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JPH11220793

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DESCRIPTION JPH11220793
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
bass enhancement circuit that compensates for the absence of bass component and enhances
bass feeling when a poor loudspeaker with low bass response is used.
[0002]
2. Description of the Related Art A speaker mounted on a television receiver or the like can not
reproduce sufficient low-frequency components due to size and shape restrictions, and a digital
high-performance music source such as BS (satellite broadcasting) or high-definition television.
Although it was broadcasted, it had the problem that only poor bass reproduction could be
enjoyed.
[0003]
In order to compensate for this defect, products equipped with speakers and amplifiers dedicated
to low-frequency range reproduction have been put on the market, but there are many problems
such as the need for an installation place and box sounds of a set (chatter noise).
[0004]
For example, the configuration of FIG. 6 has been proposed as a low-frequency component
compensation method for solving these problems.
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[0005]
Hereinafter, an example of the low frequency range component compensation method will be
described with reference to FIG.
In FIG. 6, reference numeral 7 is a low pass filter (hereinafter referred to as "LPF") for extracting
the bass component, 8 is a normalizer for normalizing the amplitude of the input signal, and 9 is
a 2nd harmonic generating a second harmonic. A generator 10 is a 3rd harmonic generator that
generates 3rd harmonics, 11 is an nth harmonic generator that generates nth harmonics, and 12
is an adder that adds signals.
[0006]
The operation of the bass range compensating method configured as described above will be
described.
2nd harmonics generator 9 and 3rd harmonics generator 10 which generate harmonics through
normalizer 8 which extracts only the low frequency range component with LPF7 and normalizes
the amplitude information to make it constant. And an n-th harmonic generator 11 that
generates harmonics sequentially.
[0007]
The harmonic components can be generated by performing the following mathematical
processing.
That is, assuming that the original sound is cos ?, the second harmonic can be obtained as cos
2? = 2 и cos 2?-1 by squaring the original sound, and similarly, the third and fourth harmonics
have the original sound in the third and fourth powers. Cos3? = 4 и cos3?-3 и cos?cos4? = 8 и
cos4?-8 и cos2? + 1 is obtained by the following processing up to the n-th harmonic to generate
coefficients with appropriate levels, The input original sound is mixed with the adder 12 to be
the final output.
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[0008]
That is, as shown in FIG. 7A, the speaker used in the television receiver or the like has poor
reproduction of the low tone range, and a sufficient low tone range is not reproduced.
[0009]
As a means to eliminate this, it is a bass range reproduction method using the psychoacoustic
effect of human hearing.
That is, by generating the second and third harmonics of the low frequency range component
shown in FIG. 7 (b) and outputting it as a composite sound within the reproduction range of the
speaker, it is as if the low range is being reproduced. hear.
[0010]
However, in the above-described conventional configuration, the scale of the circuit to be realized
becomes large, and the realization in an analog circuit is very difficult. In addition, although it can
be easily realized by using a digital signal processor (DSP), the program size for processing
becomes very large and the cost is also greatly increased.
[0011]
In addition, it will cause discomfort when it thinks in music. For example, when the sound of 55
Hz is input, the second harmonic becomes a sound of 110 Hz, and the third harmonic becomes a
sound close to 165 Hz. These are reproduced as second- and third-order synthetic chords to
become dissonances, and have problems that can not be said to be true to the pitch of the
original sound.
[0012]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the bass
enhancement circuit of the present invention is configured to reduce bass components below the
speaker reproduction limit to frequencies one octave higher using a simple full-wave rectifier. By
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converting, the bass range can be artificially enhanced by reproducing the bass range
components that can not be reproduced within the speaker reproduction band.
[0013]
According to the first aspect of the present invention, only the bass component below the
speaker reproduction limit is extracted from the input audio signal, the frequency is converted to
an octave, and the reproduction is not completed. The bass range can be artificially enhanced by
reproducing the bass range component, which has been possible, in the speaker reproduction
zone.
[0014]
Next, the bass amplifier circuit according to claim 2 of the present invention comprises a first
adder for adding the input audio left channel signal and the input audio right channel signal, and
a speaker reproduction limit of the added signals. A low pass filter that extracts only the
following bass component, a full wave rectifier that converts it to a frequency one octave higher,
and an amplifier that amplifies a signal generated from the full wave rectifier in series, The bass
component can be realized by a second adder that adds the bass component converted and
amplified to the following frequency to the input voice left channel signal and the voice right
channel signal respectively.
