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JP2011082960

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DESCRIPTION JP2011082960
An object of the present invention is to provide a pseudo bass generator in which deterioration of
sound quality is suppressed. An absolute value circuit outputs an absolute value of a signal
according to an input signal. The clip circuit 18 clips the signal S 'corresponding to the input
signal at positive and negative limit values. The first multiplier 32 multiplies the signal S
'corresponding to the input signal by a predetermined coefficient. The first adder 34 subtracts
the output signal S3 of the first multiplier 32 from the output signal S2 of the clipping circuit 18.
The second adder 26 adds the signal S 4 ′ corresponding to the output signal S 4 of the first
adder 34 and the signal S 1 ′ corresponding to the output signal S 1 of the absolute value
circuit 16. The third adder 30 adds the signal S5 'according to the input signal S and the output
signal S5 of the second adder 26. [Selected figure] Figure 2
Pseudo-bass generator and generation method
[0001]
TECHNICAL FIELD The present invention relates to a technique for generating pseudo bass.
[0002]
A pseudo-bass is used as a method of generating bass lower than the band from a speaker or
headphones (hereinafter, collectively referred to as a speaker).
Assuming that the frequency of the bass to be reproduced is f1, if the frequency f2 which is twice
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f1 and the frequency f3 which is three times f1 are input to the speaker, the difference frequency
(f3-f2), that is, the original frequency f1 (Listener) can perceive.
[0003]
For example, when a signal of the double wave 100 Hz and the triple wave 150 Hz is input to a
speaker which can not reproduce the band of 50 Hz or less, the listener perceives as if the sound
of 50 Hz is being reproduced.
[0004]
JP, 2005-318598, A JP, 2008-304670, A JP, 2009-44655, A
[0005]
As a result of studying the above-described pseudo bass generator, the inventor has come to
recognize the following problems.
FIGS. 1A and 1B are a block diagram and an operation waveform showing a configuration of a
pseudo bass generator according to a comparison technique.
The pseudo bass generator 200 is configured by a DSP (Digital Signal Processor). The pseudo
bass generator 200 includes HPF (high pass filter) 202 and 210, LPF (low pass filter) 204 and
218, an absolute value circuit 206, a clipping circuit 208, multipliers 212 and 214, and adders
216 and 220. The HPFs 202 and 210 remove low frequency components of the input signal. The
LPFs 204 and 218 remove high frequency components of the input signal. The adders 216 and
220 add two input signals. The absolute value circuit 206 outputs the absolute value of the input
signal. The clip circuit 208 clips (clamps) the input signal at positive and negative limit values.
The multipliers 212 and 214 respectively multiply the input signal by a predetermined
coefficient.
[0006]
FIG. 1B shows the waveforms of the input signal SIN and the output signals S1 and S2 of the
absolute value circuit 206 and the clip circuit 208, respectively. An output signal S1 of the
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absolute value circuit 206 includes, as main components, an input signal (also referred to as a
fundamental wave component) SIN and even harmonics including a double wave of the input
signal SIN. The output signal S2 of the clipping circuit 208 has, as main components, the
fundamental wave component SIN and odd harmonics including the third harmonic of the input
signal SIN.
[0007]
In the circuit of FIG. 1, since the signals S1 and S2 both include the fundamental wave
component SIN, when the amplitude of the fundamental wave component SIN becomes large, an
overflow may occur in the adder 216, the adder 220 or the circuit in the subsequent stage. There
is. When an overflow occurs, the audio signal is distorted and the sound quality is degraded.
[0008]
The present invention has been made in view of these problems, and an exemplary object of an
embodiment of the present invention is to provide a pseudo-bass generator with suppressed
deterioration in sound quality.
[0009]
One aspect of the present invention relates to a simulated bass generator.
