Vectors are quantized by representing the vectors by quantized values using a codebook having granular regions which are based on a coset code, and which lie inside a boundary region which is based on another coset code, the boundary region being other than an N-cube and other than the Voronoi region of a sublattice .LAMBDA..sub.b =M.LAMBDA..sub.g of a lattic .LAMBDA..sub.g upon which the granular regions may have been based.