Volume control circuit and electronic equipment

Abstract

The utility model relates to the field of power electronics, and provides a volume control circuit and electronic equipment, the volume control circuit comprises a compression module, a detection module and a voltage regulation module, when an input audio signal exceeds a threshold voltage, the gain of the input audio signal is regulated to be less than 1, so that the output audio signal is limited, and the output audio signal is output. When the input audio signal is smaller than the threshold voltage, the gain of the input audio signal is adjusted to be 1, so that the amplitude of the output audio signal is equal to the amplitude of the input audio signal, control over the output volume is achieved, and due to the fact that an analog circuit is adopted, cost is saved, the response speed is increased, and time delay is reduced.

Description

Technical Field

[0001] The present application belongs to the field of power electronics technology, and in particular relates to a volume control circuit and an electronic device. Background Art

[0002] In the related art, the purpose of controlling the output volume range is generally achieved through digital signal processing, and the audio input signal is usually an analog signal. During the conversion of the analog signal to a digital signal and the subsequent digital signal processing, a delay of more than 100ms will be introduced. This delay time is easily distinguished by the human ear, resulting in a poor user experience. On the other hand, the analog signal is converted into a digital signal, and then converted into an analog signal output after digital signal processing. The required electronic devices such as ADC (Analog to Digital Converter), digital signal processing chip, DAC (Digita to Analog Converter) and so on are relatively expensive. Utility Model Content

[0003] The purpose of the present application is to provide a volume control circuit and an electronic device, aiming to solve the problems of high cost and long delay of the current circuit for controlling the output volume range.

[0004] In a first aspect, an embodiment of the present application provides a volume control circuit, comprising:

[0005] A compression module, used for receiving an input audio signal, performing gain adjustment on the input audio signal based on a gain control voltage, and outputting a gained output audio signal;

[0006] a detection module, connected to the compression module, for detecting the voltage amplitude of the output audio signal and outputting a waveform representing a change in the voltage amplitude of the output audio signal;

[0007] A voltage regulating module is connected to the detection module and is used to compare the amplitude of the waveform with a threshold voltage, and when the amplitude of the waveform is greater than the threshold voltage, output a gain control voltage for adjusting the gain of the input audio signal to be less than 1, and when the amplitude of the waveform is less than or equal to the threshold voltage, output a gain control voltage for adjusting the gain of the input audio signal to be 1.

[0008] In one of the embodiments, the compression module includes a first diode, a second diode and a first resistor;

[0009] The first end of the first resistor constitutes the input end of the volume control circuit, the anode of the first diode is used to access the gain control voltage, the cathode is connected to the anode of the second diode and the second end of the first resistor, the cathode of the second diode is connected to the negative gain control voltage, and the second end of the first resistor constitutes the output end of the volume control circuit.

[0010] In one embodiment, the first diode and the second diode have the same parameters.

[0011] In one embodiment, when the gain control voltage is greater than the conduction voltage drop of the first diode and the second diode, the gain is 0;

[0012] When the gain control voltage is less than 0, the gain is 1;

[0013] When the gain control voltage is greater than 0 and less than the conduction voltage drop of the first diode and the second diode, the gain changes between greater than 0 and less than 1 following the change of the gain control voltage.

[0014] In one of the embodiments, the detection module includes a voltage follower unit and a charge and discharge unit;

[0015] The voltage follower unit is connected to the output end of the volume control circuit, and is used to receive and output the output audio signal after gain;

[0016] The charge and discharge unit is connected to the voltage following unit and the voltage regulating module, and is used to charge based on the output audio signal after gain when the voltage amplitude of the output audio signal after gain is greater than the voltage value of the charge and discharge unit itself, and discharge when the voltage amplitude of the output audio signal after gain is less than the voltage value of the charge and discharge unit itself, so as to form and output a waveform representing the change in the voltage amplitude of the output audio signal.

