Time-domain synthesized pressure signal. (a) temporal envelope (black) and blowing pressure parameter γ (red). (b) Normalized spectrogram (dB) with regime names indicated (unstable ones between parentheses): equilibrium (Eq.), second register, quasi-periodic and first register. The signal is extracted from the same blowing pressure ramp as in Figure 4, between γ = 0.45 and γ = 0.51 (at first occurrence of oscillation).