Figure 4
From: An Overview of the Coding Standard MPEG-4 Audio Amendments 1 and 2: HE-AAC, SSC, and HE-AAC v2
Illustration of the mismatch in noise level of the reconstructed high-band if no additional noise information is transmitted to the decoder. This can be used for an analysis-by-synthesis method in the SBR encoder in order to assess the amount of noise that should be added on the decoder side. The upper panel shows the spectrum of the (synthetically generated) input signal, and the lower panel shows a spectrum of the signal obtained after HF generation based on the low-band signal without noise correction. The SBR range covers the frequency range from 5.5 kHz to 15 kHz.