[0017] In one of the embodiments, the voltage follower unit includes a first operational amplifier, a third diode and a second resistor;

[0018] The non-inverting input terminal of the first operational amplifier serves as the input terminal of the voltage follower unit and is connected to the output terminal of the volume control circuit. The output terminal of the first operational amplifier is connected to the anode of the third diode, and the cathode of the third diode is connected to the first end of the second resistor. The second end of the second resistor serves as the output terminal of the voltage follower unit and is connected to the inverting input terminal of the first operational amplifier and the charge and discharge unit.

[0019] In one embodiment, the charging and discharging unit includes a first capacitor and a third resistor; the first end of the first capacitor is connected to the second end of the second resistor and the voltage regulating module, the second end of the first capacitor is grounded, and the third resistor is connected in parallel with the first capacitor.

[0020] In one embodiment, the voltage regulating module includes a subtractor circuit, the input end of the subtractor circuit is connected to the output end of the detection module, the output end of the subtractor circuit is coupled to the power supply end of the compression module, and the subtractor circuit is also connected to the threshold voltage. The subtractor circuit is used to output a gain control voltage with a voltage value greater than 0 when the amplitude of the waveform is greater than the threshold voltage, and to output a gain control voltage with a voltage value less than 0 when the amplitude of the waveform is less than or equal to the threshold voltage.

[0021] In one embodiment, the subtractor circuit includes a second operational amplifier, a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor;

[0022] The first end of the fourth resistor is connected to the detection module, the second end of the fourth resistor is connected to the non-inverting input terminal of the second operational amplifier and the first end of the fifth resistor, the second end of the fifth resistor is grounded, the first end of the sixth resistor is connected to the threshold voltage, the second end of the sixth resistor is connected to the inverting input terminal of the second operational amplifier and the first end of the seventh resistor, the second end of the seventh resistor is connected to the output terminal of the second operational amplifier, and the output terminal of the second operational amplifier outputs a gain control voltage.

[0023] In a second aspect, an embodiment of the present application provides an electronic device having an audio playback function and a volume control circuit as described above.

[0024] Compared with the related art, the embodiment of the present application has the following beneficial effects: the volume control circuit provided in the embodiment of the present application adopts an analog circuit. When the input audio signal exceeds the threshold voltage, the input audio signal is adjusted to a gain less than 1, so that the output audio signal is limited. When the input audio signal is less than the threshold voltage, the input audio signal is adjusted to a gain of 1, so that the amplitude of the output audio signal is equal to the amplitude of the input audio signal, thereby realizing the control of the output volume. Since the analog circuit is used for implementation, the cost is saved, the response speed is improved, and the delay is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the structure of a volume control circuit provided in an embodiment of the present application;

[0026] Figure 2 for Figure 1 A circuit diagram of a compression module in a volume control circuit shown;

[0027] Figure 3 for Figure 1 The structural diagram of the detection module in the volume control circuit shown;

[0028] Figure 4 for Figure 1 The circuit diagram of the detection module in the volume control circuit shown;

[0029] Figure 5 for Figure 1 A circuit diagram of a voltage regulating module in a volume control circuit shown;

[0030] Figure 6 This is a simulation diagram of operation signals of a volume control circuit provided in one embodiment of the present application;

[0031] Figure 7 for Figure 6 A partial enlarged view of

[0032] Figure 8 for Figure 6 A partial enlarged view of

[0033] Fig. 9 The input signal of the volume control circuit provided in one embodiment of the present application is an input and output signal waveform diagram at an input signal of 20Hz1Vpk;

[0034] Fig.10 The input and output signal waveform diagram of the volume control circuit provided in one embodiment of the present application when the input signal is 20kHz and 1Vpk. DETAILED DESCRIPTION

[0035] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0036] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0037] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0038] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "plurality" means two or more, unless otherwise clearly and specifically defined.

[0039] See also Figure 1 An embodiment of the present application provides a volume control circuit, including a compression module 110, a detection module 120 and a voltage regulation module 130.

