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JPH06141391

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JPH06141391
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sound reproducing apparatus for converting an input sound signal into a sound signal containing
high frequency components not contained in the sound signal, for example, the input sound
signal is digital. The present invention relates to a sound reproduction apparatus suitable for
being a signal.
[0002]
2. Description of the Related Art Natural sounds and musical tones of natural musical
instruments are recorded as digital signals on a CD (compact disc) or the like. The digital signal
recorded on the CD or the like is converted into an analog signal representing sound by the
sound reproducing device, and is reproduced as sound through a speaker or the like.
[0003]
When sound is recorded as a digital signal on a CD or the like, sampling is performed at a
frequency twice or more the maximum frequency of the waveform of the sound to be
reproduced. The audible band of human beings is about 20 Hz to 20 kHz, and for this reason, a
digital signal sampled at about 40 kHz is recorded on an acoustic recording medium such as a CD
so as to be reproduced up to about 20 kHz.
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[0004]
However, although natural sounds and sounds of natural musical instruments also contain high
frequency components of about 20 kHz to about 50 to 70 kHz, and it is said that the human ear
can not hear the sound itself of 20 kHz or more, There are many people who can distinguish the
difference between 'tones' between sounds with frequencies below 20 kHz and sounds with
frequencies above 20 kHz. On the other hand, as described above, since the digital signal
recorded on a CD or the like is sampled at about 40 kHz, this digital signal is converted into an
analog signal by a conventional sound reproducing device and reproduced through a speaker or
the like. The sound does not contain frequency components exceeding 20 kHz. For this reason,
there is a problem that, particularly when the sound changes rapidly, for example, at the moment
when a certain sound utters, it may be heard as a 'tone color' different from the natural sound.
[0005]
Some conventional sound reproducing apparatuses employ a DA conversion system called
"legato link conversion system" to solve this problem. This "legato link conversion system" is a
system for recovering a signal of 20 kHz or more which is not included in a CD or the like by
digital operation using a DSP (digital signal processor). The method of using this DSP determines
the interpolation function according to the principle that the output level of natural musical
instruments tends to decrease in inverse proportion to the frequency of any music, and this
interpolation function is used to digitalize a CD etc. It is a method to interpolate between
sampling points at the time of recording a signal and reproduce a sound of 20 kHz or more (see
ASCII, vol. 16, # 7 July 1992).
[0006]
In the method using this DSP, it is not easy to identify the interpolation function, and there is a
problem that the structure of the sound reproducing apparatus becomes complicated and the
cost becomes high. An object of the present invention is to provide a low-cost sound reproducing
apparatus which converts an input sound signal into a sound signal representing a high
frequency component not included in the sound signal.
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[0007]
In order to achieve the above object, according to the first sound reproducing apparatus of the
present invention, an acoustic signal is input, and the acoustic signal is mixed with a sine wave
signal of a predetermined frequency. Mixing means for generating a mixing signal including the
sum and difference frequency components of the signal frequency and the sine wave signal
frequency, and a harmonic signal consisting of sum frequency components of the mixing signal
output from the mixing means It is characterized by comprising a high pass filter to be extracted,
and addition means for adding a harmonic signal outputted from the high pass filter to an
acoustic signal.
[0008]
Here, it is preferable that the above-mentioned sound reproducing apparatus be provided with a
weighting means for weighting harmonic signals.
Further, it is preferable that the above-mentioned sound reproducing apparatus be provided with
phase adjustment means for adjusting the phase of the harmonic signal. Further, according to a
second sound reproducing apparatus of the present invention for achieving the above object, the
frequency of the sound signal and each sine wave are input by inputting the sound signal and
mixing the sound signal with sine wave signals having different frequencies. A plurality of mixing
means for generating each mixing signal including the frequency component of the sum and
difference with the frequency of the signal, and each harmonic consisting of the frequency
component of the sum among the mixing signals output from each of the plurality of mixing
means A plurality of high-pass filters for extracting a signal, and addition means for adding each
harmonic signal output from each of the plurality of high-pass filters to an acoustic signal are
provided.
