An audio processing device includes a signal processing circuit, a power switch circuit, a power amplifier and a detection circuit. The signal processing circuit is configured to process an audio input to generate an audio signal. The power switch circuit is configured to generate an operating voltage. The power amplifier is coupled with the signal processing circuit and the power switch circuit, and configured to drive a load circuit by the operating voltage according to the audio signal. The detection circuit is coupled with the signal processing circuit and the power switch circuit, configured to obtain a volume value from the audio signal and compare the volume value with a first volume threshold to generate a comparison result, and configured to control, according to the comparison result, the power switch circuit to set the operating voltage to have a corresponding one of multiple voltage levels.

An example first playback device includes programming to perform functions including: (1) storing an active volume state variable in memory, wherein the active volume state variable corresponds to a current playback volume; (2) storing a volume limit state variable in memory, wherein the volume limit state variable corresponds to a playback volume limit of the first playback device; (3) detecting a command to begin playback of media at a proposed playback volume different from the current playback volume; (4) based on comparing (i) the playback volume limit and (ii) the proposed playback volume, selecting a startup playback volume; (5) playing back media at the startup playback volume; and (6) causing at least a second playback

Radio Frequency (RF) amplifiers with voltage limiting using non-linear feedback are presented herein. According to one aspect, an RF amplifier comprises an amplifier circuit having an input terminal and an output terminal and a non-linear feedback circuit having an input terminal and an output terminal. The input terminal of the non-linear feedback circuit is connected to the output terminal of the amplifier circuit and the output terminal of the non-linear feedback circuit is connected to the amplifier circuit to reduce the gain of the amplifier circuit when an RF voltage swing present at the input terminal of the non-linear feedback circuit exceeds a predefined threshold. In one embodiment, the output terminal of the non-linear feedback circuit is connected to the input terminal of the amplifier circuit. In another embodiment, the output terminal of the non-linear feedback circuit is connected to a bias circuit of the amplifier circuit.

An audio processing device includes a signal processing circuit, a power switch circuit, a power amplifier and a detection circuit. The signal processing circuit is configured to process an audio input to generate an audio signal. The power switch circuit is configured to generate an operating voltage. The power amplifier is coupled with the signal processing circuit and the power switch circuit, and configured to drive a load circuit by the operating voltage according to the audio signal. The detection circuit is coupled with the signal processing circuit and the power switch circuit, configured to obtain a volume value from the audio signal and compare the volume value with a first volume threshold to generate a comparison result, and configured to control, according to the comparison result, the power switch circuit to set the operating voltage to have a corresponding one of multiple voltage levels.

An example first playback device includes programming to perform functions including: (1) storing an active volume state variable in memory, wherein the active volume state variable corresponds to a current playback volume; (2) storing a volume limit state variable in memory, wherein the volume limit state variable corresponds to a playback volume limit of the first playback device; (3) detecting a command to begin playback of media at a proposed playback volume different from the current playback volume; (4) based on comparing (i) the playback volume limit and (ii) the proposed playback volume, selecting a startup playback volume; (5) playing back media at the startup playback volume; and (6) causing at least a second playback device of the media playback system to play back media at the startup playback volume.

An example first playback device includes programming to perform functions including: (1) storing an active volume state variable in memory, wherein the active volume state variable corresponds to a current playback volume; (2) storing a volume limit state variable in memory, wherein the volume limit state variable corresponds to a playback volume limit of the first playback device; (3) detecting a command to begin playback of media at a proposed playback volume different from the current playback volume; (4) based on comparing (i) the playback volume limit and (ii) the proposed playback volume, selecting a startup playback volume; (5) playing back media at the startup playback volume; and (6) causing at least a second playback device of the media playback system to play back media at the startup playback volume.

An example playback device includes programming to perform functions including storing an active volume state variable in memory, where the active volume state variable corresponds to a current playback volume. The functions also include storing a volume limit state variable in memory, where the volume limit state variable corresponds to a playback volume limit of the playback device. The functions also include receiving, from a control device, a command to begin playback of media, and determining whether the control device is located in a second zone of the media playback system different from the first zone. Based on whether the control device is located in the second zone of the media playback system different from the first zone, the functions include selecting a startup playback volume to be one of the current playback volume or the playback volume limit, and then playing back media at the startup playback volume.

Disclosed is a wire control earphone, comprising a USB plug, an earphone wire, left and right ear receivers and a volume adjuster. The USB plug has a power-supply pin, a grounding pin and two signal pins. The earphone wire has a power-supply wire, two receiver wires and a ground wire which are correspondingly connected with the pins of the USB plug. The right ear receiver is connected between the right ear receiver wire and the ground wire. The volume adjuster is powered via the power-supply wire and comprises an adjustment triggering unit for outputting a volume adjustment signal, a processing unit for determining a voltage adjustment value according to the volume adjustment signal and outputting a digital voltage adjustment value, and a digital-to-analog conversion unit for converting the digital voltage adjustment value into an analog voltage adjustment value and applying the analog voltage adjustment value to the two receiver wires.

An example first playback device includes programming to perform functions including: (1) storing an active volume state variable in memory, wherein the active volume state variable corresponds to a current playback volume; (2) storing a volume limit state variable in memory, wherein the volume limit state variable corresponds to a playback volume limit of the first playback device; (3) detecting a command to begin playback of media at a proposed playback volume different from the current playback volume; (4) based on comparing (i) the playback volume limit and (ii) the proposed playback volume, selecting a startup playback volume; (5) playing back media at the startup playback volume; and (6) causing at least a second playback

Disclosed are drive-by-wire headphones, comprising a USB plug, a headphone cable, a left-ear receiver, a right-ear receiver, and a volume regulator. The USB plug is provided with a power-supply pin, a ground pin, and two signal pins. The headphone cable is provided with a power-supply wire, a ground wire, and two receiver wires corresponding to the pins of the USB plug. The right-ear receiver is connected between the right-ear receiver and the ground wire. The volume regulator is supplied with power by means of the power-supply wire. The volume regulator comprises: a regulation triggering unit used for outputting a volume regulating signal; a processing unit used for determining a voltage regulation value according to the volume regulating signal and outputting the digital voltage regulation value; and a digital-to-analog conversion unit used for converting the digital voltage regulation value to an analog voltage regulation value and applying the analog voltage regulation value to the two receiver wires. Headphones in the present disclosure can regulate the volume and thus would not occupy resources of a processor of an electronic device, thereby improving the response speed of the electronic device to other functions.