Separation of fine crackles from vesicular sounds by a nonlinear digital filter.

Crackles are discontinuous adventitious sounds, and their separation is an important process in the analysis of lung sounds. In order to separate the crackles from vesicular sounds automatically, we used a nonlinear digital filter which was designed to separate nonstationary from stationary signals. We applied this filter to the lung sounds recorded from six patients with pulmonary fibrosis. The separation was satisfactory enough to make this method useful in clinical medicine.