[0015]
Next, the bass enhancement circuit according to claim 3 of the present invention is the sum of an
input voice left channel signal, a voice right channel signal, and a first adder for adding a
frequency-converted signal. Among the signals, a low-pass filter that extracts only bass
components below the speaker reproduction limit, a full-wave rectifier that converts it to a
frequency one octave higher, and an amplifier that amplifies the signal generated by the fullwave rectifier A second adder for adding the bass component converted and amplified to a
frequency one octave higher to the input audio left channel signal and the input audio right
channel signal, and the amplifier output as an input, A level adjuster for level adjustment and a
circuit having the level adjuster output as the first adder input, and one octave converted and
amplified signal is further looped. By turning it, it converts it to a frequency two or four octaves
higher, and reproduces even bass components that did not reach the speaker playback band even
if one octave frequency conversion, to achieve bass enhancement with further enhanced effects.
It is possible.
[0016]
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Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to
5.
(Embodiment 1) Hereinafter, embodiments of the invention described in claim 1 and claim 2 of
the present invention will be described with reference to FIGS. 1, 2 and 3. FIG.
[0017]
FIG. 1 shows a block diagram of a bass boost circuit in an embodiment of the present invention.
In FIG. 1, reference numeral 1 is an adder for adding the left channel signal and right channel
signal of the input voice, 2 is an LPF for extracting only a bass range, and 3 is a full wave rectifier
for generating even harmonics and frequency converting And 4 are amplifiers for signal
amplification, and 5 is an adder for adding the left and right channel signals of the input speech
and the amplified second harmonic.
[0018]
The operation of the bass amplifier circuit configured as described above will be described.
FIG. 3A shows an example of the characteristic of a speaker used in a television receiver or the
like, and a small speaker can generally reproduce only up to about 100 Hz.
[0019]
On the other hand, the music signal has an f1 signal in the low frequency range of 100 Hz or less
as an audio component, and includes an element capable of providing a powerful low frequency
sound. However, as described above, the speaker characteristics are poor. Does not play and can
not enjoy enough bass.
[0020]
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The f1 signal below the bass range reproduction limit of this speaker is shown in FIG. 3 (b).
In such a case, the frequency is converted to a pitch one octave higher and reproduced in the
reproduction band of the speaker to produce a bass sound. This generation operation will be
described below with reference to FIG.
[0021]
In FIG. 1, the left channel signal and the right channel signal of the input voice are added by the
adder 1 and an LPF 2 is used to extract frequency components below the low-range reproduction
limit of the speaker used from the added voice signal. , Extract the bass component, and generate
even-order harmonics in the full-wave rectifier 3.
Assuming that an input signal of the full wave rectifier 3 is B = sin (wt) (1), an output signal C
processed by the full wave rectifier 3 is expressed by the following equation when it is Fourierexpanded.
[0022]
C = (2 / ?) + (4 / ?) и {sin (2 wt) / 3-sin (4 wt) / 15 + sin (6 wt) / 35 ...} (2) That is, even-order
harmonics are More than 80% is the second harmonic, as it appears and, as can be seen by the
coefficients. In other words, it is a conversion of one octave.
[0023]
Next, the full-wave rectified waveform is amplified to a signal of an appropriate level by the
amplifier 4 and added to the audio signals of the left channel and the right channel input by the
adder 5, and the output signals of the left channel and the right channel Do.
[0024]
FIG. 2 shows an operation waveform of each part of FIG. 1, and it can be understood as a
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waveform that a second harmonic is generated.
Also, the bass component is normally input in phase to the left channel and the right channel,
and may be simple addition.
[0025]
In this way, second harmonics are generated and converted to signals within the reproducible
band of the speaker used, as shown in FIG. 3 (b). By the way, it is a harmonic of only the second
order, and the pitch is only converted by one octave, so it is not a dissonance.
[0026]
In addition, since the low-frequency component below 100 Hz is converted into a signal one
octave higher experimentally, it can only be recognized as a sense of bass unless the exact score
is known.
[0027]
In other words, it is more effective than not being reproduced at all, and can exert a bass
enhancement effect rather than forcibly raising the low range level with tone control.
