Removal of swirl artifacts from celp-based speech coders
AssigneeHughes Electronics Corporation
InventorsKalyan Ganesan, Ho Lee, Prabhat Gupta
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Abstract
The perception of speech processed by a CELP based coder, such as a VSELP coder, when operating in noisy background conditions is improved by removing swirl artifacts during silence periods. This is done by removing the low frequency components of the input signal when no speech is detected. A speech activity detector distinguishes between a periodic signal, like speech, and a non-periodic signal, like noise by using most of the VSELP coder internal parameters to determine the speech or non-speech conditions. To prevent the VSELP coder from determining pitches for non-periodic signals, a high pass filter is applied to the input signal to remove the pitch information for which the VSELP coder searches.
Claims15
A system for combatting the effect of swirl artifacts created by low frequency components of an input signal in a code excited linear prediction (CELP) based encoder comprising:
- a switch connected to receive an input signal, the input signal containing periodic and non-periodic signals;
- a high pass filter also connected to receive the input signal and operable to remove low frequency components likely to cause the production of swirl artifacts from the input signal, the switch being controllable to selectively supply the input signal or an output of the high pass filter to the CELP based encoder;
- and
- a detector connected to receive the input signal and information from the CELP based encoder and generate an output indicating the presence of periodic signals in the input signal, the detector controlling the switch to connect the input signal to the CELP based encoder when periodic signals are detected and to connect the output of the high pass filter to the CELP based encoder when non-periodic signals are detected;
- wherein low frequency components likely to cause the production of swirl artifacts are alternately filtered from the CELP based encoder input signal to thereby prevent the production of swirl artifacts.
A method for combatting the effects of swirl artifacts created by low frequency components of an input signal to a code excited linear prediction (CELP) based speech encoder comprising the steps of:
- sampling an input signal and converting input signal samples to digital values, the input signal containing periodic and non-periodic signals,
- high pass filtering the digital values of the input signal to remove low frequency components likely to cause the production of swirl artifacts from samples of the input signal, said low frequency components corresponding to pitch information;
- determining the presence of periodic signals in the input signal by receiving the digital values of the input signal and information from the CELP based speech encoder;
- and
- selectively supplying the digital values of the input signal or high pass filtered digital values to the CELP based speech encoder, the digital values of the input signal being connected to the CELP based speech-encoder when periodic signals are detected and the high pass filtered digital values being connected to the CELP based speech encoder when non-periodic signals are detected.
Dependencies are inferred from the claim text.