A method of designing parallel‐type pseudo‐minimum‐phase FIR QMF banks
Tsuyoshi Takebe, Tadashi Yoshida · Electronics and Communications in Japan (Part III Fundamental Electronic Science) · 1991
Abstract Subband coding (SBC) is a low bit‐rate speed transmission system in which a quadrature mirror filter (QMF) is used to split a speech into frequency bands of the transmitter and recombine these subband signals to form an approximation to the input speech at the receiver. In the conventional parallel‐type FIR multiband pseudo‐QMF bank, the linear‐phase filters are employed in the transmitter and receiver, which gives rise to a problem wherein a large delay is produced. This paper presents a design method for the equal‐bandwidth parallel‐type QMF bank with smaller delay by allowing some delay distortion. The amplitude and phase constraints on each channel filter are shown so that the transmitted signal can be reconstructed approximately at the receiver. A design example is presented for the 4‐band filter bank, where the amplitude constraint is satisfied by a minimum‐phase filter and the phase constraint is satisfied by a allpass circuit cascaded to the filter. The designed low‐pass filter is of 50 percent roll‐off, and the bandpass filter is a 100 percent roll‐off. The attenuation is 43 dB. The delay is almost flat in characteristic and the amount is reduced to approximately one‐half that of the linear‐phase filter bank.