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Claims  |
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What is claimed is:
1. An audio reproduction system comprising:
an amplifier for amplifying a gain of a reproduced audio signal supplied
thereto in a full effective frequency range, said amplifier having a
positive and a negative input terminal and an output terminal, and said
output terminal outputting an amplified audio signal;
a first variable resistor for controlling a gain of the amplified audio
signal, said first variable resistor having two ends and a movable
contact, one end of said two ends of said first variable resistor being
connected to said output terminal of said amplifier, and said movable
contact of said first variable resistor outputting a first controlled
output;
a negative feedback loop circuit for feeding back a part of the amplified
audio signal to said negative input terminal of said amplifier;
a tone control unit for controlling a gain of a part of the reproduced
audio signal in a predetermined frequency range, said tone control unit
having an input and an output terminal, said input terminal of said tone
control unit being connected to said positive input terminal of said
amplifier, and said output terminal of said tone control unit outputting a
tone-controlled audio signal;
a second variable resistor for controlling a gain of the tone-controlled
audio signal, said second variable resistor having two ends and a movable
contact, said movable contact of said second variable resistor being
connected to said output terminal of said tone control unit, and one end
of said two ends of said second variable resistor being connected to said
negative input terminal of said amplifier and outputting a second
controlled output; and
a gang control unit for linking said movable contact of said first variable
resistor to said movable contact of said second variable resistor in order
to control a gain of the second controlled output at said second variable
resistor depending on a degree to which a gain of the first controlled
output at said first variable resistor has been reached.
2. An audio reproduction system according to claim 1, wherein said gang
control unit comprises means for controlling said second variable resistor
to reduce the gain of the second controlled output when the gain of the
first controlled output at said first variable resistor is increased to a
higher level, and for controlling said second variable resistor to
increase the gain of the second controlled output when the gain of the
first controlled output at said first variable resistor is reduced to a
lower level.
3. An audio reproduction system according to claim 1, wherein said tone
control unit comprises a resonant circuit for extracting a signal
component in the predetermined frequency range, said resonant circuit
including an RC network circuit, and a third variable resistor for
controlling a gain of the signal component in the predetermined frequency
range, said third variable resistor having two ends and a movable contact,
one end of said two ends of said third variable resistor being connected
to said input terminal of said tone control unit, another end of said two
ends of said third variable resistor being connected to said output
terminal of said tone control unit, and said movable contact of said third
variable resistor being connected to said resonant circuit.
4. An audio reproduction system according to claim 3, wherein said second
variable resistor provides the function of said third variable reistor.
5. An audio reproduction system according to claim 3, wherein said tone
control unit comprises a plurality of resonant circuits.
6. An audio reproduction system according to claim 3, wherein said third
variable resistor comprises a plurality of variable resistors, and said
resonant circuit comprises a plurality of resonant circuits, said
plurality of resonant circuits being associated with respective ones of
said plurality of variable resistors.
7. An audio reproduction system according to claim 3, wherein said third
variable resistor includes switch means for selectively switching the gain
of the signal component in the predetermined frequency range of said part
of said reproduced audio signal between a predetermined level and a zero
level.
8. An audio reproduction system according to claim 3, wherein at least one
of said first variable resistor and said second variable resistor
comprises a resistor and a slide contact slidable on said resistor in a
direction.
9. An audio reproduction system according to claim 8, wherein said first
variable resistor comprises a first arcuate resistor extending around an
axis, and a first slide contact rotatable about said axis for sliding
movement on said first arcuate resistor, and said second variable resistor
comprises a second arcuate resistor extending around an axis, and a second
slide contact rotatable about said last-mentioned axis for sliding
movement on said second arcuate resistor, said gang control unit
comprising means for rotating said second slide contact in the same
direction as said first slide contact.
