From a digital signal processing perspective, we have described the EMD algorithm as a time-varying multirate signal processing system.

We have described spline interpolation for knots spaced nonuniformly by a time-varying interpolation with a time-varying spline filter.

We have depicted IMFs as the output of spline filters in time domain by using a matrix formulation.

We have presented a general expression for the EMD algorithm with extrema spaced nonuniformly.