Abstract: Embodiments are provided for intelligently activating an amplifier in a playback device based on proximity detection. The playback device may be in a quasi-idle state when the playback device is not rendering media content. The quasi-idle state of the playback device may involve an amplifier in the playback device being inactive, while some other components or modules of the playback devices remain active. The playback device may include a proximity sensor configured to detect movement relative to the playback device. If movement is detected indicating that a user input to cause the playback device to render media content is anticipated, the amplifier may be pre-emptively activated such that the playback device enters an active state from the quasi-idle state. In some cases, the playback device may send a message to one or more other playback devices to cause the other playback devices to enter an active state.

Abstract: An interface circuit is provided that is adapted to connect a microphone circuit to a preamplifier. The microphone circuit has a microphone and at least an output node and the preamplifier has at least an input node connected to the output node by the interface circuit. The interface circuit has at least a decoupling capacitor for DC decoupling the input node from the output node. The decoupling is connected between the input node and the output node. The interface circuit has at least one active circuit, comprising a resistor connected the decoupling capacitor. The resistor acts as part of a resistance multiplier and has an equivalent resistance that together with the decoupling capacitor defines a high-pass filter connected between the microphone and the preamplifier. The interface circuit may also have a biasing circuit connected to the resistor.

Abstract: A loudspeaker arrangement includes a loudspeaker and a trigger circuit for electrically triggering the loudspeaker. The loudspeaker has a loudspeaker diaphragm for generating an acoustic signal. A digital pulse test signal is applied to the loudspeaker via the trigger circuit during a respective test sequence, the digital pulse test signal having a duty cycle that is predetermined to change such that the duty cycle increases over a plurality of periods of the test sequence at the beginning of the test sequence, and the duty cycle decreases over a plurality of periods of the test sequence at the end of the test sequence. During the respective test sequence, a measurement variable, representative of a voltage drop on a reference circuit connected in series to the loudspeaker, is detected, and the loudspeaker arrangement is classified as functional on the basis of a comparison of the measurement variable and a predetermined reference value.

Abstract: Disclosed is a differential microphone pre-amplifier circuit (120) for providing an amplified differential signal at a first (A) and a second (B) output terminal of the microphone pre-amplifier (120), including a first voltage controlled current generator (101), a second voltage controlled current generator (102) and a third voltage controlled current generator (103) all being configured to receive, amplify and convert a voltage signal generated by an associated microphone (110) to a current signal output.

Abstract: A peripheral apparatus, for connecting to a first or a second transmission port of an electronic device, includes a signal transmission interface, a triggering unit, an amplifying unit and an adjusting unit. The signal transmission interface, coupled to the first or the second transmission port, includes a first and a second group of pins. The triggering unit is coupled to the signal transmission interface. When the signal transmission interface is coupled to the first or the second transmission port, the triggering unit outputs a first or a second voltage level signal, respectively. The amplifying unit is coupled to the signal transmission interface and a functional unit. The adjusting unit, coupled to the signal transmission interface, the triggering unit, the amplifying unit and the functional unit, changes an output power transmitted from the amplifying unit to the functional unit according to the first or the second voltage level signal.

Abstract: An electronic signal processor for processing signals includes a complex first filter, one or more gain stages and a second filter. The first filter is characterized by a frequency response curve that includes multiple corner frequencies, with some corner frequencies being user selectable. The first filter also has at least two user-preset gain levels which may be alternately selected by a switch. Lower frequency signals are processed by the first filter with at least 12 db/octave slope, and preferably with 18 db/octave slope to minimize intermodulation distortion products by subsequent amplification in the gain stages. A second filter provides further filtering and amplitude control. The signal processor is particularly suited for processing audio frequency signals.

Abstract: A power converter has an output that is coupled in parallel with an energy reservoir circuit and a power supply node of an audio power amplifier. The converter can set an upper limit on its input supply current that is variable in accordance with a control input. A controller is to produce a signal, coupled to the control input of the power converter, that is responsive to a measure of input supply voltage of the power converter and either output voltage of the power converter or output power of the amplifier. Other embodiments are also described and claimed.

Abstract: The invention relates to an audio amplifier (1) for amplifying an input signal into an output signal, comprising an output amplification stage (6), wherein the output amplification stage (6) for the amplification of an intermediate signal into the output signal is designed as an amplifier operating in switching operation, and further comprising a limiter device (4), which from a programming and/or a circuit design point of view is designed to generate the intermediate signal on the basis of the input signal, wherein the level of the intermediate signal is always limited by a maximum load as a function of a settable maximum output and a load impedance which is coupled and/or can be coupled the audio amplifier or equivalent parameter thresholds such that the output signal does not exceed the maximum load at the load impedance, or the equivalent parameter thresholds, independently of the input signal.

