Patent ID: 7698132

Claim:
A method for forming an excitation waveform in a speech coder, the method comprising: determining whether an acoustic signal in an analysis frame is a band-limited signal; if the acoustic signal is a band-limited signal, then using a sub-sampled sparse codebook to generate the excitation waveform, wherein the sub-sampled sparse codebook comprises either only even track positions or only odd track positions from the sparse codebook; and if the acoustic signal is not a band-limited signal, then using a sparse codebook to generate the excitation waveform, wherein the sparse codebook comprises a set of predetermined possible positions and the sub-sampled sparse code book comprises a subset of the predetermined positions, such that the excitation waveform is generated through placement of pulses within the predetermined positions or the subset; and wherein using the sub-sampled sparse codebook to generate the excitation waveform comprises generating an initial excitation waveform, determining whether the initial excitation waveform comprises mostly odd track positions or mostly even track positions, and decimating the initial excitation waveform to generate the excitation waveform.