Abstract: A receiver, which is compatible with a mobile industry processor interface (MIPI) C-PHY physical layer, includes a plurality of variable-gain amplifiers responsive to respective multi-level signals (e.g., 3-level signals), and a plurality of filters having variable cutoff frequencies. The plurality of filters are responsive to respective signals generated by the plurality of amplifiers. An array of comparators is provided, which is responsive to signals generated by the plurality of filters. A jitter detection circuit is provided, which is configured to set respective gains of the plurality of variable-gain amplifiers and respective cutoff frequencies of the plurality of filters (e.g., high-pass filters), in response to signals generated by the array of comparators.

Abstract: A method includes calculating a processing tool offset for a processing tool based on process control parameters, wherein the processing tool offset is a first portion of a process offset time attributable to a processing tool. The method further includes calculating a product offset based on the process control parameters, wherein the product tool offset is a second portion of the process offset time attributable to a product. The method further includes determining whether the product offset is stable based on a difference between a processing time for different products being within a pre-determined tolerance and a number of processed wafers exceeding a threshold amount. The method further includes calculating an offset time for processing the product using the processing tool based on the calculated processing tool offset, without considering the product offset in response to a determination that the product offset is stable.

Abstract: A noise squelch processor generates a noise squelch determination signal by comparing a noise level and a threshold value with each other. A carrier detector generates a carrier determination signal indicating whether or not a reception signal is present based on a signal strength of the reception signal. An integrator controller controls an integrator to set a cutoff frequency of the integrator to a second cutoff frequency higher than a first cutoff frequency at a first timing when the carrier detector generates a carrier determination signal indicating that the reception signal is present, and to switch the cutoff frequency of the integrator from the second cutoff frequency to the first cutoff frequency at a second timing after an elapse of a predetermined period from the first timing.

Abstract: A method performs radio communication between a controller and a transport user. A controller creates voice signals which are transmitted via a switching system to a transmitting antenna as a radio signal. The voice signals are received via a receiving antenna and are transmitted to the switching system. A squelch signal is created and indicates whether the signal applied to the receiving antenna contains voice messages. A component of the voice signal emitted by the controller and is received with a time delay, is removed from the received voice signal or is compensated for, and a corrected voice signal is determined. The corrected voice signal is transmitted to the controller, if the squelch signal is present, the signal which is emitted by the controller and does not reach the switching system with a time delay is superimposed on the corrected voice signal and the latter is transmitted to the controller.

Abstract: The present invention is related to a method and apparatus for processing multiple wireless communication services in a receiver. A receiver receives more than one wireless communication service simultaneously via a wireless interface. Each service is transmitted via a different carrier frequency band. The multiple received carrier signals are down-converted to an intermediate frequency (IF) band using a mixer and a local oscillator (LO). The LO frequencies are set such that the down-converted IF bands of the multiple services are fallen into a single IF band.

Abstract: A sound source generating unit 101 generates from a narrowband audio signal not passing through noise suppression a sound source signal including a fine structure of a band to be restored. On the other hand, a noise suppressing unit 102 performs noise suppression of the narrowband audio signal and a spectral envelope estimating unit 103 estimates an spectral envelope of the band to be restored. A signal synthesizing unit 104 generates a pseudo-audio signal by combining the sound source signal and the spectral envelope, and the band-pass filter unit 105 passes the pseudo-audio signal of the band to be restored, and the signal addition unit 106 generates a broadband audio restoration signal by adding the pseudo-audio signal of the band to be restored to the narrowband audio signal.

Abstract: A method of controlling a portable electronic device includes detecting a touch on a touch-sensitive display, adjusting a first threshold based on detected conditions during the touch, comparing a value related to the touch on the touch-sensitive display to the first threshold, and when the value related to touch meets the first threshold, turning off the display.

Abstract: A method (10) of establishing an alternate HRPD signaling link between and HRPD access network and an access terminal over a non-HRPD access is disclosed. It includes: providing (12) a signal forwarding function (SFF) (22) between an access terminal (AT) (24) and a high rate packet data (HRPD) access network (AN) (26); establishing (14) a data tunnel (28) between the access terminal (24) and the SFF (22); exchanging (16) HRPD signaling messages and HRPD data via the data tunnel (28); identifying (18) the HRPD access network (26) and the access terminal (24) over non-HRPD access by the SFF (22), by reading a header with certain identifiers and mapping the header to an address of the access terminal or network; and forwarding (20) the HRPD signaling messages and the HRPD data that arrive at the SFF (22) from the access terminal (24) and the HRPD access network (26) to the HRPD access network (26) and the access terminal (24), respectively.

