JP4505427B2 - Noise canceling headphones and noise canceling control mode switching method - Google Patents

Description

  The present invention relates to a noise-canceling headphone and a noise-canceling control mode switching method, and in particular, a noise-canceling headphone that can reduce abnormal noise caused by feedback control according to noise when reproduction of an audio signal is stopped, And a noise cancellation control mode switching method.

  In recent years, noise canceling headphones capable of canceling ambient noise and listening to music have been commercialized by various companies. These noise-canceling headphones are designed to reduce noise by inputting ambient noise from a microphone and canceling noise output from the speaker in the opposite phase. JP-A-6-343195 (Patent Document 1) and the like can be cited as a related art relating to noise-canceling headphones.

  FIG. 5 shows a simplified control circuit configuration of a headphone that realizes noise cancellation by feedback control.

  In FIG. 5, reference numeral 31 denotes a noise canceling headphone control circuit unit. Reference numeral 2 denotes a sound reproduction unit (hereinafter referred to as a headphone) of a noise canceling headphone. Reference numeral 3 denotes an audio signal reproducing apparatus that outputs an audio signal such as music. In FIG. 5, a silicon player (a portable audio apparatus in which a storage medium for storing music data is a semiconductor memory) is used. The control circuit unit 31 and the headphones 2 may be configured integrally or may be configured separately. In addition to the headphone type, the headphone 2 may be an earphone type.

  The audio signal input from the audio signal reproduction device 3 is processed by the control circuit unit 31 and output to the headphones 2 to be reproduced as audio. In the following description, it is described as sound including sound and sound.

  The control circuit unit 31 includes a correction circuit 4, a signal addition unit 5, a filter 6, a headphone amplifier 7, a microphone amplifier 8, and the like. The headphone 2 includes a speaker 13, a microphone 14, a headphone housing 15, a band 16, and the like. Reference numeral 17 is a simplified illustration of the user's ear.

  The output unit of the audio signal reproduction device 3 is connected to the input unit of the correction circuit 4. The output unit of the correction circuit 4 is connected to the positive input unit of the signal adding unit 5. The output unit of the signal adding unit 5 is connected to the input unit of the filter 6. The output part of the filter 6 is connected to the input part of the headphone amplifier 7. The output section of the headphone amplifier 7 is connected to the speaker 13. The speaker 13 and the microphone 14 are attached in close proximity to the headphone housing 15. When the user wears the headphones 2, the microphone 14 collects both sound from the speaker 13 and ambient noise that reaches the microphone 14 via the headphone housing 15.

  The correction circuit 4 corrects the audio signal input from the audio signal reproduction device 3 so that the frequency characteristic in the audible frequency range of the audio output from the speaker 13 is substantially flat. It is. The signal adder 5 is a subtractor that takes the difference between the audio signal from the correction circuit 4 input to the positive input unit and the feedback signal from the microphone amplifier 8 input to the negative input unit. Yes. The filter 6 is a band-pass filter having a large gain in a frequency band where noise is desired to be reduced. The headphone amplifier 7 amplifies the input signal and supplies it to the speaker 13. The microphone 14 collects sound and noise output from the speaker 13, converts them into electric signals, and supplies them to the microphone amplifier 8. The microphone amplifier 8 amplifies the signal from the microphone 14 and feeds it back as a feedback signal to the negative input section of the signal adding section 5.

As described above, the sound reproduction system including the control circuit unit 31, the headphone 2, and the sound signal reproduction device 3 has a negative feedback by the signal addition unit 5, the filter 6, the headphone amplifier 7, the speaker 13, the microphone 14, and the microphone amplifier 8. Construct a loop. Noise is canceled by this negative feedback feedback loop.
JP-A-6-343195

  The noise-canceling headphones with the above feedback control have the feature that the noise reduction effect can be increased by increasing the open-loop gain of the noise-canceling feedback control circuit, but if the open-loop gain is increased, the noise caused by the feedback control is reduced. There is a problem that occurs.

  FIG. 6 shows how the open loop gain characteristic and the open loop phase characteristic are related to the abnormal noise when the noise cancellation feedback loop characteristic is expressed by a Bode diagram.

  FIG. 6A shows the open loop gain characteristic of the noise cancellation feedback loop, and shows two characteristic examples of a large open loop gain and a small open loop gain. (B) is a phase characteristic and shows a phase margin for the two characteristic examples of (a). (C) shows the input / output (O / I) gain characteristics of the control circuit unit 31. In the vicinity of the cut-off frequency of the open loop gain characteristic, the gain increases, indicating that abnormal noise is generated even when the audio signal is no signal. Also, increasing the open loop gain increases the noise reduction effect, but the phase margin decreases and abnormal noise increases.

  The abnormal noise resulting from this feedback control is annoying for the user. This is particularly noticeable in a quiet state where no sound is heard from the speaker when the sound reproduction is stopped.

  In view of the above problems, an object of the present invention is to provide a noise-canceling headphone that can effectively reduce the annoying abnormal noise that can be heard when sound reproduction is stopped in relation to ambient noise. To do.

