Time frequency distributions of TMJ sounds

Summary For analysis of time‐varying signals such as the TMJ sounds, it is often desirable to know how the frequency components change with time, using methods of time‐frequency analysis. The aim of this study was to compare two of the most familiar methods for energy density representation with a newly developed technique. The sounds were recorded with a microphone fastened to the subject's forehead, transformed to the time‐frequency domain and displayed as 3D‐ and contour plots using spectrogram, Wigner distribution (WD), and the reduced interference distribution (RID) to display their time‐frequency energy distributions. The spectrogram resolved only the low‐frequency components. The WD provided higher resolution but also exhibited strong interference between components. The RID gave a detailed representation of the TMJ signals' relative energy distribution in the time and frequency domains, with a great reduction in the interference or cross terms. The RID therefore appears to be most useful in the application of time‐frequency distributions in classification of TMJ sounds.