37. A method of inverse quantizing a vector representative of a portion of a speech or audio signal in a decoder, the vector being quantized in an encoder according to the steps of: determining, among a set of candidate codevectors that include line spectral frequencies (LSFs), a best candidate codevector not belonging to an illegal space representative of illegal vectors, wherein the illegal space is defined by invalid spacing characteristics of LSFs, and transmitting to the decoder a quantizer index identifying the best legal candidate codevector, where the best legal candidate codevector corresponds to a quantization of the vector, the method of inverse quantizing comprising: (a) producing a reconstructed codevector based on a received quantizer index; (b) determining whether the reconstructed codevector does not belong to the illegal space; and (c) outputting a reconstructed portion of the speech or audio signal based on the reconstructed codevector when the reconstructed codevector does not belong to the illegal space.
37. A method of inverse quantizing a vector representative of a portion of a speech or audio signal in a decoder, the vector being quantized in an encoder according to the steps of: determining, among a set of candidate codevectors that include line spectral frequencies (LSFs), a best candidate codevector not belonging to an illegal space representative of illegal vectors, wherein the illegal space is defined by invalid spacing characteristics of LSFs, and transmitting to the decoder a quantizer index identifying the best legal candidate codevector, where the best legal candidate codevector corresponds to a quantization of the vector, the method of inverse quantizing comprising: (a) producing a reconstructed codevector based on a received quantizer index; (b) determining whether the reconstructed codevector does not belong to the illegal space; and (c) outputting a reconstructed portion of the speech or audio signal based on the reconstructed codevector when the reconstructed codevector does not belong to the illegal space. 43. The method of claim 37 , wherein: step (b) comprises determining whether at least a portion of the reconstructed codevector does not belong to the illegal space; and step (c) comprises outputting a reconstructed portion of the speech or audio signal based on the reconstructed codevector when at least a portion thereof does not belong to the illegal space.