The noise-canceling headphone of the present invention is a noise-canceling headphone that can input a sound signal and hear a sound in which ambient noise is canceled. The sound signal is input to a positive input portion and a signal from a microphone amplifier is negatively input. A signal adding unit that is input to the unit and the difference is output, a plurality of amplifiers that amplify the output signal of the signal adding unit with different amplification factors smaller than 1, an output signal of the signal adding unit to an output of the plurality of amplifiers Open loop gain switching means for selecting and outputting one of the signals, a headphone amplifier for inputting and amplifying and outputting the signal from the open loop gain switching means, and an output signal of the headphone amplifier for inputting and generating sound A speaker, a microphone that collects sound generated by the speaker and ambient noise, converts the sound into an electrical signal, and outputs the electric signal; Speech detecting the noise cancellation feedback control circuit for canceling the ambient noise that the output signal is constituted by the microphone amplifier, is fed back to the negative input of the signal adding portion of the click, the level of the audio signal Signal level detection means, and noise level detection means for cutting off the output of the headphone amplifier and detecting only the ambient noise level based on the output of the microphone amplifier , and the signal level of the audio signal has a predetermined value. upon detecting that the audio signal level detecting means that below, the open loop gain switching means one of the plurality of amplifier output signals in response to the noise level detected by said noise level detecting means It is characterized by switching to select .
In the noise-canceling headphone according to the present invention, the audio signal level detecting means may reproduce the audio signal when the audio signal reproduction device is in the reproduction mode and the audio signal when the audio signal reproduction device is in the reproduction stop mode. Reproduction mode / reproduction stop mode detection means for detecting that the signal level of the audio signal is lower than the predetermined value by detecting the reproduction stop mode by utilizing the fact that the signal is not reproduced; when the reproduction stop mode detecting means detects the reproduction stop mode, the open loop gain switching means either in the output signal of said plurality of amplifiers in accordance with the noise level detected by said noise level detecting means 1 It is characterized by switching to select one .
In the noise-canceling headphone of the present invention, the audio signal level detection unit is an input audio signal level detection unit that detects the signal level of the input audio signal, and the open loop gain switching unit is the input loop when the said signal level of the audio signal level detecting means by the audio signal has been detected to be less than the predetermined value, the open loop gain switching means said plurality of amplifiers in accordance with the noise level which the noise level detecting means detects The output signal is switched so as to select any one of the output signals .
In the noise-canceling headphone according to the present invention, when the input audio signal level detecting unit detects that the signal level of the audio signal is lower than the predetermined value, the open loop gain switching unit has the noise level set in advance. When the noise level is smaller than a predetermined noise judgment level, the noise level is switched so that the open loop gain of the noise cancellation feedback control circuit is smaller than when the noise level is larger than the noise judgment level.
In the noise canceling headphone of the present invention, the open loop gain switching means is disposed in a feedback loop of the noise canceling feedback control circuit and transmits the signal without changing the signal level in the playback mode of the audio signal playback device. a first path, a second path for transmitting by reducing the level of signal from the first path when above the noise judgment levels the noise level is predetermined in a said reproduction stop mode, the playback When the noise level is lower than the predetermined noise judgment level in the stop mode, the noise level detecting means detects a third path that transmits a signal level lower than that of the second path. Further, the present invention is characterized in that it is configured as a route switching means for switching according to the noise level.
Also, the noise canceling headphone of the present invention, the second path is transmitted to reduce the level of the signal by the amplifier having an amplification factor of 1 / M that is 1 greater than the M, the third path The signal level is reduced and transmitted by an amplifier having an amplification factor of 1 / N where N is greater than 1 and M <N.
In the noise canceling headphone according to the present invention, the M may be arbitrarily set to a value greater than 1, and the N may be arbitrarily set to a value greater than 1 and M <N. .
Further, the noise cancel control mode switching method of the noise canceling headphones of the present invention, in the noise cancel control mode switching method of the noise canceling headphones can hear the voice ambient noise is canceled by inputting the audio signal, the noise In the cancel headphone, the audio signal is input to the positive input unit, the signal from the microphone amplifier is input to the negative input unit and the difference is output, and the output signal of the signal addition unit is different from 1 A plurality of amplifiers that amplify at an amplification factor, an open loop gain switching unit that selects and outputs one of an output signal from the signal adding unit to an output signal of the plurality of amplifiers, and a signal from the open loop gain switching unit A headphone amplifier that amplifies and outputs, and outputs the sound from the headphone amplifier output signal. A speaker that generates sound, a microphone that collects sound generated by the speaker and ambient noise, converts the sound into an electrical signal, and outputs the electrical signal; and inputs an output signal of the microphone and returns it to the negative input unit of the signal adding unit A noise cancellation feedback control circuit for canceling ambient noise composed of a microphone amplifier is provided, and the audio signal is reproduced and reproduced by the audio signal reproduction device when the audio signal reproduction device is in a reproduction mode. By detecting the reproduction stop mode using the fact that the audio signal is not reproduced when the stop mode is entered, it is detected that the signal level of the audio signal is lower than a predetermined value, and according to the detected noise level, and characterized in that switching between the open loop gain switching means so as to select one in the output signal of said plurality of amplifiers That.
Further, the noise cancel control mode switching method of the noise canceling headphones of the present invention, the mode switching signal outputted from the audio signal reproducing apparatus is output to the noise level detecting means, said noise level detecting means, said mode input when the switching signal is the reproduction stop mode, the relative open loop gain switching means such that said open loop gain of the noise cancellation feedback control circuit is smaller than the reproducing mode, depending on the detected noise level the A selection signal for selecting any one of the output signals of the plurality of amplifiers is output, and the open-loop gain switching means is configured to output one of the output signals of the plurality of amplifiers according to the selection signal from the noise level detection means. It is characterized by switching so that any one of these may be selected .
Further, the noise cancel control mode switching method of the noise canceling headphones of the present invention, in the noise cancel control mode switching method of the noise canceling headphones can hear the voice ambient noise is canceled by inputting the audio signal, the noise In the cancel headphone, the audio signal is input to the positive input unit, the signal from the microphone amplifier is input to the negative input unit and the difference is output, and the output signal of the signal addition unit is different from 1 A plurality of amplifiers that amplify at an amplification factor, an open loop gain switching unit that selects and outputs one of an output signal from the signal adding unit to an output signal of the plurality of amplifiers, and a signal from the open loop gain switching unit The headphone amplifier that amplifies and outputs the sound A speaker that generates sound, a microphone that collects sound generated by the speaker and ambient noise, converts the sound into an electrical signal, and outputs the electrical signal; and inputs an output signal of the microphone and returns it to the negative input unit of the signal adding unit microphone amplifier is provided with a noise cancellation feedback control circuit for canceling the ambient noise, which is constituted by, detects the signal level of the inputted audio signal, the signal level of the detected the voice signal is given When it is detected that the value is below the value, the open loop gain switching means switches so as to select any one of the output signals of the plurality of amplifiers according to the ambient noise level detected by the noise level detecting means. It is characterized by that.

