Motorola Corporation

John E Lane

Dan Hoory

Johnny Choe

Garth D Hillman

Robert Victor Holland

Zhao Li

Phillip K Brewer, Jr

Patrick K Kelly

Eduardo F Martinez

An echo canceller ( ) for a full-duplex communication system ( ) such as a speakerphone determines a gain factor to be used in sub-band adapter coefficient updates by using both time domain and sub-band signals to determine the state of the system ( ). In one embodiment a gain factor controller ( ) uses the sampled time domain signal to determine if the system ( ) is in the silence state, and if not uses the sub-band signals to determine whether the system ( ) is in the talk, double-talk, or listen state. The gain factor controller ( ) selectively changes the gain factor and selectively performs coefficient updating based on the state. In another embodiment the gain factor controller ( ) determines the state and selectively updates coefficients using state information developed on a band-by-band basis.

Echo canceller for a full-duplex communication system and method therefor

A speakerphone system ( ) implements automatic gain control (AGC) when it is in a talk mode. While in the talk mode, the speakerphone system ( ) applies a gain factor determined by conventional AGC techniques. The inverse of this gain factor is applied to the received signal to avoid the need to adapt the coefficients of an echo canceller, such as an acoustic echo canceller (AEC) ( ), as the volume level changes. The speakerphone system ( ) determines whether it is in the talk, double-talk, or listen mode by adaptively changing energy thresholds which define these modes, in dependence on the distribution of ratios of the transmitted energy to received energy. The speakerphone system ( ) also varies a loop gain in dependence on the separation between the distribution of energy ratios in the talk mode and in the receive mode. This automatic loop gain adjustment ensures loop stability.

Method and apparatus for controlling a full-duplex communication system

A method (FIGS. 6-8) for detecting and attenuating N feedback frequencies in a digitized signal uses a tree structure containing a plurality of staged filters. In a step (602), an array of digital filters (FIG. 8) having N branches (40) is constructed. The array is arranged in a tree structure with each branch (40) having several stages (42, 44, and 46). Many of the N filters are used simultaneously in multiple different branches of the tree structure thus reducing the total number of filters required to detect all N feedback frequencies. Within each branch, N-1 of the N filters are notch filters, and each of the N- 1 notch filters attenuates the digitized signal at one of the N feedback frequencies. The remaining one filter in each of the N branches is a bandpass filter that passes the remaining of the N feedback frequency. Therefore, each branch of the tree passes a unique feedback frequency absent of all other N-1 feedback frequencies.

Method and apparatus for suppressing acoustic feedback in an audio system

A data processing system (10) implements a symmetrical filtering function about the unity gain line using a single filter (33). The data processing system (10) includes a bus (12), an I/O port (12), memory (16), and a processor (18). The I/O port (12) receives filter control parameters (20) and receives and transmits digitized data. The processor receives the filter control parameters (20) and calculates filter coefficients (44, 48, 52). The processor (18) implements the single stage filter (33) based upon the filter coefficients (44, 48, 52) to filter the digitized input data (22) and produce filtered digitized data (24). The single stage filter (33) may include a band pass, high pass, or low pass function. The single stage filtering function (33) produces a filtering function that is symmetrical about the unity gain line. Variable Q operation of the data processing system (10) allows Q of the filtering function to vary with boost/cut level (34). A method (150), a graphic equalizer (200), and digital telephone (250) also incorporate the symmetrical filtering function.

Symmetrical filtering apparatus and method therefor

Acoustic feedback is removed from an audio signal (50) by digitizing the audio signal (50) to produce a digitized audio signal (54). The digitized audio signal (54) is then filtered with an adaptive bandpass filter (56) to detect the frequency of the acoustic feedback, where the adaptive bandpass falter (56) is aligned with the feedback based on a phase relationship between the input and the output of the adaptive bandpass filter (56). A notch filter (58) is then configured based on the frequency of the acoustic feedback, and the digitized audio signal (54) is filtered with the notch filter (58) to attenuate the feedback. The feedback-attenuated digitized signal (62) is converted to a feedback-attenuated analog signal (70).

A method (100) and data processing system (120) for filtering unfiltered signals (134) to produce filtered signals (136) in accordance with desired filter control parameters (124). Adjusted filter control parameters (130) are generated based upon user provided filter control parameters (124) and operational characteristics (128) of a filter (132) to be implemented. The adjusted filter control parameters (130) are provided to the filter (132) which filters the unfiltered signal (134) to produce the filtered signal (136). Using the adjusted filter control parameters (130), the filter (132) has a filtering function that agrees with the desired filter control parameters (124) to effectively band decouple the filter from bands of surrounding filters. A graphic equalizer (250) implements a multi-band digital filter function that substantially reduces the effects of interband coupling, producing a more accurate match to the original filter response specification.

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Satellite Beach, FL, United States of America

John E Lane