The range of audibility of the human ear can be represented as a graph of sound intensity versus frequency. The lower boundary of the range is the threshold of hearing: for example, at a frequency of 256 vibrations per second (middle-C on the musical scale), a sound must have a intensity level of about 20 decibels (the loudness of rustling leaves) to be heard at all. The upper limit of the range of audibility is the threshold of pain. At the frequency of middle-C the limit of pain has an intensity level of about 130 decibels, slightly less than the sound of a leaf blower at close range.
Think of the graph of human audibility as a blank canvas upon which nature paints with sound. For example, the shrill double-note of the blue jay (three-tiered in frequency, at 3000, 2000, and 1000 vibrations per second, repeated twice), and the cacophonous caw of the crow (between 1000 and 2000 vibrations per second), add dollops of color to the canvas in the mid-decibel range. The chickadee's call is more sharply defined in frequency (at about 2800 vibrations per second), but can range widely in loudness depending on the distance of the bird. The nuthatch fills in the low-decibel part of the graph with its tap-tap-taps and a loudness in a conifer forest just above the threshold of hearing. There are other natural sounds that can only be heard in the complete absence of noise: the papery shiver of beech leaves on their branches, the ethereal whir of mourning doves rising from the ground, the rattle of the seedpods of wild indigo when stirred by the wind.
The roar of a leaf blower -- or trail bike or snowmobile -- is the equivalent of throwing a bucket of black paint onto the ear's white canvas.