JP2004214765A - Headphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a headphone capable of performing audio reproduction with high quality without being affected by a power noise, a board pattern, and an external disturbance noise or the like. <P>SOLUTION: The headphone is configured by having: a plug 1 plugged in/removed from an optical output terminal of a digital audio apparatus; an optical fiber 2 acting line a transmission path of an optical digital signal received from the plug 1; an optical signal/1-bit signal converter 3 for generating a 1-bit signal on the basis of the optical digital signal received through the optical fiber 2; and speakers 4L, 4R for outputting sound in response to the 1-bit signal. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to headphones used by being connected to digital audio equipment.
[0002]
[Prior art]
Recently, digital recording media such as CDs (compact disks) and MDs (mini disks) have been widely and widely used as recording media for audio signals. The reproduction characteristics of the digitally recorded audio signal include no deterioration in sound quality due to the characteristics of the recording medium, which has been a subject of analog recording media (such as a cassette tape), and a high S / N, a high dynamic range, and a low distortion rate. For example, higher sound quality than analog recording media has been realized in various aspects.
[0003]
To reproduce an audio signal from the digital recording medium, a digital audio device such as a CD player or an MD player is used. At this time, a speaker or headphones are required to output the audio signal as sound finally. Note that a speaker is often used at the time of reproduction indoors, and a headphone is often used at the time of reproduction outdoors or at night. In recent years, more and more users use headphones indoors in order to enjoy pure audio reproduction by cutting off external sounds.
[0004]
FIG. 3 is a block diagram showing a main configuration of a general disc reproducing apparatus. The disk reproducing device 5 shown in FIG. 1 is a device that reads an audio signal from a disk 51 (a digital recording medium represented by a CD or an MD) and reproduces and outputs the audio signal. The signal processing circuit 52 subjects the audio data extracted from the disk 51 by an optical pickup (not shown) to a series of signal processing (demodulation processing, error correction processing, data expansion processing for compressed data, etc.) and performs PCM [ Pulse Code Modulation] signal. The digital / analog converter 53 (hereinafter, referred to as a D / A [Digital / Analog] converter 53) converts the PCM signal generated by the signal processing circuit 52 into an analog signal and sends the analog signal to the headphone jack 54.
[0005]
The headphone jack 54 is a three-terminal jack used for attaching / detaching headphones, and its ground line is common to both L / R channels. The digital output modulating section 55 modulates the PCM signal generated by the signal processing circuit 52 into a predetermined format (format standardized by EIAJ [Electronic Industries Association of Japan] or the like) and sends it to the optical converter 56. The optical converter 56 converts the modulated digital signal generated by the digital output modulator 55 into an optical signal and outputs the optical signal to an external digital device (such as an MD recording / reproducing device having an optical digital input terminal).
[0006]
In the disk reproducing apparatus 5 having the above configuration, the processing from the disk 51 to the signal processing circuit 52 is mainly digital signal processing, and the generated PCM signal is usually subjected to independent signal processing in both the left and right channels. I have. Since the PCM signal is a digital signal, the PCM signal is hardly affected by sound quality degradation due to analog elements such as power supply noise and board patterns.
[0007]
FIG. 4 is a schematic diagram showing a configuration example of a conventional headphone. As shown in the figure, the conventional headphones include a headphone plug 6, a headphone cord 7, and a headphone body 8. The headphone plug 6 is a terminal that is attached to and detached from the headphone jack 54 of the disk reproducing device 5, and a ground line is common to both the L and R channels, similarly to the headphone jack 54. On the other hand, a headphone cord 7 in which the L / R channels are separated (the ground line is also separated for the L / R channels) is often used. The headphone body 8 includes a pair of small speakers that are applied to both ears of the user and an arm that connects them.
[0008]
[Patent Document 1]
Japanese Utility Model Laid-Open No. 123633/1998
[Problems to be solved by the invention]
Certainly, if the headphones having the above configuration are used, it is possible to enjoy outdoor audio reproduction and nighttime audio reproduction.
[0010]
However, since the headphones having the above-described configuration are configured to transmit analog signals to and from the disk playback device 5 through the headphone cord 7, the playback sound quality has the following problems.
