Figure 3
From: An Overview of the Coding Standard MPEG-4 Audio Amendments 1 and 2: HE-AAC, SSC, and HE-AAC v2
T/F grid selection example. The white dashed lines illustrate the borders of the time-frequency tiles superimposed on the spectrogram of the input signal. The leading edge and decay of the transient is encoded with short low frequency resolution envelopes, and the quasistationary passages in between transients are represented by longer high-frequency resolution envelopes.