Perhaps I should point out that the third and fourth harmonics in that diagram are 15 dB below the chosen formant, while still higher formants are 35dB down. In each case I am taking the peak magnitude of the second harmonic as the reference. Recall that 15dB down is lower than NORMAL +72 dBA conversation level, so 35dB down at about +50dBA is hardly worth considering. The calibration marks are 10dB steps with zero at the base-line and +100 dB at the top. Reg.