coefficient for each band to correct the characteristics of the noise signal propagated into the air, thereby generating a noise cancellation signal having a reverse phase. Variation characteristic correction filter; And an amplifier for amplifying the converted signal and a DAC for adding the optimized noise canceling signal and the audio signal output from the adaptive signal processor and converting the same to an analog signal. The filter of claim 4, wherein the variation characteristic correction filter A phase correction unit for correcting a phase difference of a noise signal propagated into the air by using a phase coefficient provided from the adaptive signal processor; A delay compensator for compensating for the delay of the signal output from the phase corrector with a delay coefficient provided from the adaptive signal processor; An amplitude correction unit for correcting the amplitude of the signal output from the delay compensation unit by the section amplitude variation coefficient provided from the adaptive signal processor; The band-pass filter bank for correcting the frequency characteristics of each band of the signal output from the amplitude correction unit with the band-specific frequency characteristic coefficients provided by the adaptive signal processor, adds all the outputs of the amplification stage and each band amplifying stage And an adder for outputting. The method of claim 4, wherein the adaptive signal processor A residual signal detector comprising an amplifier, a time advance / delay unit, and a subtractor for separating and detecting the residual signal from the signal collected from the second microphone of the earphone unit; A phase difference detector for calculating a phase coefficient of the residual signal output from the residual signal detector; A delay coefficient detector for calculating a delay coefficient of the residual signal output from the residual signal detector; An interval amplitude variation detector for calculating an interval amplitude variation coefficient of the residual signal output from the residual signal detector; A band-specific frequency spectrum analyzer for calculating band-specific frequency characteristic coefficients of the residual signal output from the residual signal detector; And an adaptive filter for optimizing the noise canceling signal output from the variance characteristic correction filter in order to minimize the residual signal output from the residual signal detection unit below a minimum audible sound pressure level. Active noise control device. The method of claim 4, wherein the earphone unit A blocking wall which blocks the sound output from the speaker unit from being transmitted to the first microphone using air in the earphone unit as a medium; A dust absorbing material or a dust absorbing module for blocking the sound output from the speaker unit from being transmitted to the first microphone by vibration using the earphone body and the blocking wall as a medium; Active sound control device comprising a sound absorbing material or a sound absorbing module for reducing the impact of the non-speech signal due to wind, contact from the outside affects the first microphone.
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PCT/KR2009/002331 WO2009134107A2 (en) 2008-05-02 2009-05-01 Noise cancelling apparatus

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