1. A method for signal processing, said method comprising: encoding a first frame and a second frame of a speech signal to produce corresponding first and second vectors, wherein the first vector represents a spectral envelope of the speech signal during the first frame and the second vector represents a spectral envelope of the speech signal during the second frame; generating a first quantized vector, said generating including quantizing a third vector that is based on at least a portion of the first vector; calculating a quantization error of the first quantized vector; calculating a fourth vector, said calculating including adding a scaled version of the quantization error to at least a portion of the second vector; and quantizing the fourth vector.