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JPH08213862

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH08213862
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sound reproducing apparatus for emitting sound according to an audio signal input from a
speaker into an acoustic space, and in particular to reproduce low frequency components such as
low frequency components below the resonance frequency of the speaker. The present invention
relates to a sound reproduction device capable of improving the quality.
[0002]
2. Description of the Related Art In a conventional sound reproduction apparatus, a loudness
compensation circuit, a bass enhancement circuit (graphic equalizer), etc. are used as means for
improving the reproduction quality of the bass range. That is, the reproduction signal of a
desired frequency band (bass band) is reproduced electrically larger than the other frequency
bands by these circuits, and the reproduction quality of the bass band is thereby improved.
[0003]
SUMMARY OF THE INVENTION In terms of electric circuit, it is possible to arbitrarily manipulate
the characteristics of a desired frequency band by taking the above method. However, in the
sound reproducing apparatus, the signal thus processed is finally supplied to the speaker and
reproduced as sound. Therefore, even if the signal processing that does not take into
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consideration the electro-acoustic conversion characteristics of the speaker is performed, the
quality of the finally reproduced sound is hardly improved as expected. This cause is dominated
by the resonance frequency f0 of the speaker. The reproduction frequency characteristic of the
speaker largely changes at the resonance frequency f0 (about 100 Hz). That is, in the frequency
band lower than the resonance frequency f0, the sound pressure of the reproduced sound is
significantly reduced (see FIG. 4A) and the reproduction distortion is greatly increased (see FIG.
4B). FIG. 5 shows the f characteristic of the speaker in detail.
[0004]
For this reason, when the bass range is enhanced by the equalizer due to the lack of bass below
the resonance frequency f0 (see FIG. 4C), the sound is slightly enhanced, but the distortion is
further increased and the quality of the reproduced sound is degraded. That is, no effective
sound pressure can be expected regardless of how much the signal component below the
resonance frequency f0 of the speaker is increased and supplied by the graphic equalizer, the
loudness compensation circuit, etc., on the contrary, the reproduction distortion increases. As a
result, the quality of the reproduced sound is greatly impaired. Such a phenomenon is
particularly difficult to secure a sufficient volume of a so-called enclosure to which an acoustic
reproducing apparatus (for example, a radio cassette player, a television, etc.) or a speaker using
a small aperture speaker having a relatively high resonance frequency is attached. It appears
prominently in reproduction equipment etc.
[0005]
From the above, it is an object of the present invention to provide an acoustic reproduction
device capable of improving the reproduction quality of low frequency components, particularly
low frequency components lower than the resonance frequency of the speaker. Another object of
the present invention is to provide a sound reproducing apparatus capable of improving the
reproduction quality of low frequency components with a simple configuration.
[0006]
According to the present invention, the above object is achieved by a separating circuit for
separating an audio signal into a low band component and a high band component, and a
frequency multiplying circuit for multiplying an audio signal frequency of the low band
component, This is achieved by the sound reproducing apparatus including a synthesizing unit
that synthesizes the high frequency component and the frequency multiplying circuit output and
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outputs the synthesized signal to the speaker side.
[0007]
[Operation] An audio signal is separated into a low band component and a high band component
by a separation circuit (band pass filter and high pass filter), and an audio signal frequency of the
low band component is multiplied (for example, doubled) by a frequency multiplication circuit
The high frequency component and the frequency multiplication circuit output are synthesized
and output to the speaker side.
The frequency of the low frequency audio signal lower than the resonance frequency f0 of the
speaker is multiplied (for example, doubled) and the audio signal multiplied by the frequency is
input to the speaker, and the speaker correctly corrects the sound according to the audio signal
multiplied by the frequency Radiate into acoustic space. By the way, it has been proved that if
psychoacoustically only harmonics of a fundamental sound appear, human feels a sound even if
there is no fundamental sound as if there is a fundamental sound. For this reason, the listener
recognizes low-frequency speech below the fundamental frequency, that is, the resonance
frequency f0, from the sound corresponding to the frequency-multiplied signal. In this way, since
no low frequency audio signal below the resonance frequency f0 is input to the speaker, there is
no distortion, and low frequency audio below the resonance frequency f0 can be recognized by
the psychoacoustic effect, and the reproduction quality of the bass is improved. can do.
[0008]
Also, the high frequency component is delayed by the time required for frequency multiplication,
and it is possible to listen to the sound without time deviation by combining it with the
frequency-multiplied audio signal and outputting it. Furthermore, if the gain of the audio signal
frequency-multiplied by the variable gain amplifier can be adjusted, the bass can be increased or
decreased according to the listener's preference.
