1. A method for coding excitation signal of a target speech on a computing device, comprising: extracting from a set of training normalised residual frames a set of relevant normalised residual frames with the computing device, wherein the set of training normalised residual frames is extracted from training speech, synchronised on Glottal Closure Instants (CGI), and normalised in pitch and energy; determining a target excitation signal from the target speech on the computing device; dividing the target excitation signal into GCI synchronised target frames on the computing device; determining a local pitch period and energy of the GCI synchronised target frames on the computing device; normalising the GCI synchronised target frames in relation to the determined local pitch period and energy on the computing device to obtain target normalised residual frames; and determining coefficients of linear combination of the extracted set of relevant normalised residual frames on the computing device to build synthetic normalised residual frames close to each target normalised residual frames, wherein coding parameters for each of the target normalised residual frames comprise the determined coefficients.