Measure Noise in Your Browser: Real-Time dB with an Online Sound Level Meter (dBA/dBC, FFT, Calibration)

No installs. No plugins. Open your browser, allow the mic, and start measuring.
Try it now: https://soundlevelmeter.org/

When you need to answer “How loud is it right now?”—whether for apartment noise, classrooms, offices, podcasting, or music practice—an online sound level meter is the fastest way to get reliable numbers. This guide shows you how to use a browser-based meter to capture real-time decibels (dB), switch A/C/Z weightings (dBA/dBC/dBZ), read an FFT frequency spectrum, and improve accuracy with calibration. We’ll also cover practical scenarios and FAQs so you can get trustworthy results in minutes.

What this tool does (at a glance)

• Real-time measurement: Continuous dB readout with smooth live updates.
• Professional weightings: Toggle dBA / dBC / dBZ (Z-weighting) to match your use case.
• Frequency analysis (FFT): View the spectrum to see where the noise energy lives.
• Session metrics: Track MIN / AVG / MAX / PEAK while you measure.
• Visual charts: History/time series, bar meters, and spectrum—clear at a glance.
• Calibration controls: Adjust offset (dB) and sensitivity (%) to align with a known reference.

Getting started (2 minutes)

1. Open the site → https://soundlevelmeter.org/
2. Allow microphone access when your browser asks.
3. Watch the live dB value update. Use the update-rate control (e.g., Realtime / Fast / Slow) to balance responsiveness and stability.
4. Pick your weighting (A, C, or Z) and observe how readings change with the same sound.
5. Check metrics (MIN/AVG/MAX/PEAK) to understand overall loudness and the loudest moments.
6. Optional: Calibrate (see below) for tighter accuracy on your device.

Which weighting should you use—A, C, or Z?

• dBA (A-weighting): Approximates human hearing sensitivity (less sensitive to low bass). This is the default for environmental noise and many guidelines.
• dBC (C-weighting): Flatter response with more low-frequency content. Useful when bass or low-frequency vibration is the complaint.
• dBZ (Z-weighting / Flat): Essentially no weighting. Use when you want the raw signal behavior (e.g., technical analysis).

Rule of thumb: For neighbor/office/classroom noise, start with dBA. If residents complain about “rumbling” or “thumping,” compare against dBC to capture low-frequency impact.

Reading the FFT frequency spectrum (simple but powerful)

The FFT spectrum shows how energy is distributed across frequencies:

• Sharp narrow peaks → tones or resonances (e.g., a fan at ~120 Hz).
• Broad mounds → broadband noise (traffic, wind, crowd).
• Left side (bass) emphasizes rumbles and vibration; right side (treble) indicates hiss or harshness.

Use the spectrum to answer “what kind of noise is this?” and to identify whether low-frequency energy is the real culprit.

What MIN / AVG / MAX / PEAK actually tell you

• MIN: The quietest level during the session (useful for background baseline).
• AVG: The average—good for comparing rooms or before/after interventions.
• MAX: The highest sustained level observed.
• PEAK: A true instantaneous spike; great for catching pops, bangs, or clipping risks.

Tip: If MAX is moderate but PEAK is very high, your environment has brief transients (e.g., door slams). If AVG is high, the noise is persistent.

Calibration: squeeze the most accuracy from your mic

Smartphone and laptop mics vary. You can still get reliable results with light calibration:

1. Offset (dB): If you have access to a known sound pressure level (e.g., a reference 94 dB @ 1 kHz source or a trusted meter), match your reading by applying a small offset.
2. Sensitivity (%): Fine-tune responsiveness if your device is noticeably hot or quiet.
3. Stable setup: Hold the device at a consistent distance; avoid touching the mic; reduce wind noise.
4. Room reflections: For room comparisons, measure at similar positions and heights to keep reflections consistent.

Legal or compliance measurements may require certified hardware. A browser meter is excellent for monitoring, diagnostics, and documentation—and often enough to guide decisions or escalate complaints.