Abstract: Novel active phantom-powered ribbon microphones that provide switchable proximity effect response filtering for voice and music applications are disclosed with unique adjustable interfaces. In one embodiment of the invention, a slider-based full frequency response vs. low frequency response and high pass filtering adjustment interface on a surface of a microphone casing provides a convenient switching between a “Music” mode and a “Voice” mode, wherein the “Voice” mode reduces the undesirable proximity effect in an active phantom-powered ribbon microphone, when a sound source is situated overly close to the active phantom-powered ribbon microphone. Furthermore, in one embodiment of the invention, a slider-based or a knob-based variable voice mode adjustment interface can also be integrated on a surface of a microphone casing to provide various preset levels of low frequency reduction and/or proximity effect response filtering when the “Voice” mode is enabled.

Abstract: Audio input tubes and power output tubes in a vacuum tube amplifier are powered and controlled by solid state controllers. The solid state controllers sample incoming audio and anticipate and apply changes and biases in grid and plate voltages before the audio signals arrive in the power output tubes. Any mains voltage is filtered, regulated and converted to a standard voltage which is converted to plural DC voltages that are applied to sensors, tube cathode heaters, grids and plates and are varied on screen grids and plates with stepped increases and autobias. The solid state components have sensors and feedback to control voltages. Sensed overvoltages fold back power to the solid state devices and heaters, screens and plates to provide uninterrupted amplification without endangering the tubes or components.

Abstract: A true ground amplifier circuit in which a voltage sensor senses the output voltage and generates a binary output which indicates whether the output is above or below a threshold. A variable gain feedback system generates a feedback signal for combination with the digital input, thereby to provide offset cancellation. The variable gain is reduced over time to provide offset cancellation during an initial period of time of operation of the amplifier circuit. This provides offset cancellation during a start-up period, for example.

Abstract: A portable electronic device having a speaker module is provided. The speaker module includes: a speaker unit; a back chamber; a channel coupled between the speaker unit and the back chamber; and a porous material filled inside at least a portion of the front chamber, the back chamber, and/or the channel, for improving and extending bass performance and relieving a channel effect caused by the channel. Moreover, the portable electronic device is advantageously able to compensate a resonance degradation caused by the porous material.

Abstract: A speaker device including: a hollow case; a drive unit housed in the case and configured to cause a diaphragm to vibrate; and a curved diaphragm having a flat plate curved and arranged to stand in an upright position on an upper surface of the case, wherein a diaphragm of the drive unit is exposed at a part of a surface of the case, and a part of a base end of the curved diaphragm abuts on the diaphragm of the drive unit, and the curved diaphragm is compressively deformed through a standing pole arranged to extend between a tip end of the curved diaphragm and the case, whereby vibration of the diaphragm of the drive unit is allowed to propagate to the curved diaphragm and the case so that sound is allowed to come out of the diaphragm of the drive unit, the curved diaphragm, and the case.

Abstract: A horn loudspeaker with gain shading. The horn loudspeaker includes an acoustic horn. The acoustic horn includes side walls, for determining the horizontal dispersion angle of the acoustic horn, top and bottom walls, for determining the vertical dispersion angle of the acoustic horn, and a plurality of acoustic drivers coupled to the acoustic horn by a diffraction slot having segments. Each of the segments is separated from the adjacent segments by less than one half of the wavelength of the highest frequency of the operational range of the horn loudspeaker. The horn loudspeaker further includes circuitry for transmitting an audio signal to the plurality of acoustic drivers, the circuitry comprising a first signal attenuation element electrically coupling an audio signal input element and a first of the acoustic drivers.

Abstract: A microphone amplifier comprises a microphone terminal for connecting a microphone, particularly a MEMS microphone, and an amplifier circuit with an amplifier input that is connected to the microphone terminal, and with an amplifier output that is connected to an output of the microphone amplifier. The amplifier circuit is designed to amplify an input signal present at the amplifier input in order to generate an output signal at the amplifier output. The microphone amplifier further comprises an overload circuit that is designed to detect an overload state within the amplifier circuit and to connect the amplifier input via a switching element, in particular with a low impedance, to a reference potential terminal if the overload state is detected for more than a predetermined time span.