[0040] The compression module 110 is used to receive the input audio signal, and adjust the gain of the input audio signal V_IN based on the gain control voltage VC, and output the output audio signal V_OUT after gain. It can be understood that the input and output ends of the compression module 110 constitute the input and output ends of the volume control circuit.

[0041] The detection module 120 is connected to the compression module 110 and is used to detect the voltage amplitude of the output audio signal V_OUT and output a waveform representing the change of the voltage amplitude of the output audio signal V_OUT.

[0042] The voltage regulating module 130 is connected to the detection module 120, and is used to compare the amplitude of the waveform with the threshold voltage. When the amplitude of the waveform is greater than the threshold voltage V_ref, the voltage regulating module 130 outputs a gain control voltage VC for adjusting the gain of the input audio signal V_IN to be less than 1. When the amplitude of the waveform is less than or equal to the threshold voltage V_ref, the voltage regulating module 130 outputs a gain control voltage VC for adjusting the gain of the input audio signal V_IN to be 1.

[0043] It is understandable that the gain in the compression module 110 is controlled by the gain control voltage VC. The waveform output by the detection module 120 indicating the voltage amplitude change of the output audio signal V_OUT is a positive envelope waveform close to the output audio signal V_OUT, reflecting the amplitude of the output audio signal V_OUT of the audio control circuit.

[0044] Among them, when the amplitude of the waveform is greater than the threshold voltage V_ref, the output is used to adjust the gain of the input audio signal V_IN to be less than 1, that is, the compression module 110 compresses the input audio signal V_IN according to the gain control voltage VC, and when the amplitude of the waveform is less than or equal to the threshold voltage V_ref, the output is used to adjust the gain of the input audio signal V_IN to 1, that is, the compression module 110 does not compress the input audio signal V_IN according to the gain control voltage VC.

[0045] Since the volume control circuit is implemented by an analog circuit, the cost is saved, the response speed is improved, and the delay is reduced.

[0046] See also Figure 2 , in one embodiment, the compression module 110 includes a first diode D1, a second diode D2 and a first resistor R1;

[0047] The first end of the first resistor R1 constitutes the input end of the volume control circuit, the anode of the first diode D1 is used to access the gain control voltage VC, the cathode is connected to the anode of the second diode D2 and the second end of the first resistor R1, the cathode of the second diode D2 is connected to the negative gain control voltage VC, and the second end of the first resistor R1 constitutes the output end of the volume control circuit. It can be understood that the negative gain control voltage VC is to take a negative value of the gain control voltage VC, when the gain control voltage VC is greater than 0, that is, the negative gain control voltage VC is negative, otherwise it is positive.

[0048] In one embodiment, the parameters of the first diode D1 and the second diode D2 are the same, so that the circuits at both ends of the output end of the volume control circuit are symmetrical and easy to debug.

[0049] In one embodiment, when the gain control voltage VC is greater than the conduction voltage drop of the first diode D1 and the second diode D2, the output of the volume control circuit is 0, that is, the gain is 0.

[0050] When the gain control voltage VC is less than 0, the first diode D1 and the second diode D2 are cut off, and the voltage of the input audio signal V_IN is equal to the output audio signal V_OUT, that is, the gain is 1;

[0051] When the gain control voltage VC is greater than 0 and less than the conduction voltage drop of the first diode D1 and the second diode D2, the gain changes between greater than 0 and less than 1 following the change of the gain control voltage VC. Specifically,

[0052] Among them, R1 is the resistance value of the first resistor R1, Rd is the AC resistance of the first diode D1 and the second diode D2, Rd is determined by the static operating point, and the gain control voltage VC determines the static operating point of the first diode D1 and the second diode D2, so the circuit gain is greater than 0 and less than 1, and the gain size is controlled by the gain control voltage VC.