10. An audio reproduction system according to claim 8, wherein said first
variable resistor comprises a first arcuate resistor extending around an
axis, and a first slide contact rotatable about said axis for sliding
movement on said first arcuate resistor, and said second variable resistor
comprises a second arcuate resistor extending around an axis, and a second
slide contact rotatable about said last-mentioned axis for sliding
movement on said second arcuate resistor, said gang control unit
comprising means for rotating said second slide contact in the opposite
direction to said first slide contact.
11. An audio reproduction system according to claim 8, wherein said first
variable resistor comprises a first linear resistor, and a first slide
contact linearly slidable on said first linear resistor, and said second
variable resistor comprises a second linear resistor, and a second slide
contact linearly slidable on said second linear resistor, said gang
control unit comprising means for linearly moving said second slide
contact in the same direction as said first slide contact.
12. An audio reproduction system according to claim 8, wherein said
resistor of said second variable resistor has a width which is constant in
a direction perpendicular to said direction in which the slide contact
moves.
13. An audio reproduction system according to claim 8, wherein said
resistor of said second variable resistor has a width which is
progressively greater in a spatial direction which is perpendicular to
said direction in which the slide contact moves, wherein change in said
width is determined with respect to said direction.
14. An audio reproduction system according to claim 8, wherein said
resistor of said second variable resistor has a width which is
progressively smaller in a spatial direction which is perpendicular to
said direction in which the slide contact moves, wherein change in said
width is determined with respect to said direction.
15. An audio reproduction system according to claim 12, wherein said
resistor of said second variable resistor comprises a plurality of
resistor members which are discontinuous in said direction in which said
slide contact slides, and a conductive member connected between said each
resistor member.
16. An audio reproduction system according to claim 12, wherein said
resistor of said second variable resistor comprises a plurality of
resistor members which are discontinuous in said direction in which said
slide contact slides, and another resistor member connected between said
each resistor member.
17. An audio reproduction system according to claim 1, further comprising a
gain limiting unit for limiting the gain of the first controlled output.
18. An audio reproduction system according to claim 1, wherein said tone
control unit comprises means for varying arbitrarily a quantity for
controlling the gain of the signal in the predetermined frequency range of
the reproduced audio signal supplied thereto.
19. An audio reproduction system comprising: an amplifier for amplifying a
gain of a reproduced audio signal supplied thereto in a full effective
frequency range, said amplifier having a positive and a negative input
terminal and an output terminal, and said output terminal outputting an
amplified audio signal;
a first variable resistor for controlling a gain of the amplified audio
signal, said first variable resistor having two ends and a movable
contact, one end of said two ends of said first variable resistor being
connected to said output terminal of said amplifier, and said movable
contact of said first variable reisistor outputting a first controlled
output;
a negative feedback loop circuit for feeding back a part of the amplified
audio signal to said negative input terminal of said amplifier;
a tone control unit for controlling a gain of a part of the reproduced
audio signal in a predetermined frequency range, by selecting a gain of a
signal from a plurality of predetermined gain characteristics, said tone
control unit having an input and an output terminal, said input terminal
of said tone control unit being connected to said positive input terminal
of said amplifier, and said output terminal of said tone control unit
outputting a tone-controlled audio signal;
a second variable resistor for controlling a gain of the tone-controlled
audio signal, said second variable resistor having two ends and a movable
contact, said movable contact of said second variable resistor being
connected to said output terminal of said tone control unit, and one end
of said two ends of said second variable resistor being connected to said
negative input terminal of said amplifier and outputting a second
controlled output; and
a gang control unit for linking said movable contact of said first variable
resistor to said movable contact of said second variable resistor in order
to control a gain of the second controlled output at said second variable
resistor depending on a degree to which a gain of the first controlled
output at said first variable resistor has been reached. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to an audio reproduction system such as an
audio preamplifier, an audio control amplifier, or the like, and more
particularly to an improved tone control apparatus for use in such an
audio reproduction system.
Generally, preamplifiers and control amplifiers for use in stereo
reproduction systems have tone control circuits for altering the frequency
response of the amplifiers thereby to adjust the tone of reproduced sound.
