Ormsby filter

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A filter of trapezoidal shape specified by four corner frequencies, f 1, f 2, f 3, f 4. The filter rejects below f 2 and above f 3, is linear from f 1 to f 2 and from f 3 to f 4, and flat from f 2 to f3.