[0011]
The first problem is that when the audio signal is a stereo signal, the ground line should be separated for each of the L / R channels, but in the headphone having the above configuration, as described above, the headphone plug 6 Since the ground line is common to both the left and right channels, the separation of the two signals is poor, crosstalk occurs and the reproduced sound quality is degraded. In addition, if the ground line is common, a small speaker constituting the headphone body is driven by a BTL (Bridged TransLess) drive method (a drive method in which the ground potential is not fixed and, for example, a reverse polarity signal of the L channel signal is used; (Also referred to as a bridge drive system), which is disadvantageous in driving low voltage and large output and reducing switching noise.
[0012]
A second problem is that in the headphones having the above-described configuration, a very thin conductive wire is used as the headphone cord 7 having a length of usually 1 [m] or more to ensure flexibility. This means that the analog signal transmitted by the loudspeaker has a large resistance loss and the reproduced sound quality is degraded.
[0013]
A third problem is that in the headphones having the above-described configuration, since the transmission signal via the headphone cord 7 is an analog signal, the reproduced sound quality is deteriorated due to analog elements such as power supply noise, board pattern, and disturbance noise. That is.
[0014]
As described above, the headphones having the above-described configuration lack the consideration for improving the reproduction sound quality as compared with a speaker whose sound quality has been improved by accumulating various methods and know-how, and even in indoors. A user who uses headphones feels unsatisfactory.
[0015]
Heretofore, various optical audio transmission systems for optically transmitting audio signals in the air have been disclosed and proposed (for example, refer to Patent Document 1). It was constructed mainly for the purpose of omitting wiring to speakers that are fixedly arranged at a close distance, and there was no consideration or mention of application to headphones.
[0016]
The present invention has been made in view of the above circumstances, and has as its object to provide headphones capable of performing high-quality audio reproduction without being affected by power supply noise, board patterns, disturbance noise, and the like.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, a headphone according to the present invention includes a plug attached to and detached from an optical output terminal of a digital audio device, an optical fiber serving as a transmission path of an optical digital signal input from the plug, and the optical fiber And an optical signal / drive signal converter that generates a speaker drive signal based on an optical digital signal input through the speaker, and a speaker that outputs audio according to the speaker drive signal. With this configuration, the transmitted optical digital signal is hardly lost, so that the reproduced sound quality can be improved. In addition, since the signal to be transmitted is a digital signal, deterioration due to analog elements such as power supply noise, board pattern, disturbance noise, and the like does not occur, and the reproduced sound quality can be improved.
[0018]
In the headphones having the above configuration, the optical signal / drive signal converter includes a light receiving element that converts the optical digital signal into an electric signal, a digital input demodulator that demodulates the electric signal to generate a PCM signal, A PLL circuit that generates a clock signal synchronized with the optical digital signal and sends the clock signal to the digital input demodulation unit; a sampling rate converter that converts a sampling frequency of the PCM signal; ΔΣ modulator for modulating a multi-level PDM signal, PWM modulator for modulating the PDM signal into PWM signals for L / R channels, a driver for amplifying each PWM signal, and unnecessary output signals from the driver And a filter for removing the component and sending it to the speaker. With such a configuration, analog signal processing after the PWM modulator is performed completely independently for each of the L / R channels. Therefore, the separation of both signals is increased as compared with the conventional configuration in which the ground line is common to both the L and R channels, so that it is possible to reduce the crosstalk and improve the reproduced sound quality. In addition, since the ground line is made independent for both the left and right channels, the speaker can be controlled by the BTL driving method, so that low voltage, large output driving and switching noise reduction can be achieved.
[0019]
Further, in the headphone having the above configuration, the optical signal / drive signal converter includes a sampling rate converter, a ΔΣ modulator, and an oscillation circuit that generates a reference clock signal used for each signal processing in the PWM modulator. It has a configuration. As described above, by making the sampling rate converter asynchronous to the optical digital signal, it is possible to perform stable signal processing that does not depend on the fluctuation of the extracted clock signal caused by the jitter of the received light signal, etc. It is possible to improve.
[0020]
Further, in the headphones having the above-described configuration, the optical signal / drive signal converter may be configured to be incorporated into one of the pair of speakers applied to both ears of the user or an arm unit connecting them. With such a configuration, unnecessary increase in the size of the headphones can be avoided, so that the user does not feel uncomfortable when wearing the headphones and in appearance.