Abstract: A method comprises detecting whether or not a frequency modulation broadcast receiver is tuned to an overdeviated frequency modulated broadcast, or is at a location where overdeviated frequency modulated broadcasts exist or has received a user input indicating the presence of an overdeviated frequency modulated broadcast; and in response to the detection, automatically adjusting operation of the frequency modulated broadcast receiver. Automatically adjusting operation comprises adjusting one or more parameters or settings in such a way as to alter the susceptibility of a speaker arrangement to the possibility of being overdriven by overdeviated frequency modulated broadcasts.

Abstract: A receiver suppresses noise simultaneously using a noise suppressor and an automatic gain controller (AGC). The receiver divides a received signal into an audio period and a non-audio period, analyzes whether the noise characteristic of the non-audio period corresponds to a non-static noise or a static noise, and if the noise characteristic corresponds to the static noise, analyzes whether the static noise is caused by a network or a transmitter side terminal. In accordance with the analyzed noise characteristic, the noise suppressor firstly suppresses the noise by determining the noise suppressing intensity, and sends a signal, from which the noise has been firstly suppressed, to the AGC. The AGC secondly suppresses the noise included in the signal. In this case, the threshold value of the AGC is controlled in real time in accordance with the noise characteristic.

Abstract: A holder for a mobile phone includes a body having an opening to receive the mobile phone and having a bottom. The holder further includes a latch coupled to the body for holding the holder with the opening up; and an acoustic horn coupled to the body and having a sound receiving end and a sound emitting end. The sound receiving end is configured to be adjacent to a transducer of the mobile phone, and the sound emitting end is configured to direct sound in an upward direction. The holder further includes a set of tactile guides to tactilely guide a user's touch to a set of buttons on the mobile phone so that a user does not need to look at the buttons to activate the buttons.

Abstract: User operates a selection switch to instruct temporary activation of an application. For the application of which the temporary activation has been instructed, a CPU of a console allocates resources necessary for signal processing by a DSP of an engine and for a parameter editing function of the console. In the DSP, a bypass parameter is set to ON. Thus, there is provided a state capable of accepting various parameter setting operation related to the application, but the signal processing based on the application program is prevented from being started in a substantive manner. In response to a full activation instruction of an application via a full activation instruction switch, the bypass parameter is set to OFF, so that audio signal processing based on the application can be started. In this way, preparatory work for setting parameters related to the application can be performed efficiently.

Abstract: A radio-to-SIP adapter is shown to include a voice detection algorithm processor as well as other circuitry to provide an interface between a radio and SIP adapter to accommodate a transition from half duplex to full duplex and to cause a radio to transmit when human speech is present in an audio signal from a telephony network.

Abstract: A signal quality estimation and control system for controlling a signal having noise. The system may include a signal strength determination system having an input configured to receive the signal and an output configured to output information indicative of the strength of the signal, a noise strength determination system having an input configured to receive the signal and an output configured to output information indicative of the strength of the noise in the signal, and a signal quality evaluation system. The signal quality evaluation system may have an input configured to receive the output of the signal strength determination system, an input configured to receive the output from the noise strength determination system, and an output configured to output information indicative of the quality of the signal based on the output from the signal strength determination system and the output from the noise strength determination system.

Abstract: In a cellular phone applicable as an information processing apparatus of the invention, an audio data transfer control unit controls streaming transfer of encoded audio data to a headset through wireless communication, and a hands-free control unit controls hands-free communication with the headset through wireless communication. Furthermore, a transmitting/receiving unit transmits/receives data to/from the headset in the streaming transfer of the encoded audio to the headset through the wireless communication or in control over hands-free communication with the headset through wireless communication, and a retransmission control unit controls the retransmission of the data to be transmitted to the headset through the transmitting/receiving processing unit.

Abstract: An audio system may comprise a transceiver configured to receive, detect, and transmit audio signals on a first channel frequency and to receive and detect audio signals on at least one additional channel frequency. The at least one additional channel frequency may include a second channel frequency. The system may include a controller configured to output a first audio cue while outputting audio signals received from the at least one additional channel frequency, to output a second audio cue at a time when the controller begins outputting an audio signal received from the first channel frequency, and to output a third audio cue at a time when the controller begins outputting an audio signal received from the second channel frequency. The first, second, and third audio cues may be different from one another.

