Noise canceler

Abstract: The object of the noise canceler of the present invention is to allow hands-free conversation from either of two microphones through a parallel construction having two noise cancelers using FIR adaptive filters. When microphone 2 (at the driver's seat) is used for conversation, microphone 3 (at the passenger seat) is used for collecting noise and a noise-reduced voice signal 105 is obtained by using FIR adaptive filter 14; and when microphone 3 is used for conversation, microphone 2 is used for collecting noise and a noise-reduced voice signal 104 is obtained using FIR adaptive filter 13. These two voice signals 104, 105 are added at adder 17 and the result outputted as voice output signal 103.

Description: The present invention relates to a noise canceler, and particular to an adaptive control noise canceler for hands-free conversation in an automobile telephone that suppresses a background noise component arising from travel of a mobile body that is acoustically interfered to a voice signal. In the prior art, noise cancelers used for hands-free conversation in automobile telephones have been individually provided for each voice microphone and noise microphone. Fig. 1 is a block diagram showing an example of the basic construction of a noise canceler of this type. Such a noise canceler 4 converts voice signal 112 from voice microphone 5 and noise signal 111 from noise microphone 6 into digital signals by means of A/D converters 41, 42, respectively; generates a cross-correlative noise signal by means of FIR (Finite Impulse Response) adaptive filter 43; and outputs noise signal 113. The noise canceler 4 further reduces noise by subtracting this noise signal 113 from the voice signal coming from voice microphone 5 by means of adder 44; returns the signal to an analog signal by means of D/A converter 45; and outputs output signal 114. Fig. 2 is a block diagram showing the structure of an example of this type of noise canceler having improved characteristics as described in JP-A-191884/93. A noise canceler according to this example of the prior art has two adaptive control noise canceler sections 9, 10 arranged in a two-stage construction wherein noise is canceled by the two stages from voice signal 111 from voice microphone 7 and noise signal 112 from noise microphone 8, and output signal 115 is outputted. Such a device is particularly aimed at using a two-stage construction to improve characteristics by lessening the effect upon the voice signal caused by voice picked up by the noise microphone, and simultaneously, reducing the noise component to a minimum. EP-A-0 525 456 describes a digital filter comprising a main adaptive digital filter and a sub adaptive digital filter, these two adaptive digital filters sharing a filter coefficient to be controlled. JP-A-05-259 928 discloses a method and a device for canceling adaptive control noise. In the above-described example of the prior art, the voice microphone and noise microphone are each used in a fixed manner, and consequently, installation of the voice microphone at the driver's seat of an automobile and the noise microphone within the same automobile presents the problem that conversation is limited to the voice microphone, i.e., to the driver's voice, and a passenger in the car is unable to converse. Moreover, such a device fails to completely solve the problem that voice mistakenly inputted to the noise microphone cancels the voice signal inputted to the voice microphone. These problems are overcome with a noise canceler according to the present invention. The above and other objects, features, and advantages of the present invention will become apparent from the following description based on the accompanying drawings which illustrate an example of a preferred embodiment of the present invention. Fig. 1 is a block diagram of the first example of the prior art. Fig. 2 is a block diagram of the second example of the prior art. Fig. 3 is a block diagram of an embodiment of the present invention. An embodiment of the present invention will next be explained with reference to the accompanying drawing. Fig. 3 is a block diagram showing an embodiment of the present invention. In the figure, microphone 2 is installed at the driver's seat of an automobile, and microphone 3 is installed at the passenger is seat. The internal construction of noise canceler 1 is composed of A/D converters 11, 12 which convert signals 101, 102 from microphones 2, 3 to digital signals; adder 16 and FIR adaptive filter 14 which operate as a noise canceler when microphone 2 is used for speech and microphone 3 is used for noise; adder 15 and FIR adaptive filter 13 that operate as a noise canceler when microphone 2 is used for noise and microphone 3 is used for speech; adder 17 that adds the output signals of adder 16 and adder 15; and D/A converter 18 that returns the output signal of adder 17 to an analog signal and outputs the result as output signal 103. As to the operation of this canceler, FIR adaptive filter 14 generates an estimated noise signal which is the estimated noise component contained in the voice signal of microphone 2 based on the noise signal from microphone 3. Adder 16 outputs noise-reduced output signal 105 by subtracting the estimated noise signal from the voice signal from microphone 2. This voice signal 105 is fed back as a residual signal for adapting FIR adaptive filter 14 and used as the coefficient update of the FIR filter for the next input. In the same way, FIR adaptive filter 13 generates an estimated noise signal which is the estimated noise component contained in voice signal of microphone 3 based on the noise signal from microphone 2. Adder 15 outputs voice signal 104 in which noise is reduced by subtracting this estimated noise signal from the voice signal from microphone 3. Adder 17 next adds the two noise-reduced voice signals 104, 105 and outputs to D/A converter 18. D/A converter 18 returns the added signals to an analog signal and outputs the result as voice output signal 103. In other words, this voice output signal 103 is the noise-reduced voice output signal when microphone 2 (driver's seat) is used for speaking or the noise-reduced voice output signal when microphone 3 (passenger seat) is used for speaking. The noise canceler of the present invention according to the foregoing description is a construction that provides noise cancelers for voice signals from two microphones whereby whichever microphone is used for speech, the other operates for noise detection, thereby having the effect of enabling hands-free conversation from the driver's seat microphone as well as from the passenger seat microphone. In addition, even when voice is mistakenly inputted to the passenger seat microphone when the driver's seat microphone is being used for speech, the present invention has the effect of reducing the effect upon the voice output signal because voice from the passenger seat is added. It is to be understood, however, that although the characteristics and advantages of the present invention have been set forth in the foregoing description, the disclosure is illustrative only, and changes may be made in the arrangement of the parts within the scope of the appended claims.

Claims: An adaptive control noise canceler that suppresses a background noise component arising from travel of a mobile body said background noise component acoustically interfering with a voice signal, said adaptive control noise canceler comprising: a first noise canceler that uses a first FIR Finite Impulse Response adaptive filter (14) that takes as input signals voice signals outputted when a first microphone (2) is used by a speaker and noise signals outputted when a second microphone (3) is used for noise collection; a second noise canceler that uses a second FIR adaptive filter (13) that takes as input signals noise signals outputted when said first microphone (2) is used for noise collection and voice signals outputted when said second microphone (3) is used by a speaker; and an adder (17) that adds output signals of said first and second noise cancelers. An adaptive control noise canceler according to claim 1, comprising: first and second A/D converters (11, 12) that convert voice signals or noise signals (101, 102) from said first and second microphones (2, 3), respectively, to digital signals; wherein said first FIR adaptive filter (14) is adapted to generate and output from output signals of said second A/D converter (12) noise signals which are estimated noise components contained in said voice signals (101) from said first microphone (2); and wherein said second FIR adaptive filter (13) is adapted to generate and output from output signals of said first A/D converter (11) noise signals which are estimated noise components contained in said voice signals from said second microphone (3); a first adder (16) that adds noise signals from said first FIR adaptive filter (14) and voice signals from said first A/D converter (11); a second adder (15) that adds noise signals of said second FIR adaptive filter (13) and voice signals from said second A/D converter (12); and a third adder (17) that adds output signals (105, 104) of said first and second adders (16, 15) and outputs the result as an output signal (103).

Inventors: HOSOI YOSHIAKI, HOSOI, YOSHIAKI, Hosoi, Yoshiaki, NEC Saitama, Ltd.
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1996
Main classification: H04R3
IPC codes: G10K11, H03H17, H04M1, H03H21, H04B7, H04R3