Sounds in our Life
Below I record some screenshots of data taken with VisualAudio on my iPhone X in various settings. I have been interested in sounds for a long time, but recently got so annoyed at a recent hotel room that I decided to do some measurements. You see, the room at this very popular hotel in Hangzhou, China had a most annoying ringing sound in the background. I didn't make much of it at first, as I had checked in late at night after 17 hours of flights and just went right to sleep. However, in the morning I immediately noticed this audible frequency and couldn't ignore it, making it impossible to concentrate on anything of importance. Even mediation was impossible, as it felt as if someone were driving a tuning fork into the back of my head. So I pulled out my phone and decided to see what the culprit was. Immediately in the top row of figures below, you see there is a pronounced frequency at about 220Hz, roughly a lower-A on the piano, smack in the middle of human hearing range. Moving about the room and into the hallway, I looked to maximize the signal, ending up next to the elevator which adjoined my room. Indeed, the elevator shaft was continuously emitting this frequency. Needless to say, I showed these plots to the hotel staff, who were noticeably aghast -- though either at the fussiness of the guest or the precision of the complaint, I cannot say -- and switched my room to one further down the hall, away from the elevator. When I returned to the U.S. I started thinking whether these sounds actually exist all the time and we simply don't notice. Was I perhaps really being a persnickety foreign guest, when in fact various machines and instruments are playing A's, C#'s, and who knows what else all the time around us? Afterall, the overall noise level in the room was quite low (~51 dB, see first plot), on par withe "average home" according to VisualAudio. Thus I went investigating. First in my relatively quiet house ("deathly quiet" to my Chinese wife, who often pines for the hustle and bustle of the mother country). Surprisingly, it is just as noisy (or even more so) as the hotel room at 52 dB (second row of plots). However the spectrogram shows no weird peaks, aside from a barely audible whir of distant highway traffic, alas so unavoidable in suburbia. Next, I went on to the park nearby where I like to do Tai-chi due to the relative isolation and quiet immersion in nature. That day I was the only one there, in a gazebo perched high up on a hill, with only a few park maintenance workers weeding here and there. Perhaps it wasn't surprising this was slightly more noisy than at home, being exposed in the open air and all, and measured 54 dB (third row of plots). And the spectrogram was again very flat, except for the occasional bird chirp, some of which apparently are so high frequency I cannot hear them, but you can clearly see and hear the one at ~2200Hz (far end of the piano keyboard). My experiments there were cut short by one of the park workers turning on a buzzsaw, which of course wrought all havoc on the spectrogram (fourth plot).
So what do I conclude from this? I believe I was right to complain about the background frequency in the hotel room. Such intense frequencies really aren't natural and common in our everyday lives.
|Hotel room in urban China, noise level acceptable by industry standards.||Piercing frequency dominates the spectrum. Later I discovered this was from the elevator next door.||Here we see the elevator frequency truly stands out.||Most sound energy is low band.|
|Noise levels in my quite suburban residence. Nominally louder than the hotel room!||Spectrogram is fairly flat; the line near ~120Hz is actually distant thruway traffic.||Very few frequencies go above 20db.||Sound energy is spread over whole spectrum.|
|Noise levels in a quiet park, which was empty aside from me and a few park employees.||Spectrogram is again fairly flat; bird chirps appear perdiodically at higher frequencies.||Fairly broad spectrum. We see a bird chirp at ~2200Hz||Once one of the park employees turned on a buzzsaw, all hell broke loose in the spectrum.|