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JP2011091605

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2011091605
An audio reproduction apparatus capable of emphasizing and reproducing low-frequency
components of an audio signal without breaking of sound. A band division unit divides an input
audio signal into audio signals of a plurality of bands. The waveform detection unit determines
whether or not the level of a low frequency signal lower than a predetermined frequency among
audio signals divided by the band division unit decreases with time. When the waveform
detection unit determines that the waveform of the low band signal is decreasing with the lapse
of time, the waveform controller controls so that the decrease in level of the low band signal is
gradual. [Selected figure] Figure 2
Audio playback device
[0001]
The present invention relates to an audio reproduction apparatus for emphasizing and
reproducing low frequency components of an audio signal.
[0002]
Generally, with a small speaker connected to a portable audio player or the like, it is difficult to
reproduce the low frequency component (for example, 20 Hz to 500 Hz) of the audio signal
powerfully and clearly.
[0003]
08-05-2019
1
For this reason, the low frequency component of the audio signal is emphasized using harmonics.
That is, even if the fundamental sound does not exist in the low-pass component of the audio
signal, if there is a higher harmonic overtone relationship with the fundamental sound, the
fundamental sound exists in the reproduced sound. It uses the psychoacoustic phenomenon of
hearing as it is.
[0004]
Specifically, an audio signal in which the low-frequency component is emphasized by shaping the
signal waveform of the low-frequency component of the audio signal with respect to time,
generating high-order harmonics and adding this to the original audio signal. There is a device
that reproduces (see Patent Document 1).
[0005]
JP 2005-318598 A
[0006]
However, according to the technique disclosed in Patent Document 1, when the original audio
signal is added with a missing fundamental effect, higher harmonics that are not present in the
original audio signal are added. Therefore, there is a problem that the reproduced sound has an
unnatural sense of harmonics to the listener, particularly in the case of music where the audio
signal is played by a single instrument.
[0007]
In addition, simply amplifying the low frequency component of the audio signal may break the
reproduced sound depending on the performance of the speaker.
[0008]
Therefore, an object of the present invention is to provide an audio reproduction apparatus
capable of emphasizing and reproducing low-frequency components of an audio signal without
breaking of sound.
[0009]
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2
Therefore, in order to solve the problems described above, the present invention divides the
input audio signal into audio signals of a plurality of bands, and an audio signal divided by the
band division unit (31). Among them, a waveform detection unit (32) that determines whether
the level of a low frequency signal lower than or equal to a predetermined frequency decreases
with the passage of time, and the waveform detection unit (32) And a waveform control unit (33,
34) for performing control so that the level decrease of the low band signal is gradual when it is
determined that the level decreases with the passage of time. .
[0010]
According to the present invention, it is possible to provide an audio reproduction apparatus
capable of emphasizing and reproducing low-frequency components of an audio signal without
breaking of sound.
[0011]
It is a block diagram which shows the structure of the audio reproduction apparatus of this
invention.
FIG. 1 is a block diagram showing a circuit configuration of a digital signal processing circuit of a
first embodiment.
It is a flowchart which shows operation | movement of a waveform detection part and a gain
control signal generation circuit.
It is a figure which shows the input-output waveform of a gain control circuit.
FIG. 7 is a block diagram showing a circuit configuration of a digital signal processing circuit of a
second embodiment.
5 is a flowchart showing the operation of the digital signal processing circuit of the second
embodiment.
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3
FIG. 7 is a diagram showing an output waveform of a gain control circuit of Example 2;
FIG. 7 is a block diagram showing a circuit configuration of a digital signal processing circuit of a
third embodiment.
[0012]
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to
8.
[0013]
An audio reproduction apparatus A according to the present invention, as shown in FIG. 1,
includes an audio signal input unit 10, an analog / digital conversion circuit 20, a digital signal
processing circuit 30, a digital / analog conversion circuit 40, and an amplifier circuit 50. , And a
speaker 60.
[0014]
The audio signal input unit 10 receives an analog audio signal from the outside.
The analog audio signal is then input to the analog to digital conversion circuit 20.
For example, the audio signal input unit 10 receives an audio signal obtained by reproducing an
optical disk in which music data is recorded by an optical disk drive, or an audio signal supplied
from a flash memory or hard disk drive in which music data is recorded. .
[0015]
When the audio signal supplied from the audio signal input unit 10 is an analog audio signal, the
analog / digital conversion circuit 20 converts the analog audio signal into a digital audio signal
and outputs the digital audio signal to the digital signal processing circuit 30.
