Sound level means the quantity in decibles measured by a sound level meter satisfying the requirements of American National Standards Specification for Sound Level Meters S1.4-1971. This publication is available from the American National Standards Institute, Inc., 1430 Broadway, New York, New York 10018. Sound level is the frequency-weighted sound pressure level obtained with the standardized dynamic characteristic fast or slow and weighting A, B, or C; unless indicated otherwise, the A-weighting is understood.
40 CFR § 202.10
As used in this part, all terms not defined herein shall have the meaning given them in the Act: