STILL / FIELD NOTES 07

How to read a sound spectrum on your iPhone

A spectrum separates a captured signal into frequency components. Horizontal position represents frequency and vertical height represents the chosen level display. A prominent peak suggests a strong component in that recording; it does not by itself identify the machine or activity that caused it.

September 8, 2026 · Arve Tech, maker of Still

Start with a controlled change

In Still, use the FFT view while keeping the phone in one place. Compare the same source switched between known settings. Change one thing at a time and check whether a feature in the spectrum changes consistently.

Display choices affect interpretation

Linear and logarithmic frequency scales distribute horizontal space differently. Frequency resolution, microphone response and background sounds also influence what you see. A narrow peak is not a precision calibration, and a missing peak does not prove a source is absent.

Try a repeatable approach

1. Note the input route and frequency scale.
2. Compare the source with a repeatable baseline.
3. Save the context instead of guessing a source from one peak.

Source and scope

Brüel & Kjær: environmental noise measurement handbook

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.