HUM That Suddenly Appears

Followed the sound of a HUM that suddenly appeared last night. To my surprise it got louder the further I walked from our house. Turns out HUM comes from the Mall, over 1500 feet away.

When I entered the big parking lot, I could really hear the HUM filling the whole space. Went all the way to the MacDonalds/Walmart entrance, and it probably originates from the roof.

Went home and wrote a HUM emulation in Csound. It appears there are 4 sine wave tones. 2 are at 112Hz and tuned between .5 and 3 cents apart, creating periodic changes in amplitude and 2 are an octave above, with a somewhat higher relative amplitude.

freq     dB
112     82     
112.5  82
224     72    
225     72

It is always there, constantly, 24 hours a day. It does not want to go away.

Listen to an excerpt from "Hum with Birds and Ephemera" (opus 72)