Abstract: Signal processing apparatus produces an audio signal suitable for conveying a psychoacoustic perception of a low frequency audio signal to a listener, the apparatus generates harmonics of the low frequency signal by shaping the waveform of the low frequency signal with respect to time and/or level. This may be achieved using a peak-hold generator and a rectifier, or using a peak-hold-decay generator.

Abstract: A receiver architecture for receiving an FSK signal having a predetermined number of modulation levels includes a selectivity filter (206) for selectively passing a wanted channel and rejecting unwanted channels. The selectivity filter has a filter bandwidth of about one-half the bandwidth of a pre-modulation filter in a transmitter sending the FSK signal. A discriminator (208) is coupled to the selectivity filter for demodulating the signal. A symbol recovery processor (210) is coupled to the discriminator for recovering the symbols through a maximum likelihood sequence estimation (MLSE) technique utilizing N states for each symbol time, wherein N equals the predetermined number of modulation levels, and wherein templates used in the MLSE for symbol transitions are optimized with a bandwidth substantially less than the bandwidth of the pre-modulation filter.

Abstract: A signal transmission arrangement includes a signal transmitter and a signal receiver wirelessly communicating with the signal transmitter. The signal transmitter includes a hybrid signal device to hybridize the audio signal with the control signal to form a consolidating signal, a frequency modulator to high-frequency modulate the consolidating signal, wherein the consolidating signal is amplified and sent to the signal receiver in a wireless manner. The signal receiver includes a frequency demodulator to demodulate the consolidating signal and a signal dissociating unit to dissociate the consolidating signal to restore the audio signal and the control signal. Therefore, the signal transmission arrangement provides a low-bit rate coding transmission in control signals, in lieu of the high-bit rate coding transmission which requires the expensive high performance integrated circuit, so as to ensure the quality of the audio signal while being cost effective.

Abstract: A squelch circuit for operating at high speed and at high frequencies includes a squelch input unit, a low swing pre-amplifier and a sampling and decision circuit. The squelch input unit pre-processes the positive and negative signals of an input signal to generate four pre-processed signals that are paired and sent to the low swing pre-amplifier. The outputs of the low-swing pre-amplifier are then over-sampled by the sampling and decision circuit. Multi-phase clocks are used to control the over-sampling in the sampling and decision circuit. A logic circuit then determines if the state of the input signal based on multiple samples.

Abstract: A computer system provides a wireless audio signal transmitter module which is capable of transmitting audio signal wirelessly from a host computer to at least one remote wireless signal receiver. The wireless audio signal transmitter module is connected to a sound effect interface for receiving audio signal from the computer. The audio signal is processed, modulated, and then transmitted out by an antenna. The wireless signal is received and processed by the audio signal receiver located within an effective transmission distance. The signal is then transmitted to a user via a microphone.

Abstract: A method for detecting a tone signal having a predetermined tone frequency includes receiving an analog communication signal, using a sampling frequency to convert the analog communication signal into a digital communication signal, selecting a plurality of signal sectors corresponding to a predetermined frequency range of the digital communication signal where the predetermined tone frequency agrees with the predetermined frequency range, and using the number of samples of each signal sector to determine whether the analog communication signal contains the tone signal.

Abstract: A method of masking interruptions in the playback of received radio signals is provided, in which lengthy interruptions are allowed only when modulation of the radio broadcast program currently being received is recognized as speech, and a modulation pause in the received radio signal is detected. This method permits essentially complete masking of lengthy interruptions in playback or making them inaudible, in which these interruptions are necessary, e.g., for analysis/testing for a transmission frequency of transmitted RDS information to be used as an alternative to a transmission frequency currently being received.

Abstract: A method for detecting a tone signal having a predetermined tone frequency includes receiving an analog communication signal, using a sampling frequency to convert the analog communication signal into a digital communication signal, selecting a plurality of signal sectors corresponding to a predetermined frequency range of the digital communication signal where the predetermined tone frequency agrees with the predetermined frequency range, and using the number of samples of each signal sector to determine whether the analog communication signal contains the tone signal.