Graphic equalizers are used as an independent circuit for fine adjustment
of the frequency response of amplifiers connected thereto. Human ears
suffer the natural loss of hearing sensitivity at lower and higher
frequencies when the level of the reproduced sound level is low. Loudness
control circuits are employed to compensate for such a tendency of human
hearing by boosting or emphasizing high and low frequencies so that the
reproduced sound heard by human ears has apparently flat frequency
characteristics. The above tone control circuits, graphic equalizers, and
loudness control circuits will be refered to as tone control units.
In any of the above tone controls, the adjusted frequency characteristics
of an audio signal can be adjusted again manually by using a control knob
or the like, but has nothing to do with changes in the volume level.
Therefore, the adjusted frequency characteristics of an audio signal
remain the same irrespective of whether the volume level of the signal is
increased or reduced.
In designing an audio main amplifier, the gain of the main amplifier is
selected such that the reproduced sound will not be distorted when the
volume level is maximum, in order to ensure powerful impressions which the
listener will have when the signal is reproduced with high output power.
However, the reproduced sound will nevertheless be distorted if a signal
in excess of an allowable maximum level is applied to the main amplifier.
Such an excess signal is given, for example, when the volume level is
increased while lower frequencies are being emphasized by a tone control
unit. If the volume level is increased while lower frequencies are being
accentuated, then only the bass portion of the frequency spectrum will be
distorted. Some small-size stereo reproduction systems have a circuit for
emphasizing low frequencies because the loudspeakers are too small to
reproduce low frequencies. Car audio stereo systems also incorporate FIX
equalizers, DSP circuits, or the like to achieve particular frequency
characteristics for improving the acoustic properties of passenger
compartments of cars. The amplifiers for use in those stereo systems must
be set at a low gain level to prevent the reproduced sound at particular
frequencies from being distorted. If the gains are selected in the usual
manner, then the reproduced sound will be distorted at particular
frequencies when the volume level is increased. The low-frequency
distortion is particularly liable to occur with car audio stereo
amplifiers whose gains are low and whose maximum output power is small.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an audio reproduction
system which includes means for correlating a tone control level to a
volume level, so that the tone control level can automatically be
controlled depending on the volume level.
According to the preferred embodiment of the present invention, there is
provided an audio reproduction system comprising a tone control unit for
controlling tones by increasing or reducing a gain, or keeping an
increased or reduced gain, of a signal in a particular frequency range of
an audio signal supplied thereto, a volume control unit for increasing or
reducing a gain of the audio signal in a full effective frequency range,
and a gain control unit for controlling the gain which has been increased
in the particular frequency range by the tone control unit, depending on
the degree to which the gain has been increased by the volume control
unit.
The tone control unit includes a variable resistor for increasing or
reducing the gain of the signal in the particular frequency range. The
volume control unit also has a variable resistor which is interconnected
to the variable resistor of the tone control unit through the gain control
unit.
When the knob of the volume control unit is shifted toward a higher scale
level position, the gain of the signal in the particular frequency range
is lowered by the gain control unit, thereby preventing the reproduced
sound from being distorted. When the knob of the volume control unit is
shifted toward a lower scale level position, the gain of the signal in the
particular frequency range is increased by the gain control unit.
The variable resistor of the tone control unit, which is interlinked with
the variable resistor of the volume control unit, may have any of various
different resistive characteristics to cause the signal gain to vary
according to any of various patterns.
Each of the variable resistors of the tone and volume control units may
comprise an arcuate or linear resistor and a slide contact slidable on the
resistor.
Alternatively, the volume control unit may comprise a voltage controlled
amplifier.
The tone control unit may comprise an analog-to-digital converter, a
digital signal processor, and a digital-to-analog converter. The digital
signal processor may be controlled by a system controller to vary the gain
of the signal in the particular frequency range.
The audio reproduction system may further includes a limiter for limiting
the gain of the signal from the volume control unit.
