Oversampling complex-modulated digital filter bank pairs suitable for extensive subband-signal amplification

Oversampling, complex-modulated digital subband coder filter banks are commonly adopted in modern hearing aids to allow for individual amplification of subband signals in order to compensate for hearing losses of impaired persons. Minimum power consumption and low group delay have been the main concern in the design of these filter banks. Guaranteeing frequency-independent and low group delay in case of subband-signal amplification has, however, been neglected in the past. In this contribution, we investigate the delay and amplification properties of oversampling complex-modulated FIR filter banks in case of extensive subband signal amplification. Based on these results, a sufficient condition for constant group delay is derived. Furthermore, we present a compensation method which allows for constant group delay, even if the sufficient condition is violated. An illustrative design example demonstrates the potential of the compensation method.