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When the audio signal input to the audio signal input unit 10 is a digital audio signal, the analog
to digital conversion circuit 20 can be omitted.
[0016]
The digital signal processing circuit 30 is a main part of the present invention, and is constituted
by a DSP (Digital Signal Procecseor) or the like, and the digital audio signal supplied from the
analog / digital conversion circuit 20 is subjected to digital signal processing described later. The
digital audio signal is output to the digital / analog conversion circuit 40.
[0017]
The digital-to-analog conversion circuit 40 converts the digital audio signal output from the
digital signal processing circuit 30 into an analog audio signal and outputs the analog audio
signal to the amplification circuit 50.
[0018]
The amplification circuit 50 amplifies the analog audio signal output from the digital / analog
conversion circuit 40 and outputs the amplified signal to the speaker 60.
[0019]
The speaker 60 emits the analog audio signal output from the amplification circuit 50 to the
outside as sound.
[0020]
Next, digital signal processing of the digital signal processing circuit 30 described above will be
specifically described using (Example 1) to (Example 3).
[0021]
Embodiment 1 A digital signal processing circuit 30A, which is an example of the digital signal
processing circuit 30 in this embodiment, has a band division filter (band division unit) 31, a
waveform detection unit 32, and a gain as shown in FIG. A control signal generation circuit 33, a
gain control circuit 34, and an audio signal synthesis circuit 35 are provided.
[0022]
The band division filter 31 is a digital audio low band obtained by dividing the digital audio
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5
signal input from the analog-to-digital converter circuit 20 into two low frequency bands lower
than a predetermined frequency and higher than a predetermined frequency. It outputs a signal
and a digital audio high band signal (hereinafter referred to as "low band signal" and "high band
signal", respectively).
[0023]
The high band signal output from the band division filter 31 is output to the audio signal
synthesis circuit 35.
Further, the low band signal output from the band division filter 31 is output to the waveform
detection unit 32, and is output to the gain control circuit 34 through the waveform detection
unit 32.
[0024]
In the band division performed by the band division filter 31, for example, when the entire
frequency band of the digital audio signal is 20 Hz to 20 kHz, the frequency band of the low
band signal is 20 Hz to 500 Hz and the frequency band of the high band signal is 500 Hz to 20
kHz Thus, it may be divided into two bands of low band and high band, and, if necessary, low
band, middle band and high band 3 depending on the DSP data processing capability of the
digital signal processing circuit 30A. The band may be divided into more than the band.
Here, the band division filter 31 will be described as being divided into two low and high bands.
[0025]
The waveform detection unit 32 collectively collects low-pass signals supplied from the band
division filter 31 for each fixed number of samples (for example, 256) per one frame (one frame
= about 5 ms in the case of sampling frequency Fs = 48 kHz). Level detection is performed, and it
is determined whether the waveform of the low-pass component of the audio signal is a rising
waveform or a falling waveform based on the average level of each frame.
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These detections can also be performed by sampling the low-pass signal for each sample, but as
described above, in order to reduce the load on the DSP (to shorten the processing time), it is
collectively performed in frame units. And level detection processing.
[0026]
In addition, the method of these detection is explained in full detail later.
In each embodiment, rising of the waveform means that the level of the signal is rising with the
passage of time, and falling of the waveform means that the level of the signal is lowered with the
passage of time. Shall mean that
[0027]
When the waveform detection unit 32 detects the rise of the waveform immediately before the
peak position, the gain control signal generation circuit 33 generates a low-pass signal in which
the level of the low-pass signal corresponding to the rise waveform is rapidly increased. The
control signal is output to the gain control circuit 34.
[0028]
On the other hand, when the waveform detection unit 32 detects the fall of the waveform
immediately after the peak position, the attenuation of the level of the low band signal portion
corresponding to this fall waveform is made gentle for a certain time (the decay time is delayed
for a certain time) A gain control signal for generating a low band signal is output to the gain
control circuit.
[0029]
The gain control circuit 34 makes the steep rise immediately before the peak position of the low
band signal steeper in accordance with the gain control signals supplied from the gain control
signal generation circuit 33 or a sharp fall immediately after the peak position. And outputs the
waveform-shaped low-pass signal to the audio signal synthesis circuit 35.
[0030]
As described above, the gain control signal generation circuit 33 and the gain control circuit 34
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cooperate with each other to operate as a waveform control unit which makes the slope of the
waveform of the low band signal gentle or steep.
