An MLS coherence function and its performance in measurements on time-varying systems

A new MLS coherence function has been developed and tested in various room acoustic measurements. The new measure, which takes values between zero and unity just as the ordinary coherence, can be used only if averaging over several periods of the MLS signal is carried out. It indicates possible contamination by extraneous noise in the same manner as the the ordinary coherence function does in measurements with FFT analysers.

It is also very sensitive to disturbances such as reflections caused by moving surfaces during the measurement. Very weak time-variance effects caused by a small change in the temperature are also reflected in reduced coherence.