[0053] See also Figure 3 In one embodiment, the detection module 120 includes a voltage following unit 121 and a charging and discharging unit 122; the voltage following unit 121 is connected to the output end of the volume control circuit, and is used to receive and output the output audio signal V_OUT after gain; the charging and discharging unit 122 is connected to the voltage following unit 121 and the voltage regulating module 130, and is used to charge based on the output audio signal V_OUT after gain when the voltage amplitude of the output audio signal V_OUT after gain is greater than the voltage value of the charging and discharging unit 122 itself, and discharge when the voltage amplitude of the output audio signal V_OUT after gain is less than the voltage value of the charging and discharging unit 122 itself, so as to form and output a waveform representing the voltage amplitude change of the output audio signal V_OUT.

[0054] See also Figure 4 In one embodiment, the voltage follower unit 121 includes a first operational amplifier U1, a third diode D3 and a second resistor R2.

[0055] The non-inverting input terminal of the first operational amplifier U1 is used as the input terminal of the voltage follower unit 121, connected to the output terminal of the volume control circuit, the output terminal of the first operational amplifier U1 is connected to the anode of the third diode D3, the cathode of the third diode D3 is connected to the first terminal of the second resistor R2, and the second terminal of the second resistor R2 is used as the output terminal of the voltage follower unit 121, connected to the inverting input terminal of the first operational amplifier U1 and the charge-discharge unit 122. The third diode D3 can prevent the current from flowing back to the first operational amplifier U1 when the voltage of the output audio signal V_OUT is low, thereby improving the circuit reliability.

[0056] See also Figure 4 In one embodiment, the charge and discharge unit 122 includes a first capacitor C1 and a third resistor R3; the first end of the first capacitor C1 is connected to the output end of the voltage follower unit 121 and the voltage regulating module 130, the second end of the first capacitor C1 is grounded, and the third resistor R3 is connected in parallel with the first capacitor C1.

[0057] The voltage follower unit 121 is used to compensate for the forward conduction voltage of the third diode D3, so that once the output audio signal V_OUT exceeds the voltage of the first capacitor C1, the first capacitor C1 begins to be charged; the charging and discharging speed of the charge and discharge unit 122 is determined by the values ​​of the second resistor R2, the first capacitor C1, and the third resistor R3.

[0058] The input signal of the detection module 120 is the output audio signal V_OUT of the volume compression circuit, and the output signal is the voltage V1 across the first capacitor C1. The third diode D3 is also used to control whether the first capacitor C1 is in a charging or discharging state. When the voltage amplitude of the output audio signal V_OUT decreases to less than the voltage of the first capacitor C1, the third diode D3 is cut off, and the first capacitor C1 starts to discharge, so that the voltage V1 across the first capacitor C1 can reflect the input signal amplitude at this time.

[0059] Before the output audio signal V_OUT is input, the voltage V1 across the first capacitor C1 is 0. After the output audio signal V_OUT is input, when the output audio signal V_OUT is greater than the voltage across the first capacitor C1, the first capacitor C1 is charged, and the voltage across the first capacitor C1 increases. When the output audio signal V_OUT voltage is less than or equal to the voltage across the first capacitor C1, the third diode D3 is cut off, the first capacitor C1 stops charging, and starts to discharge to the third resistor R3, and the voltage across the first capacitor C1 decreases. Charging time = R2*C1, discharging time = C1*R3. By controlling the appropriate charging and discharging time, the voltage waveform across the first capacitor C1 can be made close to the positive envelope of the output audio signal V_OUT. The output signal of the circuit reflects the voltage amplitude of the output audio signal V_OUT of the audio control circuit.

[0060] In one embodiment, the voltage regulating module 130 includes a subtractor circuit, the input end of the subtractor circuit is connected to the output end of the detection module 120, the output end of the subtractor circuit is coupled to the power supply end of the compression module 110, and the subtractor circuit is also connected to the threshold voltage V_ref. The subtractor circuit is used to output a gain control voltage VC with a voltage value greater than 0 when the amplitude of the waveform is greater than the threshold voltage V_ref, and output a gain control voltage VC with a voltage value less than 0 when the amplitude of the waveform is less than or equal to the threshold voltage V_ref. The gain control voltage VC with a voltage value greater than 0 can control the gain of the input audio signal V_IN to be greater than or equal to 0 and less than 1. The gain control voltage VC with a voltage value less than 0 can control the gain of the input audio signal V_IN to be equal to 1.

