Wind Turbine Noise Recommendations
For average noise exposure, the GDG [Guideline Development Group] conditionally recommends reducing noise levels produced by wind turbines to below 45 dB[A] Lden* [at the most exposed façade, outdoors], as wind turbine noise above this level is associated with adverse health effects.
To reduce health effects, the GDG conditionally recommends that policy-makers implement suitable measures to reduce noise exposure from wind turbines in the population exposed to levels above the guideline values for average noise exposure. No evidence is available, however, to facilitate the recommendation of one particular type of intervention over another.
Download original document: “Environmental Noise Guidelines for the European Region ”
Download the Executive Summary 
*ISO 1996-1:2016 Section 3.6 : Lden is the average of all (12-15 hours of day, 4 hours of evening [if defined], 8-9 hours of night) levels, with evening and night levels weighted: +5 dB added to the evening levels and +10 dB to the night levels.