  According to the present invention, it is possible to provide a noise-canceling headphone that can effectively reduce abnormal noise caused by feedback control when sound reproduction is stopped.

  The best mode for carrying out the present invention will be specifically described below with reference to the drawings.

(First embodiment)
FIG. 1 shows a first embodiment of a control circuit configuration of a noise canceling headphone according to the present invention.

  First, the control circuit configuration of the noise-canceling headphone of this embodiment will be described.

  In FIG. 1, reference numeral 1 denotes a control circuit unit of a noise canceling headphone. Reference numeral 2 denotes a sound reproduction unit (hereinafter referred to as a headphone) of a noise canceling headphone. Reference numeral 23 denotes an audio signal reproducing device that outputs an audio signal such as music. In FIG. 1, a silicon player (a portable audio device in which a storage medium for storing music data is a semiconductor memory) is used. The control circuit unit 1 and the headphones 2 can be configured as a single body or as separate bodies. Further, the headphone 2 can be an earphone type in addition to the headphone type.

  The audio signal input from the audio signal reproduction device 23 to the control circuit unit 1 is subjected to audio signal processing by the control circuit unit 1 and output to the headphones 2 to be reproduced as audio.

  The control circuit unit 1 includes a correction circuit 4, a signal addition unit 5, a filter 6, a headphone amplifier 7, a microphone amplifier 8, an open loop gain changeover switch 9, an amplifier 10 having an amplification factor of 1 / M (M is greater than 1), and amplification. It comprises an amplifier 11 having a rate of 1 / N (N is greater than 1 and M <N), a noise level detection circuit 12, a noise level detection period signal generation circuit 20, and the like. Here, the values of M and N may be set to predetermined fixed values, but may be set to arbitrary values in the above range according to the user's preference.

  The headphone 2 includes a speaker 13, a microphone 14, a headphone housing 15, a band 16, and the like. Reference numeral 17 is a simplified illustration of the user's ear.

  The audio signal reproduction device 23 is provided with a PLAY / STOP mode changeover switch 18 for operating reproduction / stop of the audio signal, and also detects the operation state of this switch and outputs the PLAY / STOP mode to the control circuit unit 1. A part 19 is provided. Here, the PLAY mode is a reproduction mode for reproducing an audio signal, and the STOP mode is a reproduction stop mode for not reproducing an audio signal.

  The audio signal output unit of the audio signal reproduction device 23 is connected to the audio signal input unit of the correction circuit 4. The output unit of the correction circuit 4 is connected to the positive input unit of the signal adding unit 5.

  The output section of the signal adding section 5 is connected to the terminal A of the open loop gain changeover switch 9, connected to the terminal B of the open loop gain changeover switch 9 via the amplifier 10, and opened loop gain via the amplifier 11. It is connected to a terminal C of the changeover switch 9. The terminal D of the open loop gain changeover switch 9 is connected to the input part of the filter 6, and the output part of the filter 6 is connected to the input part of the headphone amplifier 7.

  The output section of the headphone amplifier 7 is connected to the input section of the speaker 13. The speaker 13 and the microphone 14 are attached in close proximity to the headphone housing 15. When the user wears the headphones 2, the microphone 14 collects both sound from the speaker 13 and ambient noise that reaches the microphone 14 via the headphone housing 15.

  In addition, the microphone 14 collects sound and noise output from the speaker 13, converts them into electric signals, and supplies them to the microphone amplifier 8. The microphone amplifier 8 amplifies the signal from the microphone 14 and feeds it back to the negative input unit of the signal adding unit 5 as a feedback signal.

  The correction circuit 4 corrects the audio signal input from the audio signal reproducing device 23 so that the frequency characteristic in the audible frequency range of the audio output from the speaker 13 is substantially flat. It is. The signal adder 5 is a subtractor that takes the difference between the audio signal from the correction circuit 4 input to the positive input unit and the feedback signal from the microphone amplifier 8 input to the negative input unit. . The filter 6 is a band-pass filter having a large gain in a frequency band where noise is desired to be reduced.