The pseudo bass generator includes an absolute value circuit that outputs an absolute value of a
signal according to the input signal, a clipping circuit that clips a signal according to the input
signal with positive and negative limit values, and a signal according to the input signal. A first
multiplier for multiplying a predetermined coefficient, a first adder for subtracting the output
signal of the first multiplier from the output signal of the clipping circuit, a signal according to
the output signal of the first adder, and an absolute value circuit And a third adder for adding the
signal corresponding to the input signal and the output signal of the second adder. The pseudo
bass generator outputs a signal according to the output signal of the third adder.
[0010]
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According to this aspect, the first adder can attenuate the fundamental wave component of the
output signal of the clipping circuit. Therefore, even when the amplitude of the fundamental
wave component is large, the occurrence of the overflow in each adder can be suppressed, and
hence the deterioration of the sound quality can be suppressed. The “signal B according to the
signal A” may be the signal A itself or a signal subjected to the signal processing of the signal A.
[0011]
When the positive and negative limit values set in the clip circuit are set to β (β is a constant of
the real number) times of the positive and negative peak values, the constant β and the
predetermined coefficient α satisfy 0.95 <α + β <1. It is desirable to satisfy the relationship of
.25. When this relationship is satisfied, the fundamental wave component can be suitably
attenuated.
[0012]
One aspect of the present invention also relates to a simulated bass generator. The pseudo bass
generator includes an absolute value circuit that outputs an absolute value of a signal according
to the input signal, a clipping circuit that clips a signal according to the input signal with positive
and negative limit values, and a signal according to the input signal. A first multiplier for
multiplying a predetermined coefficient, a first adder for subtracting the output signal of the first
multiplier from the output signal of the absolute value circuit, a signal corresponding to the
output signal of the first adder, and a clip circuit And a third adder for adding a signal
corresponding to the input signal and a signal corresponding to the output signal of the second
adder, wherein the output signal of the third adder is added to the second adder. Output the
corresponding signal.
[0013]
According to this aspect, the first adder can attenuate the fundamental wave component of the
output signal of the absolute value circuit. Therefore, even when the amplitude of the
fundamental wave component is large, it is possible to suppress the occurrence of the overflow in
the signal processing of each adder and the subsequent stage, and it is possible to suppress the
deterioration of the sound quality.
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[0014]
Yet another aspect of the present invention also relates to a simulated bass generator. The
pseudo bass generator includes an absolute value circuit that outputs an absolute value of a
signal according to an input signal, a clipping circuit that clips a signal according to the input
signal with positive and negative limit values, and an output signal of the absolute value circuit A
second adder that adds the signal corresponding to the signal corresponding to the output signal
of the clip circuit, a third adder that adds the signal corresponding to the input signal and the
output signal of the second adder, and a third adder And an output high pass filter for cutting a
frequency component to be artificially reproduced from an output signal of the controller.
[0015]
According to this aspect, the output high-pass filter can attenuate the fundamental wave
component of the output signal of the absolute value circuit. Therefore, even when the amplitude
of the fundamental wave component is large, the occurrence of the overflow in the signal
processing in the subsequent stage can be suppressed, and hence the deterioration of the sound
quality can be suppressed.
[0016]
The pseudo bass generator may be integrated on one semiconductor substrate. "Integrated
integration" includes the case where all of the circuit components are formed on a semiconductor
substrate, and the case where the main components of the circuit are integrally integrated. A
resistor, a capacitor or the like may be provided outside the semiconductor substrate.
[0017]
It is to be noted that any combination of the above-described constituent elements, or one in
which the constituent elements and expressions of the present invention are mutually replaced
among methods, apparatuses, systems, etc. is also effective as an aspect of the present invention.
[0018]
According to the pseudo low tone generator of the present invention, it is possible to suppress
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the deterioration of the sound quality.
[0019]
FIGS. 1A and 1B are a block diagram and an operation waveform showing a configuration of a
pseudo bass generator according to a comparison technique.
It is a block diagram which shows the structure of the pseudo | simulation bass generator which
concerns on 1st Embodiment.
