JP2008219713A - Noise cancel headphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a noise cancel headphone capable of prolonging the service life of a battery without deteriorating playback sound quality by sacrificing the noise cancel effect a little when a battery voltage is reduced. <P>SOLUTION: The present invention relates to a digital noise cancel headphone comprising a microphone 4 for detecting noise, a DSP 3 for performing digital processing on a noise signal detected by the microphone 4 to produce a cancel signal of an inverse phase to the noise signal, a synthesizing means 6 for synthesizing the cancel signal generated by the DSP 3 and a musical signal, and a speaker unit 7 which is driven by a signal synthesized from the synthesizing means 6. A voltage detection section 2 is provided for detecting the voltage of a power supply battery 1 and when the voltage detection section 2 detects that the voltage of the power supply battery 1 is reduced to a prescribed voltage, the DSP 3 switches to a coefficient, with a little number of taps, being set at the time of the voltage, from among filter coefficients incorporated beforehand. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a noise-canceling headphone, and more particularly to a digital-type noise-canceling headphone that can extend the noise-canceling operation time by changing the processing operation of a signal processing unit in accordance with the voltage of a power supply battery. It has been devised.

  With the spread of portable music players, headphones for personally listening to musical sounds are also widely used. Portable music players are often used in streets with high noise levels and in vehicles such as trains and buses, and external noises can be heard through headphones as well as music played by the player. When listening to music in the noise, the music may be drowned out by external noise. May cause unpleasant feelings. In addition, even when high-quality musical sounds are reproduced with headphones, noise entering from the outside affects the musical sounds, which may reduce the quality of reproduced sounds that can be heard by the user.

Therefore, noise canceling headphones that are designed to cancel noise entering from the outside and reduce the sound pressure of the noise so that only the musical sound can be heard by the user's ears are becoming widespread. The principle of the noise-canceling headphones is that a noise entering the headphones is detected by a microphone, a cancel signal having a phase opposite to that of the detected noise signal is generated, and the noise is canceled by the cancel signal. More specifically, a noise signal having a phase opposite to that of the noise signal is generated by passing the noise signal collected by the microphone and converted into an electrical signal through a filter or a delay circuit. After the musical sound signals are synthesized (added), the power is amplified and input to the speaker unit.
The sound output from the speaker is the result of converting the combined signal of the noise cancellation signal and the tone signal into sound, and the sound converted from the noise cancellation signal cancels all or part of the external noise entering the headphones. The sound that enters the user's ear is almost only the sound converted from the musical sound signal.

  In recent years, digital noise canceling headphones are becoming popular. Digital noise-canceling headphones convert noise picked up by a microphone into a digital signal, digitally process the signal to generate a signal with the opposite phase to the noise signal, convert it into an analog signal, and input from the player It is synthesized with the musical sound signal. By inputting this synthesized signal to the speaker unit, the speaker unit reproduces the sound and music that have the opposite phase to the noise signal, and the noise is canceled by the sound that has the opposite phase to the noise signal. Can do.

  A typical digital noise canceling headphone includes a digital signal processing device (hereinafter referred to as “DSP”). The DSP operates in synchronization with a clock signal having a predetermined frequency, and performs arithmetic processing based on a filter coefficient having a predetermined number of taps. The operating frequency of the DSP and the number of taps of the filter coefficient in the conventional digital noise canceling headphones are constant, and therefore, arithmetic processing is performed at a constant operation processing speed. In order to enhance the noise canceling effect, it is necessary to increase the DSP operating frequency and the number of filter coefficient taps. Then, there is a problem that the built-in power supply battery is consumed quickly and the operation time is shortened.

  FIG. 4 shows changes on the time axis of the power supply voltage and the operating frequency in the conventional digital noise canceling headphones. In order to perform the noise canceling operation effectively, the power supply voltage needs to be equal to or higher than a predetermined voltage. The minimum voltage necessary for the DSP to operate is shown as “end voltage” in FIG. When the battery is used as a power source, the power supply voltage gradually decreases from the start of use of the battery, eventually reaches the end voltage, and the noise canceling operation stops. The time from the start of use to the end voltage is referred to herein as “driving time”.