  In the open loop gain changeover switch 9, the terminal D is switched and connected to one of the terminals A, B, and C according to the output of the noise level detection circuit 12. As will be described later, the output signal of the noise level detection circuit 12 is a 2-bit signal (11), (10), (01), (00) as shown in FIG. When the output signal of the noise level detection circuit 12 is (11), the terminal A is connected to the terminal D, when the output signal is (10), the terminal B is connected to the terminal D, and when the output signal is (01), the terminal C is connected to the terminal D. , (00), the connection relationship between the terminals is held. Note that the above connection relation between the output signal of the noise level detection circuit 12 and the terminals A, B, C, and D is an example, and other connection relations may be adopted.

  When the D terminal of the open loop gain changeover switch 9 is switched to be connected to the A terminal, the magnitude of the output signal of the signal adder 5 is input to the filter 6 without being changed.

  On the other hand, when the D terminal of the open loop gain changeover switch 9 is switched to be connected to the B terminal, the magnitude of the output signal of the signal adder 5 is multiplied by 1 / M via the amplifier 10 and input to the filter 6. Is done.

  When the D terminal of the open loop gain changeover switch 9 is switched to be connected to the C terminal, the magnitude of the output signal of the signal adding unit 5 is multiplied by 1 / N through the amplifier 11 and input to the filter 6. Is done.

Noise level detection period signal generation circuit 20 receives the signal from the PLAY / STOP mode detection unit 19 of the audio signal reproducing apparatus 23, upon detection of a fall portion is switched to the STOP mode, the noise level of a predetermined time width _{T 1} The detection period signal is output to the noise level detection circuit 12 and the headphone amplifier 7. The predetermined time width T ₁ is a period for detecting the level of ambient noise.

The noise level detection circuit 12 that has received the noise level detection period signal from the noise level detection period signal generation circuit 20 outputs (00) as an output signal. Thus the terminal A of the open loop gain changeover switch 9 at this time, B, C, connection of D is held for a predetermined time width T _1.

Further, headphone amplifier 7 which has received the noise level detection period signal from the noise level detection period signal generation circuit 20 blocks the output by the predetermined time width T _1. During this period, no sound is output from the speaker 13. Therefore, at this time, the microphone 14 can collect only ambient noise, and the noise level detection circuit 12 can correctly detect the ambient noise level.

The ambient noise collected by the microphone 14 in the noise level detection period T ₁ is converted into an electrical signal and input to the noise level detection circuit 12 via the microphone amplifier 8.

Since the signal from the PLAY / STOP mode detection unit 19, the signal from the noise level detection period signal generation circuit 20, and the signal from the microphone amplifier 8 are input to the noise level detection circuit 12, the noise level detection period When a noise level detection period signal is input from the signal generation circuit 20, the level of the signal from the microphone amplifier 8 is determined, and either (10) or (01) is output according to the level. The timing of changing the output signal from (00) to any one of (10) and (01) is immediately after the predetermined time width T ₁ has elapsed in the example of FIG. 2, but may be within the predetermined time width T ₁ . .

  When the noise level detected by the noise level detection circuit 12 is greater than a predetermined noise judgment level, an amplifier 10 having a gain of 1 / M is inserted into the path of the feedback control circuit for the purpose of reducing noise. The At this time, the output signal (10) is output from the noise level detection circuit 12, and the terminal B and the terminal D are connected.

  When the noise level detected by the noise level detection circuit 12 is smaller than a predetermined noise determination level, the amplifier 11 having a gain of 1 / N is used for the purpose of reducing abnormal noise caused by feedback control. It is inserted into the path of the feedback control circuit. At this time, an output signal (01) is output from the noise level detection circuit 12, and the terminals C and D of the open loop gain changeover switch 9 are connected.

  The noise level detection circuit 12 sets the output signal to (11) when the signal from the PLAY / STOP mode detection unit 19 corresponds to the PLAY mode. As a result, the terminal A and the terminal D of the open-loop gain changeover switch 9 are connected, and the output signal of the signal adder 5 is input to the filter 6 without changing its magnitude, and sound reproduction is performed by noise cancellation control.

  As described above, the audio reproduction system including the control circuit unit 1, the headphones 2, and the audio signal reproduction device 23 has the signal addition unit 5, the filter 6, the speaker 13, and the microphone 14 when the audio signal reproduction device 23 is in the PLAY mode. The microphone amplifier 8 constitutes a negative feedback feedback loop. Further, when the sound signal reproduction device 23 is in the STOP mode, if the surrounding noise level is larger than a predetermined noise judgment level, the signal adding unit 5, amplifier 10, filter 6, speaker 13, microphone 14, microphone amplifier 8 forms a negative feedback feedback loop. When the ambient noise level is smaller than a predetermined noise judgment level, the signal adder 5, amplifier 11, filter 6, speaker 13, microphone 14 and microphone amplifier 8 provide negative feedback feedback. Configure a loop.

  The gain 1 / M of the amplifier 10 is set such that M is greater than 1, and the gain 1 / N of the amplifier 11 is set such that N is greater than 1 and M <N. Therefore, when the audio signal reproducing device 23 is in the STOP mode, the control circuit unit 1 increases the open loop gain of the feedback loop to 1 / M times that is relatively large when the noise is in an environment greater than a predetermined noise determination level. And operates so that ambient noise is reduced. Further, when the sound signal reproduction device 23 is in the STOP mode, when the noise is in an environment smaller than a predetermined noise judgment level, the control circuit unit 1 has a relatively small 1 / N open loop gain of the feedback loop. The noise is doubled, and the noise caused by the feedback control is reduced.

