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JP2004040292

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DESCRIPTION JP2004040292
PROBLEM TO BE SOLVED: To improve a rising distortion and reproduce soft tones with a low
sound quality in bass reproduction. SOLUTION: An amplifier 4 for amplifying an output signal of
the LPF 2, a rectification circuit 5 for level rectification, and a level detection circuit for detecting
a rectified signal level are provided at a stage subsequent to the LPF 2 for extracting a bass
component of an input audio signal. 6 and the bass detection control circuit unit 3 including the
integration circuit 7 that integrates the level detection section detected by the level detection
circuit 6, and the voltage waveform of the bass detection section obtained by the bass detection
control circuit unit 3 Addition including a volume control amplifier 8 for controlling and
amplifying the output signal of the LPF 2 as a control signal, and adding the output of the volume
control amplifier 8 and the audio signal passed through the HPF 1 for extracting middle to high
tone component of the input audio signal The unit 9 is provided to achieve soft tone
reproduction. [Selected figure] Figure 1
Bass reproduction circuit
TECHNICAL FIELD [0001] The present invention relates to bass reproduction for sound
reproduction. In particular, it relates to bass reproduction of poor TV sets with bass
reproduction. [0002] A speaker mounted on a TV set can not reproduce sufficient bass
components due to size and shape restrictions, and digital high-performance music sources such
as BS (satellite broadcasting) and high-definition broadcast are broadcasted Despite this, there
was a problem that only poor bass reproduction could be enjoyed. Recently, opportunities for
connecting to external source devices such as CDs and DVDs have increased, and the need for
bass reproduction has been desired. Usually, to boost the bass, it is sufficient to boost the bass
with the tone control circuit (tone control), but usually this tone control circuit is often integrated
into an IC, and the dynamic range is It is decided, naturally, the amount to be amplified is limited.
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In order to compensate for this defect, as shown in Japanese Patent Laid-Open No. 5-236589,
the amplification factor of the bass is controlled according to the level of the audio signal, the
amplification effect is eliminated at the minute level, and the volume is small. A bass
enhancement method is known which performs sufficient bass enhancement and suppresses the
enhancement effect so as not to exceed the dynamic range at high volume. An example of bass
enhancement will be described below with reference to FIGS. 4 and 5. In FIG. 4, reference
numeral 21 denotes an LPF for extracting a bass component, 22 denotes a volume control
amplifier (hereinafter abbreviated as VCA) for amplifying the bass component, and 23 denotes an
amplified bass component and an input audio signal. An adder for adding, an effective value
conversion circuit for detecting an effective value of the input audio signal, a small level
detection circuit, and a maximum value detection circuit are provided. The operation of the bass
boost constructed as described above will be described. The input level is detected by the
effective value conversion circuit 24 using the input audio signal, and the amplification effect is
eliminated by the minute level detection circuit 25 and the maximum value detection circuit 26
when the level is small, and the dynamic range is large when the volume is large. In order not to
exceed, the VCA 22 is controlled to amplify the bass component passed through the LPF 21, and
the input audio signal is added by the adder 23. That is, as shown in FIG. 5A, when the bass
component is amplified and added at a fixed amplification factor, the input audio signal leads to
noise enhancement at a minute level, and distortion occurs at a large volume. By making the
amplification factor of this VCA 22 variable, as shown in FIG. 5B, it is possible to enhance the
bass with suppressed noise increase and distortion.
