2021 Volume 15 Issue 2 Pages 111-120
One of the efforts to preserve a sound environment is regulation by based on the noise level. The noise level is a sensory quantity in which the loudness of the sound is weighted using the characteristics of hearing, but the pitch and/or timbre cannot be evaluated. As the movement to improve the quality of life becomes more active, activities leading to the evolution of the sound environment to a better one will become more vigorons in the future. Therefore, the pitch and timbre are also important factors in the evaluation of environmental sounds. In frequency analysis, the pitch and timbre characteristics can be investigated using the spectrum, but there is no index that represents the waveform characteristics, and it cannot be quantified or evaluated in the same way as the noise level. The authors propose to consider the pitch and timbre as the complexity of the waveform by measuring the complexity as the strength of self-similarity taking advantage of the fact that the fractal dimension can be used for the evaluation. Since the fractal dimension of the waveform can be expressed by one real number, it can be numerically evaluated similarly to the noise level. Previous studies have revealed that complexity can be discriminated by hearing. It is also known that the fractal dimension differs depending on the regional characteristics such as airport and railway lines. In this paper, we introduce an outline of the noise regulation law and its operation, and describe the background focusing on the complexity of waveforms, the method of evaluating complexity using the fractal dimension, analysis examples, and prospects.
