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■ Noise removal device in sound reproduction ■ Japanese Patent Application No. 45-4335
[phase] Application No. 45 (1970) January 17 @ inventor Shigeyama Akihiro-Kawasaki-shi Ikuta
205 same Yamada upbringing part 817 Hazawa-cho, Kana-ku, Yokohama-shi 4 of the same
Kondo Arihiro Urawa city Yanagise 66 11 ■ Applicant Trio Co., Ltd. Tokyo Tokyo Meguro Ward
Aobadai 3 6 17
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the present invention, FIG.
2 is a schematic view showing an outline of a part of FIG. 1, and FIG. 3 is a frequency by peak
level average data in an octave configuration in sound reproduction. FIG. 4 is a characteristic
diagram showing a distribution state, FIG. 4 is a characteristic diagram showing a masking state
of pure tones by noise (when IKHz is at the center), and FIG. 5 is a characteristic of each
constitution according to the present invention. A] is a band pass filter characteristic diagram [B]
is an output characteristic diagram, and [C] is a characteristic diagram of the control circuit.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for
improving noise in sound reproduction. In sound reproduction, it is known that when the
frequency distribution of the reproduced sound is measured in an octave configuration, the
characteristic as shown in FIG. 3 is obtained. As can be seen from the characteristic curve based
on this average data, no difference in the distribution of each frequency is seen at the peak level,
but when measured as a time rate of 1% (36 seconds) to 10 relationships (6 minutes), It can be
seen that there are many, and the low and high range is small. As shown in the characteristic
diagram showing the masking state in FIG. 4, assuming that the center frequency is, for example,
1 KHz, the masking effect is greatly affected as the center frequency is closer to 1 KHz, and the
masking effect is obtained when slightly apart from [111111] intercardiac wave number Is
known to be difficult to receive. Therefore, in the low / high range where the acoustic frequency
signal shown in FIG. 3 is relatively small, the probability that noise is masked with a pure tone is
small, and the signal level is large especially at 4 KHz etc. in the high range. There is a drawback
that the noise that has been masked due to this can be deafening as it can be heard as the signal
level decreases. In view of the above-mentioned drawbacks, the present invention is intended to
obtain a device in which a frequency band in which noise is particularly distracting as the signal
level becomes smaller is attenuated in the other frequency bands and noise can not be heard. is
there. Hereinafter, embodiments of the present invention will be described based on the
drawings. Reference numeral 1 denotes an input terminal of an acoustic frequency signal, and 2
and 3.4, first, second and third variable gain circuits provided in series in a line for transmitting
the acoustic frequency signal, which are composed of a transistor 5 and the like. 6. ? , 8 takes out
part of the input signal to the first variable gain circuit 2. I: The first, second, and third control
circuits for controlling the first, second, and third variable gain circuits respectively, and the
acoustic frequency is high as shown in FIG. 5 [A]. The frequency division is a * bec and the
control operation is performed independently for each circuit. First, second and third control
circuits γ, 8 have the same resonant frequency as the first resonant circuit 61 ° γ1, 81, and
the first resonant circuit 61, 7L81, the rectifier circuit 62.72.82, the variable impedance circuit
63.73.83, And the second resonant circuit 64 and 74.84. First resonant circuit 61. γ1, 81 are
connected between the signal line of the first variable gain circuit 2 and the ground line, and
each of the resonant circuits 61. The resonance frequency is made different from ft-h and fs for
each of γ1 and 81, and the high frequency band of the acoustic same wave number signal is
selected so as to be frequency-divided as shown in FIG. 5 [A].