[0031]
The audio signal synthesis circuit 35 synthesizes the high band signal supplied directly from the
band division filter 31 and the waveform-shaped low band signal supplied from the gain control
circuit 34, and digitalizes the synthesized digital audio signal. It outputs to the analog conversion
circuit 40.
[0032]
Thus, the digital signal processing circuit 30A emphasizes the low frequency component by
making the rising of the low-frequency signal of the digital audio signal input from the analog-todigital converter 20 sharper and the falling of the low-frequency signal slower. A digital audio
signal can be output to the digital / analog conversion circuit 40.
[0033]
Next, the method of detecting the rise and fall of the waveform of the low frequency component
of the audio signal performed by the waveform detection unit 32 and the specific operation of
the gain control signal generation circuit 33 will be described with reference to the flowchart of
FIG. This will be described using the waveform diagram of FIG.
FIG. 4A is a diagram for explaining a method of detecting the state of the waveform by the
waveform detection unit 32. FIG. 4B shows an input waveform W1 input to the gain control
circuit 34 and gain control. An output waveform W2 output from the circuit 34 is shown.
Further, F1 to F4 indicate the temporal width of each frame, and L1 to L4 are average levels of
audio signals included in the frames F1 to F4.
[0034]
First, when the low band signal of the audio signal is input from the band division filter 31, the
waveform detection unit 32 detects an average level for each frame (step S1).
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[0035]
In the next step S2, the waveform detection unit 32 determines whether the average level of the
frame detected in step S1 is equal to or higher than the threshold L.
If the average level of the frame is less than the threshold L, the process returns to step S1, and
the waveform detection unit 32 detects the average level of the next frame.
It is desirable that the threshold L be equal to or greater than the noise component included in
the low band signal supplied from the band division filter 31 to the waveform detection unit 32.
[0036]
On the other hand, if the average level of the frame is greater than or equal to the threshold L in
step S2, the process proceeds to step S3, and the waveform detection unit 32 compares the level
of the frame whose level is detected with the level of the frame immediately before that frame.
Specifically, the average level of the immediately preceding frame is subtracted from the average
level of the current frame.
For example, in FIG. 4, when the average level L2 of the frame F2 is detected, L2 ≧ L, so the
waveform detection unit 32 calculates L2-L1.
[0037]
In the next step S4, the waveform detection unit 32 determines whether the difference between
the current frame and the previous frame is a positive (plus) value.
In FIG. 4A, when the average levels of the frames F1 to F3 are calculated in step S1, the average
level of the immediately preceding frame is smaller and the level difference is positive (plus), and
the frames F4 and F5 are obtained. When the average level of is calculated, the level difference
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becomes negative (minus) because the average level of the immediately preceding frame is
larger.
[0038]
In step S4, when the level difference is positive, in step S5, the waveform detection unit 32
determines that the waveform W1 is rising, and in the next step S6, the gain control signal
generation circuit 33 generates a low frequency signal. Output a gain control signal for rapidly
increasing the level of
Thereafter, the process returns to step S1, and the waveform detection unit 32 calculates the
average level of the next frame.
[0039]
On the other hand, if the level difference is not positive in step S4, that is, if the level difference is
negative, the waveform detection unit 32 determines that the waveform W1 is falling in step S7,
and proceeds to the next step S8. The gain control signal generation circuit 33 outputs a gain
control signal to make the level of the low frequency band signal gentle.
Thereafter, the process returns to step S1, and the waveform detection unit 32 calculates the
average level of the next frame.
[0040]
The gain control circuit 34 amplifies the waveform W1 based on the gain control signal from the
gain control signal generation circuit 33 output as described above, and the low band signal
supplied from the band dividing filter 31 to the waveform detection unit 32. The waveform W2
(FIG. 4B) of the waveform-shaped low-pass signal which makes the rising of the waveform W1
steeper and makes the falling gentler can be output to the audio signal synthesis circuit 35. It is
possible to obtain a reproduced sound in which the sense of volume and clarity of low-pass
components (low-pass signals) is emphasized.
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Further, the gain control circuit 34 may delay the falling of the output waveform W2 by delaying
the input waveform W1 for a predetermined time.
[0041]
Example 2 In general, the bass component of the audio signal has a waveform with periodic
peaks. This embodiment focuses on that point, and changes the degree of slowing down of the
waveform of the bass component depending on the length of time interval between peaks (peak
interval), so that the sense of rhythm and tempo of reproduced sound can be It can be prevented
from being damaged.
