JPH11136791

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DESCRIPTION JPH11136791
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
reproducing apparatus, and more particularly to a reproducing apparatus that reproduces audio
signals in the audible range using a transducer to generate a change in sound pressure.
[0002]
2. Description of the Related Art Conventionally, in order to provide an audio signal to a listener,
a drive current corresponding to the audio signal is supplied to a transducer (electric-to-sound
pressure conversion element) such as a speaker, headphone or earphone to In response to the
change in sound pressure was caused.
[0003]
FIG. 3 is a block diagram showing an example of a conventional reproducing apparatus.
[0004]
In the figure, reference numeral 102 denotes a preamplifier, which performs predetermined
processing on the audio signal in the audible band from the input terminal 101 and outputs it.
Reference numeral 103 denotes a power amplifier (power amplifier), which amplifies the power
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of the preamplifier output and outputs a drive current.
This drive current is supplied to the speaker 104. The speaker 104 is a known structure having a
diaphragm or the like driven and operated by a drive current, and reproduces a sound by this
vibration.
[0005]
However, in the conventional reproduction apparatus, the operating current of the transducer
changes in accordance with the magnitude of the audio signal, but there has been a case where
non-linearity in a small signal becomes a problem.
[0006]
FIG. 4 is a waveform diagram for explaining this problem, and shows signal waveforms of
respective parts in FIG.
In FIG. 4, (A) is an input audio signal at the input terminal 101, and (B) is an output signal of the
preamplifier 102.
[0007]
The figures (C) and (D) show two examples of the drive current waveform to the speaker 104, (C)
shows the time of small level reproduction, and (D) shows the time of large level reproduction.
[0008]
Here, the speaker 104 operates linearly outside the area of the small signal indicated by the
broken line, but the speaker 104 operates non-linearly within the area of the small signal.
This is because the operating current of the speaker 104 changes according to the size of the
input audio signal, but it is difficult to vibrate the diaphragm itself or change the air pressure on
the surface of the diaphragm when the signal is small. There is no change in sound pressure
according to Therefore, distortion occurs in the small signal area, and only a voice with poor
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linearity can be reproduced. That is, as can be understood from FIGS. 7C and 7D, most of the
input signal enters the area where the linearity of the speaker 104 is bad at the time of small
level signal reproduction. In addition, even at the time of large level signal reproduction, the
small amplitude portion enters an area of poor linearity.
[0009]
Therefore, the present invention has been made in view of the above-mentioned point, and an
object of the present invention is to provide a reproducing apparatus which solves the abovementioned problems.
[0010]
In order to achieve the above object, according to the device of the present invention as set forth
in claim 1, an input means for inputting an audio signal in the audible band and a drive signal in
a wider band than the audible band are provided. Conversion means for generating a
corresponding sound pressure change, and a drive means for outputting the drive signal to the
conversion means based on the audio signal, the reproduction apparatus for reproducing the
audio signal comprising: Is characterized by comprising: signal generation means for generating
an alternating current signal of a fixed level; and mix means for mixing the alternating current
signal and the audio signal and supplying the mixed signal to the drive means.
[0011]
Here, in the device according to the second aspect of the present invention, when the peak value
is supplied to the converting means through the driving means, the mixed sound signal is a signal
of the converting means. It may be a value that falls within a linear operable region outside the
non-linear region of the electrical-sound pressure conversion characteristics.
[0012]
Here, in the device according to the third aspect of the present invention, the signal generation
means may be an oscillator that generates a sine wave signal as the alternating current signal.
[0013]
Here, in the device according to the fourth aspect of the present invention, the frequency of the
alternating current signal from the oscillator can be higher than the maximum frequency of the
audio signal.
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[0014]
Here, in the device according to the fifth aspect of the present invention, the frequency of the
alternating current signal from the oscillator may be lower than the minimum frequency of the
audio signal.
[0015]
Here, in the apparatus according to the sixth aspect of the present invention, the alternating
signal may be amplitude-modulated with the audio signal by the mixing means.
[0016]
Here, in the device according to the seventh aspect of the present invention, the drive means may
be a power amplifier for supplying a drive current of a speaker as the conversion means.
[0017]
Here, in the device according to the eighth aspect of the present invention, the drive means may
be a power amplifier for supplying a drive current of headphones as the conversion means.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will
now be described in detail with reference to the drawings.
[0019]
FIG. 1 is a block diagram showing an embodiment of a playback apparatus to which the present
invention is applied.
[0020]
In the figure, reference numeral 2 denotes a preamplifier which performs predetermined
processing on an audio signal in the audible band (20 Hz to 20000 Hz) input from the input
terminal 1 and outputs the processed signal.
For example, in the case of an audio tape recorder or a video tape recorder, equalization is
performed, and in a stereo audio system, this is boost control for each band such as balance
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control, treble, and bus.
Reference numeral 3 denotes a power amplifier (power amplifier), which amplifies the power of
the input audio signal and outputs a drive current.
The drive current is supplied to the speaker 4.
[0021]
The speaker 4 is a known configuration having a diaphragm or the like driven and operated by a
drive current, and reproduces voice by changing the air pressure in the vicinity of the diaphragm
by this vibration.
