Infrasound Frequency Detector
Specialized detector for frequencies below 20 Hz. Identify Schumann resonance (7.83 Hz), seismic activity, wind turbine infrasound, thunder, ocean waves, and building sway. Features long-duration recording, slow waveform display, energy-over-time tracking, and source identification.
Infrasound Frequency Detector Tool
| Source | Frequency | Notes |
|---|---|---|
| Ocean waves | 0.05–0.5 Hz | Microbarom, ocean–atmosphere coupling |
| Building sway | 0.1–1 Hz | Tall structures in wind, seismic response |
| Thunder | 1–3 Hz | Low rumble component, storm proximity |
| Wind turbines | 1–5 Hz | Blade-pass frequency, felt not heard |
| Seismic activity | 1–10 Hz | Earthquakes, volcanic tremor |
| Schumann resonance | 7.83 Hz | Earth–ionosphere waveguide, ~7.83 Hz fundamental |
| Industrial machinery | 5–15 Hz | Large engines, compressors, turbines |
| Explosions / sonic booms | 0.5–10 Hz | Blast waves, re-entry vehicles |
| Avalanche / landslide | 1–5 Hz | Large mass movement events |
| Severe weather | 0.5–5 Hz | Tornados, hurricanes, microbursts |
| Time | Peak Hz | Level dB | Likely Source |
|---|
How to Use the Infrasound Frequency Detector
Connect a Low-Frequency Sensor
For real infrasound detection, connect a measurement microphone, accelerometer, or specialized infrasound sensor. Built-in laptop and phone microphones filter out frequencies below 80 Hz and cannot capture true infrasound.
Start Long-Duration Listening
Click "Start Listening" and grant microphone access. Infrasound events are often intermittent — leave the detector running for extended periods to capture transient events like seismic activity or wind turbine pulses.
Read the Infrasound Display
The large Hz number shows the dominant detected frequency below 20 Hz. The Source Identification card matches the frequency against known infrasound sources including Schumann resonance, seismic waves, and industrial machinery.
Analyze the Slow Waveform
The 10-second waveform shows slow pressure variations characteristic of infrasound. The Energy Over Time chart tracks infrasound energy across 60 seconds for spotting periodic events.
Export Your Data
Use Export CSV to download the event log with timestamps, frequencies, and source identifications for analysis or documentation.
Understanding Your Results
Frequency Ranges
Infrasound occupies the frequency range from approximately 0.001 Hz to 20 Hz. This tool focuses on the 0.5–20 Hz range, which covers the most commonly encountered natural and man-made infrasound sources. Frequencies below 0.5 Hz require extremely long recording windows and specialized equipment beyond what browser-based audio can provide.
Source Identification Confidence
Source matching is based on frequency overlap with known infrasound sources. Multiple sources can produce similar frequencies, so the identification should be treated as a suggestion rather than a definitive diagnosis. Environmental context (proximity to wind farms, geological activity, industrial sites) is essential for accurate identification. For long-term monitoring, running this tool as a continuous infrasound monitor with CSV export lets you build a dataset for deeper infrasound analysis over hours or days.
Level Readings
Decibel values shown are relative to the microphone's sensitivity and are not calibrated sound pressure levels. For calibrated infrasound measurements, professional equipment with known sensitivity curves is required. If you need to measure the dominant frequency across the full audible spectrum rather than just the infrasound band, the peak frequency detector identifies the loudest frequency from 20 Hz upward with A-weighting and noise diagnostics.
Technical Background
Infrasound — sound below the threshold of human hearing at 20 Hz — permeates our environment from both natural and artificial sources. Low frequency vibration in this sub-20 Hz band travels through walls, soil, and water with little absorption, which is why it is so hard to isolate or block once it enters a building. The Earth’s atmosphere acts as a waveguide for infrasound, allowing these extremely low frequencies to propagate over thousands of kilometers with minimal attenuation. This property makes infrasound monitoring valuable for detecting volcanic eruptions, nuclear tests, meteorite entries, and severe weather events at great distances. Unlike audible sound, infrasound is felt rather than heard — perceived as pressure changes, vibrations, or a vague sense of unease. To understand how these frequencies compare to bass and sub-bass audio, the sub-bass frequency detector covers the adjacent 20–100 Hz range where infrasound transitions into audible low-frequency sound.
FFT Configuration for Sub-Hz Resolution
This tool uses an FFT size of 32,768 samples, the maximum supported by the Web Audio API. At a typical sample rate of 48 kHz, this yields a frequency resolution of approximately 1.46 Hz per bin (48000 / 32768). While this is adequate for identifying infrasound sources in the 1–20 Hz range, true sub-Hz resolution would require even longer analysis windows. The tool applies parabolic interpolation around peak bins to refine frequency estimates beyond the raw bin resolution.