[0009]
(a) Principle of the Invention It is better not to forcibly input an audio signal component which
can not be output by the speaker to the speaker. However, in this case, low-frequency signal
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components lower than the resonance frequency f0 of the speaker included in the actual audio
signal are cut, and the user can not hear the bass. Therefore, it is the best if the listener can hear
the low-frequency signal component without inputting the low-frequency signal component
below the resonance frequency to the speaker by any method. By the way, it has been proved
that if psychoacoustically only harmonics of a fundamental sound appear, human feels a sound
even if there is no fundamental sound as if there is a fundamental sound. For example, although
the timbre is determined by the basic sound and its harmonics, human beings can correctly
recognize the sound of the instrument if the harmonics can be accurately reproduced without the
basic sound.
[0010]
According to such psycho-acoustic theory, the frequency of the low frequency range audio signal
below the resonance frequency f0 of the speaker is multiplied (for example, doubled), and if the
multiplied signal is input to the speaker, the speaker accurately sounds according to the signal Is
emitted to the acoustic space, and the listener recognizes low-frequency speech below the
fundamental frequency, that is, the resonance frequency f0, from the sound corresponding to the
multiplied signal. This allows the listener to recognize undistorted bass and improve the bass
reproduction quality.
[0011]
(b) Overall Configuration FIG. 1 is a diagram showing the configuration of the sound reproducing
apparatus according to the present invention, and FIG. 2 is an operation explanatory diagram. In
FIG. 1, reference numeral 11 denotes a high pass filter (H.P.F) having a pass band equal to or
higher than the frequency fc, and the frequency fc is made to coincide with, for example, the
resonance frequency f0 (about 100 Hz) of the speaker (see FIG. 2 (b)). 12 is a band pass filter
(BPF) in the pass band fc1 to fc2, and the frequency fc2 on the high frequency side is matched
with the resonance frequency f0 (about 100 Hz) of the speaker, and the frequency fc1 on the low
frequency side is a frequency multiplication factor to be described later If so, fc1 = f0 / a (see
FIG. 2B). That is, fc1 = f0 / a
[0012]
Reference numeral 13 denotes a frequency multiplying circuit for multiplying the frequency of
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the low-pass speech signal passed through the band pass filter 12 by a. Preferably, a is an
integer, for example, a = 2. Assuming that the multiplication rate a is 2 and the resonance
frequency f0 of the speaker is 100 Hz, fc = 100 Hz, fc1 = 50 Hz, and fc2 = 100 Hz. 14 is a delay
circuit (DELAY) for delaying the mid-high frequency component output from the high-pass filter
11 by the time required for frequency multiplication; 15 is a gain for controlling the amplitude of
the frequency-multiplied audio signal output from the frequency multiplication circuit 13 A
variable amplifier, 16 is an amplifier (may be variable in gain), and 17 is a combining unit, which
combines the signals input through the amplifiers 15 and 16 and outputs the combined signal to
the speaker side.
[0013]
(c) Operation of Sound Reproduction Device An audio signal Sin having flat frequency
characteristics (FIG. 2A) output from an audio source such as a tape player, a CD player, an FM
tuner, etc. is transmitted to the high pass filter 11 and the band pass filter 12. input. The high
pass filter 11 removes low frequency components below fc (= 100 Hz) and passes audio signal
components above 100 Hz, that is, middle low frequency components. On the other hand, the
band pass filter 12 extracts and outputs a bass range component of frequencies fc1 to fc2 (= 50
Hz to 100 Hz) (see FIG. 2C). The frequency multiplication circuit 13 multiplies the frequency of
the bass component passing through the band pass filter 12 by a, for example, 2 times. As a
result, the original bass signal of fc1 to fc2 (= 50 Hz to 100 Hz) is converted into a signal having
frequency components of 2 fc1 to 2 fc2 (= 100 Hz to 200 Hz) (see FIG. 2D). Thereafter, the
frequency-multiplied signal is input to the combining unit 17 through the variable gain amplifier
15.
[0014]
On the other hand, the delay circuit 14 delays the middle to high frequency range component
that has passed through the high pass filter 11 by the time required for frequency multiplication,
and inputs it to the combining unit 17 via the amplifier 16. The synthesizing unit 17 synthesizes
the outputs of the frequency multiplying circuit 13 and the delay circuit 14 inputted through the
amplifiers 15 and 16 (see FIG. 2E), and an audio circuit (equalizer, Input to the electronic volume
circuit etc. and finally input to the speaker.