FIG. 5 is an operation waveform diagram of the pseudo bass generator of FIG. 2; It is a figure
which shows the relationship between the magnitude | size of the spectrum of the nonreproduction low frequency component contained in the output signal of the pseudo | simulation
bass generator of FIG. 2, and the coefficient (alpha). It is a block diagram which shows the
structure of the pseudo | simulation bass generator which concerns on 2nd Embodiment. FIGS.
6A and 6B are block diagrams showing an example of the configuration of the second LPF shown
in FIG.
[0020]
Hereinafter, the present invention will be described based on preferred embodiments with
reference to the drawings. The same or equivalent components, members, and processes shown
in the drawings are denoted by the same reference numerals, and duplicating descriptions will be
omitted as appropriate. In addition, the embodiments do not limit the invention and are merely
examples, and all the features and combinations thereof described in the embodiments are not
necessarily essential to the invention.
[0021]
First Embodiment FIG. 2 is a block diagram showing a configuration of a pseudo bass generator
100 according to a first embodiment. The pseudo bass generator 100 receives a digital audio
input signal (hereinafter, simply referred to as an input signal) SIN and performs pseudo bass
reproduction processing by performing signal processing. An output signal SOUT of the pseudo
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low tone generator 100 is converted into an analog audio signal by a D / A converter (not shown)
at a subsequent stage, and supplied to an electroacoustic transducer (not shown) such as a
speaker or a headphone. This electro-acoustic transducer is poor in reproduction capability in the
low band, for example, can reproduce a signal (non-reproducible low frequency signal) of
frequency components lower than 50 Hz or lower than 100 Hz (hereinafter referred to as nonreproducible low frequency) Can not. In such a situation, the pseudo bass generator 100 causes
the user to perceive the non-reproducible low frequency signal as if the non-reproducible low
frequency signal is being reproduced from the speaker.
[0022]
Hereinafter, the configuration of the pseudo bass generator 100 will be described. The pseudo
bass generator 100 includes a first HPF 12, a first LPF 14, an absolute value circuit 16, a clipping
circuit 18, a second HPF 20, a second multiplier 22, a third multiplier 24, a second adder 26, a
second LPF 28, and a third adder. 30, a first multiplier 32 and a first adder 34.
[0023]
The first LPF 14 cuts, from the input signal SIN, a frequency component to be pseudoreproduced, that is, a frequency component higher than the non-reproducible low frequency. The
cut includes not only complete removal but also attenuation. The first LPF 14 extracts a nonreproducible low frequency signal. The first HPF 12 cuts, from the input signal SIN, a frequency
component (ultra-low frequency component) lower than the non-reproducible low frequency
desired to be artificially reproduced. By providing the first HPF 12, it is possible for the circuit in
the subsequent stage to perform signal processing efficiently. A signal corresponding to the input
signal SIN that has passed through the first HPF 12 and the first LPF 14 is referred to as a basic
low frequency signal SIN '. The first HPF 12 and the first LPF 14 may be interchanged.
[0024]
The absolute value circuit 16 receives the basic low frequency signal SIN '. The absolute value
circuit 16 outputs an absolute value (hereinafter, a first signal) S1 of the basic low frequency
signal SIN '. That is, the basic low frequency signal SIN 'is full-wave rectified by the absolute value
circuit 16. The second HPF 20 cuts the DC component of the first signal S1. The second
multiplier 22 multiplies the output signal of the second multiplier 22 by a predetermined
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coefficient.
[0025]
The clipping circuit 18 clips the input signal SIN 'at positive and negative limit values. The
positive and negative limit values are set to β (0 <β <1) times of the positive and negative peak
levels of the input signal SIN ′. For example, the value of β is 0.7.
[0026]
The first multiplier 32 multiplies the input signal SIN ′ by a predetermined coefficient α. When
β = 0.7, α = 0.3 to 0.5 is preferable.
