ESDU 98008 provides a means of estimating the noise generated by fans or compressors in turbojet and turbofan engines@ with and without inlet guide vanes. Sound pressure levels in one-third octave bands in the frequency range of 50 Hz to 10 kHz are calculated for lossless@ free-field@ still ambient conditions. OASP and dBA values are calculated as well. The main input parameters that need to be specified are the mass flow rate@ the total temperature rise associated with a fan stage@ both the design point and the operating point values of the rotor tip relative inlet Mach number and certain data about the fan geometry. Noise from the inlet and the exhaust ducts are considered separately. Up to five fan stages can be considered. Two computer programs are provided@ A9808 and B9808. Program A9808 provides the user with a means to estimate fan noise. Program B9808 can be used to help the user generate input files easily.