This tool breaks your noise floor into octave bands — the standard way acousticians describe the shape of noise. Each band is one octave wide (its upper edge is double its lower edge), centred on 31.5, 63, 125, 250, 500 Hz, 1, 2, 4, 8 and 16 kHz. For every band the analyzer sums the power in that frequency range from an FFT and reports a level, so you can see whether your noise is dominated by low-frequency rumble, midrange, or high-frequency hiss.
Instead of a jumpy instantaneous reading, it computes Leq — the equivalent continuous level, the average power since you started (or last reset). That’s the meaningful way to characterise steady noise. The per-band powers are calibrated so they sum to the broadband total, which is measured directly from the waveform in dBFS.
Flat (Z) vs A-weighting
Flat (Z) shows the true energy in each band. A-weighting applies the standard curve that approximates how sensitive human hearing is at each frequency — it heavily discounts low frequencies and slightly boosts the 2–4 kHz region. A-weighted noise is closer to how annoying the noise sounds: a floor dominated by sub-100 Hz rumble looks high on the flat view but drops a lot when A-weighted, because you don’t hear low frequencies as loudly.
Reading the result
- Dominant band — the band with the most energy (in the current weighting). Low-band dominance ⇒ rumble/HVAC/handling; high-band ⇒ hiss/fans; a single mid band ⇒ a tonal source.
- Broadband Leq — the overall averaged floor in dBFS. Lower is better; what matters is the gap to your signal.
- A-weighted Leq — the overall floor as perceived. If it’s much lower than the flat figure, your noise is mostly inaudible low-frequency energy.
How this differs from the Background Noise Detector
The Background Noise Detector is the quick consumer check — a single quiet/moderate/noisy verdict plus hum hunting. This analyzer is the technical view: octave-band Leq, A vs Z weighting, and the spectral distribution of your floor. Use that one to spot hum fast; use this one to characterise the noise.
What is Leq and why use it?
Leq is the equivalent continuous level — the constant level that carries the same energy as the fluctuating signal over the measurement period. For steady noise it’s far more stable and meaningful than an instantaneous reading, which is why this tool averages power over time rather than showing a single snapshot. Let it run for several seconds, then read the Leq.
Why dBFS and not dB SPL?
A browser can’t access calibrated sound-pressure levels, so the analyzer measures the digital signal level (dBFS), not acoustic loudness in dB SPL. The shape across bands and the A-vs-Z comparison are meaningful and calibration-independent — but the band shape still reflects your microphone’s own frequency response (most consumer/laptop mics roll off at the low and high extremes), so read it as indicative, not a lab-grade spectrum. The absolute numbers are relative to full scale and depend on your input gain, so don’t read them as room SPL.
What’s the difference between A-weighting and flat?
Flat (Z) shows the actual energy in each band. A-weighting applies a frequency curve matching human hearing sensitivity — discounting lows, slightly lifting 2–4 kHz. A-weighted levels better reflect how loud/annoying the noise is to a listener; flat levels better reveal the physical energy distribution (useful for chasing rumble).
Why are octave bands used instead of a fine spectrum?
Octave bands summarise the noise shape into ten meaningful slices that map to how we describe sound (lows, mids, highs). They’re standard in acoustics, average out the randomness of broadband noise, and make it easy to see which region dominates — without drowning you in thousands of FFT bins. For a fine spectrum, use the Audio Spectrum Analyzer.
Should I stay silent during the measurement?
Yes — the point is to characterise the noise floor, the level when nothing is happening. Any speech or sound you make is averaged into the Leq and will skew the result. Stay quiet; if you accidentally make noise, press Reset average and start again.
My low bands are very high — is that bad?
Not always. Low-frequency energy (rumble from HVAC, traffic, handling) is common and often inaudible, which is why it shrinks under A-weighting. If the A-weighted figure is acceptable it may not matter for listening — but it can still eat headroom and trip up compressors, so a high-pass filter is often worthwhile.
Does it disable noise suppression?
Yes — it requests the raw signal with noise suppression and auto-gain off so you measure the true floor. If your OS forces processing that can’t be disabled, the bands will look artificially clean; turn off microphone "enhancements" in system settings for an accurate analysis.
Is any audio recorded?
No. The signal is analyzed in real time to accumulate band-power statistics only; nothing is recorded, saved, or transmitted. The microphone is released when you press Stop or close the tab.