EP1074970A2 - Digitales vorwärtsgeregeltes System für aktive Lärmkontrolle - Google Patents

Digitales vorwärtsgeregeltes System für aktive Lärmkontrolle Download PDF

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Publication number
EP1074970A2
EP1074970A2 EP00122367A EP00122367A EP1074970A2 EP 1074970 A2 EP1074970 A2 EP 1074970A2 EP 00122367 A EP00122367 A EP 00122367A EP 00122367 A EP00122367 A EP 00122367A EP 1074970 A2 EP1074970 A2 EP 1074970A2
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EP
European Patent Office
Prior art keywords
signal
error
antinoise
acoustic
gains
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Granted
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EP00122367A
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English (en)
French (fr)
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EP1074970B1 (de
EP1074970A3 (de
Inventor
Anthony J. Brammer
Jianhua Pan
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National Research Council of Canada
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National Research Council of Canada
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Priority claimed from EP96920661A external-priority patent/EP0836736B1/de
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Publication of EP1074970A3 publication Critical patent/EP1074970A3/de
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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17821—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the input signals only
    • G10K11/17825—Error signals
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17813—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms
    • G10K11/17817—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms between the output signals and the error signals, i.e. secondary path
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17821—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the input signals only
    • G10K11/17823—Reference signals, e.g. ambient acoustic environment
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1785—Methods, e.g. algorithms; Devices
    • G10K11/17853—Methods, e.g. algorithms; Devices of the filter
    • G10K11/17854—Methods, e.g. algorithms; Devices of the filter the filter being an adaptive filter
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1785—Methods, e.g. algorithms; Devices
    • G10K11/17855—Methods, e.g. algorithms; Devices for improving speed or power requirements
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1785—Methods, e.g. algorithms; Devices
    • G10K11/17857—Geometric disposition, e.g. placement of microphones
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1787—General system configurations
    • G10K11/17879—General system configurations using both a reference signal and an error signal
    • G10K11/17881—General system configurations using both a reference signal and an error signal the reference signal being an acoustic signal, e.g. recorded with a microphone
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/10—Applications
    • G10K2210/108—Communication systems, e.g. where useful sound is kept and noise is cancelled
    • G10K2210/1081—Earphones, e.g. for telephones, ear protectors or headsets
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3027—Feedforward
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3053—Speeding up computation or convergence, or decreasing the computational load
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/321—Physical
    • G10K2210/3213—Automatic gain control [AGC]

