To provide an attainment method of reduction of an aircraft EPNL value by shift in the sound frequency, reduction of necessary sound correction, or both of them.

A method is provided, for determining the degree of attainment of a selected acoustic wave energy emissions determination criteria by a configuration of a propulsion system, based on acquiring a plurality of acoustic frequency spectra representations of a noise representation of the gas turbine propulsion system over an operating duration. Then, relative peaks in the acoustic frequency spectra representations are located, and the forms of at least one of those peaks is altered with respect to an acoustic frequency, in manners substantially matching acoustic wave energy emission changes corresponding to configuration changes in the propulsion systems which are then evaluated to provide an operating parameter noise value. One of these operating parameter noise values that best meets the selected acoustic wave energy emission criteria is used to aid in determining the corresponding configuration changes to, thereby better meet those determination criteria.