Fig. 3
From: A new approach for analysis of heart rate variability and QT variability in long-term ECG recording
A comparison of different time–frequency (TF) analysis tools on the simulated signal. On the left column, from top to bottom, we show the ideal TF representation, the multitaper (MT) synchrosqueezed spectrogram, the concentration of frequency and time (ConceFT), and the ConceFT superimposed with the ground truth time-varying frequencies of the two components. On the right column, from top to bottom, we show the smoothed pseudo Wigner-Ville distribution (SPWVD), the Choi-William distribution (CWD), the spectrogram, and the scalogram. The ideal TF representation is the ground truth that we would like to recover. It encodes the precise frequency and amplitude of the oscillatory components. Interested reader could read Eq. 4.2 in (1) for details. It is clear that while the dynamics (like time-varying frequency and existence period) can be captured, ConceFT provides a sharper result compared with other approaches