Definitions

  • This invention relates to the field of sound controllers, and in particular to an adaptive feedforward active noise control method.
  • Noise control and particularly active noise reduction, has been an objective for many years, particularly to reduce the ambient noise in airplanes or in industrial environments.
  • Such systems have generally utilized feeding a canceling sound (referred to as antinoise hereinafter) in inverse phase to a sound that is to be reduced or eliminated.
  • Systems have been designed which are comprised of open loop control systems or closed loop control systems, analog or digital, the antinoise being applied in a feedback or in a feedforward system.
  • the performance of the device is influenced by changes in coupling of the ambient noise to the ear (e.g., by changes in the fit of the device, by head movement), by relative movements of the components, and by the stability of the electronic components. Moreover it operates using vacuum tubes, and so cannot be practically operated on batteries. Further, due to its size, it is not portable.
  • FIG. 1 A simplified view of such a system is shown in Figure 1.
  • a sound u k which is to be controlled passes along a duct 1, and is detected by a microphone 3 from which the signal is passed to a control system 5.
  • An electroacoustic transducer 7 is located downstream of the microphone 3, which injects sound into the pipe, in accordance with a control signal applied by control system 5, e.g., in intensity, frequency and phase such as to cancel the sound u k , resulting in the sound ur k , which desirably can be null.
  • a microphone 9 in the duct downstream from the transducer 7 closes the loop by detecting any residual sound following the cancellation, and returns an error signal to the control system 5, which responds by modifying the control signal applied to transducer 7 so as to minimize urk detected at microphone 9.
  • control system 5 operating in the digital mode, has a limitation in speed based on the inherent operating speed of its processor and due to the sampling rate of the primary signal from microphone 3, the error signal from microphone 9 and the control signal provided to the electroacoustic transducer 7. Consequently in practical systems this approach has been limited to applications, wherein the microphone can be placed far upstream of transducer 7, in order to be able to sample the arriving signal as early as possible and thus compensate for the inherent time delay within a digital system.
  • this system has not been able to be adapted to the control of random noise entering an earcup without substantial loss in peformance, since microphone 3 is required to be close to the outside boundary of the earcup, and therefore there is insufficient processing time available for the control system to properly control the sound in the earcup.
  • Embodiments of the present invention provide means and methods for utilizing a feedforward digital control system in applications in which the difference in time of arrival of sound at microphones 3 and 9 is small, such as an earcup sound control apparatus, with substantial sound control.
  • Key aspects of the invention substantially overcome the inherent time delay within the control system and reduce the processing load of the control system, thus allowing it to generate a practical anti-noise control signal for an earcup type system.
  • FIG. 2 an earcup type of sound control system is shown.
  • a sound attenuating earcup 11 is fitted over the ear 13 of a user, and seals to the skin of the user.
  • a reference microphone 15 is located just outside of the earcup, e.g. on an axis with the ear canal 17 of the user.
  • An electroacoustic transducer (earphone 19) is located within the volume between the earcup 11 and the ear 13, also preferably on the axis with the ear canal and microphone 15.
  • An error microphone 21 is also located in the volume between the earcup 11 and the ear 13, also preferably on the aforenoted axis.
  • the microphone 15 corresponds to microphone 3 in Figure 1
  • the earphone 19 corresponds to the transducer . 7 of Figure 1
  • the microphone 21 corresponds to the microphone 9 of Figure 1.
  • the earcup structure which typically may be in the form of ear protectors/earphones of a helicopter pilot
  • the microphones 15 and 21 are very close to the earphone 19, allowing little processing time in the control system due to the very short time that it takes for sound to traverse these short distances, and it being not practical to move microphone 15 a significant distance from the earcup.
  • Figure 4 illustrates an embodiment of the present invention.
  • a transmission path formed by the earcup and cushion against the skin, and air leaks around the cushion, is represented by H p .
  • Figure 3 shows an air conduction path.
  • H 2 and H 3 have corresponding transfer function blocks in Figure 3, while the transfer function H 1 in Figure 4 has corresponding element ⁇ in Figure 3.
  • the signal derived from H 1 ( ⁇ ) is applied to an adaptive FIR filter W, which applies an antinoise signal via transfer function H 2 to a summer ⁇ , to which the acoustic signal to be controlled is also applied.
  • the summer is actually the cavity in front of and in the region of the transducer 7 within the duct 1, while in the system of Figure 4, the summer is the region within the cup 11 particularly between the earphone 19 and the ear canal 17.
  • the antinoise signal from H 2 output from FIR filter W passing via transfer functions H 2 (and H a in Figure 4), is added to the acoustic signal so as to cancel it.
  • control system WF Figure 3
  • control system LMS Figure 4
  • These control systems obtain the error signal from transfer function H 3 , represented by E in Figure 4 and ⁇ k in Figure 3, as well as a reference signal R ( Figure 4) or v k ( Figure 3).
  • This reference signal is derived by a modification of the sampled reference signal from microphone 3 ( Figure 1), using transfer function H 4 in Figure 3, which forms an error model of the system.
  • the error model in the prior art system ( Figure 3) is derived from continuous sampling of the system signals, and is a characteristic of the system.
  • the control system WF after an error model has been determined, varies the coefficients of the adaptive FIR filter W so as to cause an output signal to be applied to the summer to control the sound which is detected at the error microphone 9.
  • FIG. 5A A representation of the error path impulse response model of the prior art system of Figure 3 is illustrated in Figure 5A, wherein each dot on the graph represents a ditferent sampling time (the horizontal axis representing the time sequence of consecutive samples).
  • the impulse response model H e is synthesized so that it eliminates the need for system identification.
  • a synthesized error-path impulse response model used for H e instead of a synthesized error-path impulse response model used for H e , a truncated measured impulse response model, or a truncated synthesized impulse response model could be used.
  • the outputs X and E of the microphones 15 and 21 respectively are applied to low pass filters 23A and 23B respectively, in which the bandwidth is limited to low frequencies, which are the frequencies most likely to penetrate the ear cup.
  • the outputs of the filters are applied to A/D converters 25A and 25B respectively, in which the analog signals are converted to digital signals.
  • the output signals of A/D converters 25A and 25B are subjected to an interface delay 27A and 27B, and from the interface delays the signals are filtered in decimation filters 29A and 29B.
  • the interface delays 27A, 27B and 39 are dependent on the hardware implementations of the active noise control system, which is taken to include any phase delay in the low pass filters 23A, 23B and 43, and is commonly related to the sampling time interval.
  • the filtered signal from the reference microphone is then applied to error path FIR filter 31 and to controller FIR 33, while the filtered signal from the error microphone is applied to LMS control filter adapter 35.
  • Error path FIR filter 31 corresponds to and provides the transfer function H e in Figure 4
  • LMS adapter 35 corresponds to the LMS adapter in Figure 4.
  • Controller FIR 33 in Figure 7 corresponds to FIR filter W in Figure 4, which in a successful embodiment was a 200 tap FIR filter, controlled by LMS adapter 35.
  • the output signal of filter 33 is applied to an interpolation filter 37, after which the signal is subjected to an interface delay 39.