In audio equipment and the like, a device for extending the battery life, that is, for increasing the “drive time” has been devised. For example, in a digital audio device, when the user operates the operation unit to instruct a shift to a power saving playback operation, the digital data of the sound source is thinned out, the playback condition is changed, or the playback volume is reduced. Some are configured to shift to a power-saving reproduction operation (see, for example, Patent Document 1).
Alternatively, when the wireless audio device is in the operation mode and the remote control signal instructing the stop mode is transmitted from the receiver, the audio device enters the stop mode and the reception circuit of the audio device is intermittent. Some have been devised to extend the battery life by performing a receiving operation (see, for example, Patent Document 2).
In addition, a remaining amount detection circuit that detects that the remaining voltage of the battery is equal to or less than a predetermined value and outputs a detection signal, and receives a detection signal from the remaining amount detection circuit and outputs a BEEP signal to the power amplifier. There is known a battery remaining amount notification device that is provided with a BEEP signal generation circuit and informs a user that the remaining battery amount has decreased (see, for example, Patent Document 3).

JP 2002-189486 A JP 7-74663 A JP 2002-189486 A

The invention described in Patent Document 2 is designed so that the power supply battery is not wasted during the operation of the audio device. As in the invention of the present application, the digital noise canceling headphone is provided with a unique device. It is different from the one that lengthens the driving time.
The invention described in Patent Document 3 is merely to notify when the power supply voltage drops below a predetermined voltage, and again, as in the present invention, a digital noise-cancelling headphone is devised. It ’s different.

  According to the invention described in Patent Document 1, when a user selects a power saving mode in a digital audio device, a power saving reproduction operation is performed by means such as thinning out digital data of a sound source, changing a reproduction condition, or reducing a volume. Is. Therefore, according to the invention described in Patent Document 1, problems such as a decrease in sound quality and a decrease in volume occur, so for music lovers who want to reproduce with high sound quality, when the remaining voltage of the battery is low, The power saving mode is unavoidably selected while the sound quality deteriorates.

  The present invention has been made in view of the above-described conventional technology. By taking advantage of the characteristics of the digital noise cancellation headphones, when the battery voltage decreases, the accuracy of the noise cancellation is reduced, thereby reducing the reproduction sound quality. An object of the present invention is to provide a noise-canceling headphone that does not deteriorate and can prolong battery life.

The present invention relates to a microphone that detects noise, a digital signal processing unit that digitally processes a noise signal detected by the microphone and generates a cancellation signal having an opposite phase to the noise signal, and a cancellation signal generated by the digital signal processing unit A digital noise canceling headphone comprising a synthesizing unit for synthesizing a musical sound signal and a speaker unit driven by a signal synthesized by the synthesizing unit, and comprising a voltage detection unit for detecting the voltage of the power supply battery When the voltage detection unit detects that the voltage of the power supply battery has dropped to a predetermined voltage, the digital signal processing unit has the number of taps set at that voltage from among the filter coefficients built in in advance. The main feature is to switch to a smaller coefficient.
When the voltage detection unit detects that the voltage of the power battery has dropped to a predetermined voltage, the digital signal processing unit converts the filter coefficient built in advance to a coefficient with a small number of taps set at that voltage. In addition to switching, the operating frequency of the digital signal processing unit may be lowered.

When the voltage detection unit detects that the voltage of the power battery is equal to or higher than the predetermined voltage, the digital signal processing unit performs arithmetic processing using a filter coefficient with a large number of taps, and outputs a highly accurate cancel signal. Generate noise cancellation operation. When the voltage detection unit detects that the voltage of the power supply battery has become equal to or lower than a predetermined voltage, the digital signal processing unit switches to a filter coefficient with a small number of taps. As a result, the accuracy of the generated cancel signal is reduced, but the reproduction sound quality of the musical sound signal is not deteriorated, and the power consumption of the power supply battery is reduced and the battery life can be extended.
When the voltage detection unit detects that the voltage of the power battery has dropped to a predetermined voltage, in addition to switching to a filter coefficient with a small number of taps, if the operating frequency of the digital signal processing unit is lowered, further Battery life can be extended.
In order to extend the battery life, the operating frequency of the DSP may be lowered. However, if the DSP operating frequency is lowered, the processing speed is slowed down. Therefore, if a filter coefficient having a large number of taps capable of high-precision processing is used, the processing cannot be performed in time. Therefore, processing is performed with reduced accuracy using filter coefficients with a small number of taps.

Hereinafter, embodiments of a noise canceling headphone according to the present invention will be described with reference to the drawings.
FIG. 1 is a functional block diagram showing an embodiment of a noise canceling headphone according to the present invention. In FIG. 1, reference numeral 8 denotes a circuit board built in the headphones, and the circuit board 8 includes a voltage detection unit 2, a digital signal processing unit, that is, a DSP 3, and a synthesis unit 6. The headphone is also loaded with a power supply battery 1, and power is supplied from the power supply battery 1 to the DSP 3 and other appropriate circuit units (not shown) such as an amplifier, and the voltage detection unit 2 detects the terminal voltage of the power supply battery 1. It has become.