Abstract: Described is a transmission system (10) comprising a transmitter (12) for transmitting a narrowband audio signal to a receiver (14) via a transmission channel (16). The receiver (14) comprises a frequency domain bandwidth extender (18) for extending a bandwidth of the received narrowband audio signal by complementing the received narrowband audio signal with a highband extension thereof. The bandwidth extender (18) comprises an amplitude extender (24) for extending the bandwidth of an amplitude spectrum of the received narrowband audio signal by mapping narrowband amplitudes onto highband amplitudes. The bandwidth extender (18) further comprises a phase extender (26) for extending the bandwidth of a phase spectrum of the received narrowband signal and a combiner (28) for combining the extended amplitude spectrum and the extended phase spectrum into a bandwidth extended audio signal.

Abstract: A radio carrier signal is detected (20) after being converted to digital form and is filtered (22). A noise estimator (24) generates a noise estimate signal by estimating the noise in the detected signal due to atmospheric conditions and the noise due to the gain in noise figure properties of the circuitry. The output of the noise estimator is used to calculate a threshold signal (50) and another detection operation (52) determines whether the power of a signal derived from the detected signal exceeds the threshold. If the threshold is exceeded, the detected signal is passed through a signal conditioner, such as a switch (54) to an output path (56).

Abstract: A method of masking interruptions in the playback of received radio signals is described, wherein lengthy interruptions are allowed only when

Abstract: A squelch circuit for a radio receiver that detects the presence of speech by utilizing a filter bank for filtering an intermediate frequency or baseband signal from the radio receiver into band-pass signals, detecting the magnitude of the band-pass signals, and separating the signal magnitudes into a speech and noise detector. The speech detector determines if speech is present by determining if syllabic variations are present in the speech detector signals and selects a voice band average signal with a maximum difference in syllabic variations, and generates a speech detector decision when speech is present. The noise detector makes a noise detector decision when speech is present by obtaining a minimum noise detector signal and comparing the minimum noise detector signal to a threshold scaled voice band average signal associated with the maximum difference in syllabic variations.

Abstract: A mobile communication receiver generates an audio signal from a radio signal received on a communication channel, detects conditions on the communication channel, mutes the audio signal according to a first rule when the channel conditions are bad, and un-mutes the audio signal according to a second rule when the channel conditions are good. The first rule is more stringent than the second rule; as a result, sporadic muting and choppy muting are avoided.

Abstract: The method is used for optimizing a user signal, which is to be transmitted, in a stationary or mobile voice terminal by means of which a user signal consisting of a voice signal and a first background signal is picked up via a microphone, is supplied, possibly after analog or digital signal processing, to an output stage and is delivered by the latter to a transmission medium. In the voice terminal, a memory unit is provided in which at least one second background signal is stored which is called up by a control unit and is superimposed during the entire period or part of the period of the call on the voice signal to be transmitted.

Abstract: A circuit arrangement for brief mute switching of the reproduction of an LF signal in a radio receiver for performing additional control operations is described, in which the mute switching is effected by varying the current flow through the control path of an interrupter by means of a reversing switch, as a consequence of the change in charge of a capacitor acted upon by a blanking signal.

Abstract: An FM receiver capable of instantaneous muting while receiving a broadcast includes a switch circuit provided in series in an audio signal line in the front end of a deemphasizing capacitor, a variable impedance element connected to the capacitor in parallel, and a waveform shaping circuit for smoothing the rise and fall of a muting signal, wherein the muting signal is fed to the switch circuit as a control signal to turn the switch circuit off during the muting signal period, and wherein an output signal of the waveform shaping circuit is fed to the variable impedance element to change the impedance of the variable impedance element correspondingly to the level of output signal of the waveform shaping circuit.

Abstract: An audio editing device for use with a television including a memory device for storing data representative of predetermined audio signals. Also included is a comparator for comparing the digital form of an input audio signal with the data of the memory device and, upon making a match, generating a first flag at a beginning of the data. A second flag is also generated at an end of the data upon locating a match. Finally, a squelch circuit comprises a flag sensor adapted to, upon the detection of the first flag, squelch the data until the sensor detects the second flag whereat the squelch circuit resumes the unmanipulated passage of audio signals to a television set.

Abstract: A squelch circuit (111) that is contained in an communications receiver (100) estimates (403, 405) the energy of an input signal in an audio band and in a first portion of the audio band. The squelch circuit (111) then determines (407) whether the energy in the first portion of the audio band is at least a predetermined proportion of the total energy in the audio band. When the energy in the first portion of the audio band is at least a predetermined proportion of the total energy in the audio band, the squelch circuit increases (409) the audio band energy estimate to produce an updated audio energy estimate. The squelch circuit (111) can then use the updated audio energy estimate to adjust (413) a so-called squelch threshold that is subsequently used to determine (419) the presence of the radio frequency signal at an input (101) to the communications receiver (100).

