Efficient Digital Filters with Variable Cut-off Based on All-pass and Sharpening Digital Filters

All-pass digital filters are known as excellent prototype filters in many applications, such as control systems, signal processing and communications. Efficient filters can be designed because transfer function is very robust to small element changes. The drawback of digital filters based on all-pass filter sections is that they are not suitable for tuning and the design of filters with variable cut-off frequency. In this paper there is proposed a new design method suitable for the design of filters that may satisfy different attenuation specifications and variable cut-off based on low-order wave digital filters. The method is derived using computer algebra system.