  • the signal is then converted to analog form in D/A converter 41, and the resulting analog signal is applied to low pass filter and earphone driver 43.
  • the canceling or otherwise acoustic modifying signal from driver 43 is applied to earphone 19.
  • decimation and interpolation filters should all be implemented in a digital signal processor, such as 32 bit floating point type TMS320C31 manufactured by Texas Instruments Inc., illustrated in Figure 7 as block 45 contained within the dashed line.
  • the synthesized simplified error path impulse response model is implemented in error path FIR 31, to provide a filtered signal to the adapter 35.
  • the LMS controller algorithm can follow what is described in the aforenoted article by Burgess or algorithms for feedforward control described in "Active Noise Control:Algorithms and DSP Implementations" by S.M. Kuo and D.R. Morgan, Wiley, New York, 1996.
  • the signals from either or both of the microphones should be digitally oversampled.
  • FIG 8 illustrates timing, using the oversampling and decimation filters 29A and 29B.
  • the signal in the top graph shows sampling intervals, t IO , of the A/D converters 25A and 25B.
  • the frequency of sampling is at the oversampling rate described above.
  • the resulting digital signal is received by the digital signal processor 45, as illustrated in the second row of Figure 8. It has been found that not all of the sampled data need be processed; the input data from time spaced samples can be processed, and the second row of Figure 8 illustrates every fourth sample being processed.
  • the third row in Figure 8 illustrates that the processing time for each sample passed to the DSP 45 is less than one sampling interval at the control system sampling rate, t CTRL .
  • t CTRL control system sampling rate
  • the correction (antinoise) signal for the earphone 19 is passed to the D/A converter.
  • the same digital correction signal is applied to the earphone at the oversampled rate until the correction signal changes at which time a changed correction signal (e.g., corresponding to the fifth, or ninth, oversampled reference input signal) will be applied to the earphone.
  • the total time delay between sampling the input signal and the production of the correction signal may be seen to be only two oversampling delay time intervals t IO , which is a substantial decrease from the time if the oversampling and decimation method is not used.
  • the oversampling frequency was 40 kHz
  • the control frequency that is, resulting from the processing of a fraction of the oversampled samples, was 10 kHz (i.e., every fourth sample was processed).
  • the noise bandwidth was 150-800 Hz.
  • the error and/or reference and/or control signals can be filtered by means of electrical, acoustical and/or electroacoustic filters, as part of transfer functions H 3 , H 1 and H 2 .
  • a filter is illustrated in Figure 4 as filter 47 in the error signal path, and it is preferred to be a low order analog filter (i.e. a filter with amplitude changing with frequency of no more than 12 db/octave), for example the high pass filter shown in Figure 9.
  • the example electrical filter 47 shown is comprised of a pair of capacitors in series with one conductor and resistors connected across the pair of conductors between the capacitors and across the input and output. Electrical and acoustical filters of this type are well known and their operation need not be described further herein.
  • Filter 47 acts to reduce the system response at frequencies at which noise reduction is not required. Band limiting can result in improved noise reduction performance at frequencies at which control is required, reduced power and performance requirements of the secondary acoustic source (earphone 19), and consequent simplification of hardware.
  • Filter 47 and filters 23A, 23B and 23C permit spectrum shaping of the reference and/or error signals to satisfy predetermined performance requirements, such as psychoacoustic detection criteria or physiological injury criteria.
  • the low pass filters 23A, 23B and 43 may be replaced by low-order acoustical or electrical filters to simplify further the device.
  • An example of a low-order, low-pass acoustical filter applied to the earphone 19 within an earcup is shown in Figure 10, as cavity 49 containing exit port 50 (e.g. a small tube) in front of the ear channel 17, coupled to loudspeaker 51 or the equivalent contained in a loudspeaker enclosure 52 via a larger diameter tube 53, being similar in diameter to the active surface of the loudspeaker (the microphones 15 and 21 not being illustrated).
  • exit port 50 e.g. a small tube
  • This can be realized by specialized electronic circuits that simultaneously adjust the electronic amplification of signals X, U and E such that the product of the electronic amplification of signals E and U remains constant, or the product of the electronic amplification of signals E and U, and the ratio X/E remain constant.
  • variable fixed-ratio gain amplifiers 49 can be inserted between the low pass filters 23A and/or 23B, and the following A/D converters 25A and/or 25B respectively, and a variable reciprocal gain amplifier between D/A converter 41 and low pass filter/driver 43.
  • the dashed lines represent a bypass of the straight through conduction path otherwise shown to accommodate amplifiers 49.
  • a similar structure is inserted in the other conduction paths as noted above.
  • a variable, reciprocal gain and fixed-ratio gain arrangement can be made by means of linear amplifiers having automatic gain control signal paths, as for example channels 1, 2 and 3 illustrated in Figure 11.
  • the circuit can be implemented as shown in Figure 11 by matched field effect transistors (FETs) 60 and 61 having their source drain circuits respectively connected between ground and, for FET 60, the noninverting input of operational amplifier 62, and for FET 61, the inverting input of operational amplifier 63.
  • FETs field effect transistors
  • the inverting input of amplifier 62 is connected to its output and the non-inverting input of amplifier 63 is connected to the output through a resistor 65, which has a value R.
  • the gate of FET 60 is connected to a gain control input 67 via resistor 69, and to its source and drain via resistors 71 and 72.
  • the gate of FET 61 is connected to gain control input 67 via resistor 74 and to-its source and drain via resistors 76 and 77.
  • the noninverting input of amplifier 62 is connected to input terminal 78, called channel 1, carrying the U-signal, via resistor 79, which has similar value as resistor 65.
  • Terminal 78 is connected to ground via a resistor 80.
  • the noninverting input of amplifier 63 is connected to an input terminal 81, called channel 2, carrying the E signal, and to ground via resistor 83.
  • Output terminals 85 and 87 carry the output signals of channels 1 and 2 respectively.
  • the amplifier circuit for channel 3, carrying the X signal is similar to that of channel 2, except for the value of the feedback resistor around the operational amplifier.
  • An FET 89 which is matched to FETs 60 and 61 has its source-drain circuit connected between ground and the inverting input of an operational amplifier 91.
  • the gate of FET 89 is connected via register 93 to gain control input 67, and to its source and drain via resistors 95 and 96.
  • Feedback resistor 98 which has a value R', is connected between the output of amplifier 91 and its inverting input.
  • the input 100 for channel 3, carrying the signal X, is connected to the non-inverting input of amplifier 91, and to ground through resistor 102.
  • the output of the amplifier 91 is connected to output terminal 104.
  • Variable gain is provided by matched FETs to obtain the same value of r ds .
  • G 3 (1+ R '/ r DS )
  • a laboratory prototype of the above-described invention has also demonstrated that it adapts to new conditions, such as when the seal between the cushion of the earcup is broken, as could occur when the user turns his head.
  • the frequency response of the synthesized error path model with impulse response shown in Figure 5B is given by the solid line in Figure 12.
  • a measured error path frequency response for the same device when the earcup is poorly sealed to the head is shown by the dashed line in Figure 12.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)
EP00122367A 1995-07-03 1996-07-02 Digitales vorwärtsgeregeltes System für aktive Lärmkontrolle Expired - Lifetime EP1074970B1 (de)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US83495P 1995-07-03 1995-07-03
US834P 1995-07-03
EP96920661A EP0836736B1 (de) 1995-07-03 1996-07-02 Digitales vorwärtsgeregeltes system für aktive lärmkontrolle