Abstract: An apparatus to facilitate volume control for route aural guidance. When supplying a guidance voice to a loudspeaker 34a, a voice control section 30 disconnects the loudspeaker 34a from audio and outputs the guidance voice through the loudspeaker. A volume control screen is displayed on a display section 28 where the user adjusts the volume by touching the screen. When the voice control section 30 switches a signal to the loudspeaker 34a, a mute circuit 40a is operated to mute the voice output before the voice is output through the loudspeaker 34a. When the user terminates volume adjustment, the voice control section 30 outputs a voice for volume confirmation or check at the adjusted volume through the loudspeaker 34a. The user can check the adjusted volume at this time.

Abstract: A process for the microbial production of a protein susceptible to inactivation in a fluid production medium by continuously and reversibly protecting said protein against said inactivation during the production stage, separating the protein from the production medium, deprotecting the protein, and recovering the protein product. The process is especially useful for obtaining substantially increased yields of the protein in question by continuously precipitating said protein.

Abstract: An apparatus for detecting noise in communications channels in electrical power transmission systems and generating squelch signals, for transfer-trip receivers for performing protection and control functions, detects changes in a period of an analog signal and generates a signal in response to such changes. The apparatus receives an analog signal, generates zero-pulses corresponding to zero-transitions of the analog signal, generates an error pulse when an interval between successive ones of the zero-pulses either exceeds a preselected long window interval or is less than a preselected short window interval, and generates, in response to the error pulse, a squelch signal.

Abstract: A radio communication device (10) comprises a radio transceiver (12), having a received signal strength indicator (RSSI) (16), an audio section (22), and a controller (16) for deactivating the audio section whenever the RSSI indicates the the received signal strength is below a predetermined threshold. The controller also operates as a counter (26) for indicating the length of time that the received signal strength has been below the predetermined threshold.

Abstract: Differential signals are employed in a distributed audio system to improve noise immunity of the low level differential signals transmitted between a main unit and a power amplifier. The power amplifier may be in an auxiliary output unit which is locally muted by employing a field-effect transistor connected between the differential signals. When the field-effect transistor is turned on by a mute signal, the common mode rejection of the differential amplifier is employed to mute the amplifier output.

Abstract: An audio squelch control for transceiver stations in which all transceivers are initially in a Call mode with the squelch control turned on. While in the Call mode, the squelch control is turned off, enabling the speaker, by receiving the station's coded address, plus a flag bit that is set, from a transmitting station. In addition to having the squelch circuit turned off, the receiving station is changed from the Call mode to an Auto mode. When in the Auto mode, the squelch control is turned off by receiving the station's coded address with the flag bit turned off. The squelch control of a station in one mode does not respond to a station in the opposite mode even if it receives its own coded address.

Abstract: In a radio employing continuous tone or digital coded squelch system, fast settling tone processing circuitry is disclosed for a tone processing path which includes an FM detector, low pass filters and a tone limiter. In an exemplary embodiment, a capacitor at the output of the FM detector in the tone/data processing path is charged as rapidly as possible to a new DC level, for example, by an off frequency transmitter. A pulse is generated by, for example, the transceiver microprocessor which initiates the rapid charging of the capacitor as soon as it is detected that data needs to be read from the tone/digital data processing circuitry for decoding. Such a pulse is generated by the microprocessor whenever channel frequencies are changed and/or the carrier activity sensor becomes active.

Abstract: A radio receiver capable of receiving more than one channel, one of which channels may be a priority channel, wherein some communications may be accompanied by a sub-audible continuous identifying signal, which signal can be detected by the radio in an adaptive way. In particular, a wideband, rapid detect approach can be utilized in the absence of a determination that adjacent identifying signals are present. To the extent such adjacent signals are present, the radio selects a narrowband, slower detection approach, or, in the alternative, shifts the bandpass characteristics of the wideband approach in an attempt to avoid the adjacent interfering signal.

Abstract: The period of time that the squelch circuit maintains a radio receiver's audio amplifier active after the signal strength of a received carrier fades below a threshold level is inversely proportional to the strength of the received carrier immediately before the fade. This threshold level is also variable. If, immediately before the fade, the received signal strength exceeds a predetermined trigger level (Vtrg) the threshold level is raised. A buffer amplifier (102) charges a capacitor (C) to a voltage which is proportional to the strength of a received carrier. If the carrier fades below a threshold (Vth2 or Vth3, the buffer is disabled and the capacitor slowly discharges through a resistor (R). When the voltage at the capacitor crosses a reference voltage (Vref1) the output of a comparator (104) switches, thereby deactivating the receiver's audio amplifier.