[0027]
The first adder 34 subtracts the output signal (third signal) S3 of the first multiplier 32 from the
output signal (second signal) S2 of the clip circuit 18. The third multiplier 24 multiplies the
output signal (fourth signal) S4 of the first adder 34 by a predetermined coefficient.
[0028]
The second adder 26 adds the output signal S1 ′ of the second multiplier 22 corresponding to
the first signal S1 and the output signal S4 ′ of the third multiplier 24 corresponding to the
fourth signal S4, and 5. Generate signal S5. The second LPF 28 cuts, from the fifth signal S5, a
frequency component four or more times higher than the non-reproducible low frequency. Since
the harmonic components of the basic low-frequency signal SIN ′ are inherently distortion
components, by cutting off the fourth harmonic or higher, other than the second harmonic and
third harmonic necessary for pseudo bass reproduction. , Distortion can be reduced.
[0029]
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The third adder 30 adds the original input signal SIN and the signal S5 'according to the fifth
signal S5 passed through the second LPF 28. The pseudo bass generator 100 outputs a signal
SOUT corresponding to the output signal of the third adder 30 to the circuit of the subsequent
stage.
[0030]
The above is the configuration of the pseudo bass generator 100. Subsequently, the operation
will be described. FIG. 3 is an operation waveform diagram of the pseudo bass generator 100 of
FIG. The vertical and horizontal axes in FIG. 3 are appropriately scaled up and down to facilitate
understanding, and each waveform shown is also simplified for ease of understanding. The other
figures are also the same. The input signal SIN is an audio signal including a low frequency of
about 20 Hz to a high frequency of about 17 kHz.
[0031]
The basic low frequency signal SIN ′ includes a non-reproducible low frequency component of
about 50 Hz to 100 Hz to be subjected to pseudo reproduction. In FIG. 3, only a single frequency
spectral component having the non-reproducible low frequency signal SIN ′ is extracted and
shown for easy understanding.
[0032]
As shown in FIG. 3, since the second signal S2 is a waveform obtained by clipping (clamping) the
basic low frequency signal SIN ′, the waveform is similar to that of the basic low frequency
signal SIN ′, and hence the non-reproducible low frequency It contains many spectral
components. The closer the value of parameter β is to 1, the larger this spectral component.
[0033]
In the pseudo bass generator 200 according to the comparison technique of FIG. 1, overflow is
likely to occur in the adder 216, the adder 220 and the circuits in the subsequent stages due to
the large non-reproducible low frequency component included in the second signal S2. It had
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become. On the other hand, in the pseudo bass generator 100 of FIG. 2, the non-reproducible low
frequency component is removed by subtracting the third signal S3 obtained by multiplying the
basic low frequency signal SIN ′ by α from the second signal S2. The amplitude of the effective
signal can be reduced. As a result, it is possible to suppress the occurrence of overflow inside and
at the subsequent stage of the pseudo low tone generator 100. Further, the reduction of the
overflow can suppress the deterioration of the sound quality. Even if the low frequency
component which can not be reproduced is removed, it is not directly reproduced from the
speaker or the headphone at the subsequent stage, so there is almost no influence on hearing.
[0034]
In the pseudo bass generator 100 of FIG. 2, the effect of removing the non-reproducible low
frequency component by the first multiplier 32 and the first adder 34 is set in the parameter β
set in the clip circuit 18 and the first multiplier 32. Changes according to the coefficient α. FIG.
4 is a diagram showing the relationship between the size of the spectrum of the non-reproducible
low frequency component contained in the output signal SOUT of the pseudo bass generator 100
of FIG. 2 and the coefficient α. The relationship in FIG. 4 shows the case of β = 0.7. In this case,
α = 0.4 is preferable because it can most effectively remove the non-reproducible low frequency
component. For practical use, it is desirable to set α to about 0.3 to 0.5.
