An efficient algorithm for the evaluation of tonality and the determination of the tonal frequency according to IEC 61400-11

The terms of tonality and tonal audibility of the noise emitted by wind turbines are defined and described in the standard IEC 61400-11. The procedure for tonality assessment at different wind speeds based on the narrowband analysis is explained in section 9.5 of the standard. After sorting spectra into wind speed bins, the overall tonal audibility is determined if at least six of ten of the narrowband spectra have an identified tone with the same origin. The standard describes a procedure for tonality assessment by means of a flowchart. Tones of the same origin are treated and reported as one tone. However, the standard does not specify the final value of the frequency of the tone. An efficient algorithm has been developed to evaluate the tonality of the noise emitted by wind turbines. Likewise, different alternatives to specify the final frequency of the tone are discussed, based either on their frequency of appearance in the total of the number of measurements or on the tone levels produced by such frequency.