[0021]
Further, in the headphones having the above configuration, the optical signal / drive signal converter may be configured to be driven by a battery. With such a configuration, it is not necessary to draw a power supply line from the digital audio device.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail by taking headphones as an example connected to a portable MD playback device. FIG. 1 is a schematic configuration diagram showing an embodiment of the headphones according to the present invention. As shown in the figure, the headphones of the present embodiment include a headphone plug 1, a headphone cord 2, an optical signal / 1-bit signal converter 3, and a headphone body 4.
[0023]
The headphone plug 1 is a terminal that is attached to and detached from an optical converter (the internal configuration is the same as that in FIG. 3 described above) of the MD playback device, and is a plug (EIAJ or the like) that transmits an optical signal instead of an electric signal. Of the same standard as the standard optical input plug). The headphone cord 2 is a transmission path for transmitting the optical digital signal input from the MD playback device via the headphone plug 1 to the next-stage optical signal / one-bit signal converter 3, and transmits an optical signal instead of an electric signal. It is formed by an optical fiber.
[0024]
The optical signal / 1-bit signal converter 3 converts the optical signal input via the headphone cord 2 into a 1-bit signal, and drives the small speakers 4L, 4R of the headphone body 4 based on the 1-bit signal. The headphone body 4 includes a pair of small speakers 4L and 4R that are applied to both ears of the user, and an arm 4A that connects them. The optical signal / one-bit signal converter 3 may be miniaturized (integrated into an IC or an LSI) and incorporated in one of the small speakers 4L and 4R or an arm 4A connecting them.
[0025]
Subsequently, the internal configuration and operation of the optical signal / 1-bit signal converter 3 will be described in detail. FIG. 2 is a block diagram showing the internal configuration of the optical signal / 1-bit signal converter 3. As shown in the figure, the optical signal / one-bit signal converter 3 of the present embodiment includes a battery 30a, a power supply circuit 30b, a light receiving element 31, a digital input demodulation unit 32, and a PLL [Phase-Locked-Loop]. A circuit 33, an asynchronous sampling rate converter 34, a ΔΣ (delta sigma) modulator 35, a PWM (Pulse Width Modulation) modulator 36, a crystal oscillation circuit 37, drivers 38L and 38R, and low-pass filters 39L and 39R ( (Hereinafter, referred to as LPFs 39L and 39R).
[0026]
The battery 30a is a power supply for driving the optical signal / 1-bit signal converter 3. In addition, as the battery 30a, a small button battery or the like that can be easily incorporated into the arm portion 4A is preferable. The power supply circuit 30b is a circuit for supplying power to each component of the optical signal / 1-bit signal converter 3, and includes a regulator IC (not shown) and the like. By adopting such a battery drive system, it is not necessary to draw out a power supply line from the MD playback device. Of course, a method of driving by receiving power supply from the MD playback device may be adopted.
[0027]
The light receiving element 31 is an element (photodiode or phototransistor) that converts an optical digital signal input via the headphone cord 2 into an electric signal. The digital input demodulation unit 32 demodulates the electric signal obtained by the light receiving element 31 to generate a PCM signal. The PLL circuit 33 generates a clock signal (a clock signal synchronized with the light receiving signal) used for the demodulation process and sends the clock signal to the digital input demodulation unit 32.
[0028]
The asynchronous sampling rate converter 34 converts the sampling frequency (32 [kHz], 44.1 [kHz], 48 [kHz], etc.) of the input PCM signal into a sampling frequency 44.1 [kHz] suitable for post-processing. I do. The ΔΣ modulator 35 modulates the input PCM signal into a multi-level PDM (Pulse Density Modulation) signal. The PWM modulator 36 modulates the input PDM signal into a PWM signal for each of the L / R channels, that is, a 1-bit (binary) signal. Note that a configuration may be employed in which the PCM signal is pre-modulated into a binary PDM signal by the ΔΣ modulator 35.
[0029]
The signal processing so far is pure digital signal processing, and its operation is controlled based on the reference clock signal generated by the crystal oscillation circuit 37. It should be noted that the asynchronous sampling rate converter 34 may be replaced with a synchronous type. In that case, however, the extracted clock signal may fluctuate due to the jitter of the received light signal. It is desirable to adopt the configuration of the present embodiment.
[0030]
The drivers 38L and 38R switch and amplify the PWM signals for the respective L / R channels input from the PWM modulator 36. The LPFs 39L and 39R remove the unnecessary high-frequency components (noise components) of the amplified signals input from the drivers 38L and 38R, and send the signals to the small speakers 4L and 4R. The circuits from the ΔΣ modulation circuit 35 to the LPF 39 are called “1 bit digital amplifier”.