Abstract: Disclosed is a technique for reducing noise superimposed on an output signal while keeping loop gain constant without increasing the circuit scale and without changing the transfer function of the amplifier apparatus (frequency characteristics of gain and phase). According to the technique, there are included a power-supply voltage control unit 7 for detecting the amplitude level S9 of an input audio signal S1 and outputting power with a voltage value indicated by target set voltage value information Vs corresponding to this amplitude level S9, and a PWM modulation unit 2 including a PWM converter 23 for converting the pulse width of the input audio signal S1 and a correction unit for correcting the signal modulated by the PWM converter 23. The PWM modulation unit 2 corrects the pulse width of a PWM signal S5 modulated by the PWM converter 23 so that the correction unit will cancel out a change in amplification gain of a power amplification unit 4 according to the target set voltage value information Vs.

Abstract: An apparatus is described that includes an audio power amplifier having an input and an output. An alternating-current to direct-current power converter is coupled to the audio power amplifier in a single package to supply power to the audio power amplifier.

Abstract: A selector selects an analog audio signal input to one input port from among analog audio signals input to multiple input ports according to an instruction from the user. An analog gain control circuit amplifies the analog audio signal received from the selector, with a corresponding one of the gains set for the respective input ports. An analog gain control circuit is configured to gradually change its gain when the gain is switched. An A/D converter converts an output signal of the analog gain control circuit into a digital audio signal. A first audio signal processing circuit is monolithically integrated on a signal semiconductor substrate.

Abstract: A transparent ultrasonic audio speaker includes an emitter and a driver. The emitter can include first and second transparent conductive sheets. The conductive sheets can comprise a base layer and a conductive layer, and can be transparent. The transparent ultrasonic audio speaker can be configured to be positioned on or in place of the display screen of a content device.

Abstract: A method and device for driving a digital speaker based on code conversion are provided in the invention. The method comprises the steps of: (1) converting input format; (2) performing multi-bit ?-? modulation; (3) thermometer code conversion; (4) dynamic mismatch-shaping processing; (5) pulse width modulation code conversion; and (6) controlling on/off status switching of the MOSFET of a full-bridge power amplification network to drive a digital speaker load sound. The device comprises a sound source, an input format converter, a multi-bit ?-? modulator, a thermometer coder, a dynamic mismatch shaper, a code converter, a multi-channel digital amplifier and a digital speaker load which are connected to each other in sequence.

Abstract: An audio system that reduces or eliminates click and pop noise during power up and power down operations. In particular, the audio system includes an amplifier with an input adapted to receive an input audio signal and an output adapted to produce an amplified output audio signal for an associated speaker. The audio system further includes a noise reduction circuit adapted to smoothly apply and remove a DC voltage to and from the output of the amplifier in a manner that reduces or eliminates click and pop noise from being generated by the associated speaker. The DC voltage at the output of the amplifier may be derived from a DC reference voltage source and/or from the input audio signal.

Abstract: A throat-vibration-type sensor includes a ceramic sheet and a copper sheet received in a box body, wherein the ceramic sheet and the copper sheet are electrically connected to an amplification circuit for voice communications. The volume and thickness of the throat-vibration-type sensor is reduced, the cost thereof is reduced, the assembly thereof is easy, and the reception effect is increased. The throat-vibration-type sensor is combined with a communication hand-free device which includes a control circuit board, a sound amplification device and a battery unit. The throat-vibration-type sensor is used for relieving the interference of external noise. The communication hand-free device combined with the throat-vibration-type sensor avoids the inability of identifying a voice signal because of a wind shear sound caused by a high moving speed of a wearer, to improve the overall utilization efficiency of the communication hand-free device.

Abstract: An ultrasonic emitter is provided, where at least one of an amplifier, driver circuit, and signal processing circuitry is integrated onto or into the ultrasonic emitter. The ultrasonic emitter may include a backing plate and an amplifier and/or associated processing integrated directly onto the backing plate for amplifying and matching an audio modulated ultrasonic carrier signal to the ultrasonic emitter. The emitter is configured to launch a pressure-wave representation of the audio modulated ultrasonic carrier signal into the air.

Abstract: Sound pressure level limiter with anti-startle feature for audio systems are disclosed. The anti-startle feature may be implemented with a delta incident detector for detecting delta acoustic incidents that exceed a predetermined acoustic startle boundary, a delta limiter for determining an anti-startle gain, and an amplifier to apply the anti-startle gain to the input signal. The delta incident detector may detect delta incidents based on an estimated true SPL delivered by a transducer to a predetermined datum point. The estimated true SPL may be determined by based on a measured receiving frequency response of the transducer. An SPL limiter may also determine an SPL gain in response to detecting an SPL acoustic incident that exceeds a predetermined SPL threshold, and an amplifier may apply the SPL gain to the input signal to reduce it below the threshold.

