Analog Audio Tape Equalization: Why a Time Constant instead of a Corner Frequency?
Obviously, time constant and corner frequency are directly related: FC = 1/(2&pi;&tau;). It's really just a matter of historical convention. When equalization was first invented (for disk recording and FM broadcast, for example), the engineers who came up with those standards preferred to think in terms of time constants. It became the convention that later standards (for tape recording, etc.) also followed.