[0061] See also Figure 5 In one embodiment, the subtractor circuit includes a second operational amplifier U2, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7.

[0062] A first end of the fourth resistor R4 is connected to the detection module 120, a second end of the fourth resistor R4 is connected to the non-inverting input terminal of the second operational amplifier U2 and a first end of the fifth resistor R5, a second end of the fifth resistor R5 is grounded, a first end of the sixth resistor R6 is connected to the threshold voltage V_ref, a second end of the sixth resistor R6 is connected to the inverting input terminal of the second operational amplifier U2 and a first end of the seventh resistor R7, a second end of the seventh resistor R7 is connected to the output terminal of the second operational amplifier U2, and the output terminal of the second operational amplifier U2 outputs a gain control voltage.

[0063] The output signal of the subtractor circuit is the difference between the output signal of the detection module 120 and the threshold voltage V_ref. Specifically, it is determined whether the output audio signal V_OUT of the audio control circuit exceeds the threshold voltage V_ref. If it exceeds the threshold voltage V_ref, the output voltage value is greater than 0, and the gain control voltage VC is less than 0.

[0064] In a second aspect, an embodiment of the present application provides an electronic device, which includes the volume control circuit as described above.

[0065] Combination Figures 6 to 8 It can be observed that when the input audio signal V_IN exceeds the threshold voltage V_ref, the output audio signal V_OUT is limited, and when the input audio signal V_IN is less than the threshold voltage V_ref, the amplitude of the output audio signal V_OUT is equal to the amplitude of the input audio signal V_IN.

[0066] When the amplitude of the input audio signal V_IN suddenly increases, it can be observed that the output audio signal V_OUT is attenuated to a stable value after a period of time, such as Figure 7 This period of time can be defined as the start-up time. Figure 7 The start-up time is 30 μs, and the start-up time is controlled by the charging time in the detection module 120 .

[0067] When the input audio signal V_IN suddenly decreases (voltage), it can be observed that the output audio signal V_OUT returns to a stable value after a period of time, such as Figure 8 This period of time can be defined as the release time. Figure 8 The release time is 8.8 ms, and the release time is controlled by the discharge time in the detection module 120 .

[0068] Since the technical solution of the embodiment of the present application does not require digital-to-analog conversion and digital signal processing, but is pure analog signal processing, the delay time is much less than 100ms. The audio signal range that the human ear can hear is 20Hz-20kHz. After circuit simulation, see Fig. 9, when the input signal is 20Hz 1Vpk, the delay is 54.7us; see Fig.10 , when the input signal is 20kHz 1Vpk, the delay is 7.863us. It can be seen that the delay is much lower than the conventional solution.

[0069] Compared with the related art, the beneficial effects of the embodiment of the present application are as follows: the volume control circuit provided in the embodiment of the present application adopts an analog circuit. When the input audio signal V_IN exceeds the threshold voltage V_ref, the input audio signal V_IN is adjusted to a gain less than 1, so that the output audio signal V_OUT is limited. When the input audio signal V_IN is less than the threshold voltage V_ref, the input audio signal V_IN is adjusted to a gain of 1, so that the amplitude of the output audio signal V_OUT is equal to the amplitude of the input audio signal V_IN, thereby realizing the control of the output volume. Since analog circuits are used, costs are saved, response speed is improved, and delay is reduced.

[0070] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A volume control circuit, characterized in that: include: A compression module, used for receiving an input audio signal, performing gain adjustment on the input audio signal based on a gain control voltage, and outputting a gained output audio signal; A detection module, connected to the compression module, for detecting the voltage amplitude of the output audio signal and outputting a waveform representing a change in the voltage amplitude of the output audio signal; A voltage regulating module is connected to the detection module and is used to compare the amplitude of the waveform with a threshold voltage, and when the amplitude of the waveform is greater than the threshold voltage, output a gain control voltage for adjusting the gain of the input audio signal to be less than 1, and when the amplitude of the waveform is less than or equal to the threshold voltage, output a gain control voltage for adjusting the gain of the input audio signal to be 1.

