Abstract: A level detecting circuit for use in a noise reduction circuit and which produces a level detected output signal in response to an input signal, includes an operational amplifier with at least one feedback diode for logarithmically converting the input signal to produce a logarithmically converted signal; a first PN junction element comprised of a first diode supplied with the logarithmically converted signal; a second PN junction element comprised of a second diode connected in series with the first diode at a connection point, the series-circuit of the first and second diodes having a first saturation current; a first integrating capacitor having a first capacitance and connected to the connection point for producing an integrated signal; a third PN junction element comprised of series-connected third and fourth diodes connected in parallel with the series connection of the first and second diodes and having a second saturation current greater than the first saturation current; a second integrating capacito

Abstract: A noise reduction circuit for use in an audio signal recording/reproducing apparatus is comprised of a first signal path including a voltage-controlled amplifier for amplifying a signal supplied thereto with controllable gain and a differentiating circuit for differentiating at least that portion of the signal passing through the voltage-controlled amplifier within the audio range; a level detecting circuit for controlling the gain of the voltage-controlled amplifier in response to the level of the signal passing through the voltage-controlled amplifier; a feedback resistor connected as a negative feedback path with the first signal path for providing an upper limit to the gain imparted to the signal supplied to the noise reduction circuit; a subtraction circuit for subtracting the negatively fed back signals from the signal supplied to the noise reduction circuit to produce an input signal for the first signal path; a second resistor or a low-pass filter connected as a positive feedforward path between the i

Abstract: A noise reduction circuit for use in an audio signal recording/reproducing apparatus is comprised of a first signal path including a voltage-controlled amplifier for amplifying a signal supplied thereto with controllable gain and integrating circuit for integrating at least that portion of the signal passing through the voltage-controlled amplifier within the audio range; a level detecting circuit for controlling the gain of the voltage-controlled amplifier in response to the level of the signal passing through the voltage-controlled amplifier; a feedforward resistor connected in parallel with the first signal path for providing a lower limit to the gain imparted to the signal supplied to the noise reduction circuit; an adder circuit for adding the output signals from the first signal path and the feedforward resistor; a second resistor or a low-pass filter connected as a negative feedback path between the output of the adder circuit and the input of the first signal path for providing an upper limit to the g

Abstract: A level detecting circuit for producing a level detected output signal in response to an input signal includes a logarithmic converting amplifier which logarithmically converts the input signal into a logarithmically converted signal; a differential error amplifier which produces a logarithmically amplified signal in response to the logarithmically converted signal and at least one feedback signal; an integrating capacitor supplied with the logarithmically amplified signal through a PN junction for producing an integrated signal; a voltage dividing circuit for voltage dividing the integrated signal and the logarithmically amplified signal in accordance with a selected ratio and supplying at least one resultant voltage divided signal as the at least one feedback signal to the differential error amplifier; and an output PN junction for producing the level detected output signal in response to the integrated signal.

Abstract: A noise reduction circuit for use in an audio signal recording/reproducing apparatus includes a first filter circuit for providing frequency emphasis to a signal supplied thereto; a first signal path connected in series with the first filter circuit, and including a voltage-controlled amplifier for amplifying a signal supplied thereto with controllable gain and a second filter circuit for providing frequency emphasis to the signal passing through the voltage-controlled amplifier; a level detecting circuit for controlling the gain of the voltage-controlled amplifier in response to the level of the signal passing through the voltage-controlled amplifier; a resistor connected to the first signal path for reducing the effect of the frequency emphasis by the second filter circuit when the level of the signal passing through the voltage-controlled amplifier is reduced; and a low pass filter circuit connected with the first signal path for reducing the effect of the frequency emphasis by the first and second filter