  The PLAY / STOP mode detection unit 19 detects whether the audio signal reproduction device 23 is in the PLAY mode or the STOP mode. However, it is indirect that the signal level of the audio signal is 0 in the STOP mode. It is also an audio signal level detecting means for detecting automatically.

  FIG. 2 shows how the open loop gain of the noise cancellation feedback loop in the present embodiment is switched depending on the sound reproduction state (PLAY / STOP mode) of the sound signal reproduction device 23.

  In FIG. 2, (a) shows an audio reproduction state (PLAY / STOP mode signal) of the audio signal reproduction device 23. In FIG. 2A, PLAY indicates a state where the audio signal reproduction device 23 is in the PLAY mode, and STOP indicates a state where the audio signal reproduction device 23 is in the STOP mode.

Moreover, (b) of FIG. 2 shows a noise level and shows a difference with respect to the noise determination level _LN .

  FIG. 2C shows a noise level detection signal output from the noise level detection circuit 12, which is a 2-bit output signal (11), (10), (01), (00). ing. The output signal (11) corresponds to the PLAY mode, the output signal (10) corresponds to the STOP mode when the ambient noise is high, and the output signal (01) corresponds to the STOP mode when the ambient noise is low, The output signal (00) corresponds to the noise level detection period.

  FIG. 2D shows the switching state of the open loop gain changeover switch 9. In the figure, A shows a state in which the terminal A and the terminal D of the open loop gain changeover switch 9 are connected and the signal from the terminal A is inputted to the filter 6. B indicates a state in which the terminal B and the terminal D of the open loop gain changeover switch 9 are connected and the signal from the terminal B is input to the filter 6. C indicates a state in which the terminal C and the terminal D of the open loop gain changeover switch 9 are connected and the signal from the terminal C is input to the filter 6.

FIG. 2 (e) shows what the open loop gain will be. Here, _GP represents the magnitude of the open loop gain when the terminal A and the terminal D of the open loop gain changeover switch 9 are connected. G _P / M is the magnitude of the open loop gain when the terminal B and the terminal D of the open loop gain changeover switch 9 are connected. When the amplifier 10 is inserted, the open loop gain is 1 of _GP . / M times. G _P / N is the magnitude of the open loop gain when the terminal C and the terminal D of the open loop gain changeover switch 9 are connected. When the amplifier 11 is inserted, the open loop gain is 1 of _GP . / N times.

  The operation of the present embodiment will be described with reference to FIG.

First, the time _{t 1} before there PLAY / STOP mode switch 18 of the audio signal reproducing apparatus 23 to the STOP mode, the audio reproduction is stopped. At this time, the output signal of the PLAY / STOP mode detector 19 is at a low level. At this time, the ambient noise level is higher than the noise determination level _LN by ΔN1, and the noise level detection circuit 12 outputs the signal (10). As a result, the open loop gain changeover switch 9 is in a state in which the terminal B and the terminal C are connected, so that the amplifier 10 is inserted in the feedback loop. Therefore, the open loop gain of the feedback loop is _GP / M.

The user switches the PLAY mode PLAY / STOP mode switch 18 of the audio signal reproducing apparatus 23 from the STOP mode at time _{t 1.} The PLAY / STOP mode detection unit 19 detects this switching state and switches the output signal from the low level to the high level and outputs it to the control circuit unit 1.

  The noise level detection circuit 12 detects that the signal from the PLAY / STOP mode detection unit 19 has been switched from the low level to the high level, and sets the output to (11).

The open loop gain changeover switch 9 is switched so as to connect the terminal A and the terminal D when the signal of the noise level detection circuit is switched to (11) (state A in FIG. 2 (d)). At this time, since the terminal A and the terminal D are connected, the open loop gain of the feedback loop is _GP (the state of _{GP in} FIG. 2E).

The user switches the PLAY / STOP mode switch 18 of the audio signal reproducing apparatus 23 from the PLAY mode to STOP mode at time _{t 2.} The PLAY / STOP mode detection unit 19 detects this switching state and switches the output (PLAY / STOP mode switching signal) from the high level to the low level and outputs it to the control circuit unit 1.

When the noise level detection period signal generation circuit 20 detects that the signal from the PLAY / STOP mode detection unit 19 is switched from the high level to the low level, and outputs a pulse signal having a predetermined time width T _1. Noise level detecting circuit 12 holds a terminal connection state of the open loop gain selector 9 receives a pulse signal having a predetermined time width T ₁ of the from the noise level detection period signal generation circuit 20 and the output as (00).

Further, the headphone amplifier 7 that has received the pulse signal having the predetermined time width T ₁ from the noise level detection period signal generation circuit 20 cuts off the output during the predetermined time width T ₁ . Accordingly, the speaker 13 is silent and the microphone 14 collects only ambient noise. A signal from the microphone 14 is input to the noise level detection circuit 12 via the microphone amplifier 8, and the noise level is detected. Since the noise level is lower than the noise determination level by ΔN ₂ , the noise level detection circuit 12 changes its output from (00) to (01) and outputs it.

When the output of the noise level detection circuit 12 becomes (01), the open loop gain changeover switch 9 switches so as to connect the terminal C and the terminal D (state C in FIG. 2D). At this time, since the terminal C and the terminal D are connected, the amplifier 11 is inserted into the feedback loop. Therefore, the open loop gain of the feedback loop is _GP / N (the state of _GP / N in FIG. 2C).