The above and other objects, features and advantages of the present
invention will become more apparent from the following description when
taken in conjunction with the accompanying drawings in which preferred
embodiments of the present invention are shown by way of illustrative
example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(A) is a block diagram of an audio reproduction system according to a
first embodiment of the present invention;
FIG. 1(B) is a block diagram of a modification of the audio reproduction
system shown in FIG. 1(A);
FIGS. 2 through 6 are circuit diagrams of frequency characteristics control
devices according to second through sixth embodiments of the present
invention;
FIG. 7(A) is a detailed circuit diagram of a frequency characteristics
control device according to the present invention;
FIG. 7(B) is a diagram showing operation of the frequency characteristics
control device shown in FIG. 7(A);
FIGS. 8 through 10 are views of different linked mechanisms for an audio
reproduction system according to the present invention;
FIGS. 11(A) through 12 are diagrams illustrative of operation of the linked
mechanisms;
FIGS. 13(A) through 20(C) are diagrams showing gain control units for an
audio reproduction system according to the present invention;
FIGS. 21 and 22 are circuit diagrams of frequency characteristics control
devices according to seventh and eighth embodiments of the present
invention;
FIGS. 23 through 25 are block diagrams of frequency characteristics control
devices according to ninth through eleventh embodiments of the present
invention; and
FIG. 26 is a circuit diagram of frequency characteristics control device
according to twelfth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
FIG. 1(A) shows, in block form, an audio reproduction system according to a
first embodiment of the present invention. The audio reproduction system
shown in FIG. 1 includes an information pickup device 1, a frequency
characteristics control device 2, an amplifier 3, and a loudspeaker 4. The
information pickup device 1 is connected to the frequency characteristics
control device 2, and has physical means for reading audio information
recorded on a recording medium or audio information supplied from an
external source, and converting the read audio information into an audio
signal that is then applied to the frequency characteristics control unit
2. The information pickup device 1 may be a device, such as a compact disc
player, an analog disc player, a cassette tape deck, a DAT deck, or the
like, which reads recorded audio information from a recording medium and
converts the audio information into an audio signal, or a device, such as
an FM/AM tuner, a microphone, or the like, for reading audio information
supplied from an external source and converting the audio information into
an audio signal, or a device, such as a video tape recorder, a video disc
player, a TV tuner, or the like, which separates and reads audio
information from supplied audio-video signals and converts the audio
information into an audio signal. The frequency characteristics control
device 2 is connected to the output terminal of the information pickup
device 1 and the input terminal of the amplifier 3. The frequency
characteristics control device 2 controls the tone and volume of the audio
signal received from the information pickup device 1, and supplies the
audio signal with the controlled tone and volume to the amplifier 3. The
amplifier 3 is connected to the output terminal of the frequency
characteristics control device 2 and the input terminal of the loudspeaker
4. The amplifier 3 amplifies the audio signal received from the frequency
characteristics control device 2, and applies the amplified audio signal
to the loudspeaker 4. The loudspeaker 4 is connected to the output
terminal of the amplifier 3, and coverts the audio signal received from
the amplifier 3 into sound waves and radiates the sound waves.
The frequency characteristics control device 2 comprises a tone control
unit 21, a volume control unit 22, and a gain control unit 23. The tone
control unit 21 is connected to the output terminal of the information
pickup device 1 and the input terminal of the volume control unit 22. The
tone control unit 21 boosts (emphasizes) or reduces (attenuates) the gain
of the audio signal, variably or in a fixed manner, in desired plural
frequency ranges, and supplies the tone-controlled audio signal to the
volume control unit 22. The tone control unit 21 may be a control unit,
such as a tone control circuit or a graphic equalizer, which can boost or
cut off the gain of the audio signal variably in desired plural frequency
ranges, or a control unit, such as a loudness control circuit, for
boosting or reducing the gain of the audio signal at certain points in the
frequency range thereof with a fixed ratio based on a certain frequency
characteristic curve, or for turning off the gain of the audio signal
uniformly at certain points in the frequency range thereof, or a control
unit, such as an RIAA characteristic equalizer or an NAB characteristic
equalizer in a tape deck, for boosting or reducing the gain of the audio
signal at certain points in the frequency range thereof with a fixed ratio
based on a certain frequency characteristic curve, or a sound field
control circuit, such as an FIX equalizer, a DSP circuit, or the like,
which has fixed or variable frequency characteristics. The volume control
unit 22 is connected to the output terminals of the tone control unit 21
and the input terminal of the amplifier 3. The volume control unit 22 is
externally operated on to control the volume level of the audio signal
from a zero level to a maximum level, and applies the audio signal with
the volume level controlled to the amplifier 3. The gain control unit 23
is connected to the volume control unit 22 and the tone control unit 21.