[0042]
Therefore, in the present embodiment, gain control signal generation circuit is focused on the
fact that such rhythm feeling and tempo feeling are generated by a continuous state with a
substantially constant period regardless of the length of the peak interval of a predetermined
level L or more. In the case 33, when the peak interval is relatively long (peak interval of peak
Pa-Pb shown in FIG. 7A), based on the waveform W3 of the low band signal, the time when
falling from the peak Pa is lengthened is lengthened A gain control signal for generating the
waveform W4 (FIG. 7A) of the waveform shaping low-pass signal is generated and output to the
gain control circuit 34.
[0043]
On the other hand, when the peak interval is relatively short (each peak interval of the peaks PcPd, Pd-Pe, Pe-Pf shown in FIG. 7B), the gain control signal generation circuit 33 generates the
waveform W5 of the low band signal. On the basis of this, the falling time from each peak Pc, Pd,
Pe, Pf is shorter than in the case of FIG. 7A to obtain the waveform W6 of the waveform-shaped
low-pass signal (FIG. 7B). A gain control signal is generated and output to the gain control circuit
34.
[0044]
That is, the longer the peak interval, the slower the falling of the waveform, and the shorter the
peak interval, the smaller the degree of slowing the falling of the waveform.
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As a result, even when peaks having relatively short peak intervals occur continuously, the falling
waveform from the peak and the rising waveform become clear, so it is possible to emphasize the
sense of rhythm and tempo of the reproduced sound.
[0045]
An example of the digital signal processing circuit 30B according to the second embodiment
which performs the above operation will be described in detail with reference to FIG.
[0046]
As shown in FIG. 5, in the configuration of the digital signal processing circuit 30A (FIG. 2), the
digital signal processing circuit 30B is cascaded between the output side of the waveform
detection unit 32 and the input side of the gain control signal generation circuit 33. The
connected peak detection unit 36 and peak interval calculation unit 37 are connected in parallel.
Since there is no change other than this, only the operations of peak detection unit 36, peak
interval calculation unit 37 and gain control signal generation circuit 33 will be described, and
the same components as those described above will be assigned the same reference numerals. ,
The explanation will be omitted.
[0047]
The peak detection unit 36 calculates the peak position based on the average level of each frame
supplied from the waveform detection unit 32 and the state of the waveform W3 (W5) of the low
frequency component of the audio signal.
Specifically, the peak detection unit 36 sets the frame immediately before the frame in which the
waveform W3 (W5) turns from rising to falling as a peak position. The peak detection unit 36
sequentially stores the peak positions as data, sequentially reads out the stored peak position
data, and outputs the peak position data to the peak interval calculation unit 37 (FIG. 6, steps
S10 and S11).
08-05-2019
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[0048]
The peak interval calculation unit 37 calculates the interval between the peak position data and
the peak position data immediately before it based on the peak position data supplied from the
peak detection unit 36, and outputs the peak interval information to the gain control signal
generation circuit. It outputs to 33 (FIG. 6, step S12).
[0049]
The gain control signal generation circuit 33 sequentially stores peak interval information
supplied from the peak interval calculation unit 37, sequentially reads the stored peak interval
information, and responds to the waveform W3 (W5) falling from the peak according to this. The
attenuation factor of the gain control signal to be calculated is calculated (FIG. 6, step S13).
That is, the gain control signal is output so as to increase the fall time from the peak and obtain a
gentle fall as the peak interval is longer. Thus, the waveform W4 of the waveform-shaped low
band signal based on the waveform W3 of the low band signal can be obtained ((A) in FIG. 7).
[0050]
On the other hand, the gain control signal generation circuit 33 shortens the falling time from
the peak as the peak interval is shorter. That is, the gain control signal generation circuit 33
outputs a gain control signal with a smaller amplification factor as the peak interval is shorter.
Thus, the waveform W6 of the waveform-shaped low band signal based on the waveform W5 of
the low band signal can be obtained (FIG. 7 (B)).
[0051]
Further, at that time, the gain control signal generation circuit 33 performs gain control or signal
delay such that the level of the bass component at the temporal position immediately before the
next peak arrives becomes the threshold L, and the waveform W4 (W6) It's even better to slow
down.
[0052]
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13
Also, the data may be buffered to change the degree to which the falling waveform W4 (W6) is
made gentle depending on the next coming peak.
