How to use the decibel meter
- 1
Start the meter
Press Start meter and allow the microphone when your browser asks. - 2
Read the level
The large number is the level right now, updated ten times a second. The bar shows the same level from −60 to 0 dBFS. - 3
Compare
Minimum, maximum and average cover everything since you started. Reset clears them while the meter keeps running, so you can measure one moment on its own.
What dBFS means
dBFS stands for decibels relative to full scale. 0 dBFS is the strongest signal digital audio can hold, so every reading is a negative number, and the closer it gets to 0, the stronger the signal. Each reading is the RMS level of about a tenth of a second of sound, so a steady tone that fills the whole scale reads about −3 dBFS. The average is worked out from signal power, so loud moments count for more than quiet ones.
Why a browser cannot measure real decibels
The decibels on a noise chart are sound pressure level, written dB SPL. To measure that, an instrument has to be calibrated: it must know which number a known sound pressure produces. A browser cannot know this. It receives digital values from a microphone of unknown sensitivity, after your system has applied its input volume. The same room can read very differently on two laptops, so a reading here cannot be converted into dB SPL.
For a noise complaint, a workplace assessment or anything about hearing safety, use a calibrated sound level meter.
What this meter is good for
- Comparing moments on the same device. With the same microphone, position and input volume, a lower number means less signal, so you can see whether closing a window helps.
- Checking a recording setup. Speak as you will in the real recording. If the level stays near the bottom of the bar, move closer or raise the input volume. If it gets close to 0 dBFS, lower it, because the sound may distort.
- Seeing how far your voice sits above the room. Measure the quiet room, press Reset and speak. The bigger the gap between the two averages, the easier the recording will be to follow.
The tool asks the browser to turn off echo cancellation, noise suppression and automatic gain, because they change the level by themselves. If your browser keeps any of them on, the tool says so.
The sound is analysed in your browser and is not recorded or uploaded. The microphone closes when you press Stop or leave the page. If you record an interview and want the words, interview transcription gives you a draft to check against the audio.