The second resonant circuit 64.74.84 includes the first, the [111111] EndPage: 12, the third
variable gain circuit 6. For example, γ, 8 are connected between the emitter side of the
transistor 3 and the ground, and have the same resonance frequency f, f2, fs corresponding to
the first resonance circuit 61t 71.81. The rectifier circuits 62 and 72.82 are composed of the
diode 9 and the smoothing capacitor 10, respectively rectify the resonant frequency signals of
the first resonant circuit 61 and γ1 and 81, and apply them to the variable impedance circuits
63 and 73.83. The variable impedance circuit 83.73.83 is composed of a variable resistor 11 for
human power signal level adjustment, a transistor 12 and the like, and the impedance is changed
in accordance with the rectified current level from the rectifier circuit A second
resonant circuit 64. between the ground side and the emitter side of the transistor 3 in the
variable gain circuit 7.8. Connected in parallel with γ4, 84 respectively. 13 is an
output terminal. As the number of control circuits in L is increased and the division of the
acoustic frequency signal is made finer, better results are obtained. Also, although the townchanging impedance circuits 63 and 73 are used in the transistor type, it is needless to say that
other means using other means can be used. Next, the case of removing noise in the device of the
present invention will be described. When the level of the acoustic frequency signal applied to
the input terminal 1 is, for example, about -10 dB or more, the control circuit 6. The first
resonant circuit 61.71.81 of each of γ and 8 resonates at a high frequency f1 · f2 · fs in the
acoustic frequency signal. First resonant circuit 61. γ1. The resonant frequency signal
resonating with B1 is rectified by the rectifier circuits 62.72.82, respectively, and applied to the
variable impedance circuit 63.73 ° 83. The transistor 12 of the variable impedance circuit 73.83 is in the conduction region between g and h of the characteristic curve shown
in FIG. 5 [C]. Therefore, the transistor 5 of the variable gain circuit 2 or 3.4 has a small emitter
load. In the case of an acoustic frequency signal of around 10 dB or less shown in FIG. 5 CB, 1
shown in FIG. It can be supplied as it is. In this case, the second resonant circuit 64, γ4, 84
connected between the variable gain circuit 2.3.4 and the ground is included in the acoustic
frequency signal as in the first resonant circuit 61 ° γ1, 81. The gain should be reduced by
increasing the emitter load of the transistor 5 of each variable gain circuit 2.3.4 in resonance
with the periodic [111111] wave number ft, 12-fs, but as described above, the second Resonant
circuit of. Since the town-changing impedance circuit 2, 3 connected in parallel with γ4, 84 has
a low impedance, the second resonant circuit 64.74.84 Q-dumps, and the variable gain circuit 2,
3.4 is It does not become the emitter load of the transistor 5 of
Next, when an acoustic frequency signal is applied to the input terminal 1 at a level where noise
such as 30 dB or 50 dB is not masked to the signal, the resonant signal output of the first
resonant circuit 61.7L81 is extremely small, and thus the variable impedance circuit 63. The
rectified current supplied to γ3 ° 83 is small and the variable impedance circuit 63. The
impedance of 虱 3, 83 between the characteristic curves g-e-d shown in FIG. 5 [C] is high. Then,
the second resonant circuit 64. γ4 ° 84 performs resonance operation at its resonance
frequencies f1, f2 and fs, and the emitter load of the transistor 5 in the variable gain circuit 2.3.4
is increased at each resonance frequency f1 * f29, as shown in FIG. As shown in the
characteristic curve of the case where the human power of the acoustic frequency signal is, for
example, 30 dB and -50 dB, attenuation significantly occurs at other resonance frequency bands
f1, f2 and fs. In the case of L, it has been described that the acoustic frequency is reduced equally
to the level of the acoustic frequency, for example, the level 1 of the band a shown in FIG. When
the contained noise can be heard without being masked (for example, -40 dB), the resonance
signal output supplied from the first resonance circuit 61 of the control circuit 6 to the
rectification circuit 62 is extremely small and variable impedance The impedance of the circuit
63 is high. Then, the second resonance circuit 64 starts the resonance operation at the resonance
frequency f1, increases the emitter load of the transistor 5 in the variable gain circuit 2 at the
resonance frequency f1, and attenuates significantly at the resonance frequency f1 compared to
other frequency bands. The noise of the frequency ft part which is not masked is not supplied to
the output terminal 13. Accordingly, the present invention has a small amount of acoustic
frequency signals shown in the characteristic curve of FIG. 3 as shown in E, and is masked and
especially in the high range. For example, it is divided into octave bands, and [111111] EndPage:
2 according to the sound frequency signal level can be attenuated from other sound frequency
bands to remove noise, and noises that cause distraction to the output amplifier etc. It is possible
to obtain a sound reproduction device that can not be supplied.