A gap of 15 dB or more suggests the sound is mostly low frequency, the part dBA turns down.
Dashed lines: 65 dB at 31.5 Hz and 70 dB at 63 Hz. A note in ANSI S12.9-2005 Part 4 (Annex D) said low-frequency annoyance is generally minimal below these levels; the 2021 revision dropped it and its committee could not trace where the method came from. Shown for orientation only; any real comparison needs a Type 1 or 2 meter at the property line.
Calibration (uncalibrated)
Uncalibrated, readings are only good for comparing nights with each other. With a sound calibrator or a trusted meter, play a steady sound and move this until both agree.
For a miniDSP UMIK-1 or UMIK-2: use the 90 degree file and point the mic up. The file corrects the mic's frequency response.
Turn off OS mic processing (Voice Isolation on Mac, audio enhancements on Windows). It can filter out the rumble you are trying to log.
Your log
0.0 hours stored in this browserThe trend appears after a couple of minutes of logging.
| Night of | Hours | LAeq | LCeq | C minus A | LA90 | 31.5 Hz | 63 Hz |
|---|---|---|---|---|---|---|---|
| Nothing logged yet. Nights run 10 pm to 7 am; anything logged outside that shows as this session. | |||||||
Diary
Write it down when you notice it. Times go on the log next to the readings.
Ask for a proper measurement
Print a noise log with your nights, diary and a letter asking your noise or code enforcement office to measure at night with a Type 1 or 2 meter, C-weighting and octave bands. Fill in your name and address, then send it with the CSV.
No audio or readings leave your device. We count button clicks.
Data center noise FAQ
Why does a normal decibel reading miss the hum?
Most meters and most noise ordinances use A-weighting (dBA), which copies how the ear hears quiet sounds and turns down low frequencies hard: about 26 dB at 63 Hz and 39 dB at 31.5 Hz. A transformer or chiller hum can be loud enough to keep you awake and still read low in dBA. C-weighting barely discounts it, so a big gap between the C and A readings suggests the sound is mostly low frequency.
Is this accurate enough to get a citation?
No, and it is not meant to be. Ordinances are enforced with a Type 1 or Type 2 meter run by an officer, usually at the property line. A browser and a built-in mic should be treated as roughly ±5 to 10 dB and unreliable below about 100 Hz. What this log is good for is showing when the sound happens and what kind of sound it is, so you can ask the city or county to come and measure properly, at night, with C-weighting and octave bands.
Phone, laptop or a USB measurement mic?
Built-in mics in phones and laptops roll off low frequencies, which is the part you care about. A USB measurement mic such as a miniDSP UMIK-1 (about $100) has much better low-end response, and its calibration file corrects that response here. Its level is only as good as the offset: with input volume at 100%, use the suggested offset from the file, or better, set it against a sound calibrator. Done that way, expect roughly ±1 to 2 dB. Use the 90 degree calibration file and point the mic at the ceiling or sky. Set your computer's input volume to 100% and turn off any OS mic enhancements (Voice Isolation on Mac, audio enhancements on Windows), which can filter out rumble.
Where should I put the microphone?
Noise limits are almost always measured outdoors at your property line, so that is the most useful position if you can do it safely (a window ledge facing the source is a reasonable compromise). Indoor readings are still useful for the diary, but pick the position honestly; it is stamped on every reading and printed on the log.
Does this record me?
No audio is recorded or stored. Each second, the page keeps only the sound levels: one A-weighted and one C-weighted number and nine octave-band numbers. They stay in this browser until you export or clear them. We count button clicks (like starting a log or printing a report), never readings or audio.
Can it measure infrasound?
No. Browser audio and consumer microphones do not capture meaningful energy below about 20 Hz, and this tool ignores everything under 10 Hz. Felt vibration goes in the diary.
What do I do with the noise log?
Print it or save it as a PDF, fill in your name and address, and send it to your city or county noise or code enforcement office along with the CSV. It asks them to measure at night with a proper meter. Get your local ordinance text first: most limits are in dBA at the property line with a lower night limit, and some states, New Jersey for one, also set octave-band limits.
Just want a quick reading? Try the decibel meter or the spectrum analyzer.