[0009]
The principle of mixing audio signals in the mixing circuit of the audio reproduction apparatus of
the present invention will be described. In general, an acoustic signal f (t) having a period T has a
Fourier series if there is no DC component,
[0011]
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It is represented as: ここで
[0013]
【0013】である。 Here, cos (nωt) · cos (ω0t) = 1⁄2 {cos (nω−ω0) t + cos (nω + ω0) t} sin
(nωt) · cos (ω0t) = 1⁄2 {sin (nω + ω0) t + sin (Nω-ω0) t}
[0015]
【0015】となる。 As shown in the above principle, in the mixing circuit, a sine wave signal
of a predetermined frequency (in the above, ω 0) is mixed with the input sound signal f (t) to
obtain the frequency and the sine wave of the input sound signal. A mixing signal is generated
that includes the frequency components of the sum and the difference with the frequency of the
signal.
[0016]
Next, in the high pass filter, the harmonic signal consisting of the frequency component of the
sum is extracted from the mixing signal output from the mixing circuit, and then the harmonic
signal output from the high pass filter is an acoustic signal in the addition means. Is added to As
a result, an acoustic signal including frequency components not included in the input acoustic
signal is generated.
[0017]
Here, when the weighting circuit is provided, the harmonic signal is weighted, so that it is
possible to generate an acoustic signal representing a sound that is closer to a natural sound or a
musical tone of a natural musical instrument. Note that the acoustic signal f (t) is considered to
be piecewise continuous up to the first derivative, so that an and bn in the above equation (1) can
be expressed as | an | <1 / n, | bn | <1 / n. For this reason, for example, when the weighting of
the harmonic signal is determined to have a characteristic of −20 log 2 n, that is, −6 dB down /
octave, the value of this weighting is 1/2, and in this case, it is not necessary to weight
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particularly. .
[0018]
In addition, when the phase adjustment circuit is provided, the phases of the input acoustic signal
and the harmonic signal are adjusted, so in this case as well, an acoustic signal representing an
acoustic closer to that of a natural sound or a natural musical instrument is generated. be able to.
Furthermore, when a plurality of mixing circuits and a plurality of high pass filters are provided,
and a plurality of harmonic signals are added to the input acoustic signal by the addition means,
the acoustic signal including various high frequency components is As a result, an acoustic signal
is generated that represents an even closer sound to a natural sound or a musical instrument
musical tone.
[0019]
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is
a block diagram showing a schematic configuration of a sound reproduction apparatus according
to a first embodiment of the present invention. A digital sound signal is input to the sound
reproducing apparatus 10 of the present embodiment from an external device such as a CD. This
digital acoustic signal is expressed by the following equation, but does not contain components
of angular frequency ω 0 (frequency 20 kHz; ω 0 = 2π × 20 kHz).
[0022] The acoustic signal is first converted to an analog acoustic signal by the D / A converter
12, and the analog acoustic signal is input to each of the three mixing circuits 14a, 14b and 14c.
In each of the three mixing circuits 14a, 14b and 14c, the analog sound signal is mixed with a
sine wave signal of frequency ω0, 2ω0 and 3ω0, respectively. For example, taking the case of
the mixing circuit 14a as an example, the frequency component of the sum and difference of the
frequency of the analog acoustic signal and the frequency ω0 of the sine wave signal is included
as shown in the following equation (2). Mixed signal is generated.
[0024] The mixing signal generated by the mixing circuit 14a is schematically shown in FIG. As
shown in FIG. 2, the mixing signal 14 contains a frequency component 14d of sum and a
frequency component 14e of difference, and these two frequency components are symmetrical
with respect to the frequency .omega.0. Similarly, in the mixing circuits 14b and 14c, mixing
signals including frequency components symmetrical with respect to the frequencies 2ω 0 and
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3ω 0 respectively are generated. As described above, the mixing circuits 14a, 14b, and 14c
generate mixing signals including frequency components that are not included in the digital
sound signal input to the sound reproduction device 10.
[0025] The respective mixing signals outputted from the mixing circuits 14a, 14b and 14c are
inputted to the high pass filters 16a, 16b and 16c, and harmonic signals consisting of frequency
components of the sum of the respective mixing signals are outputted from the high pass filters
16a, 16b and 16c. Each is extracted. The extracted harmonic signals are respectively input to
weighting circuits 18a, 18b and 18c and subjected to weighting represented by k1, k2 and k3.