[0028]
Second Embodiment Next, an embodiment of the invention described in claim 3 of the present
invention will be described with reference to FIG. 4 and FIG.
[0029]
FIG. 4 shows a block diagram of a bass boost circuit in an embodiment of the present invention.
In FIG. 4, reference numeral 1 is a first adder for adding the left channel signal and right channel
signal of the input voice and the signal subjected to frequency conversion, and 2 is an LPF for
extracting only bass components below the speaker reproduction limit. , 3 is a full-wave rectifier
that generates even-order harmonics and converts the frequency, 4 is an amplifier that performs
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signal amplification, 5 is a summation that adds the left and right channel signals of the input
voice and the amplified harmonics A level adjuster 6 adjusts the level of the frequency-converted
and amplified signal.
[0030]
The operation of the bass amplifier circuit configured as described above will be described.
In FIG. 4, the left channel signal and the right channel signal of the input voice are added by the
adder 1 and the extracted audio signal is extracted by the LPF 2 to extract frequency components
below the low-range reproduction limit of the speaker used , Extract only the low frequency
range component, and generate even harmonics in the full wave rectifier 3.
As in the first embodiment, the full-wave rectifier 3 generates even-order harmonics and, as can
be seen from the coefficient, 80% or more is a second-harmonic wave, which means one octave
conversion. The waveform obtained by full-wave rectification is amplified to a signal of an
appropriate level by the amplifier 4 and added to the audio signals of the left and right channels
input by the adder 5 to obtain output signals of the left and right channels. The level is adjusted
to an appropriate level by the level adjuster 6, input to the adder 1, and input to the full-wave
rectifier 3 again. Assuming that the input signal of the full wave rectifier 3 to be injected for the
first time is B = sin (wt) (1), the output signal C processed by the full wave rectifier 3 is expressed
by the following equation when it is Fourier-expanded. That is, C = (2 / ?) + (4 / ?) и {sin (2 wt) /
3?sin (4 wt) / 15 + sin (6 wt) / 35 иии} (2), and among them, Since the second harmonic
component is almost all, if B = sin (2 wt) (3) is input to the adder 1 as the second harmonic
component, the second full-wave rectifier 3 Pass through. The output signal C1 processed by the
second full-wave rectifier 3 is expressed by the following equation when it is Fourier-expanded.
[0031]
C1 = (2 / ?) + (4 / ?) и {sin (4 wt) / 3-sin (8 wt) / 15 + sin (12 wt) / 35...} (4), that is, the fourth
harmonic It turns into a wave and generates 2nd, 4th, 8th, etc. 2 n harmonics by rotating it in a
loop, and it can be converted within the speaker's playback band by the first octave conversion
as shown in Figure 5 When the frequency f0 lower than the original signal f1 is considered, it
becomes 4 и f0 in the second octave conversion, and can be converted into a signal within the
reproduction band of the speaker. By the way, the 2nd and 4th harmonics such as 2 n are not
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dissonances because the pitch is only converted to octave. That is, assuming an original signal of
30 Hz, it is converted to a signal of 60 Hz at the first time, but with a speaker having only a
reproduction capability up to 100 Hz, this sound can not be reproduced, but at the second octave
conversion, the sound of 120 Hz It will be reproducible. However, if the octave conversion is too
high, the low-pitched feeling disappears and the low-pitched feeling is not felt because it
becomes the mid-range. However, since the LPF 2 defines the maximum pass frequency, Will not
play. However, the setting of the level adjuster 6 must be set carefully in light of the effect so as
not to oscillate. In this way, by making the full-wave rectifier 3 as a loop, it is added to the input
left and right channel audio signals, and the output signals of the left and right channels are
reproduced by the speaker with only one octave frequency conversion. Even low frequency
signals that did not reach the band can be reproduced in a pseudo manner.
[0032]
As described above, the bass amplifier circuit of the present invention is not restricted by the
size, shape, cost or the like of the speaker, and is lower than the bass range reproduction limit of
the speaker being used by a simple circuit configuration. When the bass component is input, it is
reproduced as an audio component within the reproducible range of the speaker by octave
frequency conversion, and the previously absent bass component is compensated, and a more
bassy, powerful voice reproduction Has the advantage of being able to
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