When the volume level of the volume control unit 22 is high, the gain
control unit 23 continuously or discontinuously lowers the gain of the
tone control unit 21. When the volume level of the volume control unit 22
is low, the gain control unit 23 continuously or discontinuously increases
the gain of the tone control unit 21.
Operation of the audio reproduction system shown in FIG. 1(A) will be
described below.
The information pickup unit 1 reads audio information, converts the audio
information into an audio signal, and applies the audio signal to the
frequency characteristics control device 2.
In the frequency characteristics control device 2, the tone control unit 21
adjusts the frequency characteristics (tone characteristics) of the audio
signal received from the information pickup unit 1, and supplies the audio
signal with the adjusted frequency characteristics to the volume control
unit 22.
The volume control unit 22 is then externally operated on to control the
overall signal level (volume level) of the audio signal received from the
tone control unit 21 between the zero level and the maximum level, and
transmits the audio signal with the adjusted volume level to the amplifier
3.
When the volume level of the volume control unit 22 increases, the gain
control unit 23 operates the volume control unit 22 and the tone control
unit 21 in linked relation with a mechanical or electrical arrangement for
continously or discontinuously reducing the gain of the audio signal at
points in the frequency range thereof which are set by the tone control
unit 21. When the volume level of the volume control unit 22 decreases,
the gain control unit 23 operates the volume control unit 22 and the tone
control unit 21 in linked relation with the mechanical or electrical
arrangement for continuously or discontinuously increasing the gain of the
audio signal at points in the frequency range thereof which are selected
by the tone control unit 21.
The amplifier 3 amplifies the audio signal received from the volume control
unit 22 with a given amplification factor, and supplies the amplified
audio signal to the loudspeaker 4.
The loudspeaker 4 converts the audio electric signal received from the
amplifier 3 into sound waves, and radiates the sound waves.
FIG. 1(B) shows a modified audio reproduction system according to the
present invention. The modified audio reproduction system shown in FIG.
1(B) structurally differs from the audio reproduction system shown in FIG.
1(A) only in that the tone control unit 21 and the volume control unit 22
are switched around in position. The modified audio reproduction system
shown in FIG. 1(B) is functionally identical to the audio reproduction
system shown in FIG. 1(A).
Second Embodiment
FIG. 2 shows a frequency characteristics control device according to a
second embodiment of the present invention, for use in an audio
reproduction system. The frequency characteristics control device,
generally denoted at 2A, comprises a tone control circuit 21A as a tone
control unit, a volume control 22A as a volume control unit, and a gain
control unit 23A.
The tone control circuit 21A comprises a noninverting amplifier 200,
resistors 201, 202, a circuit 203 composed of series- and
parallel-connected capacitors and resistors, and variable resistors 204,
205.
The noninverting amplifier 200 has a positive input terminal which is
connected at a junction T.sub.7A to one terminal of the resistor 201,
whose other terminal serves as a positive input terminal of the frequency
characteristics control device 2A. The circuit 203 has one terminal
grounded and another terminal connected to the movable contact of the
variable resistor 204. One fixed terminal of the variable resistor 204 is
connected to the junction T.sub.7A, and the other fixed terminal thereof
is connected at a junction T.sub.6A to one fixed terminal of the variable
resistor 205 and also to the movable terminal T.sub.4A of the variable
resistor 205. The other fixed terminal of the variable resistor 205 is
connected at a junction T.sub.5A to a negative input terminal of the
noninverting amplifier 200 and also to one terminal of the resistor 202.
