Digital filtering is one of the key techniques in modern audio. In addition to using standard forms of digital filters, audio signal processing has required the development and deployment of special filters, often applied then also in other application fields. This paper presents an overview of some digital filter categories that have been found important in audio reproduction, covering particularly fractional delays, frequency warping techniques including Laguerre and Kautz filters, as well as filters used for physics-based modeling, including wave filters and digital waveguides. Applications of these filter categories to audio reproduction, such as loudspeaker and room response modeling and equalization, are discussed and demonstrated.