Abstract: A device and methods are provided for a guitar amplifier. In one embodiment, an amplifier includes an overdrive shaping circuit including one or more elements for harmonic shaping of a received signal. The amplifier may also include a power amplifier circuit configured to receive the harmonic shaped signal from the overdrive shaping circuit, wherein the power amplifier circuit includes a switchmode amplifier to amplify the harmonic shaped signal includes one or more elements to increase the output impedance of the switchmode amplifier. An output of the amplifier can output a signal with desired harmonic shaping and a dynamic response.

Abstract: A processing chip for a digital microphone and related input circuit and a digital microphone are described herein. In one aspect, the input circuit for a processing chip of a digital microphone includes: a PMOS transistor, a resistor, a current source, and a low-pass filter. The described processing chip possesses high anti high-frequency interference capabilities and the described input circuit possesses high high-frequency power supply rejection ratio.

Abstract: An audio mixing console comprises a first amplifier, an analogue to digital converter, a second amplifier and a gain range control unit. The first amplifier may receive an analogue audio input signal and amplify the received audio input signal with a first adjustable gain. The analogue to digital converter may receive the amplified analogue audio input signal and generate a digital audio signal by an analogue to digital conversion of the analogue audio signal. The second amplifier may receive the digital audio signal and amplify the received digital audio signal with a second adjustable gain. The gain range control unit may identify a signal level overload at the analogue to digital converter and control the gain of the first and second amplifiers, respectively.

Abstract: The present invention concerns an audio amplifier circuit designed to provide an output signal to an audio transducer, said audio amplifier circuit comprising an audio power amplifier designed to receive an audio signal and designed to generate said output signal, a sensor designed to detect an audible sound having at least one noise component, to generate a detected signal. The audio amplifier circuit also includes a processing block configured to receive said detected signal at its input and to generate an off signal at its output, the latter being located at the input of said audio power amplifier. The processing block processes the detected signal according to said input signal to identify said noise component of said detected signal to generate a reference signal. The processing block generates the off signal when the value of said input signal is lower than the value of said reference signal.

Abstract: A method, computer program product, and computer system for receiving an indication that a first module is operatively connected to a main module, wherein the first module and the main module include hardware modules. A type of speaker operatively connected to the first module is identified. The type of speaker is matched to a speaker profile, wherein the speaker profile includes a predefined sound curve setting. The first module is tuned to the predefined sound curve setting based upon, at least in part, matching the type of speaker to the speaker profile.

Abstract: A vehicle proximity annunciator device reduces an occurrence of a pop noise without an additional circuit changing an output of a power amplifier. A capacitor is located between a connection point connecting multiple resistances generating a reference voltage and a ground terminal. The capacitor causes a rise-up time of the reference voltage to delay at a start of power supply to a power source terminal. A sound emission signal is increased at substantially a same level of the reference voltage so that a variation of a differential voltage between the reference voltage and the sound emission signal falls in a pre-determined range.

Abstract: The embodiments described herein relate to amplifier circuits with power rails. The power rails are generated in response to an input signal, which will typically be an audio signal, and with a sufficient magnitude to power the amplifier and to generate an output signal corresponding to the input signal.

Abstract: An audio demonstration kit encourages understanding of audio concepts by enabling children to construct and study speaker performance. In a particular embodiment, the audio demonstration kit includes a paper speaker and instructions. The paper speaker includes a backplate, a suspension, and a diaphragm cut from a single sheet of paper. The demonstration kit may feature an amplifier that is configurable to accommodate various hardware additions as a child is ready for more progressively challenging construction. For example, the amplifier of an embodiment allows single and dual mode operation, as well as drives a rotary motor and is coordinated with a strobe light. The amplifier of an embodiment is synchronized with the strobe light and a moveable platform to create the impression of that jiggling figures attached to the table are dancing. Interfaces with smart phone, recording, and other technologies further enhances and encourages the learning experience.

Abstract: Embodiments described herein provide for acoustic signatures in a playback system. In some embodiments, a playback device includes an audio processing component configured to receive an audio input signal, receive an acoustic signature signal, generate an audio output signal based on the audio input signal and the acoustic signature signal, and output the generated audio output signal. In some embodiments, the acoustic signature identifies at least one of the playback device or a group of playback devices. Some embodiments additionally include the playback device amplifying the generated audio output signal with one or more amplifiers, and playing the generated audio output signal via one or more speakers.