The other terminal of the resistor 202 is joined at a junction T.sub.2A to
the output terminal of the noninverting amplifier 200, the resistor 202
serving as a negative feedback resistor connected across the noninverting
amplifier 200. The junction T.sub.2A is coupled to one fixed terminal of
the volume control 22A in the form of a variable resistor, whose other
fixed terminal is connected to ground. The volume control 22A has a
movable terminal T.sub.1A serving as a positive output terminal of the
frequency characteristics control device 2A. The movable contact of the
variable resistor 205 and the movable contact of the volume control 22A
are linked with each other by the gain control unit 23A.
The frequency characteristics control device 2A operates as follows:
An audio signal applied between input terminals V.sub.IN has a boosted
component in a frequency range which is determined by the CR value of the
circuit 203, the boosted component being increased or reduced by the
variable resistor 205. The boosted component is increased or reduced in
mechanical or electrically ganged relation to operation of the volume
control 22A through the gain control unit 23A. Specifically, when the
volume control 22A is shifted toward a higher scale level, the variable
resistor 205 is automatically shifted toward a higher resistance by the
gain control unit 23A, i.e., shifted in a direction to reduce the current
flowing between the circuit 203 and the negative input terminal of the
noninverting amplifier 200.
Therefore, as the volume control 22A is shifted from a lower scale level
toward a higher scale level, the boosted or emphasized level of the audio
signal in the determined frequency range is continuously or
discontinuously lowered. The frequency characteristics control device 2A
is advantageous in that it is of a relatively simple circuit arrangement
and the reduction of the boosted level in the determined frequency range
is natural because the boosted level is gradually and smoothly reduced.
When the volume level of the volume control 22A is lowered, the above
process is reversed.
Third Embodiment
FIG. 3 shows a frequency characteristics control device 2B according to a
third embodiment of the present invention, for use in an audio
reproduction system. The frequency characteristics control device 2B is
functionally identical to the frequency characteristics control device 2A
shown in FIG. 2.
The frequency characteristics control device 2B shown in FIG. 3 comprises a
tone control circuit 21B as a tone control unit, a volume control 22B as a
volume control unit, and a gain control unit 23B.
The tone control circuit 21B comprises a noninverting amplifier 210,
resistors 211, 212, a circuit 213 composed of series- and
parallel-connected capacitors and resistors, and a variable resistor 215.
The noninverting amplifier 210 has a positive input terminal which is
connected to one terminal of the resistor 211, whose other terminal serves
as a positive input terminal of the frequency characteristics control
device 2B. The circuit 213 has one terminal grounded and another terminal
connected at a junction T.sub.6B to one fixed terminal of the variable
resistor 215 and also to the movable contact T.sub.4B of the variable
resistor 215. The other fixed terminal of the variable resistor 215 is
connected at a junction T.sub.5B to the negative input terminal of the
noninverting amplifier 210 and also to one terminal of the resistor 212.
The other terminal of the resistor 212 is joined at a junction T.sub.2B to
the output terminal of the noninverting amplifier 210, the resistor 212
serving as a negative feedback resistor connected across the noninverting
amplifier 210. The junction T.sub.2B is coupled to one fixed terminal of
the volume control 22B in the form of a variable resistor, whose other
fixed terminal is connected to ground. The volume control 22B has a
movable terminal T.sub.1B serving as a positive output terminal of the
frequency characteristics control device 2B. The movable contact of the
variable resistor 215 and the movable contact of the volume control 22B
are ganged with each other by the gain control unit 23B. When the volume
control 22B is shifted from a lower scale level toward a higher scale
level, the boosted or emphasized level of the audio signal in the
determined frequency range (tone control level) is continuously or
discontinuously lowered.