[0031]
As described above, in the headphones of the present embodiment, analog signal processing after the PWM modulator 36 is performed completely independently for each of the L / R channels. By adopting such a configuration, the separation of both signals is increased as compared with the conventional configuration in which the ground line is common to both the L and R channels, so that the crosstalk can be reduced and the reproduced sound quality can be improved. As a result, it is possible to improve the S / N from about 40 [dB] to about 80 [dB]. In addition, since the ground lines are made independent for both the left and right channels, the small speakers 4L and 4R can be controlled by the BTL driving method, so that low voltage and large output driving and switching noise reduction can be achieved ( As an actual measurement example, it is possible to improve the distortion rate from about 0.1 [%] to about 0.01 [%].
[0032]
Further, in the headphones according to the present embodiment, since an optical fiber is used as the headphone cord 2, the optical digital signal transmitted via the headphone cord 2 is hardly lost, and the reproduced sound quality can be improved. .
[0033]
Further, in the headphones of the present embodiment, since the transmission signal via the headphone cord 2 is a digital signal, the reproduction sound quality is not deteriorated by analog elements such as power supply noise, board pattern, and disturbance noise, and the reproduction sound quality is improved. It becomes possible.
[0034]
In the above-described embodiment, a detailed description has been given of an example in which the present invention is applied to headphones used by being connected to a portable MD playback device. However, the application target of the present invention is not limited to this. Instead, the present invention can be widely applied to general headphones connected to digital audio equipment.
[0035]
【The invention's effect】
As described above, with the headphones according to the present invention, high-quality audio reproduction can be performed without being affected by power supply noise, board patterns, disturbance noise, and the like.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of headphones according to the present invention.
FIG. 2 is a block diagram showing an internal configuration of the optical signal / 1-bit signal converter 3.
FIG. 3 is a block diagram showing a configuration of a main part of a general disc reproducing apparatus.
FIG. 4 is a schematic diagram showing a configuration example of a conventional headphone.
[Explanation of symbols]
1 headphone plug (light)
2 Headphone cord (optical fiber)
3 Optical signal / 1 bit signal converter 30a Battery 30b Power supply circuit 31 Light receiving element 32 Digital input demodulation unit 33 PLL circuit 34 Asynchronous sampling rate converter 35 ΔΣ (delta sigma) modulation unit 36 PWM modulation unit 37 Crystal oscillation circuits 38L, 38R Driver (For L / R channels)
39L, 39R low pass filter (for L / R channels)
4 Headphone body 4L, 4R Small speaker 4A Arm 5 Disk playback device 51 Disk 52 Signal processing circuit 53 Digital / analog converter (D / A converter)
54 Headphone Jack 55 Digital Output Modulator 56 Optical Converter

Claims (5)

A plug attached to and detached from an optical output terminal of a digital audio device, an optical fiber serving as a transmission path for an optical digital signal input from the plug, and a speaker drive signal based on the optical digital signal input via the optical fiber A headphone comprising: an optical signal / drive signal converter that generates a signal; The optical signal / drive signal converter includes a light receiving element that converts the optical digital signal into an electric signal, a digital input demodulation unit that demodulates the electric signal to generate a PCM signal, and a clock synchronized with the optical digital signal. A PLL circuit that generates a signal and sends the signal to the digital input demodulation unit; a sampling rate converter that converts a sampling frequency of the PCM signal; and modulates the frequency-converted PCM signal into a binary or multi-level PDM signal. A ΔΣ modulator, a PWM modulator for modulating the PDM signal into a PWM signal for each of L / R channels, a driver for amplifying each PWM signal, and removing unnecessary components from an output signal of the driver to the speaker. The headphone according to claim 1, further comprising: a filter for transmitting. The optical signal / drive signal converter includes an oscillation circuit that generates a reference clock signal used for each signal processing in the sampling rate converter, the ΔΣ modulation unit, and the PWM modulation unit. The headphones according to claim 2. 4. The optical signal / drive signal converter according to claim 1, wherein the optical signal / drive signal converter is incorporated into one of the pair of speakers applied to both ears of a user or an arm unit connecting the speakers. The headphones according to any of the above. The headphone according to any one of claims 1 to 4, wherein the optical signal / drive signal converter is driven by a battery.

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