Abstract: Embodiments are directed toward user profile based audio adjustment techniques. The techniques are used to render various audio and/or audio/video content having different audio output parameter values in accordance with a user profile that characterizes a user's desired value and/or range of one or more of the output parameter levels.

Abstract: A channel conversion part (214) performs channel conversion on audio data of a plurality of channels so that the number of channels thereof is converted to an appropriate number of channels for which an acoustic effect can be verified or perceived by audience according to the volume level of reproduced sound, and audio is output only with a required number of channels. In addition, a frequency control part (215) for controlling the operating frequencies of switching regulators (220-223) of audio amplifiers (224-227) also performs frequency control according to the volume level of sound of each channel which performs an audio output.

Abstract: An output controller and an method for outputting a signal flow to one or more earphone jacks according to a connection status of each earphone jack. The output controller includes an interface unit having more than one earphone jacks and an output control unit. The output control unit includes a signal input terminal for receiving a signal flow, a detector, and a determining module. The detector detects whether each earphone jack is connected with an earphone and outputs one or more detected signals representing the connection status of the earphone jacks. The determining module outputs the signal flow directly to the connected earphone jack if only one earphone jack is connected to the earphone or distributes the signal flow being amplified correspondingly into each connected earphone jack if more than one earphone jack is connected to the earphones.

Abstract: An all-in-one audio system includes an audio chip, an audio interface, first and second audio signal amplifiers, a speaker, a woofer, a multi-function controller, a high definition multimedia interface (HDMI), and a switch. The multi-function controller is connected to the audio chip, the switch, the audio interface, the first and second audio signal amplifiers, and the HDMI. When the multi-function controller detects a high definition multimedia signal through the HDMI, the multi-function controller turns off the switch, decodes the high definition multimedia signal into an audio signal, and transmits the audio signal to the audio interface, and the first and second audio signal amplifiers. The first and second audio signal amplifiers amplify the audio signal and output the amplified audio signal to the speaker and woofer.

Abstract: A multi level charge pump circuit may be associated with at least two power supplies, and may provide at least four levels of positive and negative voltage. The multi level charge pump may include first and second fly capacitors, and first and second tank capacitors. A plurality of PMOS transistors and NMOS transistors may allow generation of two high voltage levels and two low voltage levels for the multi level charge pump, the low voltage levels being derived from a charging of the two fly capacitors in series. This multi level charge pump may be embodied in an audio device within a platform without a dedicated SMPS circuit.

Abstract: An alarm sounder, which incorporates a piezo-electric output transducer, can be silently monitored using a variable frequency square wave. An initial frequency, close to the upper limit of human hearing, is coupled to the sounder. The transducer draws very little current at this initial frequency. The frequency of the square wave is systematically reduced, and the current draw is continually monitored. A high current indicates a low impedance type of fault. A low current throughout the frequency range indicates a potential high frequency type of fault.

Abstract: A method of attenuating an input signal to obtain an output signal is described. The method comprises receiving the input signal, attenuating the input signal with a gain factor to obtain the output signal, applying a filter having a frequency response with a frequency-dependent filter gain to at least one of a copy of the input signal and a copy of the output signal to obtain a filtered signal, the frequency-dependent filter gain being arranged to emphasize frequencies within a number N of predetermined frequency ranges, N>1; wherein the filter comprises a sequence of N sub-filters, each one of the N sub-filters having a frequency response adapted to emphasize frequencies within a corresponding one of the N predetermined frequency ranges; determining a signal strength of the filtered signal, and determining the gain factor from at least the signal strength.

Abstract: Techniques for sensing current delivered to a load by a differential output stage, e.g., in a Class D amplifier. In one aspect, voltages across sense resistors coupled in series with first and second branches of the differential output stage are low-passed filtered and digitized. The sense resistors may be coupled in series with the sources of transistors of the first and second branches, wherein the transistors are selectively switchable on and off by input voltage driving voltages. The input driving voltages may correspond to a ternary voltage waveform such that during a given phase, the two transistors coupled in series with the sense resistors may be turned off. Further aspects provide for the first and second branches having cascoded NMOS and/or PMOS transistors, and the sense resistors being provided between a pair of cascoded transistors.