When the volume level of the volume control 22B is lowered, the above
process is reversed.
Fourth Embodiment
FIG. 4 shows a frequency characteristics control device 2C according to a
fourth embodiment of the present invention, for use in an audio
reproduction system. The frequency characteristics control device 2C is
capable of freely determining a frequency range in which the audio signal
can be controlled.
The frequency characteristics control device 2C comprises a tone control
circuit 21C as a tone control unit, a volume control 22C as a volume
control unit, and a gain control unit 23C.
The tone control circuit 21C comprises a noninverting amplifier 220,
resistors 221, 222, a plurality of circuits 223, 226.sub.i through
226.sub.n each composed of series- and parallel-connected capacitors and
resistors, and variable resistors 224, 225.
The noninverting amplifier 220 has a positive input terminal which is
connected at a junction T.sub.7C to one terminal of the resistor 221,
whose other terminal serves as a positive input terminal of the frequency
characteristics control device 2C. The circuit 223 has one terminal
grounded and another terminal connected to the movable contact of the
variable resistor 224. The circuits 226.sub.i through 226.sub.n have
terminals grounded on one side, and other terminals connected at
respective junctions T.sub.iC through T.sub.nC to either one of the fixed
terminals of the variable resistor 224. One of the fixed terminals of the
variable resistor 224 is connected to the junction T.sub.7C, and the other
fixed terminal thereof is connected at a junction T.sub.6C to one fixed
terminal of the variable resistor 225 and also to the movable terminal
T.sub.4C of the variable resistor 225. The other fixed terminal of the
variable resistor 225 is connected at a junction T.sub.5C to a negative
input terminal of the noninverting amplifier 220 and also to one terminal
of the resistor 222. The other terminal of the resistor 222 is joined at a
junction T.sub.2C to the output terminal of the noninverting amplifier
220, the resistor 222 serving as a negative feedback resistor connected
across the noninverting amplifier 220. The junction T.sub.2C is coupled to
one fixed terminal of the volume control 22C in the form of a variable
resistor, whose other fixed terminal is connected to ground. The volume
control 22C has a movable terminal T.sub.1C serving as a positive output
terminal of the frequency characteristics control device 2C. The movable
contact of the variable resistor 225 and the movable contact of the volume
control 22C are linked with each other by the gain control unit 23C.
When the volume control 22C is shifted from a lower scale level toward a
higher scale level, the boosted or emphasized level of the audio signal in
the determined frequency range is continuously or discontinuously lowered,
and the frequency range in which the audio signal is to be controlled can
freely be selected at the time the frequency characteristics control
device 2C is manufactured.
When the volume level of the volume control 22C is lowered, the above
process is reversed.
Fifth Embodiment
FIG. 5 shows a frequency characteristics control device 2D according to a
fifth embodiment of the present invention, for use in an audio
reproduction system. The frequency characteristics control device 2D
includes a loudness control circuit for turning on or off the gain of the
audio signal in a certain frequency range, or for uniformly increasing the
gain up to a certain boosted level or turning off the gain.
The frequency characteristics control device 2D shown in FIG. 5 comprises a
loudness control circuit 21D as a tone control unit, a volume control 22D
as a volume control unit, and a gain control unit 23D.
The loudness control circuit 21D comprises a noninverting amplifier 230,
resistors 231, 232, a circuit 233 composed of series- and
parallel-connected capacitors and resistors, variable resistors 234, 235,
and a switch 236.
