1. A compacted codebook CELP encoder for compressing speech, the compacted codebook CELP encoder having a weighted synthesis filter with an impulse response, an adaptive codebook, and a fixed stochastic codebook containing excitation vectors, such that a plurality of fixed stochastic codebook subframes corresponds to a single adaptive codebook subframe, the compacted codebook CELP encoder comprising an adaptive energy lookup table storing a plurality of values of at least one function of the convolution of the impulse response with the excitation vectors wherein said adaptive energy lookup table stores a plurality of values of energy terms corresponding to the excitation vectors, said adaptive energy lookup table facilitating the selection of excitation vectors.