  The voltage detector 2 may be configured to detect that the voltage of the power battery 1 has dropped to a predetermined voltage, but may be configured to detect the voltage of the power battery 1 in three stages. That is, it is detected that the voltage of the power supply battery 1 has dropped to the voltage of the first stage, and that the voltage of the power supply battery 1 has been lowered to the voltage of the second stage lower than the first stage. Furthermore, it may be configured to detect that the voltage has dropped to a lower third stage voltage. In this embodiment, the voltage detection unit 2 detects the voltage of the power supply battery 1 in three stages, and a noise canceling operation corresponding thereto is performed.

  The DSP 3 is configured to receive a noise signal that has been subjected to electroacoustic conversion by the microphone 4 and converted to a digital signal by an analog / digital converter (hereinafter referred to as “AD converter”) (not shown). The microphone 4 may be disposed inside the headphone housing or may be disposed outside depending on the design concept of the noise canceling headphone. In the headphones according to the present invention, the arrangement position of the microphone 4 is arbitrary. The DSP 3 operates in synchronization with the clock pulse supplied from the clock pulse oscillator. The DSP 3 receives a noise signal from the microphone 4 via an AD converter (not shown) at a predetermined sampling period, and the DSP 3 generates a noise cancellation signal having a phase opposite to that of the noise signal. The noise cancellation signal is converted into an analog signal by a digital / analog converter (hereinafter referred to as “DA converter”) (not shown), and input to the synthesizing means 6 including an adder. Further, the DSP 3 switches its operating frequency and the number of taps of the filter coefficient in accordance with the voltage detection result of the power supply battery 1 by the voltage detection unit 2.

  The operation of the DSP 3 based on the detection operation of the voltage detection unit 2 will be described more specifically as follows. When the voltage detection unit 2 detects that the voltage of the power supply battery 1 has decreased to the first-stage voltage V1, the DSP 3 switches to a filter coefficient with a small number of taps and lowers its operating frequency. When the voltage detector 2 detects that the voltage of the power supply battery 1 has dropped to the second-stage voltage V2 lower than the voltage V1, the DSP 3 switches to a filter coefficient with a smaller number of taps and changes its operating frequency. Make it even lower. When the voltage detector 2 detects that the voltage of the power supply battery 1 has dropped to the end voltage V3 lower than the voltage V2, the DSP 3 stops the noise canceling operation. The above operation is performed by software in the DSP 3.

  The noise canceling signal converted into an analog signal and a tone signal reproduced by a CD player, an MD player, a flash memory player, or other appropriate sound source 5 are input to the synthesizing unit 6, and the noise canceling signal and the tone signal are input. Are combined (added). This synthesized signal is input to the speaker unit 7, and sounds corresponding to the synthesized signal, that is, a musical sound and a canceling sound are output from the speaker unit 7. Ambient noise enters the headphone housing. This noise is canceled by the cancellation sound having the opposite phase to the noise phase, and the user can hear only the musical sound or can hear the musical sound in an environment where the noise level is reduced.

  By performing the noise canceling operation, the power supply battery 1 is gradually consumed, and the power supply voltage gradually decreases. The above-described embodiment is characterized in that the DSP 3 controls the operating frequency as the voltage of the power supply battery 1 decreases, and also controls the number of taps of the filter coefficient. This will be described with reference to FIGS. In FIG. 2, V1 is a voltage when the power supply battery 1 is exhausted to the first stage, and the DSP 3 operates at a predetermined operating frequency and a predetermined tap while the voltage V1 or higher is maintained. High-precision arithmetic processing is performed with a number of filter coefficients. Since the conventional noise cancellation headphones do not switch the operating frequency and the number of taps, when the voltage of the power supply battery drops to the end voltage, the DSP does not operate at that time. The operation time until the voltage of the power supply battery decreases to the end voltage is indicated by T1 in FIG.

  In the embodiment of the present invention, when the voltage detection unit 2 detects that the voltage has decreased to V1 or less, the DSP 3 decreases the operating frequency by one step as shown in FIGS. Is switched to a coefficient smaller by one step to generate a medium-accuracy noise cancellation signal. Therefore, although the noise cancellation accuracy is lowered, there is no influence on the reproduction quality of the musical sound signal, so that it is possible to listen to high-quality musical sounds. During this time, the voltage detector 2 monitors whether the voltage of the power supply battery 1 does not drop to the second-stage voltage V2 lower than V1, and when the voltage is lowered to the second-stage voltage V2, the DSP 3 further increases the operating frequency. In addition to being reduced by one step, the filter coefficient is switched to a filter coefficient having a tap number that is further reduced by one step to generate a low-accuracy noise cancellation signal. As a result, the operation time of the DSP 3 extends from T1 to T3, and the operation time of the noise cancellation headphones or the life of the power supply battery 1 is extended. As described above, switching to a coefficient with a lower number of taps while the operating frequency of the DSP 3 is lowered further reduces the noise cancellation accuracy, but the reproduction quality of the tone signal remains unchanged, and a high-quality tone is heard. be able to. During this time, the voltage detection unit 2 monitors whether or not the voltage of the power battery 1 does not drop to the third stage voltage V3 that is lower than V2.