The noninverting amplifier 230 has a positive input terminal which is
connected at a junction T.sub.7D to one terminal of the resistor 231,
whose other terminal serves as a positive input terminal of the frequency
characteristics control device 2D. The circuit 233 has one terminal
grounded and another terminal connected to a switch 236. The switch 236 is
coupled between the movable contact of the variable resistor 234 and the
circuit 233, and has a movable contact which can selectively be connected
to the movable contact of the variable resistor 234 and the junction
T.sub.7D. One fixed terminal of the variable resistor 234 is connected to
the junction T.sub.7D, and the other fixed terminal thereof is connected
at a junction T.sub.6D to one fixed terminal of the variable resistor 235
and also to the movable contact T.sub.4D of the variable resistor 235. The
other fixed terminal of the variable resistor 235 is connected at a
junction T.sub.5D to the negative input terminal of the noninverting
amplifier 230 and also to one terminal of the resistor 232. The other
terminal of the resistor 232 is joined at a junction T.sub.2D to the
output terminal of the noninverting amplifier 230, the resistor 232
serving as a negative feedback resistor connected across the noninverting
amplifier 230. The junction T.sub.2D is coupled to one fixed terminal of
the volume control 22D in the form of a variable resistor, whose other
fixed terminal is connected to ground. The volume control 22D has a
movable terminal T.sub.1D serving as a positive output terminal of the
frequency characteristics control device 2D. The movable contact of the
variable resistor 235 and the movable contact of the volume control 22D
are ganged with each other by the gain control unit 23D. When the volume
control 22D is shifted from a lower scale level toward a higher scale
level, the boosted or emphasized level of the audio signal in the
frequency range, which is determined when the loudness control circuit 21D
is turned on, is continuously or discontinuously lowered.
When the volume level of the volume control 22 D is lowered, the above
process is reversed.
Sixth Embodiment
FIG. 6 shows a frequency characteristics control device 2E according to a
sixth embodiment of the present invention, for use in an audio
reproduction system. The frequency characteristics control device 2E
includes a tone control circuit or a graphic equalizer which has bass,
treble, and midrange control knobs for boosting or reducing the gain of
the audio signal variably in a plurality of frequency ranges.
The frequency characteristics control device 2E comprises a tone control
circuit 21E as a tone control unit, a volume control 22E as a volume
control unit, and a gain control unit 23E.
The tone control circuit 21E comprises a noninverting amplifier 240,
resistors 241, 242, a plurality of circuits 243.sub.i through 243.sub.n
each composed of series- and parallel-connected capacitors and resistors,
and a plurality of variable resistors 244.sub.i through 244.sub.n and 245.
The noninverting amplifier 240 has a positive input terminal which is
connected at a junction T.sub.7E to one terminal of the resistor 241,
whose other terminal serves as a positive input terminal of the frequency
characteristics control device 2E. The circuits 243.sub.i through
243.sub.n have one respective terminals grounded, and other terminals
connected to the movable contacts of the respective variable resistors
244.sub.i through 244.sub.n, which have one fixed terminals connected to
the junction T.sub.7E. The other fixed terminals of the variable resistors
244.sub.i through 244.sub.n are connected at a junction T.sub.6E to one
fixed terminal of the variable resistor 245 and also to the movable
terminal T.sub.4E of the variable resistor 245. The other fixed terminal
of the variable resistor 245 is connected at a junction T.sub.5E to a
negative input terminal of the noninverting amplifier 240 and also to one
terminal of the resistor 242. The other terminal of the resistor 242 is
joined at a junction T.sub.2E to the output terminal of the noninverting
amplifier 240, the resistor 242 serving as a negative feedback resistor
connected across the noninverting amplifier 240. The junction T.sub.2E is
coupled to one fixed terminal of the volume control 22E in the form of a
variable resistor, whose other fixed terminal is connected to ground. The
volume control 2E has a movable terminal T.sub.1E serving as a positive
output terminal of the frequency characteristics control device 2E. The
movable contact of the variable resistor 245 and the movable contact of
the volume control 22E are ganged with each other by the gain control unit
23E.
When the volume control 22E is shifted from a lower scale level toward a
higher scale level, the boosted or emphasized level of the audio signal in
the plural frequency ranges, which are determined by the tone control
circuit 21E, is continuously or discontinuously lowered.
When the volume level of the volume control 22E is lowered, the above
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