Similarly, the open loop gain of the feedback loop is switched according to the operation of the PLAY / STOP mode changeover switch 18, and when the ambient noise level is higher than the noise judgment level when the STOP mode is entered, the feedback loop open loop is set. When the gain is switched to a relatively large gain such as G _P / M and the surrounding noise level is smaller than the noise judgment level, the feedback loop open loop gain is a relatively small gain such as G _P / N. It is switched to become. Therefore, when the sound signal reproducing apparatus is set to the STOP mode, the noise is suppressed to be small when the ambient noise is high, and the abnormal noise caused by the feedback control is suppressed when the ambient noise is low.

  As can be seen from the above description, the headphone according to the present embodiment can suppress noise caused by feedback control when the ambient noise is low and the sound reproduction is stopped. Further, when the ambient noise is high and the sound reproduction is stopped, the ambient noise is suppressed to a low level. Also, during sound reproduction, even if the noise cancellation feedback control circuit operates in a state where the open loop gain is large, the noise is small because the noise is small relative to the sound volume. Therefore, according to the present embodiment, it is possible to provide a noise-canceling headphone that does not bother unusual sounds in either the PLAY mode or the STOP mode. Moreover, if the STOP mode is set in a state where the ambient noise is large, it can be used as an earplug.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG.

  In the first embodiment, the open loop gain switching of the noise cancellation feedback loop is performed by determining the operation state of the PLAY / STOP mode switching switch 18, but in this embodiment, the audio signal reproducing device is switched. 3 is performed by detecting the level of the audio signal input from 3.

  FIG. 3 shows a configuration of the noise canceling headphone according to the present embodiment. As shown in FIG. 3, in the present embodiment, the signal level of the audio signal is less than a predetermined value based on the signal level of the audio signal input from the audio signal reproduction device 3 to the correction circuit 4. An audio signal level detection unit 22 that detects and outputs a signal is provided.

  The audio signal level detection unit 22 is provided in place of the PLAY / STOP mode detection unit 19 in the first embodiment, and its input units are the audio signal output unit of the audio signal reproduction device 3 and the correction circuit 4. It is connected between the input parts, and the output part is connected to the noise level detection circuit 12 and the noise level detection period signal generation circuit 20. The output signal of the audio signal level detection unit 22 is used in the same manner as the output signal of the PLAY / STOP mode detection unit 19 in the first embodiment.

  In addition, the same reference numerals as those shown in FIG. 1 denote the same elements. In the description of the present embodiment, points different from the first embodiment will be mainly described, and the other descriptions described in the first embodiment will be omitted.

  Hereinafter, the operation of the noise-canceling headphone according to the second embodiment will be described with reference to FIG.

Now, as in the audio signal reproducing apparatus 3 PLAY / STOP mode selector switch 11 of FIG. 4 (a), switches from the STOP mode to the PLAY mode at time _{t 1,} the PLAY mode at time _{t 4} when switched to the STOP mode To do.

Since it is in the STOP mode before time t _1, no audio signal is output from the audio signal reproduction device 3 to the correction circuit 4 as shown in FIG. At this time, the audio signal level detection unit 22 detects that the audio signal is in a level state below a predetermined audio signal determination level L _S , and the output is at a low level. It is assumed that the ambient noise level at this time exceeds the predetermined noise determination level by ΔN ₁ as shown in FIG. Therefore, the noise level detection circuit 12 outputs the signal (10). Note that the audio signal determination level L _S is preferably set to a level at which the user feels substantially silent at a level lower than that.

At this time, the terminal B and the terminal D of the open loop gain changeover switch 9 are connected, and the amplifier 10 is inserted in the feedback loop. Therefore, the open loop gain of the feedback loop at this time is _GP / M.

Next, when the user switches the PLAY / STOP mode changeover switch 11 of the audio signal reproduction device 3 to the PLAY mode at time t ₁ , an audio signal is output from the audio signal reproduction device 3 to the correction circuit 4.

Consider a case where the audio signal level falls below the audio signal determination level L _S between time t ₂ and time t ₃ as shown in FIG. Then the audio signal level detecting circuit 22 is low between time t ₁ before the low level as shown in (c) of FIG. 4, the high level between time t ₁ t _2, from time t ₂ of t ₃ A signal of a high level is output between time t ₃ and t _{4, and} a low level signal is output after time t ₄ . There is no audio signal before time t ₁ and after time t _4, and the audio signal is very small between time t ₂ and t ₃ , so these are regions where abnormal noise due to feedback control is anxious. Therefore, in this embodiment, it is considered that the open loop gain of the feedback loop is switched in these regions. At this time, considering the same as in the first embodiment, the magnitude of the open loop gain is switched according to the magnitude of ambient noise.

However, since it is also conceivable audio signal back to a large level of the original in a short time, it may impart an operation delay of the predetermined time T ₂ in the noise level detection circuit 12. This may be to switch the signal at the timer OFF the OFF timers when ON and time _{T 2} has elapsed at time _{t 2} of (d) FIG. In this way, an unnecessarily large number of open loop gain switching operations are eliminated, so that the operation is stabilized.

The operation at the time the timer OFF is the same even when the falling of the PLAY mode signal at time _{t 4.}

When the audio signal level at time t ₃ comes to exceed the audio signal determination level L _S, the output of the audio signal level detection circuit 22 becomes a high level as shown in (c) of FIG. 4, the noise level The detection circuit 12 detects this and sets its output to (11). As a result, the terminal A and the terminal D of the open loop gain changeover switch 9 are connected, and the sound is reproduced in the noise cancel mode in which the open loop gain of the feedback loop becomes _GP . Incidentally, when the audio signal level detection signal is at high level during the timer period T ₂ are, the noise level detecting circuit 12 and a noise level detection signal in response in preference to a voice signal level detection signal (11).

