1. A method of searching a signed codebook to quantize an input vector representative of a portion of a signal, the signed codebook including a set of shape codevectors, each shape codevector being associated with a positive signed codevector and a negative signed codevector, comprising: (a) weighting a shape codevector in the set of shape codevectors with a weighting function for a Weighted Mean Square Error (WMSE) criteria, to produce a weighted shape codevector; (b) correlating the weighted shape codevector with the input vector to produce a weighted correlation term; and (c) determining, based on a sign of the weighted correlation term, a preferred one of the positive and negative signed codevectors associated with the shape codevector.