Active removal of wind noise from outdoor microphones using local velocity measurements

Abstract

Wind noise in outdoor microphone measurements can significantly degrade acoustic data. An outdoor active windscreen based upon four local anemometer velocity measurements applied to an unscreened microphone is demonstrated. A simple relationship, developed from the Bernoulli equation, is used to transform hot-film anemometer wind velocity measurements into microphone wind pressure estimates. Measurements performed outdoors on a horizontally positioned microphone demonstrate that a major part of unscreened microphone wind noise is flow noise caused by interaction between the microphone and adjacent air flow. These measurements also indicate that the dominant source of wind noise in a passively screened microphone are local pressure fluctuations that are not correlated with local velocity fluctuations. This important observation indicates that the active windscreen is unlikely to significantly quiet a microphone that has conventional passive screening and that the active windscreen applied to an unscreened microphone is unlikely to surpass the performance of a passive windscreen. Wind energy reduction performance of the active windscreen is shown to be approximately 12 dB for frequencies below 200 Hz and decreases smoothly to approximately 5 dB at 500 Hz. In addition, the active system transfer functions are observed to possess significant stability of over periods of hours. a)Currently at Texas Instruments. b)Currently at California Maritime Academy.