For example, the gain control signal generation circuit 33 shortens the falling time from the peak
as the level of the peak to come next is smaller. In this way, it is possible to prevent the loss of
the attack of a low-pitched bass peak. In this case, the peak detection unit 36 calculates the level
of the next peak based on the average level of each frame supplied from the waveform detection
unit 32 and the state of the waveform W3 (W5) of the low frequency component of the audio
signal.
[0053]
Thus, in addition to the effects obtained by the digital signal processing circuit 30A (FIG. 2), the
digital signal processing circuit 30B reduces the low frequency range of the reproduced audio
signal even if a plurality of peaks are continuous and their peak intervals vary widely. It is
possible to obtain the sense of mass of the components, to emphasize its clarity, and to obtain a
clear sense of rhythm.
[0054]
In other words, when the peak position is continuously detected by the peak detection unit 36
according to the present invention, the peak interval calculation unit 37 that calculates the
interval between the peak positions is provided. The gain control signal generation circuit 33,
which is a unit, is characterized by performing gain control by obtaining an attenuation factor for
delaying the attenuation time according to the calculated interval of peak positions.
[0055]
Third Embodiment In the second embodiment described above, the tempo of the music is
calculated by detecting the peak interval of the low-pass signal of the audio signal, and the
attenuation time of the gain control signal is controlled from the tempo information. However,
for music whose tempo is not constant, historical data of past peak intervals is provided, and the
historical data is used to predict the changing tempo using a technique such as linear prediction,
etc. It is possible to set the corresponding attenuation time of the gain control signal.
In this case, since it is only necessary to predict the rough tempo in order to know the necessary
decay time, it may be simple as a prediction circuit.
08-05-2019
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[0056]
That is, as shown in FIG. 8, in addition to the configuration of the digital signal processing circuit
30B, the digital signal processing circuit 30C that is Embodiment 3 of the digital signal
processing circuit 30 includes the output side of the peak detection unit 36 and the peak interval
calculation unit A prediction circuit 38 is connected in parallel to the input side of 37.
Since there is no change other than this, only the operation of the prediction circuit 38 will be
described, the same reference numerals are given to the same components as those described
above, and the description other than this will be omitted.
[0057]
The prediction circuit 38 references the peak position data supplied from the peak detection unit
36, predicts the fluctuating peak interval using a technique such as linear prediction, and outputs
this predicted signal to the peak interval calculation unit 37.
[0058]
The peak interval calculation unit 37 calculates the peak interval based on the prediction signal
supplied from the prediction circuit 38 and outputs the peak interval signal to the gain control
signal generation circuit 33.
In this way, it is possible to predict the fluctuating peak interval and to set the attenuation time of
the gain control signal according to the fluctuating tempo for each fixed period.
[0059]
The digital signal processing circuit 30C which is the third embodiment of the digital signal
processing circuit 30 described above has a plurality of consecutive peaks and their peak
intervals in addition to the respective effects obtained in the first to second embodiments
described above. Even if the peak interval is not constant, it is possible to obtain a sense of mass
of the low frequency component of the reproduced audio signal and to emphasize its clearness
and obtain a clear sense of rhythm.
08-05-2019
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[0060]
Here, in other words, according to the third embodiment, the peak detection unit 36 stores a
predetermined number of peak positions of the waveform of the bass component from the state
of the waveform detected by the waveform detection unit 32 and the level of the bass
component. The gain control signal generation circuit 33, which is a gain control unit of the
present invention, includes the prediction circuit 38, which is a peak position prediction unit of
the present invention that predicts the next peak position based on the past peak position. The
gain control is performed to delay the decay time from the next predicted peak position
predicted by the prediction circuit 38 which is a position prediction unit.
[0061]
Further, the gain control signal generation circuit 33 which is the gain control unit of the present
invention is detected by the peak detection unit 32 more than the next predicted peak position
predicted by the prediction circuit 38 which is the peak position prediction unit of the present
invention. If the peak position comes earlier, perform gain control according to this peak
position.
[0062]
As described above, according to the audio reproducing apparatus of the present invention as
described in each embodiment, since the low frequency component of the audio signal is
emphasized by making the falling of the low frequency component gentle, the signal is
excessively amplified. Can emphasize the low frequency component of the audio signal without
breaking the sound.
[0063]
Reference Signs List 31 band division filter (band division unit) 32 waveform detection unit 33
gain control signal generation circuit 34 gain control circuit 36 peak detection unit 37 peak
interval calculation unit 38 prediction circuit (peak position prediction unit) A audio reproducing
apparatus
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