runngezhang / amplitude-modulation-analysis-matlab

Amplitude Modulation Analysis Toolbox for MATLAB / Octave

Amplitude Modulation Analysis Toolbox

The Amplitude Modulation Analysis Toolbox, for MATLAB / Octave, provides functions to compute and visualize the time-frequency and frequency-frequency domain representations of real signals.

The Toolbox includes a GUI implementation, which facilitates the exploration of the amplitude modulation by allowing changing parameters online.

In summary, the frequency-frequency representation of a signal is computed by performing two transformations:

1. Time domain (real signal) to time-frequency (spectrogram)
2. Time-frequency (spectrogram) to frequency-frequency (modulation spectrogram)

Signal processing steps involved in the calculation of the modulation spectrogram from the amplitude spectrogram of signal. The block |abs| indicates the absolute value, and the FT indicates the use of the Fourier transform.

This Toolbox provides two implementations for the time to time-frequency transformation, one based on the short-time FFT (STFFT) and the other on the continuous wavelet transform (CWF) using the Complex Morlet wavelet. The time-frequency to frequency-frequency transformation is carried out with the FFT.

Examples

Besides the functions to compute and visualize the frequency-frequency representation of real signals, example data and scripts are provided.

Example 1: example_01.m

This example shows the usage and the commands accepted by the high level GUI to explore Amplitude Modulation in ECG and EEG data. The GUI can be called with the functions: explore_strfft_am_gui() which uses STFFT, and explore_wavelet_am_gui() based on wavelet transformation. Further details in their use refer to the comments in example_01.m.

STFFT-based amplitude modulation analysis GUI

CWT-based amplitude modulation analysis GUI

Example 2: example_02.m

This script shows presents the details in the usage of the low level functions to carry on the signal transformations, as well as plotting functions. Refer to the comments in example_02.m