Synchronized encoder-decoder frame concealment using speech coding parameters including line spectral frequencies and filter coefficients
First Claim
1. A speech encoding system using an analysis by synthesis approach on a speech signal, the speech encoding system comprising:
- an encoder that generates a series of line spectral frequencies, some of the line spectral frequencies are produced out of order;
the encoder determines the number of line spectral frequencies that are produced out of order;
the encoder selectively applies a first of a plurality of correction techniques to process the series of line spectral frequencies that are produced out of order if the number of line spectral frequencies that is produced out of order exceeds a first predetermined threshold;
the encoder selectively applies a second of the plurality of correction techniques to process the series of line spectral frequencies that are produced out of order if the number of line spectral frequencies that is produced out of order exceeds a second predetermined threshold; and
the second of the plurality of correction techniques comprises reordering the series of line spectral frequencies that are produced out of order.
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Abstract
A multi-rate speech codec supports a plurality of encoding bit rate modes by adaptively selecting encoding bit rate modes to match communication channel restrictions. In higher bit rate encoding modes, an accurate representation of speech through CELP (code excited linear prediction) and other associated modeling parameters are generated for higher quality decoding and reproduction. The encoder produces a series of LSF (line spectral frequencies) vectors. For filter stability, each LSF vector comprises an ascending sequence of LSF values. Occasionally, pairs of LSF values are produced (or become through an introduction of channel error) out of ascending order. In response, the encoder performs frame erasure, LSF concealment or pair flipping. With a relatively large number of out of order pairs, frame erasure is applied. With a single out of order pair, within the LSF vector, the pair are flipped. Likewise, with two pairs out of order, the previous LSF vector is used to generate the current LSF vector using concealment. The performance of frame erasure, LSF concealment or pair flipping is also performed in the decoder as well as in the encoder in some embodiments.
140 Citations
20 Claims
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1. A speech encoding system using an analysis by synthesis approach on a speech signal, the speech encoding system comprising:
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an encoder that generates a series of line spectral frequencies, some of the line spectral frequencies are produced out of order;
the encoder determines the number of line spectral frequencies that are produced out of order;
the encoder selectively applies a first of a plurality of correction techniques to process the series of line spectral frequencies that are produced out of order if the number of line spectral frequencies that is produced out of order exceeds a first predetermined threshold;
the encoder selectively applies a second of the plurality of correction techniques to process the series of line spectral frequencies that are produced out of order if the number of line spectral frequencies that is produced out of order exceeds a second predetermined threshold; and
the second of the plurality of correction techniques comprises reordering the series of line spectral frequencies that are produced out of order. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A speech codec using an analysis by synthesis approach on a speech signal, the speech encoding system comprising:
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an encoder processing circuit that generates a series of filter coefficients, some of the filter coefficients is produced out of order;
the encoder processing circuit determines the number of filter coefficients that are produced out of order; and
the encoder processing circuit selectively applies one of a plurality of techniques to accommodate the production of the series of filter coefficients that are produced out of order if the number of filter coefficients that is produced out of order exceeds a predetermined threshold. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
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16. A method used by a speech encoder that operates on a speech signal, the method comprising:
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producing from the speech signal a series of line spectral frequencies, at least one of the line spectral frequencies being produced out of order;
determining the number of line spectral frequencies that are produced out of order; and
deciding either to reorder the series of line spectral frequencies that are produced out of order, or to replace at least a portion of the series of line spectral frequencies that are produced out of order using at least a portion of one previous series of line spectral frequencies if the number of line spectral frequencies that is produced out of order exceeds a predetermined threshold. - View Dependent Claims (17, 18, 19, 20)
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Specification