Related Parent Applications (1)

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EP96920661A Division EP0836736B1 (de) 1995-07-03 1996-07-02 Digitales vorwärtsgeregeltes system für aktive lärmkontrolle

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EP1074970A2 true EP1074970A2 (de) 2001-02-07
EP1074970A3 EP1074970A3 (de) 2001-05-09
EP1074970B1 EP1074970B1 (de) 2003-04-23

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EP00122367A Expired - Lifetime EP1074970B1 (de) 1995-07-03 1996-07-02 Digitales vorwärtsgeregeltes System für aktive Lärmkontrolle
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JP2008122729A (ja) 2006-11-14 2008-05-29 Sony Corp ノイズ低減装置、ノイズ低減方法、ノイズ低減プログラムおよびノイズ低減音声出力装置
GB2441835B (en) * 2007-02-07 2008-08-20 Sonaptic Ltd Ambient noise reduction system
US8737636B2 (en) 2009-07-10 2014-05-27 Qualcomm Incorporated Systems, methods, apparatus, and computer-readable media for adaptive active noise cancellation
GB2582374B (en) * 2019-03-22 2021-08-18 Dyson Technology Ltd Noise control
CN113421540B (zh) * 2021-07-26 2023-10-31 北京安声浩朗科技有限公司 主动降噪方法、主动降噪装置及半入耳式主动降噪耳机

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CN104185866B (zh) * 2012-03-30 2016-09-07 苹果公司 用于有源噪声消除自适应滤波器的预成形串联滤波器

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EP1074970B1 (de) 2003-04-23
EP1074970A3 (de) 2001-05-09
EP1074971A3 (de) 2001-05-09
EP1074971B1 (de) 2003-04-09
EP1074971A2 (de) 2001-02-07

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