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JPH06204799

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DESCRIPTION JPH06204799
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
apparatus for reproducing audio signals in digital audio and the like.
[0002]
2. Description of the Related Art In the case of digital recording of an audio signal, frequency
components of 1/2 or more of the sampling frequency are usually removed before A / D
conversion. Therefore, the analog signal obtained by reproducing the digital signal recorded in
this manner naturally does not contain frequency components of 1/2 or more of the sampling
frequency. That is, compared to the original analog signal before recording, the reproduced
analog signal lacks a frequency component of 1/2 or more of the sampling frequency. As the
sampling frequency, a frequency at least twice as high as the upper limit (about 20 kHz) of the
human audible band is selected. Therefore, it has been said that the missing frequency
component is a frequency component in the inaudible band, and there should be no adverse
effect on the sound quality.
[0003]
However, recently, it has been found that the lack of frequency components in the inaudible band
has some effect and that the sound quality seems to be adversely affected.
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1
[0004]
SUMMARY OF THE INVENTION In the conventional audio signal reproduction apparatus, since
the reproduction was performed with the frequency components in the inaudible band missing,
the audio signal was reproduced with a unique sound quality that is undesirable for the sense of
hearing. .
[0005]
An object of the present invention is to provide an audio signal reproduction apparatus capable
of compensating for the dropout of frequency components in the inaudible band and obtaining
an audible sound quality.
[0006]
An audio signal reproducing apparatus according to the present invention comprises an addition
circuit for adding a predetermined minute signal and a DC offset signal to generate an addition
signal, and an audio from which a frequency component in an inaudible band is removed. It has a
multiplication circuit which multiplies a signal and the above-mentioned addition signal.
The addition circuit may add the minute signal, the direct current offset signal, and the audio
signal.
[0007]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing specific
embodiments, the background of the present invention will be described.
As described above, it has recently been found that the loss of frequency components in the
inaudible band seems to have some adverse effect on the sound quality.
This can be considered as follows. The missing frequency components are frequency components
that can not be heard by the human ear. However, in consideration of linear distortion existing
inside the ear, various frequency components are generated based on frequency components in
the inaudible band by an effect generally called intermodulation, and this can be heard by the
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human ear it is conceivable that. In other words, the above-mentioned adverse effect on sound
quality (on hearing) is that the cross modulation effect that would have occurred in the original
analog signal before recording is weakened by the loss of frequency components in the inaudible
band. It is considered to be due to Therefore, the sound quality can be expected to be improved
by generating the above-mentioned cross modulation effect in a pseudo manner.
[0008]
Hereinafter, specific embodiments will be described with reference to FIG.
[0009]
The signal generator 11 generates a sine wave signal "a" (generally a repetitive signal) of a
predetermined frequency.
The attenuators 12 and 13 respectively attenuate the sine wave signal "a" and the DC offset
signal "b". The adder 14 adds the small sine wave signal “c” from the attenuator 12 and the DC
offset signal “d” from the attenuator 13. The multiplier 15 multiplies the addition signal “e”
from the adder 14 by the audio signal “g” from which frequency components in the inaudible
band have been removed, and outputs an output signal “h” having a pseudo-intermodulation
effect. It is something that occurs. The audio signal "g" is, for example, a reproduced signal in a
digital audio system, and its sampling frequency "fs" is selected to be twice or more the upper
limit (about 20 kHz) of the human audible band. The audio signal "g" may be a digital signal
before D / A conversion or an analog signal after D / A conversion. Therefore, each component
and each signal may be a digital signal or an analog signal.
[0010]
Next, the operation (calculation operation) of the embodiment of FIG. 1 will be described.
[0011]
The signal generator 11 generates a sine wave signal "a" having a frequency (2/3) times the
sampling frequency "fs".
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Then, the value of the small sine wave signal "c" from the attenuator 12 is "Vsin", the value of the
DC offset signal "d" from the attenuator 13 is "Vdc", the value of the audio signal "g" is "Vin", and
the output is Assuming that the value of the signal “h” is “Vou”, the calculation performed
by the adder 14 and the multiplier 15 results in Vou = Vin × (Vdc + Vsin) = Vin × Vdc + Vin ×
Vsin (1). Here, considering the second term of the equation (1), that is, the frequency spectrum of
“Vin × V sin”, the spectrum frequencies of the audio signal “g” and the spectrum frequency
“2 fs / 3” of the small sine wave signal “c” It can be seen that it is represented by the sum
and difference of Therefore, assuming that the spectral frequency "fo" of the output signal "h"
generated corresponding to the spectral frequency fi of the audio signal "g" is "fi = (fs
/3)+.DELTA." (Where ".DELTA." Is arbitrary) Frequency), fo = (2 fs / 3) ± fi = (2 fs / 3) ± ((fs / 3)
+ Δ) = fs + Δ, or (fs / 3) −Δ (2). The latter of the equation (2), that is, "(fs / 3)-?" Is a frequency
component in the audible band.
[0012]
As described above, the audio signal "g" does not include the frequency component of the human
audible band, but the output signal "h" has various audible bands corresponding to the value of
".DELTA." The frequency components of are to be included. And a pseudo | simulation
intermodulation effect arises by the frequency component of said "(fs / 3)-(DELTA)", and it
becomes possible to obtain a sound quality preferable on hearing.
[0013]
The following modifications can be made to the above embodiment.
[0014]
In the above embodiment, the audio signal "g" is added to the input of the adder 14, and the
minute sine wave signal "c", the DC offset signal "d" and the audio signal "g" are added by the
adder 14 It is also good.
In this case, the addition ratio of the minute sine wave signal "c", the DC offset signal "d" and the
audio signal "g" may be changed according to the magnitude of the output signal "h".
[0015]
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Further, in the above embodiment, the micro sine wave signal "c" may have a frequency other
than "2 fs / 3", or may be a signal having a plurality of sine wave spectra.
[0016]
Further, in the above embodiment, instead of the small sine wave signal "c", a signal having 1 / f
noise or a repetitive signal having a 1 / f frequency fluctuation may be used.
[0017]
Furthermore, the above modifications may be combined with each other.
[0018]
According to the present invention, since the loss of frequency components in the inaudible band
can be compensated for and pseudo modulation effects can be generated, sound quality can be
improved.
[0019]
Brief description of the drawings
[0020]
1 is a block diagram showing an embodiment of the present invention.
[0021]
14: Addition circuit 15: Multiplication circuit c: Minute signal d: DC offset signal e: Addition
signal g: Audio signal
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