[0026] The respective harmonic signals outputted from the weighting circuits 18a, 18b and 18c
are respectively inputted to the phase adjustment circuits 20a, 20b and 20c, and the phases of
the respective harmonic signals are adjusted by the phase adjustment circuits 20a, 20b and 20c. .
The above-described harmonic signals whose phases are adjusted are input to the adding circuit
22 and are added to the acoustic signal as it is output from the D / A converter 12 by the adding
circuit. The result of this addition is schematically shown in FIG. As a result of addition of the
acoustic signal 22a and the harmonic signal 22b in the state as they are output from the D / A
converter 12, as shown in FIG. 3, frequencies not included in the acoustic signal input to the
acoustic reproduction device 10 An acoustic signal containing components is generated. As a
result, an acoustic signal representing a sound close to that of a natural sound or a musical
instrument tone is obtained. This sound signal is reproduced as sound via a speaker or the like
(not shown), and a sound close to that of a natural sound or a musical instrument of a natural
musical instrument can be obtained.
[0027] In the above embodiment, the sine wave signals of the frequencies ω 0, 2ω 0 and 3ω 0
are mixed with the sound signals by the three mixing circuits 14 a, 14 b and 14 c respectively,
but the sine wave signals of the frequency ω 0 are mixed and the harmonics are mixed. It is
acoustically considerably improved just to generate. On the other hand, a sine wave signal of
frequency 4.omega.0, 5.omega.0,... May be mixed with an acoustic signal by using more mixing
circuits. In this configuration, since an acoustic signal including higher frequency components is
generated, an acoustic signal representing an acoustic closer to natural sounds or sounds of
natural musical instruments can be obtained.
[0028] A second embodiment of the sound reproducing apparatus according to the present
invention will be described with reference to FIG. The sound reproducing apparatus 10 (see FIG.
1) of the first embodiment converts the input digital sound signal into an analog sound signal by
the D / A converter 12 (see FIG. 1), and outputs the signal in the state of this analog sound signal.
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In contrast to the processing, the sound reproducing apparatus 30 of the second embodiment
processes the input digital sound signal as it is in the analog state without converting it into an
analog sound signal, and the D / A converter 32 It is configured to be converted into an acoustic
signal and output.
[0029] In this sound reproducing apparatus 30, as shown in FIG. 4, mixing circuits 34a, 34b, 34c
for respectively mixing sine wave signals of frequency ω 0, 2ω 0, 3ω 0 to the input sound
signal as in the first embodiment High-pass filters 36a, 36b, 36c for extracting respective
harmonic signals from the respective mixing signals outputted from the respective mixing
circuits 34a, 34b, 34c, and respective harmonic signals outputted from the respective high-pass
filters 36a, 36b, 36c Weighting circuits 38a, 38b and 38c for weighting represented by k1, k2
and k3, and a summing circuit 40 for adding the respective harmonic signals outputted from the
weighting circuits 38a, 38b and 38c, respectively, are provided. The sound reproducing
apparatus 10 of the first embodiment (see FIG. 1) to digital sound signals by these circuits, etc.
However, the above-described high-pass filters 36a, 36b, and 36c have a configuration in which
the phases of the input acoustic signals do not shift, and therefore, the acoustic reproduction
device 30 is not provided with a phase adjustment circuit. . The acoustic signal output from the
adding circuit 40 is converted to an analog acoustic signal by the D / A converter 32 as described
above and output.
[0030] Also in the sound reproducing apparatus 30 of the present embodiment, the same effect
as that of the sound reproducing apparatus 10 of the first embodiment can be obtained.
[0031] As described above, according to the sound reproducing apparatus of the present
invention, by mixing a sine wave signal of a predetermined frequency with the input sound
signal, it includes frequency components not included in the input sound signal Since an acoustic
signal is generated, an acoustic signal representing an acoustic close to that of a natural sound or
a musical tone of a natural instrument can be obtained. By reproducing the sound signal as
sound through a speaker or the like, a sound close to a natural sound or a musical tone of a
natural musical instrument can be obtained even if the sound changes rapidly.
[0032] In addition, the method of processing an acoustic signal performed by the sound
reproduction apparatus according to the present invention is a low-cost sound reproduction
apparatus that can perform signal processing in real time.
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