12-10 824 Reference Manual 9/29/09• The window must be in Hanning mode after an overallreset. If not, “Available only in Hanning Window” isshown.• The fundamental must be above the 4 th bin or 10 Hzwhichever is higher. In the case where the fundamentalfrequency is near the 5 th bin and it’s skirt extends intosome or all of the first four bins, the fundamental energysum calculation will include only the 3rd and/or 4 th binsbut not the 1 st or 2 nd bin. In any case the noise energy sumcalculation will never include the first four bins.• The fundamental must be higher than any of the first fourbins. There must not be excessive DC or near DC levels.• THD+n must be at least 10 dB below the fundamentallevel. There must be an identifiable tone.• The fundamental frequency will be displayed whetherthere is an identifiable tone or not.• If a harmonic is less than 10 dB above the noise floor, thelevel of the harmonic is marked with an asterisk. Thenoise floor is calculated as the maximum of theminimum in the two adjacent valleys.• If one of the harmonic’s side-bands is higher than theharmonic then the harmonic is marked with an asterisk.THD Check MenuPressing the Check c key while in the “THD” display putsyou in the check menu. The check menu is shown below:The check menu offers the following options:• View FFT - Takes you back to the FFT display
