LSP Quantization by a Union of Locally Trained Codebooks

We present a fixed rate encoding scheme for the line spectrum pair (LSP) representation of an LPC-filter, based on Gaussian mixture (GM) modeling. For each mixture component, we construct a codebook by a union of product quantizers. Each local codebook is trained, independently, using a clustering scheme similar to the generalized Lloyd algorithm (GLA), over synthetic data. The training algorithm iterates fast, due to low complexity encoding, and converges in few iterations. The overall codebook is a combination of local codebooks, and inherits their high performance, while having a moderate complexity. We provide numerical results for average spectral distortion (SD) of the proposed encoder, and benchmark them by a lower bound, according to high-rate theory. We achieve an average SD (full-band measure) of 1 dB at 23 b/frame, for speech signals sampled at 8 kHz and LPC of order 10. By tolerating additional complexity, we reach a SD within 0.01 dB of the lower bound.