Abstract: For a media clip that includes audio content, a novel method for performing dynamic range compression of the audio content is presented. The method performs an analysis of the audio content. Based on the analysis of the audio content, the method generates a setting for an audio compressor that compresses the dynamic range of the audio content. The generated setting includes a set of audio compression parameters that include a noise gating threshold parameter (“noise gate”), a dynamic range compression threshold parameter (“threshold”), and a dynamic range compression ratio parameter (“ratio”).

Abstract: An amplifier (50) for voice or audio signals, and particularly for headset applications, uses a low gm amplifier (54) for initially charging an output node (OUT) at the beginning of a power-on phase. After charging the output node, a main amplifier (56) is enabled to amplify the voice or audio signal. At power-down, a sample-and-hold circuit (58) drives an output transistor to discharge an AC coupling capacitor (20). Thus, spikes at the output node are eliminated and an external filtering capacitor is not needed.

Abstract: An amplifier including an input stage, an output stage, an adjustable bias current generator and a level detector. The input stage may receive and amplify or buffer an input signal. The input stage may be biased by a first bias current. The output stage may supply an output signal to an amplifier load. The output stage may be biased with a second bias current. The adjustable bias current generator may be operatively coupled to the input stage and the output stage to supply these with the first and second bias currents, respectively. The level detector may be operatively coupled to the input signal and the adjustable bias current generator to control the first and second bias currents depending upon the input signal. The adjustable bias current generator may adjust the respective levels of first and second bias currents in opposite directions. Disclosed is an electroacoustical transducer incorporating the amplifier.

Abstract: A multi-mode amplifier with configurable DC-coupled or AC-coupled output is described. In one design, the multi-mode amplifier includes an amplifier and at least one DC level shifting circuit. The amplifier receives and amplifies an input signal and provides an output signal that is suitable for DC coupling to a load in a DC-coupled mode and for AC coupling to the load in an AC-coupled mode. The at least one DC level shifting circuit performs DC level shifting for at least one (e.g., input and/or output) common-mode voltage of the amplifier and is controlled based on whether the amplifier is operating in the DC-coupled or AC-coupled mode. The amplifier operates between VDD and VNEG supplies in the DC-coupled mode and between VDD and VSS supplies in the AC-coupled mode. The amplifier may include at least one gain stage, an internal DC level shifting circuit, and an output stage.

Abstract: A system and method for modulating the sound pressure that is output from an audio transducer is disclosed. In one embodiment, the method includes receiving an audio signal and placing the audio signal across a voice coil of the transducer. In addition, a voltage is applied across a field coil of the transducer, the field coil being separate from the voice coil. And the voltage that is applied across the field coil is adjusted so as to modulate the sound pressure output from the audio transducer.

Abstract: An application for present invention includes a television with a set of speaker outputs including at least a left speaker and a right speaker. On screen displays are used to properly configure the speakers and assure maximum audio quality from the television. In some embodiments, a cross-point switch connects the speakers attached to the television with the correct outputs of an internal amplifier.

Abstract: A mechanism is provided for automatically controlling the operation of a media device based at least in part upon whether a portable presentation device coupled to the media device is currently being worn by a user. A portable presentation device may be any device that is meant to be worn by a user and that is capable of presenting media content to the user (e.g. earphones, headphones, goggles or faceplates with video/audio capability, etc.). With this mechanism, a user can affect the operation of the media device by simply putting on or taking off the portable presentation device. The user does not need to manually manipulate the controls of the media device. By automatically controlling the operation of the media device in this manner, use of the media device and the portable presentation device as a unit is made much simpler and more convenient.

Abstract: An audio amplifier is provided with: an amplifier circuit; a power supply circuit that generates a plurality of power supply voltages; a power supply relay that selects one of the power supply voltages as the power supply voltage supplied to the amplifier circuit; a switching condition determiner that determines whether the switching condition of the power supply relay is satisfied; a silent section detector that detects a silent section of the audio signal which is equal to or greater than the operation time of the power supply relay; and a switching instruction unit for providing the power supply relay with an instruction for switching the power supply voltage during the silent section when the switching condition is satisfied and the silent section is detected.

Abstract: Audio amplification may be improved by controlling an audio amplifier based on the audio signal being amplified. For example, when the audio signal level increases or decreases, a boost voltage provided to an audio amplifier by a boost converter may also be increased or decreased. In another example, when the audio signal level decrease below a certain level, the audio amplifier may be switched from amplifying the audio signal with a boost converter input to amplifying the audio signal with a low voltage input. Control of the audio amplifier may be implemented in a digital boost converter controller coupled to the boost converter and/or the audio amplifier.