The speaker 4 is connectable to the playback device, and by changing the specification of the
power amplifier 3, another transducer (electric-sound pressure conversion element) such as an
ear-rest type headphone or earphone is connected to supply a drive current It is well known that
it is also possible to generate a sound pressure change according to the audio signal and provide
the listener with a reproduced audio signal.
[0022]
However, in the present embodiment, the power amplifier 3 can amplify and output a signal
other than the audible band, for example, a band of DC to 30000 Hz, and the transducer also
changes the pneumatic pressure to this band other than the audible band. It shall be convertible.
However, DC may not be converted.
[0023]
An oscillator (OSC) 5 generates and outputs an AC sine wave signal outside the audible band of,
for example, 10 Hz or 30000 Hz.
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The sine wave signal has a peak value at a constant level.
A mix circuit 6 superimposes the output signal of the oscillator 5 and the preamplifier output
signal, and supplies the superimposed signal to the power amplifier 3.
[0024]
Here, FIG. 2 shows the signal waveform of each part in FIG.
[0025]
In FIG. 1, (A) is an input voice signal at the input terminal 1 and (B) is an output signal of the
preamplifier 2.
Here, the output signal of the preamplifier 2 is a signal obtained by applying a predetermined
signal processing to the input audio signal to attenuate it.
Further, this waveform shows that the amplitude of the input speech signal is attenuated, but as
described above, the frequency characteristic may be changed by the control for each band.
[0026]
FIG. 6C shows the output signal of the oscillator 5, the envelope of which is indicated by a solid
line, and the hatched portion represents a 30000 Hz sine wave that exceeds the audible band.
The envelope is a straight line, which indicates that the crest value is at a constant level.
[0027]
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Also, FIG. 6D shows the output current of the power amplifier 3, but the envelope is indicated by
a solid line, and the hatched portion indicates that a 30000 Hz sine wave exceeding the audible
band is superimposed.
This current waveform is the same as the output waveform of the mixing circuit 6, but is a
waveform obtained by AM-modulating a sine wave of a fixed level with the audio signal of the
preamplifier output.
[0028]
The envelope level of the output current is determined by the peak value of the output signal of
the oscillator 5, but the peak value of the sine wave signal supplies the output signal mixed by
the mixing circuit 6 to the transducer such as the speaker 4 via the power amplifier 3. When this
is done, the mixed audio signal is set to a value that falls within a linear operable region outside
the non-linear region of the electric-sound pressure conversion characteristic of the speaker 4.
[0029]
That is, in FIG. 2D, the speaker 4 linearly operates outside the area of the small signal above and
below the broken line, but in the area of the small signal sandwiched by the broken line, the
speaker 4 faithfully responds to the input audio signal. This is the range of non-linear operation
where no pressure change occurs.
As understood from FIG. 2D, the speaker 104 is operated by the drive current having the
envelope of the same waveform as the audio signal of FIG. 2B.
The audio signal to be reproduced exists as an envelope waveform outside the area of the small
signal in which the speaker 104 linearly operates, and there is a sine wave outside the audible
band of a certain level in the area of the small signal sandwiched by the broken lines Just do it.
[0030]
Therefore, the change in sound pressure caused by the operation of the speaker 104 is as shown
in FIG. 2D, and the listener can hear only the input sound in the audible band (20 Hz to 20000
Hz) according to the envelope waveform.
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[0031]
According to the present embodiment, the speaker is operated according to the audio signal in a
region out of the non-linear operation region of the speaker, so distortion does not occur even for
a small level, and the input signal is small. It is possible to provide high-quality reproduced
speech with good linearity over the range from level to large level.
[0032]
The present invention can be applied to an audio reproduction apparatus that drives and
reproduces not only the speaker but also other transducers.
In the above embodiment, the oscillator 5 oscillates and outputs a sine wave having a frequency
higher than the audible band. However, a sine wave having a frequency lower than the audible
band may be output.
[0033]
As described above, according to the present invention, the drive signal is output based on the
audio signal in the audible band to the conversion means that generates the sound pressure
change according to the drive signal in a wider band than the audible band. Drive means, signal
generation means for generating an alternating current signal having a constant peak value, and
mixing means for supplying a mixed signal of the alternating current signal and the audio signal
to the driving means, the conversion means using the mixed signal Can be generated to generate
a change in sound pressure, and the audible band is output as a reproduced sound, so that a
good characteristic according to the characteristic of the conversion means can be obtained by
the peak value.
[0034]
An effect is obtained.
[0035]
Brief description of the drawings
[0036]
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1 is a block diagram showing an embodiment of a reproduction apparatus to which the present
invention is applied.
[0037]
2 is a waveform diagram showing the signal waveform of each part in FIG.
[0038]
3 is a block diagram showing an example of a conventional reproduction apparatus.
[0039]
4 is a waveform diagram for explaining the problems of the conventional reproduction
apparatus.
[0040]
Explanation of sign
[0041]
1, 101 input terminal 2, 102 preamplifier 3, 103 power amplifier 4, 104 speaker 5 oscillator 6
mix circuit
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