SUMMARY OF THE INVENTION However, in the above-mentioned conventional configuration,
when the bass is reproduced using the poor TV set speaker of the bass reproduction, only
distorted and hard bass can be reproduced. Usually, the bass signal has an envelope with a large
amplitude at the rising portion and a gradual decay after that, as represented by bass
instruments. When this signal is reproduced by a speaker with a hard edge and poor response,
an overamplitude or response delay occurs, resulting in distortion such as that of the speaker
edge and distortion due to back electromotive force of the speaker. There is a problem that it is
hard and it is hard to hear it. This can not be solved only by the control operation that does not
exceed the dynamic range at high volume. SUMMARY OF THE INVENTION In order to solve the
above problems, a bass reproduction circuit according to the present invention comprises an LPF
for extracting a bass component of an input audio signal and an amplifier for amplifying the LPF
output signal. A bass detection control circuit unit comprising a rectification circuit for rectifying
a signal level, a level detection circuit for detecting a rectified signal level, and an integration
circuit for integrating a level detection section detected by the level detection circuit in the latter
stage. A volume control amplifier for controlling and amplifying the LPF output signal using the
voltage waveform of the bass detection section obtained by the bass detection control circuit unit
as a control signal, and the volume control amplifier output and the middle to high tone
component of the input audio signal An adder is added to add the HPF output signal that has
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passed through the HPF to extract H.sub.F. According to the present invention, there is provided
a bass reproduction circuit capable of reducing the load on the speaker and the load on the
power amplifier by gradually reproducing the rising portion of the bass and performing timeseries control of the bass component. it can. DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS The bass reproduction circuit according to claim 1 of the present invention is an
LPF that extracts a bass component of an input audio signal, and a signal after the amplifier that
amplifies the LPF output signal. The bass detection control circuit unit includes a rectification
circuit for rectifying a level, a level detection circuit for detecting a rectified signal level, and an
integration circuit for integrating a level detection section detected by the level detection circuit,
and A volume control amplifier for controlling and amplifying the LPF output signal using the
voltage waveform of the bass detection section obtained by the bass detection control circuit unit
as a control signal, comprising: the output of the volume control amplifier; An adder is added to
add to the HPF output signal that has passed through the HPF that extracts the component, and
it is configured to achieve bass reproduction with less distortion. Than is.
Furthermore, the bass reproduction circuit according to claim 2 comprises an LPF for extracting
a bass component of the input audio signal at a stage subsequent to an adder for adding the
input audio Lch signal and the audio Rch signal. From a rectification circuit that rectifies the
signal level downstream of the amplifier that amplifies the LPF output signal, a level detection
circuit that detects the rectified signal level, and an integration circuit that integrates the level
detection section detected by the level detection circuit And a volume control amplifier for
controlling and amplifying the LPF output signal using the voltage waveform of the bass
detection section obtained by the bass detection control circuit unit as a control signal, and the
volume control A first addition for adding the amplifier output and the output signal of the first
HPF for extracting the middle to high tone component of the input audio Lch signal And a second
adder for adding the output of the volume control amplifier and the output signal of the second
HPF for extracting middle-to-high-tone components of the input audio Rch signal, and
reproducing bass with less distortion Is configured with two channel signals. Hereinafter,
embodiments of the present invention will be described with reference to FIGS. 1 to 3.
Embodiment 1 Hereinafter, an embodiment of the invention described in claim 1 and claim 2 of
the present invention will be described with reference to FIGS. 1 and 2. FIG. FIG. 1 shows a block
diagram of a bass reproduction circuit according to an embodiment of the present invention. In
FIG. 1, reference numeral 1 denotes an HPF for extracting middle-to-high-pitched components
among the inputted audio signals, 2 denotes an LPF for extracting a bass component, and 3
denotes bass detection control for detecting an output section of the bass component and
controlling an amplification factor. A circuit unit, 4 is an amplifier for amplifying the signal level
extracted by the LPF, 5 is a rectifier circuit for rectifying the signal level, 6 is a level detection
circuit for detecting the rectified signal level, 7 is an output from the level detection circuit
Integrated circuit for integrating the output pulse, VCA for controlling and adjusting the signal
level of the bass component extracted by the LPF with the output signal of the integrator circuit,
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9 for the middle to high tone component extracted by the HPF and the VCA It is an adder that
adds the adjusted bass component. The operation of the bass reproduction circuit configured as
described above will be described. The input audio signal is extracted only by the low frequency
component by the LPF 2 and is amplified by the amplifier 4. The amplified bass component is
rectified by the rectifier circuit 5 and its envelope level is output. Based on the envelope level, the
level detection circuit 6 detects a sound interval of the bass component to form a pulse
waveform.
