Multi-stage vector quantization for audio coding

A method in a decoder to reconstruct a target vector, the method comprising:

• receiving an index that corresponds to a segment, associated column shift values, a segment codebook vector, and a global offset value vector;
• performing an upshift operation on the target vector using the column shift values to form an upshifted vector;
• performing an inverse discrete cosine transform, DCT, Type II transform of the upshifted vector to produce an output vector;
• scaling the output vector from the inverse DCT Type II transform to an original unscaled frequency domain-comfort noise generation, FDCNG, domain vector;
• and
• adding the global offset value vector back to the unscaled FD-CNG domain vector to form a fdcng_finalidx_full vector.

An encoder adapted to:

• obtain a discrete cosine transform, DCT, target vector;
• perform a sub-optimal pairwise inner search in each segment of a codebook having a plurality of segments with each segment having truncated vectors different from truncated vectors of other segments of the plurality of segments to determine, from each of the plurality of segments, a pairwise initial candidate set to form a plurality of pairwise initial candidates from the sub-optimal pairwise inner searches, wherein the DCT target vector is a target of the sub-optimal pairwise inner search in each of the plurality of segments;
• reconstruct the plurality of final candidates using an inverse type II discrete cosine transform, DCT-II, to transform the plurality of final candidates to final candidate data in an original domain;
• and
• provide the final candidate data to a second stage of a multistage vector quantizer.