2. The volume control circuit according to claim 1, characterized in that: The compression module includes a first diode, a second diode and a first resistor; The first end of the first resistor constitutes the input end of the volume control circuit, the anode of the first diode is used to access the gain control voltage, the cathode is connected to the anode of the second diode and the second end of the first resistor, the cathode of the second diode is connected to the negative gain control voltage, and the second end of the first resistor constitutes the output end of the volume control circuit.

3. The volume control circuit as claimed in claim 2, characterized in that: The first diode and the second diode have the same parameters.

4. The volume control circuit as claimed in claim 2, characterized in that: When the gain control voltage is greater than the conduction voltage drop of the first diode and the second diode, the gain is 0; When the gain control voltage is less than 0, the gain is 1; When the gain control voltage is greater than 0 and less than the conduction voltage drop of the first diode and the second diode, the gain changes between greater than 0 and less than 1 following the change of the gain control voltage.

5. The volume control circuit according to claim 1, characterized in that: The detection module includes a voltage following unit and a charging and discharging unit; The voltage follower unit is connected to the output end of the volume control circuit and is used to receive and output the output audio signal after gain; The charge and discharge unit is connected to the voltage following unit and the voltage regulating module, and is used to charge based on the output audio signal after gain when the voltage amplitude of the output audio signal after gain is greater than the voltage value of the charge and discharge unit itself, and discharge when the voltage amplitude of the output audio signal after gain is less than the voltage value of the charge and discharge unit itself, so as to form and output a waveform representing the change in the voltage amplitude of the output audio signal.

6. The volume control circuit as claimed in claim 5, characterized in that: The voltage follower unit includes a first operational amplifier, a third diode and a second resistor; The non-inverting input terminal of the first operational amplifier serves as the input terminal of the voltage follower unit and is connected to the output terminal of the volume control circuit. The output terminal of the first operational amplifier is connected to the anode of the third diode, and the cathode of the third diode is connected to the first end of the second resistor. The second end of the second resistor serves as the output terminal of the voltage follower unit and is connected to the inverting input terminal of the first operational amplifier and the charge and discharge unit.

7. The volume control circuit as claimed in claim 5, characterized in that: The charging and discharging unit includes a first capacitor and a third resistor; the first end of the first capacitor is connected to the output end of the voltage follower unit and the voltage regulating module, the second end of the first capacitor is grounded, and the third resistor is connected in parallel with the first capacitor.

8. The volume control circuit according to any one of claims 1 to 7, characterized in that: The voltage regulating module includes a subtractor circuit, the input end of the subtractor circuit is connected to the output end of the detection module, the output end of the subtractor circuit is coupled to the power supply end of the compression module, and the subtractor circuit is also connected to the threshold voltage. The subtractor circuit is used to output a gain control voltage with a voltage value greater than 0 when the amplitude of the waveform is greater than the threshold voltage, and to output a gain control voltage with a voltage value less than 0 when the amplitude of the waveform is less than or equal to the threshold voltage.

9. The volume control circuit as claimed in claim 8, characterized in that: The subtractor circuit includes a second operational amplifier, a fourth resistor, a fifth resistor, a sixth resistor and a seventh resistor; The first end of the fourth resistor is connected to the detection module, the second end of the fourth resistor is connected to the non-inverting input terminal of the second operational amplifier and the first end of the fifth resistor, the second end of the fifth resistor is grounded, the first end of the sixth resistor is connected to the threshold voltage, the second end of the sixth resistor is connected to the inverting input terminal of the second operational amplifier and the first end of the seventh resistor, the second end of the seventh resistor is connected to the output terminal of the second operational amplifier, and the output terminal of the second operational amplifier outputs a gain control voltage.

10. An electronic device, characterized in that: A volume control circuit having an audio playback function and any one of claims 1 to 9.

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