That is, the section where the bass component is present is H level. The pulse of the bass
component sound section is integrated by the integrating circuit 7, and the obtained output
voltage is set as a voltage for controlling the amplification factor of VCA 8, the bass component
outputted by the LPF 2 is amplified by VCA 8, and the adder 9 is By adding with the output of the
HPF 1 that passes middle-to-high tone among the input audio signals, the signal gently rises only
at the rising portion of the bass component. Specifically, it is as follows. In general, a bass is a
typical musical instrument that reproduces low tones, and it is assumed that the bass is played
with bonbons (referred to as bass running). In this case, one note of the base has a waveform of
several cycles, there is a blank, and the next one of the notes comes again for several cycles. In
other words, among the several cycles of waveform of this one base sound, the signal level is
gradually raised by a few cycles of the rising, the attack is weakened, the distortion generated at
the rising part of the bass is improved, and the bass reproduction of soft tone quality It is the
intent of the present invention to FIG. 2 shows a time-series waveform of each part of the bass
reproduction circuit shown in FIG. 1, and is an explanatory diagram when an audio signal
including all bands is inputted. That is, when the input voice signal (a) waveform of the entire
band is input, only the bass component is extracted by the LPF 2 and the waveform becomes (b).
The waveform (b) is amplified by the amplifier 4 and rectified by the rectifier circuit 5 to extract
the waveform (c) of the envelope signal. (C) The waveform becomes a pulse waveform (d) in the
level detection circuit 6. The H level of this pulse waveform (d) is a section where there is a bass
component. The pulse waveform (d) of the low sound component sounding interval is integrated
by the integrating circuit 7 to obtain the waveform (e). The output voltage (e) waveform obtained
by the integration circuit 7 is a voltage for controlling the amplification factor of VCA8, and the
bass component outputted by the LPF 2 is amplified by VCA2 and the bass component rises as
shown by the (f) waveform. By adding the (f) waveform and the middle to high tone component
that has passed through the HPF 1 by the adder 9, the signal level is gradually raised by a few
cycles of the rising of the low tone component. It weakens the attack, improves the distortion
that occurs at the beginning of the bass, and can play soft bass sound. Second Embodiment Next,
an embodiment of the invention described in claim 3 of the present invention will be described
with reference to FIG. The same reference numerals are used for the same configuration as the
embodiment described above, and the description is omitted.
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FIG. 3 shows a block diagram of a bass reproduction circuit according to an embodiment of the
present invention. In FIG. 3, reference numeral 10 is a HPF for extracting middle-to-high-pitched
sound components among the inputted speech signals, 11 is an adder for adding speech LR
signals, and 12 is adjusted with the middle-to-high-pitched sound components extracted by the
HPF and the VCA. Is an adder that adds the low-pitched sound components. The operation of the
bass reproduction circuit configured as described above will be described. The input signals of
the audio LR 2 channel are added by the adder 11. Normally, the bass component is an LR inphase signal in the case of two channels, and therefore can be added. Of the added signals,
through the LPF 2 for extracting the bass component, the sounded section of the bass is detected
with the same configuration as the first embodiment described above, and the VCA 8 gently
passes the bass component only at the rising portion and adds The circuit can be simplified and
the same bass can be reproduced by adding each of the middle and high-tone components to the
extracted LR. In the first and second embodiments, although the bass component level control is
performed only at the rising portion of the bass by the VCA 8 in the first and second
embodiments, it can be easily realized by a simple electronic switch and a mute circuit by a
transistor Needless to say, the amount of bass addition also needs to be adjusted. As described
above, the bass reproduction circuit according to the present invention gently reproduces the
rising portion of the bass, thereby improving the distortion generated at the rising portion of the
bass and making the bass having a soft sound quality It is possible to provide a bass
reproduction circuit that can be played back, and the load on the speaker can be reduced and the
load on the power amplifier can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a
block diagram of the bass reproduction circuit according to the first embodiment of the present
invention. FIG. 2 is a waveform diagram for explaining the operation of each part in FIG. Block
configuration diagram of bass reproduction circuit in mode 2 [FIG. 4] Block configuration
diagram of conventional bass amplifier circuit [FIG. 5] Amplification characteristic diagram of
conventional bass amplifier circuit [Description of code] 1 HPF 2 LPF 3 bass detection control
circuit unit Amplifier 5 Rectifier circuit 6 Level detection circuit 7 Integration circuit 8 Volume
control amplifier (VCA) 9 Adder 10 HPF 11 Adder 12 Adder 21 LPF 22 Volume control amplifier
(VCA) 23 Adder 24 Effective value conversion circuit 25 Minute level detection Circuit 26
Maximum value detection circuit
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