Abstract: In a dual-channel HD radio receiver, when the broadband filter channel is compromised, the broadband channel is inactivated and the narrowband channel is activated. By mixing the signals of the two channels during the change, undesirable audio artifacts can be minimized.

Abstract: A system and method for predicting and limiting distortion of an amplified signal is described. The system includes a variable total harmonic distortion (“THD”) clipping predictor, a comparator in communication with the variable THD clipping predictor and a distortion limiter in communication with the comparator. As for the method, a reference power supply value, a maximum desired total harmonic distortion value and a preamplified signal value is provided. A THD output threshold value is calculated based on the reference power supply value and the maximum desired THD value and is then compared to the preamplified signal value. Depending on if the preamplified signal value is greater than or less than the THD output threshold value, the amplitude of the preamplified signal may be increased or decreased.

Abstract: The presence or absence of a speaker connected to an output terminal of an audio system is determined based on the electro-generator properties of the speaker. The audio system includes an output amplifier coupled to the output terminal. The method includes driving the output amplifier with a predetermined drive signal sufficient to produce a predetermined speaker excursion if a speaker is connected to the output terminal. The output amplifier is then isolated from the output terminal. A signal at the output terminal is sensed after the output amplifier is isolated. The sensed signal is compared with a predetermined reference for determining whether a speaker back-EMF is present. A speaker detection signal is generated indicating absence of a speaker if the back-EMF is not present.

Abstract: The presence or absence of a speaker connected to an output terminal of an audio system is determined based on the electro-generator properties of the speaker. The audio system includes an output amplifier coupled to the output terminal. The method includes driving the output amplifier with a predetermined drive signal sufficient to produce a predetermined speaker excursion if a speaker is connected to the output terminal. The output amplifier is then isolated from the output terminal. A signal at the output terminal is sensed after the output amplifier is isolated. The sensed signal is compared with a predetermined reference for determining whether a speaker back-EMF is present. A speaker detection signal is generated indicating absence of a speaker if the back-EMF is not present.

Abstract: A method of detecting a DC offset in an audio signal provided by an audio processing unit to an audio power amplifier, wherein the audio amplifier provides a clip detect signal back to the audio processing unit, wherein the method comprises the steps of sampling the clip detect signal to determine if the clip detect is active. Detecting a power level of the audio amplifier if the clip detect is active. Next, comparing the power level to a predetermined power threshold. Then, identifying a dc offset if the power level is less than the predetermined power threshold.

Abstract: A digital radio receiver generates coherent signals for synchronous detection without use of a phase-locked loop by employing an adaptive notch filter to cancel the desired signal. The cancelling signal is employed as the coherent signal for synchronous detection. The invention obtains faster locking to the desired signal, a wider capture range, and more efficient software coding in a digital signal processing receiver.

Abstract: A digital radio receiver avoids overshoot or undershoot of an AGC control loop by isolating a carrier signal using an adaptive narrow bandpass filter. The carrier strength signal is used to control either a full AGC loop or an AGC overshoot limiter to avoid sudden changes in the audio output level.

Abstract: Digital signal processing (DSP) employing a differential mean calculation automatically distinguishes sections of blank tape from program material (such as music or voice) on cassette tapes. Blank tape produces a negligible differential mean value while program material produces substantial differential mean values. Thus, each differential mean is compared to a threshold so that a cassette player can be commanded to fast forward through a blank section of tape. A music envelope detector insures that low amplitude music signals are not detected as blank.

Abstract: A digital radio receiver generates coherent signals for synchronous detection without use of a phase-locked loop by employing an adaptive notch filter to cancel the desired signal. The cancelling signal is employed as the coherent signal for synchronous detection. The invention obtains faster locking to the desired signal, a wider capture range, and more efficient software coding in a digital signal processing receiver.

Abstract: A digital signal processing automotive audio system uses an analog audio source providing stereo output signals. One of the stereo signals is mixed to a distinct frequency band and summed with the other stereo signal to form a composite signal which can be digitized in a single analog-to-digital converter. Separate digital stereo signals are recovered using digital signal processing.