[0035]
The value of the preferred coefficient α varies according to the relationship with the parameter
β. As a result of examining the combination of the two parameters, the inventor has found that
the non-reproducible low frequency component can be effectively removed when the relationship
of 0.95 <α + β <1.25 is satisfied. For example, if .beta. = 0.8, it is desirable that .alpha. = 0.15 to
about 0.45.
[0036]
Second Embodiment FIG. 5 is a block diagram showing a configuration of a pseudo bass
generator 100a according to a second embodiment. The pseudo bass generator 100a omits the
first multiplier 32 and the first adder 34 from the pseudo bass generator 100 of FIG. 2 and
includes an output high pass filter 36 instead.
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[0037]
The second adder 26 adds the signal corresponding to the output signal S 1 of the absolute value
circuit 16 and the signal corresponding to the output signal S 2 of the clipping circuit 18. The
second LPF 28 cuts, from the output signal S6 of the second adder 26, a frequency component
four or more times higher than the non-reproducible low frequency. The third adder 30 adds the
output signal of the second LPF 28 and the original audio signal SIN. The output high-pass filter
36 cuts the non-reproducible low frequency component to be artificially reproduced from the
output signal (seventh signal) S7 of the third adder 30. That is, in the pseudo bass generator 100
of FIG. 2 and the pseudo bass generator 100 a of FIG. 5, the positions at which the nonreproduction low frequency components are cut are different. According to the pseudo bass
generator 100 a of FIG. 5, it is possible to suppress an overflow that may occur in the subsequent
stage of the pseudo bass generator 100 a.
[0038]
FIGS. 6A and 6B are block diagrams showing a configuration example of the second LPF 28 of
FIG. As shown in FIG. 6A, the second LPF 28 includes two second-order IIR (Infinite Impulse
Response) filters 28a and 28b connected in series. By passing one of the two IIR filters, for
example, the latter stage, it can be used as a second-order filter.
[0039]
FIG. 6 (b) shows the configuration of a second-order IIR filter. The second-order IIR filter includes
a plurality of delay elements D1 to D4, an adder 29, and coefficient circuits B0 to B2, A1, and A2.
The delay elements D1 to D4 delay the input signal. The coefficient circuits B0 to B2, A1 and A2
respectively multiply the input values by the coefficients B0 to B2, A1 and A2. The adder 29 adds
the output signals of the coefficient circuits B0 to B2, A1 and A2. In order to put the secondorder IIR filter in the through state, B0 = 1 and A1 = A2 = B1 = B2 may be set.
[0040]
The present invention has been described above based on the embodiments. This embodiment is
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an exemplification, and various modifications may exist in their respective components,
processing processes, and their combinations. Hereinafter, such modifications will be described.
[0041]
As an example, the pseudo bass generator 100 of FIG. 2 and the pseudo bass generator 100 a of
FIG. 5 may be combined. That is, an output high pass filter 36 may be provided downstream of
the pseudo bass generator 100 of FIG.
[0042]
Further, in FIG. 2, the first adder 34 may be disposed downstream of the absolute value circuit
16 or the second HPF 20. At this time, the first adder 34 may subtract the third signal S3 from
the signal corresponding to the first signal S1 and output the result to the second multiplier 22.
Also in this case, the overflow can be suitably suppressed.
[0043]
The frequency shown in the embodiment is also an example, and these values may naturally
change depending on the type and ability of the speaker.
[0044]
Although the present invention has been described based on the embodiments, the embodiments
only show the principles and applications of the present invention, and the embodiments deviate
from the concept of the present invention defined in the claims. However, many variations and
modifications of the arrangement are permitted.
[0045]
100 ... Pseudo-bass generator, 12 ... 1st HPF, 14 ... 1st LPF, 16 ... absolute value circuit, 18 ... clip
circuit, 20 ... 2nd HPF, 22 ... 2nd multiplier, 24 ... 3rd multiplier, 26 ... 6th 2 Adder, 28: second
LPF, 30: third adder, 32: first multiplier, 34: first adder, 36: output high-pass filter.
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