Mobile automatic volume control apparatus
First Claim
1. A mobile automatic volume control apparatus comprising:
- means for producing a signal corresponding to ambient noise;
a noise detection section for detecting an ambient noise level comprising a low-pass filter having a cut-off frequency of substantially 10 Hertz for extracting low-frequency components from said signal corresponding to ambient noise;
an audio signal detection section receiving an audio signal for detecting an input level of said audio signal;
means for producing a control signal by subtracting a quantity of logarithmic change of an audio signal detection signal obtained from said audio signal detection section relative to a reference value from a value obtained by amplifying, with an amplification factor in a range of from 1.5 to 2.5 inclusive, a quantity of logarithmic change of a noise detection signal obtained from said noise detection section relative to a reference value; and
a volume controller for increasing/decreasing an output level of said audio signal in response to said control signal.
1 Assignment
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Accused Products
Abstract
An automatic volume control apparatus for use in a mobile audio apparatus in which a detection output from a noise detection section is compared with a control output applied to a volume control section, and a capacitor inserted between a control signal input terminal of the volume control section and a reference voltage point is charged/discharged by a current source section with a constant current on the basis of the output of the comparator to thereby make it possible to make the change of volume constant or linear relative to the change of noise level. Also, a control signal for a volume controller is obtained by subtracting a quantity of logarithmic change of an audio signal detection signal obtained from an audio signal detection section relative to a reference value from a value obtained by amplifying, with an amplification factor in a range of 1.5 to 2.5, a quantity of logarithmic change of a noise detection signal obtained from a noise detection section relative to a reference value, whereby the correspondence between levels of low-frequency components of, for example, 10 Hz or less and audible frequency components of in-vehicle noise becomes higher so that it is possible to perform more natural volume control.
52 Citations
13 Claims
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1. A mobile automatic volume control apparatus comprising:
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means for producing a signal corresponding to ambient noise; a noise detection section for detecting an ambient noise level comprising a low-pass filter having a cut-off frequency of substantially 10 Hertz for extracting low-frequency components from said signal corresponding to ambient noise; an audio signal detection section receiving an audio signal for detecting an input level of said audio signal; means for producing a control signal by subtracting a quantity of logarithmic change of an audio signal detection signal obtained from said audio signal detection section relative to a reference value from a value obtained by amplifying, with an amplification factor in a range of from 1.5 to 2.5 inclusive, a quantity of logarithmic change of a noise detection signal obtained from said noise detection section relative to a reference value; and a volume controller for increasing/decreasing an output level of said audio signal in response to said control signal. - View Dependent Claims (3)
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4. A mobile automatic volume control apparatus comprising:
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a noise detection section for detecting an ambient noise level and producing a detection output corresponding to the detected noise level; a time constant circuit responsive to said detection output of said noise detection section for generating a volume control output; a volume control section receiving an audio signal for controlling an output level of said audio signal in response to said control output of said time constant circuit received at a control signal input terminal of said volume control section; a capacitor coupled between said control signal input terminal of said volume control section and a reference voltage point; said time constant circuit comprising a comparator for comparing said detection output of said noise detection section with said control output applied to said volume control section, and a current source section comprising a voltage divider having a first and a second resistor, a first constant current circuit for charging/discharging said capacitor and including said first resistor, and a second constant current circuit for discharging/charging said capacitor and including said second resistor, said comparator having an output connected to a connection point between said first and second resistors so that said capacitor is charge/discharged at a constant rate. - View Dependent Claims (5, 6)
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10. A mobile automatic volume control apparatus comprising:
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a noise detection section for detecting an ambient noise level and producing a detection output corresponding to the detected noise level; a time constant circuit responsive to said detection output of said noise detection section for generating a volume control output; a volume control section receiving an audio signal for controlling an output level of said audio signal in response to said control output of said time constant circuit received at a control signal input terminal of said volume control section; a capacitor coupled between said control signal input terminal of said volume control section and a reference voltage point; said time constant circuit comprising a comparator for comparing said detection output of said noise detection section with said control output applied to said volume control section, and a current source section comprising a first constant current circuit controlled by an output of said comparator for charging/discharging said capacitor at a constant rate and a second constant current circuit (25) which is not controlled by said output of the comparator for continuously discharging/charging said capacitor at a constant rate. - View Dependent Claims (2, 7, 8, 9, 11, 12, 13)
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Specification