Application of a low-delay bank of filters to speech coding

Applies an FIR QMF filter bank to compute the long-term prediction in a CELP coder. By splitting the frequency spectrum of the past excitation signal, a different pitch lag and gain factor can be attached to each frequency band. This strategy improves the quality of the synthetic speech, providing much more natural sounding voice. The filter bank must be designed to abide by some requirements related to low and nearly-constant group delay and band aliasing, rather than to accomplish perfect reconstruction of the output signal. In the design, which employs two-band splitting, the authors have relaxed the usual condition of linear-phase in favor of achieving less aliasing between bands