  Since Paul Leug's 1933 patent application for a system for the active control
of sound, the field of active noise control (ANC) has not flourished until the
advent of digital signal processors forty years ago. Early theoretical
advancements in digital signal processing and processors laid the groundwork
for the phenomenal growth of the field, particularly over the past
quarter-century. The widespread commercial success of ANC in aircraft cabins,
automobile cabins, and headsets demonstrates the immeasurable public health and
economic benefits of ANC. This article continues where Elliott and Nelson's
1993 Signal Processing Magazine article and Elliott's 1997 50th anniversary
commentary on ANC left off, tracing the technical developments and applications
in ANC spurred by the seminal texts of Nelson and Elliott (1991), Kuo and
Morgan (1996), Hansen and Snyder (1996), and Elliott (2001) since the turn of
the century. This article focuses on technical developments pertaining to
real-world implementations, such as improving algorithmic convergence, reducing
system latency, and extending control to non-stationary and/or broadband noise,
as well as the commercial transition challenges from analog to digital ANC
systems. Finally, open issues and the future of ANC in the era of artificial
intelligence are discussed.
