Amazon Technologies, Inc.

Colin Randall McEnroe

Jun Yang

Jian Guo

Philip Ryan Hilmes

Chad Georges Seguin

Methods and devices for reducing intermodulation distortion are described herein. In response to receiving an audio input signal, N filtered audio signals may be generated by a filter bank, corresponding to N different frequency bands. The N filtered audio signals may be delayed by a delay time D, and a determination of whether an audio frame of the filtered audio signals includes an audio event or a non-audio event. A signal level estimation may then be determined, the signal level estimation indicating an expander, a compressor, or no compression effects being present. An amount of gain is determined and applied to the delayed audio signals, which are summed across the N frequency bands to generate a full-band audio signal. In some embodiments, the full-band audio signal may be applied to a limiter to reduce any audio clipping, and a final audio signal may be generated.

Systems and methods for reducing intermodulation distortion

A gain control system is responsive to a user gain setting and to an effective signal level to calculate and adaptively vary an output gain to avoid output clipping. The effective signal level is calculated by smoothing the energy of an input audio signal in accordance with selected attenuation factors. In times during which fast transient sounds are occurring, attenuation factors corresponding to relatively low levels of attenuation are selected. In times during which fast transient sounds are not detected, attenuation factors corresponding to relatively higher levels of attenuation are selected. The effective signal level is held at a constant level during periods of silence in order to avoid increasing the output gain during these periods. The output gain is calculated based on a comparison of the effective signal level to a compression threshold.

Adaptive gain control

A reconfigurable filter bank system that has an asymmetrical tree structure with multiple stages to generate multiband outputs. Each stage may include cascaded low-pass filters (LPFs), cascaded high-pass filters (HPFs) and/or all-pass filter(s) (APF(s)) having identical phase responses. As the cascaded LPFs, cascaded HPFs and APF(s) have identical phase responses, each frequency band of the multiband output may have an identical phase shift such that the frequency bands are in-phase and can be added together. The multiband outputs of the reconfigurable filter bank may have near-perfect reconstruction (e.g., small number of cross-band ripples) and therefore only minor distortion. In addition, the number of frequency bands and corresponding non-uniform bandwidths (e.g., frequency ranges) may be user-adjustable and/or reconfigurable during device operation. Further, the reconfigurable filter bank may have reduced computational complexity and/or latency.

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San Mateo, CA, United States of America

Colin Randall McEnroe