Abstract: A two-way radio includes a receiver having a squelch circuit and a selective calling decoder. A transmitter is connected to an inhibit circuit. The inhibit circuit is responsive to the selective calling decoder for permitting transmission after reception of the radio's ID code. The inhibit circuit inhibits further transmissions if the squelch circuit indicates loss of carrier for more than a predetermined time during receive.

Abstract: A channel discriminator circuit is specifically adaptable for use in association with a radio receiver in which DC voltage signals are generated which are proportional to the FM signals received by the radio receiver and an inhibit circuit will generate an inhibit signal denoting the reception of FM signals above a predetermined detection threshold corresponding to an assigned carrier frequency. The channel discriminator circuit will determine whether the FM signals received are centered within a predetermined band width corresponding to the assigned carrier frequency by comparing the DC voltage signal generated with upper and lower reference voltage limits generated by a potentiometer network and will cause the inhibit circuit to generate an inhibit signal only if the DC voltage representing the FM signal received is within the predetermined limits established by the potentiometer network.

Abstract: An FM receiving circuit is provided with a front end section operative to select an FM signal from FM broadcasting signals and producing an intermediate frequency signal on the basis of the FM signal, and an audio signal producing section supplied with the intermediate frequency signal for producing audio signals and responsive to a first control signal for eliminating noise components due to a rapid variation in the electric field strength of the FM signal, and the audio signal producing section is associated with a level detecting circuit supplied with an intermediate frequency signal transferred from the audio signal producing section and producing a voltage signal representative of an envelope of the intermediate frequency signal, a low-pass filter circuit providing a time constant for producing the first control signal on the basis of the voltage signal and responsive to a second control signal for variation in the time constant, a high-pass filter circuit operative to differentiate the voltage signal fo

Abstract: A digital tone squelch detect circuit functions to give an enabling signal for audio transmission in an FM radio network. The circuit comprises an analog to digital converter which outputs a binary coded signal representative of the voltage level of a received audio tone signal. The binary signal is then placed into a shift register which periodically is rotated and multiplied by a reference clock signal for correlation with a stored replica of the tone. The output of the correlator, which is representative of the degree of correlation, is fed to an accumulator which integrates it and sends it to a comparator where its binary valve is compared to an arbitrary threshold binary value by a hysteresis network. After detection the hysteresis established circuit outputs a tone detect signal and lowers the detection threshold so as to maintain the tone detect signal during periods of signal fadeout.

Abstract: A noise reduction system and method for reducing noise occurring during pauses in information bearing audio signals has an audio input connected to one input of a differential output circuit. A variable gain circuit has an input connected to the audio input and an output connected to the other input of the differential circuit. A dc control signal is derived from the incoming signals and controls the variable gain circuit to cause cancellation of a noise only signal during periods of no information bearing audio signals.

Abstract: A noise blanking signal generator for an AM radio receiver includes a product detector adapted to receive an IF signal modulated by an AF signal and synchronously detect the AF signal, a first low pass filter adapted to derive from the product detector a filtered voltage indicating the average IF signal strength, a second low pass filter adapted to derive from the product detector an AF signal voltage and a reference voltage generating circuit ratiometrically related to the product detector through a common DC power supply and effective to generate a reference voltage substantially equal to the filtered voltage in the absence of an IF signal.

Abstract: A television receiver has provisions for a second audio program (SAP) and an indication for signifying when the SAP is present and a muting circuit for muting the SAP, both in response to the output signal of a SAP detector. A filter capacitor is coupled to the detector output to prevent flicker of the indicator due to noise. To prevent the filter capacitor from incorrectly maintaining an indication of the presence of a SAP, thereby preventing proper SAP muting, when a new channel is selected, channel change signal causes a semiconductor switch to discharge the filter capacitor. A SAP defeat switch coupled to the SAP provided the SAP detector output is to defeat the SAP when stereo is being received. To prevent the filter capacitor from discharging to rapidly and thereby creating an audible transient when either the defeat switch or channel change switch is operated, a resistor is coupled between the SAP detector output and the common junction of the SAP defeat and channel change switches.