Thomson Licensing

Kent Joseph Nysewander

Joel David Sawaski

Chandra Mohan

Frank Alan Nardelli

Wilhelm Ernst Riedl

Hung Chi Lai

Audio processing systems, such as full duplex digital telephone systems, are provided in which analog automatic level control (ALC) circuitry is employed to automatically control and stabilize the microphone output audio signal levels to a constant level for optimal digital signal processing. For example, an audio communication device () includes a microphone () to generate an audio signal, an analog automatic level control (ALC) circuit (), coupled to an output of the microphone (), to control a level of the audio signal output from the microphone () and output a level-controlled audio signal, and a DSP (digital signal processing) circuit () to process the level-controlled audio signal output from the ALC circuit (). The ALC () allows audio signals to be captured by the microphone () with wide dynamic range, while stabilizing the microphone output level within a reduced dynamic range compatible with the limited dynamic range of the DSP circuitry () for enhanced performance.

Full duplex telephone system employing automatic level control for improved digital signal processing of audio signals

A voltage controlled Colpitts type crystal oscillator includes a first crystal and a transistor coupled to the first crystal to provide positive feedback for generating an output oscillatory signal. A variable capacitance is coupled to the first crystal for producing a change in a frequency of the oscillatory signal when a corresponding change in the variable capacitance occurs. A first inductance is coupled in a resonant circuit that includes the variable capacitance and the first crystal having a value selected to provide a pulling range of at least 0.4% with respect to the frequency of the oscillatory signal. In one embodiment of the invention, a second crystal is coupled to the first crystal and included in the resonant circuit. An energy dissipating impedance is coupled in the resonant circuit to the first crystal for decreasing a Q characteristic of the first crystal to increase the pulling range of the oscillator. The first inductance separates the second crystal from each of the first crystal and the energy dissipating impedance to decrease an effect of the energy dissipating impedance on a Q characteristic of the second crystal.

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Mooresville, IN, United States of America

Kent Joseph Nysewander