Time _{t 4} in PLAY / When STOP mode changeover switch 18 is switched to be operated STOP mode signal level of the audio signal is below the sound signal decision level _{L S,} operates similarly to the case of time _{t 3.}

  As described above, the noise-canceling headphone according to the present embodiment operates, so that feedback is provided when the ambient noise is low and the sound reproduction is stopped or when the sound signal is below a predetermined level. Abnormal noise caused by control can be kept small. Further, when the ambient noise is high and the sound reproduction is stopped, the ambient noise is suppressed to a low level. Also, during sound reproduction, even if the noise cancellation feedback control circuit operates in a state where the open loop gain is large, the noise is small because the noise is small relative to the sound volume. Therefore, according to the present embodiment, it is possible to provide a noise-canceling headphone that does not bother unusual sounds in either the PLAY mode or the STOP mode. Moreover, if the STOP mode is set in a state where the ambient noise is large, it can be used as an earplug.

  In the above embodiment, the mode signal is high level in the PLAY mode and low level in the STOP mode. However, the mode signal can be implemented even if it is a logic signal in which high and low are reversed. The configuration of the control circuit units 1 and 19 is not limited to the configuration of the above embodiment. For example, the filter 6 and the open loop gain changeover switch 9 may be provided on the feedback side. Further, although the open loop gain changeover switch 9 is provided as means for changing the open loop gain of the feedback loop, the present invention is not limited to this. For example, the gain of the filter 6 may be changed.

Further, if the audio signal level detection unit 18 determines the level of the audio signal to have a hysteresis characteristic in the size of the audio signal determination level L _S , the audio signal level detection unit 18 does not respond to the level change within the hysteresis width. it is possible to reduce the switching operation of the open loop gain changeover switch 9 in the vicinity of the determination level L _S, it is possible to stabilize the operation.

In the above-described embodiment, an example in which the feedback loop path is switched in two ways of the amplifier 10 and the amplifier 11 by one noise determination level L _N has been described. However, the present invention is not limited to this, and the noise level is changed to a plurality of noise levels. Detection may be performed by level, and the feedback loop path may be switched among a plurality of paths.

  As mentioned above, although this invention was demonstrated by specific embodiment, it cannot be overemphasized that this invention is not limited to the said embodiment, It can change and implement in the range which does not deviate from the summary of this invention.

  The present invention can be used for a noise-canceling headphone using feedback control.

It is a control circuit block diagram which shows 1st Embodiment of the noise cancellation headphones by this invention. It is a figure explaining control operation of a 1st embodiment by the present invention. It is a control circuit block diagram which shows 2nd Embodiment of the noise cancellation headphones by this invention. It is a figure explaining control operation of a 2nd embodiment by the present invention. It is a figure which shows the control circuit structural example of the noise cancellation headphones of a prior art. It is a figure explaining abnormal noise generation | occurrence | production of the noise cancellation headphones of a prior art.

Explanation of symbols

1, 21, 31 ... Control circuit part 2 ... Headphone (sound reproduction part)
3, 23 ... Silicon player (audio signal reproduction device)
DESCRIPTION OF SYMBOLS 4 ... Correction circuit 5 ... Signal addition part 6 ... Filter 7 ... Headphone amplifier 8 ... Microphone amplifier 9 ... Open loop gain changeover switch 10, 11 ... Amplifier 12 ... Noise level detection circuit 13 ... speaker 14 ... microphone 15 ... headphone housing 16 ... band 17 ... ear 18 ... PLAY / STOP mode changeover switch 19 ... PLAY / STOP mode detector 20 ... Noise level detection period signal generation circuit 22 ... Audio signal level detection circuit

Claims (10)

