STILL / FIELD NOTES 02

dBFS vs dB SPL: why a phone reading can be negative

dBFS describes a signal relative to digital full scale. dB SPL describes sound pressure relative to a physical reference. They are different quantities: a negative dBFS value does not mean negative environmental sound, and adding a universal number does not reliably convert one to the other.

September 8, 2026 · Arve Tech, maker of Still

What Still shows before adjustment

Still labels unadjusted microphone readings as dBFS. That label preserves the distinction between the captured digital signal and estimated sound pressure. Apple also uses dBFS for audio-channel metering; that does not make it an environmental sound-pressure measurement.

What a reference changes

A suitable sound-level reference can support an adjustment for the current microphone and weighting. It does not correct every frequency, every device or every sound level. After changing the input route or measurement conditions, reconsider whether the adjustment still applies.

Try a repeatable approach

1. Read the unit printed beside the number.
2. Keep digital readings separate from calibrated SPL results in a report.
3. Record the reference and configuration when an adjustment is made.

Source and scope

Apple: audio metering in dBFS

Measurement guidance is educational. Still is not a certified sound level meter and does not establish medical, legal or workplace-compliance conclusions. App-specific statements describe version 1.0.0, currently awaiting App Store review.