Summary and Conclusions

The theory of nonstationary filtering allows great flexibility in the design and application of time-variant filters. We can choose among three different domains of application: time, frequency and mixed and we can also choose between convolution and combination. From the results shown and from many other tests that I performed I drew the following conclusions:

1.

Time domain should be preferred when filtering with ``blocky'' spectra, that is, when the filters are kept constant in each window and change abruptly from window to window.

2.

Frequency domain should be preferred when using filters that change from sample-to-sample.

3.

The mixed domain should only be used when filtering a few traces because of its large run-time.

4.

As a general rule, non-stationary combination is preferable to non-stationary convolution when the filter spectrum changes abruptly from one sample to the next. For slowly changing spectrum, non-stationary convolution is probably better.