Efficient signal coding with hierarchical lapped transforms

The hierarchical lapped transform (HLT) is defined. It is based on the modulated lapped transform (MLT). The HLT has a much lower computational complexity than a tree-structured QMF filter bank, and so with HLTs a much larger number of bands can be used in practice. The coding gain of HLTs is close to that of a full-length MLT, for the same number of bands, and therefore there is no significant loss of coding efficiency. With HLTs transient signals can be better reconstructed than with nonhierarchical transforms, as demonstrated by speech and image coding examples. In image coding applications, the HLT can also be used for progressive transmission