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DESCRIPTION JP2004104266

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DESCRIPTION JP2004104266
[Purpose] To maintain a rated output in a bone conduction headphone even when a digital
broadcast sound or the like having a wide dynamic range is set while using a normal audio
amplifier as used in an analog broadcast receiver etc. The present invention provides a digital
audio signal reproduction bone conduction output device. An audio signal output from an AV
selector 4 is input to an audio output circuit 7 for bone conduction headphones after passing
through a gain limiting circuit 8. The bone conduction headphone sound output circuit 7
amplifies the sound signal and outputs the sound signal to a bone conduction headphone not
shown. The gain limiting circuit 8 attenuates the audio signal when the audio signal output from
the AV selector 4 exceeds a predetermined level. [Selected figure] Figure 1
Digital voice signal reproduction bone conduction output device
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
digital audio signal reproduction bone conduction output device, and is used, for example, in a
digital broadcast receiver. [0002] A bone conduction headphone system for listening to voice
using bone conduction sound, which is one of human's voice conduction paths, has been in the
limelight in recent years, and an amplifier in consideration of the characteristics of this bone
conduction headphone has been developed. Development of a built-in television receiver is
currently in progress (see Non-Patent Document 1 and Non-Patent Document 2). FIG. 3 shows a
block diagram of a conventional television receiver compatible with bone conduction
headphones. A volume control circuit 5 provided in an audio output system for a speaker
receives an audio signal from the AV selector 4, receives a control signal from a remote control
transmitter or a main body key, and responds to the audio signal with volume and bass. , Control
the treble. The audio signal output from the volume control circuit 5 is amplified by the audio
output circuit 6, and audio is output by the vibration of the main speaker. In the bone conduction
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audio output system, the audio signal output from the AV selector 4 is input to the bone
conduction headphone audio output circuit 7. The bone conduction headphone sound output
circuit 7 amplifies the sound signal and outputs the sound signal to a bone conduction
headphone not shown. [Non-Patent Document 1] [online] Internet [searched on September 3,
2002] <URL: http: // www. watch. impress. co. jp / av / docs / 20020115 / sanyo. htm> [NonPatent Document 2] [online] News Release: January 15, 2002 [Search on September 3, 2002]
Internet <URL: http: // www. sanyo. co. jp / koho / hypertext 4/0201 news-j / 0115-2. [0010]
The design of the rated output of the main speaker and the bone conduction headphone as
described above is generally performed on the audio output circuit unit. However, the voltage
gain of the amplifier is usually fixed, and when designing the output of the main speaker or bone
conduction headphone, level adjustment is performed by resistance division of the amplifier
input stage to match the rated output of the bone conduction headphone. I have to. Then, in a
television receiver or the like compatible with bone conduction headphones, a signal of 100%
modulation (approximately 500 mVrms) of ground wave analog broadcasting is used as a signal
source at the time of the adjustment.
By the way, when trying to provide a bone conduction headphone compatible type with a digital
broadcast receiver such as BS digital, CS digital, or terrestrial digital, these digital broadcasts
have a wider dynamic range than terrestrial analog signals and have a level Since a large signal
may be input, when the rated output is designed as described above, it is expected that the
distortion rate of the amplifier output will be sharply deteriorated from the time of exceeding the
rating. For this reason, there is a concern that the viewer wearing the bone conduction
headphone may feel discomfort and fatigue by directly receiving the greatly distorted output
from the bone conduction headphone. At the same time, it also involves the inconvenience of
fine-tuning the volume to avoid this distortion. [0009] In view of the above-described
circumstances, the present invention uses a normal audio amplifier as used in an analog
broadcast receiver or the like, and also receives a bone even when digital broadcast audio or the
like having a wide dynamic range is set. It is an object of the present invention to provide a
digital audio signal reproduction bone conduction output device capable of maintaining a rated
output in a bone conduction output device such as a conduction headphone. SUMMARY OF THE
INVENTION In order to solve the above problems, the digital audio signal reproduction bone
conduction output device of the present invention D / A converts a digital audio signal and
outputs an analog audio signal. Means, an audio signal output means for a bone conduction
output device for amplifying an analog audio signal to be provided to a bone conduction output
device, and an analog speech signal provided at an input stage of the audio signal output means
for the bone conduction output device And an audio signal level limiting means for limiting the
output to a predetermined level when the signal is input. According to the above configuration,
since the audio signal level limiting means is provided, a dynamic audio signal is used as an audio
output means for the bone conduction output device while using a normal audio amplifier such
as that used in an analog broadcast receiver or the like. Even when a digital broadcast voice with
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a wide range is set, the bone conduction output device can maintain the rated output. The audio
signal level limiting means comprises means for generating a reference voltage corresponding to
the level of the input audio signal when the bone conduction output device is rated, and means
for comparing the reference voltage with the level of the input audio signal. And means for
attenuating the input audio signal based on the comparison result. Further, means for turning on
/ off the level restriction process of the audio signal may be provided according to the user's
instruction.
BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will
be described below with reference to FIGS. 1 and 2. Here, a configuration example in which a
digital audio signal reproduction bone conduction output device is incorporated into a broadcast
receiving apparatus is described. It shows. FIG. 1 is a block diagram showing a digital / analog
broadcast receiver 30 and FIG. 2 is a circuit diagram showing a specific configuration of the gain
control circuit in FIG. The antenna 1A receives an analog broadcast signal sent from a terrestrial
analog broadcast station, and supplies the received signal to the terrestrial analog tuner 2A. Also,
the antenna 1B receives a BS digital broadcast signal, and applies the received signal to the BS
digital tuner 2B. The terrestrial analog tuner 2A generates an intermediate frequency signal (IF)
of video and audio in the channel selection process. The description of the video processing
system is omitted. The voice intermediate frequency signal is detected to be a voice signal
containing a voice multiplex signal, and is supplied to the voice multiplex decoder circuit 3A. A
voice signal containing a voice multiplex signal is multiplexed with a frequency-modulated
secondary voice signal and an amplitude-modulated control signal, and is demodulated into
stereo voice and 2-voice signal by the voice multiplex decoder circuit 3A. The BS digital tuner 2 B
takes out a signal of a specific frequency from among high frequency digital modulation signals
including video and audio data. In addition, the tuner 2B includes a demodulation circuit, a
deinterleave circuit, an error correction circuit, and the like to demodulate the selected digital
modulation signal and output a transport stream. The DEMUX / decoder circuit 3B inputs the
transport stream, and separates the stream into an MPEG2 (Moving Picture Experts Group 2)
video stream, an audio stream, additional information, and the like. The description of the video
processing system is omitted. Then, by decoding processing, the audio stream is decoded to
generate audio data, and this audio data is subjected to D / A conversion, for example, an analog
signal of right (R) sound and an analog signal of left (L) sound. It generates or generates analog
signals of main voice and subvoice. The AV selector 4 selects an audio signal based on a
command from a CPU (not shown), switches the path to the bone conduction headphone system
or a normal main speaker system, and outputs the selected audio signal. A volume control circuit
5 provided in an audio output system for a speaker receives an audio signal from the AV selector
4, receives a control signal from a remote control transmitter or a main body key, and responds
to the audio signal with volume and bass. , Control the treble.
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The audio signal output from the volume control circuit 5 is amplified by the audio output circuit
6, and audio is output by the vibration of the main speaker. In the bone conduction audio output
system, the audio signal output from the AV selector 4 is input to the bone conduction
headphone audio output circuit 7 after passing through the gain limiting circuit 8. The bone
conduction headphone sound output circuit 7 amplifies the sound signal and outputs the sound
signal to a bone conduction headphone not shown. As shown in FIG. 2, the gain limiting circuit 8
comprises a level comparison circuit 9, an attenuation circuit 10 and a reference voltage
generation circuit 11. The reference voltage generation circuit 11 generates a voltage
corresponding to the level of the input audio signal (hereinafter referred to as a reference level)
when the bone conduction headphone output is rated. The level comparison circuit 9 compares
the level of the input audio signal with the reference level. Here, the level comparison circuit 9 is
set to output a control voltage such that the attenuation circuit 10 in the subsequent stage does
not attenuate if the level of the input audio signal is smaller than the reference level. On the other
hand, when the level of the input audio signal exceeds the reference level, the deviation between
the input audio signal and the reference level is converted into a control voltage and applied to
the attenuation circuit 10. Attenuation circuit 10 operates in response to the control voltage to
attenuate the level of the input audio signal. Thereby, while using a normal audio amplifier as
used in an analog broadcast receiver etc., the rated output can be maintained in the bone
conduction headphone even when the digital broadcast audio etc. having a wide dynamic range
is set is input. It is possible to prevent the viewer from feeling discomfort due to distortion of the
bone conduction headphone output due to excessive signal input when watching a program of BS
digital broadcasting, and to adjust the volume to avoid distortion. It is released from the trouble.
Although the digital broadcast receiver 30 incorporating the digital audio signal reproduction
bone conduction output device is shown in the above-mentioned example, the present invention
is not limited to this, and the digital audio signal reproduction bone conduction output device
may be a DVD player or the like. You may incorporate. Also, although an example of receiving BS
digital broadcast has been shown, the present invention is also suitable for CS digital broadcast
and terrestrial digital broadcast reception. Further, the level limitation process of the audio signal
may be turned on / off according to the user operation. For example, a circuit configuration in
which the gain of the attenuation circuit 10 is fixed to 1 when OFF, or a path for bypassing the
gain limiting circuit 8 is provided, and a switch for selecting either the bypass path or the output
of the gain limiting circuit 8 The circuit configuration provided may be considered.
As described above, according to the present invention, digital broadcast audio with a wide
dynamic range set while using a conventional audio amplifier as used in an analog broadcast
receiver or the like. Even when inputting etc., it is possible to maintain the rated output in the
bone conduction headphone, and it is possible to maintain a state easy for the viewer to hear. In
addition, the audio adjustment is not performed by the viewer itself, and the user is relieved from
the inconvenience. Further, since a normal audio amplifier as used in an analog broadcast
receiver or the like can be used as described above, the price of the apparatus can be reduced as
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compared with the case of newly developing an audio amplifier for digital use. The user can
arbitrarily select a desired state as long as the audio signal level restriction can be turned ON /
OFF. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a digital /
analog broadcast receiver including a digital voice signal reproduction bone conduction output
device of this embodiment. FIG. 2 is a circuit diagram showing a specific configuration of a gain
control circuit in FIG. FIG. 3 is a block diagram showing a digital / analog broadcast receiver
incorporating a conventional bone conduction output device. [Description of the code] 7 Audio
output circuit for bone conduction headphone 8 Gain limiting circuit 9 Level comparison circuit
10 Attenuation circuit 11 Reference voltage generation circuit
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