Low-frequency noise app: find the hum
That deep hum through the walls has a frequency, and a pattern. See both live, log them over days, and turn them into a clear report.
What counts as low-frequency noise?
Low-frequency noise (often called LFN) is sound in roughly the 20 to 200 Hz range, and it often comes with infrasound below 20 Hz. It is the deep hum, drone or throb that passes through walls and windows, carries far at night, and is hard to pin down because low sounds seem to come from everywhere. Common sources include heat pumps, furnaces and boilers, air handlers and rooftop fans, transformers, generators, road and rail traffic, and industrial plants.
Why a spectrogram helps
A sound level meter gives one number. A spectrogram shows which frequencies are present and when. That is how you tell a 60 Hz electrical hum from a 30 Hz fan, or prove that a throb starts every night at 11 pm. InfraSound Analyzer shows 0–100 Hz live, marks the 20 Hz infrasound line, and records per-second levels for the infrasound band (1–20 Hz) and the low band (20–95 Hz).
How to track down a hum
- Record a baseline. Open the app in the quietest room when the hum is present. Leave it running for a few minutes.
- Look for steady lines. A continuous horizontal band is a machine. Note its frequency; the event log does this for you.
- Move and compare. Record in other rooms or outside. The level rises as you get closer to the source.
- Switch things off. Turn off your own furnace, fridge or heat pump one at a time. If the line vanishes, you found it.
- Keep a log. Every recording is saved with time, category and notes. Recording at the same times over several days builds a clear pattern.
Making a report for a landlord, council or neighbour
With Pro, one click turns a recording into a clean PDF: spectrogram, level chart over time, detected events, settings and your notes. You can also export WAV audio and CSV/JSON data for an acoustic consultant. Evidence that shows what, when and how often is far more persuasive than "I can hear a hum."
Get better results
Phone microphones lose sensitivity at the lowest frequencies. For hums above about 30 Hz a phone is often enough; for lower frequencies and infrasound, a measurement mic such as the Dayton iMM-6 or miniDSP UMIK-1 makes a big difference. See the microphone guide. Keep the device still, off vibrating surfaces, and out of the wind.
Questions people ask
Is there an app to detect low-frequency noise?
Yes. InfraSound Analyzer runs in your browser and shows 0–100 Hz as a live spectrogram with an automatic event log. It is free to use; Pro adds PDF reports and data exports.
What frequency is a low hum?
Most hum complaints fall between about 20 and 120 Hz. Electrical hum is typically 50/60 Hz and its harmonics; fans, pumps and compressors often sit between 20 and 60 Hz. Some sources also produce infrasound below 20 Hz.
Can I use the recordings as evidence?
The app records time-stamped audio, frequency and level data and can produce a PDF report. Levels are relative, not calibrated, so for formal proceedings pair it with measurements from a calibrated meter or an acoustic consultant.
Why can I feel a hum but my phone barely shows it?
Very low frequencies can be felt more than heard, and phone microphones are least sensitive exactly there. A measurement microphone captures much more of it.
Does it work on iPhone?
Yes. It works in Safari on iPhone and iPad, as well as Chrome, Edge and Firefox on Android and computers. Nothing to install.