FFT spectra of the representative 1.5 M_⊙, 1 M_⊙, and 8 M_⊙ models shown in Fig. 5 (st28gm05n023, st28gm06n039, and st34gm02n001) respectively. The FFT power spectra are presented as a function of radial coordinates and frequency (scaled to show the maximum power in between 80–100% of the radius), and with the signal averaged and normalised between the thin layer beneath the stellar radius.