Coherence as an Indicator of Distortion for Wide-Band Audio Signals such as M-Noise and MusicM-Noise™ is a new scientifically derived test signal whose crest factor as a function of frequency is modeled after real music. M-Noise should be used with a complementary procedure for determining a loudspeaker’s maximum linear SPL. The M-Noise Procedure contains criteria for the maximum allowable change in coherence as well as frequency response. When the loudspeaker and microphone are positioned as prescribed by the procedure, reductions in coherence are expected to be caused by distortion. Although higher precision methods for measuring distortion exist, coherence has the advantage that it can be calculated for wide-band signals such as M-Noise as well as music.

The introduction above is an abstract of an AES Engineering Brief written by myself and Roger Schwenke presented at the 147th AES 2019 Convention in NYC which can be downloaded for free (Open Access) at www.aes.org.