IEC Acoustic Standard IEC 61400-11

Tonality
To begin
– Two minutes of FFT spectra data closest to the integer wind speed
for turbine and background
– Turbine narrowband analysis use 10-second spectra
– Background spectra are energy averaged into one spectrum for
use later in the turbine analysis
– For each turbine 10-second spectrum identify possible tones. For
each possible tone:
• Determine critical bandwidth
• Classify spectral lines in the critical band
• Determine tone level
• Determine masking level and correct for background
• Determine tonality
• Determine if the tone is reportable or “audible”
NATIONAL RENEWABLE ENERGY LABORATORY