New narrowband active noise control systems requiring considerably less multiplications

In a conventional narrowband active noise control system, a two-weight FIR-type magnitude/phase adjuster (MPA) is used as an adaptive controller in each frequency channel, and is updated by the so-called filteredx LMS (FXLMS) algorithm. Each reference cosine wave has to be filtered by an estimated secondary-path with order M̂ before it is fed to the FXLMS. We call this part x-filtering block. The number of x-filtering blocks is equal to the number of targeted frequencies (q). When q and M̂ become larger, the computational cost of the system due to x-filtering operations may form a bottleneck in implementation. In this paper, we propose a new narrowband ANC system structure which requires only one x-filtering block regardless of q. All the cosine waves are combined as an input to a x-filtering block whose output is decomposed by an efficient bandpass filter bank into filtered cosine waves for the FXLMS that follows. As a result, the computational cost of the system may be considerably reduced. The new structure is also implanted in a recently developed ANC system that is capable of mitigating the frequency mismatch (FM). Simulations demonstrate that the new systems present performance very similar to that of their counterparts, but enjoy considerable advantages in implementation.