All-pass filter phase linearization of elliptic filters in signal decimation and interpolation for an audio codec
AssigneeMotorola Mobility LLC
InventorsJonathan A. Gibbs, James P. Ashley, Udar Mittal
Life of this patent
Estimating the term…
Abstract
An audio signal processing system includes parallel speech and generic audio signal processing paths. One path includes a linear predictive coder and a resampling filter having a non-linear phase characteristic. A phase compensation filter is disposed along the one of the processing paths to compensate for the non-linearity of the resampling filter thereby enabling relatively seamless switching between the coders resulting in a reduction of audio artifacts that would otherwise result from the non-linear phase characteristic of the resampling filter during playback.
Claims21
An audio encoder for encoding an input signal, comprising:
- a first encoder path including a first resampling filter that exhibits a non-linear phase characteristic,
- the first encoder path including a first encoder having an input coupled to an output of the first resampling filter, the first encoder configured to produce a first audio signal by encoding a first frame of the input signal after resampling by the first resampling filter;
- a second encoder path including a second encoder configured to produce a second audio signal by encoding a second frame of the input signal;
- and
- a phase compensation filter disposed along the first encoder path upstream of the first encoder or along the second encoder path upstream of the second encoder,
- the phase compensation filter configured to filter the input signal before encoding such that characteristics of the first audio signal and the second audio signal are more similar than in the absence of the phase compensation filter.
An audio decoder comprising:
- a first decoder path including a first decoder configured to produce a first decoded audio signal by decoding a first encoded bitstream;
- the first decoder path including a first resampler filter that exhibits a non-linear phase characteristic, the first resampler filter coupled to an output of the first decoder, the first resampler configured to produce a resampled first decoded audio signal by resampling the first decoded audio signal;
- a second decoder path including a second decoder configured to produce a second decoded audio signal by decoding a second encoded bitstream;
- and
- a phase compensation filter disposed along the first decoder path downstream of the first decoder or along the second decoder path downstream of the second decoder,
- the phase compensation filter configured to filter the resampled first decoded audio signal or to filter the second decoded audio signal such that the resampled first decoded audio signal and second decoded audio signal have more similar characteristics than in the absence of the phase compensation filter.
An audio signal processor comprising:
- a first processing path including a resampling filter that exhibits a non-linear phase characteristic,
- the first processing path including a first coder coupled to the resampling filter, the first coder configured to produce a first output signal by coding a first frame of an audio bit stream;
- a second processing path including a second coder configured to produce a second output signal by coding a second frame of the audio bit stream;
- an all-pass phase compensation filter coupled to the resampling filter in the first processing path;
- and
- a switch coupled to an output of the first and second processing paths, wherein the switch seamlessly switches between the first out signal and the second output signal.
Dependencies are inferred from the claim text.