Non-functional tube radio warming up, making a loud 60hz hum with lots of harmonics. As a bonus it clicks off at the end. Zenith consoltone. Only because the faq says so: electro voice n/d 257a through impedance transformer into crappy gigabyte motherboard realtek high definition audio. 16bits, processed at 32bits. Audacity sound editor and/or driver wouldn't record mic level so it was very noisy after amplification. Filtered with a (mathematically equivalent) fft constructed whopping 64k length zero phase filter (blackman window) with 5 wavelength width bandpass at each harmonic from 60hz to 5,520hz. For some reason a fraction of some of the harmonics didn't get through so did another pass on the residual noise and mixed that in. Near the beginning there was a sort of brief duplicate signal that descended in pitch so it didn't make it through the filter. I added that bit in. Attenuated frequencies above 3. 6khz because they are pretty much noise, but removing them didn't sound right. Cleaned up the beginning a bit in various ways, cut it down to 15 sec and carefully appended the unfiltered "click" onto the end, which i denoised 12db with audacity's noise reduction.
Author: Hetanoyokozuki
