Adaptive gain reduction to produce fixed codebook target signal
DCFirst Claim
1. A speech system using an analysis by synthesis approach on a speech signal, the speech system comprising:
- an adaptive codebook;
a fixed codebook;
a processing circuit that sequentially identifies a first gain applied to the adaptive codebook and a second gain applied to the fixed codebook; and
the processing circuit identifies a gain reduction factor applied to the first gain identified, the gain reduction factor is used by the processing circuit to perform the identification of the second gain.
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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 applies adaptive gain reduction to optimize selection of appropriate gain contributions from the adaptive and fixed codebooks. Specifically, the encoder uses a first target signal to identify a contribution (a best code vector and a gain) from the adaptive codebook. Thereafter, a contribution from the fixed codebook is selected. The gain associated with the adaptive codebook contribution is then reduced by a factor, and the gain contribution from the fixed codebook is searched a second time, permitting fine tuning of the overall contribution. The gain reduction factor applied is adapted by considering both the encoding bit rate and a normalized correlation between the original target signal and the filtered signal from the adaptive codebook.
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Citations
20 Claims
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1. A speech system using an analysis by synthesis approach on a speech signal, the speech system comprising:
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an adaptive codebook; a fixed codebook; a processing circuit that sequentially identifies a first gain applied to the adaptive codebook and a second gain applied to the fixed codebook; and the processing circuit identifies a gain reduction factor applied to the first gain identified, the gain reduction factor is used by the processing circuit to perform the identification of the second gain. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A speech system using an analysis by synthesis approach on a speech signal, the speech system comprising:
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a adaptive codebook; a fixed codebook; a processing circuit that generates a first contribution from the adaptive codebook and a second contribution from the fixed codebook; and the processing circuit applying gain reduction to the first contribution from the adaptive codebook then regenerating the second contribution from the fixed codebook. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A speech system using an analysis by synthesis approach on a speech signal, the speech system comprising:
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an adaptive codebook; a fixed codebook; a processing circuit that attempts to minimize a first residual signal using contributions from both the adaptive codebook and the fixed codebook; and the processing circuit, after attempting to minimize the first residual signal, applying gain reduction to the contribution from the adaptive codebook and then recalculating the contribution from the fixed codebook by attempting to minimize a second residual signal. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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Specification