When the voltage of the power battery 1 drops to V3, the DSP 3 stops the noise canceling operation. The voltage V3 is the final voltage in the embodiment of the present invention, and the operation time until the voltage V3 is reached is represented by T3 in FIG.
In the example of the flowchart shown in FIG. 3, it is determined whether or not the battery voltage is maintained at the first level voltage V1 or higher (step S2, (hereinafter referred to as “S2”)), and maintained at the voltage V1 or higher. For example, the filter coefficient is calculated with 200 taps (this is the number of taps of n1), and the DSP operates at the operating frequency f1 (S3) and generates a cancel signal (S4). When the battery voltage becomes V1 or less, it is next determined whether or not the voltage is the second stage voltage V2 or more (S5). If the battery voltage is more than V2, the filter coefficient is lowered by one stage, for example, 150 taps (this is n2). Therefore, the calculation is performed with (n2 <n1)), the DSP is operated at an operating frequency f2 lower than f1 (S6), and a cancel signal is generated (S7). When the battery voltage is lower than the voltage V2 in the second stage, it is determined whether or not the voltage is higher than the voltage in the next stage (S8). The number is set to the number of taps in the next stage lower than 150, and the DSP is operated at the next stage frequency lower than f2 (S9). In this way, as the battery voltage decreases stepwise, the number of taps of the filter coefficient is decreased stepwise, and the operating frequency of the DSP is decreased stepwise. When the power supply voltage drops to a voltage insufficient to drive the DSP, the noise canceling operation is stopped (S11).

  As described above, according to the illustrated embodiment, the voltage of the power supply battery 1 is detected, and the operation frequency and the filter coefficient of the DSP are switched accordingly, so that the conventional noise cancellation headphones are compared with the conventional noise cancellation headphones. Then, although the operation time is T1, according to the above embodiment of the present invention, the noise canceling operation extends from T1 to T3, and the battery life can be extended by the extended time Tex.

  Note that it is arbitrary how many steps the power supply voltage drop is detected. As shown in FIG. 2, it may be detected over three steps, may be detected over more steps, or may be detected over two steps. May be. The operating frequency of the DSP 3 and the number of sampling data are changed according to the stage of power supply voltage detection.

It is a block diagram which shows the Example of the noise cancellation headphones concerning this invention. It is a timing chart which shows the example of a switching of the operating frequency and tap number of the digital signal processing part corresponding to the fall of the power supply voltage in the said Example. It is a flowchart which shows the example of switching of the operating frequency of the digital signal processing part corresponding to the fall of the power supply voltage in the said Example, and the number of taps. It is a timing chart which shows the example of a switching of the operating frequency and tap number of the digital signal processing part corresponding to the fall of the power supply voltage in the conventional noise cancellation headphones.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply battery 2 Voltage detection part 3 Digital signal processing part (DSP)
4 Microphone 5 Sound source 6 Synthesizer 7 Speaker unit

Claims (4)

A microphone that detects noise;
A digital signal processing unit that digitally processes a noise signal detected by a microphone and generates a cancel signal having an opposite phase to the noise signal;
A synthesizing means for synthesizing the cancel signal and the musical sound signal generated by the digital signal processing unit;
A digital noise canceling headphone comprising a speaker unit driven by a signal synthesized by a synthesizing means,
It has a voltage detector that detects the voltage of the power battery,
When the voltage detection unit detects that the voltage of the power supply battery has dropped to a predetermined voltage, the digital signal processing unit has a small number of taps set at that voltage from among the built-in filter coefficients. Noise canceling headphones characterized by switching to a coefficient.   When the voltage detection unit detects that the voltage of the power supply battery has dropped to a predetermined voltage, the digital signal processing unit is a coefficient with a small number of taps set at that voltage from among the built-in filter coefficients The noise canceling headphone according to claim 1, wherein the operation frequency of the digital signal processing unit is lowered.   The noise canceling headphone according to claim 1, wherein the voltage detection unit detects the voltage of the power supply battery and transmits the voltage value to the digital signal processing unit.   The noise cancellation headphones according to claim 1, wherein the digital signal processing unit converts the generated cancellation signal into an analog signal and outputs the analog signal.

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