US 6,188,980 B1 · Synchronized encoder-decoder frame concealment using speech coding parameters including line spectral frequencies and filter coefficients

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.

Claims20

Dependent claims

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.

3 more elements

Dependencies are inferred from the claim text.

Synchronized encoder-decoder frame concealment using speech coding parameters including line spectral frequencies and filter coefficients

Life of this patent

Synchronized encoder-decoder frame concealment using speech coding parameters including line spectral frequencies and filter coefficients

Life of this patent

Abstract

Claims20