[0015]
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If psychoacoustically, only harmonics of the fundamental sound are produced, even if there is no
fundamental sound, human beings can feel the sound as if there is a fundamental sound. For this
reason, the listener recognizes low-frequency sound lower than the fundamental frequency, that
is, the resonance frequency f0 of the speaker from the sound corresponding to the frequencymultiplied signal. As a result, even if the low frequency audio signal of resonance frequency f0 or
lower is not input to the speaker, the low frequency audio of resonance frequency f0 or lower
can be recognized by the psychoacoustic effect, and the low frequency audio signal is not input
to the speaker There is no distortion and excellent bass reproduction is possible. Also, the high
frequency component is delayed by the time required for frequency multiplication, and it is
possible to listen to the sound without time deviation by combining it with the frequencymultiplied audio signal and outputting it. Also, when it is desired to increase or decrease the bass
according to the listener's preference, a knob for varying the gain is provided in the operation
unit, and the knob of this knob is operated to adjust the gain of the gain variable amplifier 15 to
increase or decrease the bass.
[0016]
(d) Frequency Multiplication Circuit FIG. 3 is a block diagram of the frequency multiplication
circuit 13. An analog-to-digital converter (ADC) 13a samples audio signal components in the bass
region output from the band pass filter 12 at a predetermined sampling rate Sp and converts
them into digital data. 13b and 13c alternate digital audio every predetermined period T First
and second memories that store data in time series, 13d is a data distribution unit that
distributes digital data output from the AD converter 13a to the first and second memories 13b
and 13c alternately every cycle T, 13e is a thinning readout unit which alternately reads out and
outputs digital data from the first and second memories 13b and 13c every other period T every
period T, and 13f is an analog of digital data output from the thinning readout unit Is a DA
converter (DAC) that converts
[0017]
The AD converter 13a continuously converts the audio signal component of the bass region into
digital data at the sampling rate Sp, and the data distribution unit 13d first inputs the AD
converted audio data to the first memory 13b and stores it. When audio data for one cycle T is
stored in the first memory 13b, the thinning-out reading unit 13e repeatedly reads every other
audio data at the reading speed Sp from the first memory 13b, and at the same time, the data
distributing unit 13 d stores audio data from the AD converter 13 a in the second memory 13 c.
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In order to read out data alternately every other data, the thinning-out reading unit 13e reads the
same data twice during one cycle T, and the frequency of audio data is doubled and input to the
DA converter 13f.
[0018]
When one cycle is completed, the switching signal CHG is generated, and the data distribution
unit 13d stores the audio data in the first memory 13b, while the thinning-out reading unit 13e
reads one audio data at the reading speed Sp from the second memory 13c. It reads repeatedly
every time. Thereafter, such storage and decimation reading of audio data are repeated. The DA
converter 13 f converts the audio data input from the thinning readout unit 13 e into an analog
audio signal at a speed Sp and outputs it. As a result, the low frequency audio signal of 50 to 100
Hz input from the band pass filter 12 is converted into a signal having a frequency component of
100 to 200 Hz. Alternatively, audio data may be continuously read out from the first and second
memories at a speed of 2 и Sp and DA conversion may be performed.
[0019]
(e) Modifications Although the case of the frequency multiplication rate a = 2 has been described
above, the frequency is not limited to 2 but may be converted to a signal of integral multiple or
other multiple. Also, in the above, the audio signal is separated into the low band component and
the high band component at the boundary of the speaker's resonance frequency f0, but it is not
necessary to separate at the boundary of f0. Alternatively, part of the low band and high band
may overlap. Although the present invention has been described above by way of examples, the
present invention can be variously modified in accordance with the spirit of the present invention
described in the claims, and the present invention does not exclude these.
[0020]
As described above, according to the present invention, the audio signal is separated into the low
band component and the high band component, the audio signal frequency of the low band
component is multiplied (for example, doubled), the high band component and the frequency
multiplier circuit output Can be recognized psychoacoustically from the sound according to the
frequency-multiplied signal, and low frequency audio signals of resonance frequency f0 or less
can not be input to the speaker. Therefore, it is possible to listen to an excellent bass without
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distortion and improve the bass reproduction quality. In particular, even with a speaker with
relatively low bass reproduction capability, high quality bass reproduction quality can be
provided with a simple configuration. Further, according to the present invention, the high
frequency component is delayed by the time required for frequency multiplication, and is
synthesized with an audio signal frequency-multiplied and output, so that a sound without time
deviation is heard. Can. Furthermore, since the gain of the frequency-multiplied voice signal is
adjustable, the bass can be increased or decreased according to the listener's preference.
[0021]
Brief description of the drawings
[0022]
1 is a block diagram of the sound reproduction apparatus of the present invention.
[0023]
2 is an operation explanatory diagram of the present invention.
[0024]
3 is a block diagram of a frequency multiplying circuit.
[0025]
4 is an explanatory view of a conventional problem.
[0026]
5 is a detailed view of the frequency characteristics of the speaker.
[0027]
Explanation of sign
[0028]
11 иии High pass filter 12 иии Band pass filter 13 иии Frequency multiplying circuit 14 иии Delay circuit
15 и и Gain variable amplifier 16 и и Combining section
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