In the noise canceling headphones that can input the audio signal and hear the sound in which the surrounding noise is canceled,
The audio signal is input to the positive input unit, the signal from the microphone amplifier is input to the negative input unit and the difference is output, and the output signal of the signal addition unit is amplified with a different amplification factor smaller than 1. A plurality of amplifiers, an open loop gain switching means for selecting and outputting any one of the output signals of the signal adding unit to the output signals of the plurality of amplifiers, and a signal from the open loop gain switching means being input, amplified and output A headphone amplifier, a speaker that generates sound by inputting an output signal of the headphone amplifier, a microphone that collects sound generated by the speaker and ambient noise, converts the noise into an electrical signal, and outputs the electric signal; output of the microphone noise cancellation fee for canceling the microphone amplifier, ambient noise, which is constituted by the inputs of the signal fed back to the negative input of the signal adding unit And back control circuit,
Audio signal level detection means for detecting the level of the audio signal;
A noise level detection means for blocking only the output of the headphone amplifier and detecting only the ambient noise level based on the output of the microphone amplifier ;
With
When the signal level of the audio signal is the speech signal level detecting means that below a predetermined value is detected, the plurality of amplifiers according the open loop gain switching means to the noise level detected by said noise level detecting means A noise-canceling headphone that is switched to select any one of the output signals . The audio signal level detection means utilizes the fact that the audio signal is reproduced when the audio signal reproduction device is in a reproduction mode and the audio signal is not reproduced when the audio signal reproduction device is in a reproduction stop mode. Reproduction mode / reproduction stop mode detection means for detecting that the signal level of the audio signal is below the predetermined value by detecting a reproduction stop mode ;
Wherein when the playback mode / STOP mode detecting means detects the reproduction stop mode, the open loop gain switching means in the output signal of said plurality of amplifiers in accordance with the noise level detected by said noise level detecting means The noise-canceling headphone according to claim 1 , wherein the switching is performed so that any one of the two is selected . The audio signal level detection means is input audio signal level detection means for detecting the signal level of the input audio signal,
The open loop gain switching means, when said signal level of said audio signal by said input audio signal level detecting means detects that below the predetermined value, the open loop gain switching means has detected that the noise level detecting means 2. The noise canceling headphone according to claim 1 , wherein switching is performed so as to select any one of the output signals of the plurality of amplifiers according to the noise level . When the input sound signal level detecting means detects that the signal level of the sound signal is lower than the predetermined value, the open loop gain switching means is configured to detect the noise when the noise level is smaller than a predetermined noise determination level. The noise canceling headphone according to any one of claims 1 to 3, wherein switching is performed such that an open loop gain of the noise canceling feedback control circuit is smaller than when the level is greater than the noise determination level. . The open loop gain switching means
Arranged in the feedback loop of the noise cancellation feedback control circuit,
A first path for transmitting without changing the signal level during the playback mode of the audio signal playback device ;
A second path for transmitting by reducing the level of signal from the first path when above the noise judgment levels the noise level is predetermined in a said reproduction stop mode,
A third path for transmitting by reducing the level of signal from the second path when below the noise judgment levels the noise level is predetermined in a said reproduction stop mode,
Noise cancellation headphones according to claim 2, characterized in that it is configured as a path switching means for switching in response to the noise level detected by said noise level detecting means. In the second path, the signal level is reduced by an amplifier having an amplification factor of 1 / M where M is greater than 1, and transmitted.
6. The third path according to claim 5, wherein a signal level is reduced by an amplifier having an amplification factor of 1 / N where N is greater than 1 and M <N. Noise canceling headphones.   7. The noise-canceling headphone according to claim 6, wherein the M is arbitrarily set to a value greater than 1, and the N is arbitrarily set to a value greater than 1 and M <N. In the noise canceling headphone noise canceling control mode switching method, the sound signal can be heard by inputting an audio signal and the surrounding noise is canceled.
The noise canceling headphones include
The audio signal is input to the positive input unit, the signal from the microphone amplifier is input to the negative input unit and the difference is output, and the output signal of the signal addition unit is amplified with a different amplification factor smaller than 1. A plurality of amplifiers, an open loop gain switching means for selecting and outputting any one of the output signals of the signal adding unit to the output signals of the plurality of amplifiers, and a signal from the open loop gain switching means being input, amplified and output A headphone amplifier, a speaker that generates sound by inputting an output signal of the headphone amplifier, a microphone that collects sound generated by the speaker and ambient noise, converts the noise into an electrical signal, and outputs the electric signal; output of the microphone Noise canceling fee for canceling ambient noise composed of the microphone amplifier that inputs a signal and returns to the negative input unit of the signal adding unit. Back control circuit is provided,
By detecting the reproduction stop mode by utilizing the fact that the audio signal is reproduced when the audio signal reproduction device is in the reproduction mode and the audio signal is not reproduced when the audio signal reproduction device is in the reproduction stop mode. The open loop gain switching means detects that the signal level of the audio signal is below a predetermined value, and selects any one of the output signals of the plurality of amplifiers according to the detected noise level. Noise canceling headphone noise canceling control mode switching method characterized by switching. The mode switching signal output from the audio signal reproduction device is output to the noise level detection means,
The noise level detection means is configured such that when the input mode switching signal is in the regeneration stop mode, the open loop gain of the noise cancellation feedback control circuit is smaller than that in the regeneration mode with respect to the open loop gain switching means. to, and outputs a selection signal for selecting one among the output signals of said plurality of amplifiers in accordance with said detected noise level,
The said open loop gain switching means switches so that any one of the output signals of said several amplifier may be selected according to the said selection signal from the said noise level detection means . Noise cancellation Headphone noise cancellation control mode switching method. In the noise canceling headphone noise canceling control mode switching method, the sound signal can be heard by inputting an audio signal and the surrounding noise is canceled.
The noise canceling headphones include
The audio signal is input to the positive input unit, the signal from the microphone amplifier is input to the negative input unit and the difference is output, and the output signal of the signal addition unit is amplified with a different amplification factor smaller than 1. A plurality of amplifiers, an open loop gain switching means for selecting and outputting one of the output signals of the signal adding unit to the output signals of the plurality of amplifiers, a signal from the open loop gain switching means being input, amplified and output A headphone amplifier, a speaker that generates sound by inputting an output signal of the headphone amplifier, a microphone that collects sound generated by the speaker and ambient noise, converts the noise into an electrical signal, and outputs the electric signal; output of the microphone noise cancellation fee for canceling the microphone amplifier, ambient noise, which is constituted by the inputs of the signal fed back to the negative input of the signal adding unit Back control circuit is provided,
Detect the signal level of the input audio signal,
When the signal level of the detected the voice signal is detected to be below a predetermined value, the open loop gain switching means in the output signal of said plurality of amplifiers in accordance with the ambient noise level that noise level detecting means detects A method for switching a noise canceling control mode of a noise canceling headphone characterized by switching so as to select any one of the above .

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