DC Offset Removal
FFT bin 0 represents the DC component (0 Hz) of the signal — a constant offset with no oscillation. This tool explicitly ignores bin 0 during peak detection to prevent DC bias in the microphone signal from being misidentified as an infrasound frequency. Analysis begins at the lowest bin that corresponds to a frequency above 0.5 Hz.
Microphone Limitations
The most significant challenge in browser-based infrasound detection is hardware. Consumer microphones — particularly MEMS microphones in laptops and smartphones — incorporate high-pass filters with cutoff frequencies typically between 50–200 Hz. Even professional condenser microphones rarely extend flat response below 20 Hz. True infrasound measurement requires specialized equipment such as microbarometers, infrasound microphones with extended low-frequency response, or accelerometers coupled to the measurement surface. The device compatibility check in this tool evaluates whether your microphone shows any energy in the infrasound band, but the absence of detected infrasound does not necessarily mean it is not present — it may simply be below your hardware’s sensitivity.
Frequently Asked Questions
Can my phone or laptop microphone detect infrasound?
In most cases, no. Built-in MEMS microphones in phones and laptops have high-pass filters that remove frequencies below 80–200 Hz. Any readings below 20 Hz from consumer hardware are likely noise floor artifacts rather than real infrasound. For genuine infrasound detection, you need a measurement microphone, microbarometer, or accelerometer.
What is the Schumann resonance and can this tool detect it?
The Schumann resonances are electromagnetic resonances in the cavity between Earth’s surface and the ionosphere, with a fundamental frequency of approximately 7.83 Hz. These are electromagnetic, not acoustic phenomena and cannot be detected with a microphone. However, some acoustic sources in the same frequency range may appear at similar frequencies.
Why does the detector show "Device may not support infrasound" warning?
The tool checks whether your microphone produces any meaningful signal energy below 20 Hz. If the infrasound bins show only noise-floor-level readings, the warning indicates your hardware likely filters out these frequencies. This is normal for consumer microphones.
Can infrasound be harmful to health?
At very high levels (above 110–120 dB), infrasound can cause nausea, disorientation, visual disturbances, and organ resonance effects. At typical environmental levels, infrasound is generally harmless but may contribute to feelings of unease or anxiety in sensitive individuals. Prolonged exposure to moderate infrasound from sources like wind turbines is an active area of research.
What FFT size is needed for infrasound analysis?
The maximum FFT size in the Web Audio API is 32,768 samples. At 48 kHz sample rate, this gives ~1.46 Hz resolution per bin. For sub-Hz resolution, you would need an FFT size of 65,536+ or overlapping analysis windows, which exceeds current browser capabilities. This tool uses parabolic interpolation to refine estimates within the available resolution.
Is my audio data safe?
All processing runs 100% in your browser. No audio is recorded, stored, or transmitted to any server. The tool works entirely offline once loaded.
Can I use an accelerometer instead of a microphone to detect infrasound?
Yes, and for true infrasound detection it is often superior. Accelerometers and vibration sensors measure structural movement rather than air pressure, bypassing the high-pass filter built into MEMS microphones. If your accelerometer presents as a standard audio input device, this tool can analyze its output. Connect it via a USB audio interface, set sensitivity appropriately, and the infrasound spectrum display will show the vibration spectrum. For pure structural infrasound monitoring — building sway, seismic tremor, or machinery vibration — an accelerometer will give far more reliable sub-20 Hz readings than a consumer microphone.
Why do wind turbines produce infrasound, and how far does it travel?
Wind turbine infrasound is generated primarily by the blade-pass frequency — the rate at which each blade passes the tower, typically 1–5 Hz for utility-scale turbines. At this frequency, infrasound propagates with very little atmospheric absorption and can be detected kilometers from a wind farm. Regulatory bodies in several countries require infrasound impact assessments near residential areas. Research into whether wind turbine infrasound causes health effects is ongoing and contested; current evidence points to high-level exposure rather than typical residential distances as the threshold for physiological effects.
How do professional infrasound monitoring networks detect events like nuclear tests?
The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) operates a global infrasound monitoring network of over 60 stations. Each station uses an array of microbarometers — highly sensitive differential pressure sensors — spaced tens to hundreds of meters apart. Array processing techniques (beamforming) allow the network to determine the direction of arrival and apparent velocity of infrasound wavefronts, distinguishing nuclear tests from natural sources like volcanic eruptions and large meteor entries. These professional instruments operate in the 0.01–10 Hz range with flat, calibrated response — capabilities far beyond browser-based audio tools, which is why this detector is explicitly limited to educational and hobbyist use.
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