STILL / FIELD NOTES 04

A, C and Z weighting: choosing a consistent sound view

Frequency weighting changes how different parts of a sound's spectrum contribute to the displayed level. A-weighting reduces the contribution of low frequencies more than C-weighting; Z-weighting is intended to be flat over its specified range. Still also offers B-weighting.

September 8, 2026 · Arve Tech, maker of Still

One sound, different summaries

A low-frequency component can contribute differently to A- and C-weighted results. The difference is a reason to inspect the spectrum, not a diagnosis of the source. Record the weighting instead of labelling every reading simply as dB.

Consistency matters in comparisons

Choose the same weighting for a before-and-after comparison. Changing from A to C between sessions mixes the effect of your experiment with the effect of the measurement setting. A flat weighting does not imply a perfectly flat phone microphone.

Try a repeatable approach

1. Choose a weighting appropriate to the question and any relevant measurement procedure.
2. Keep it fixed for comparison sessions.
3. Include the weighting with every exported value.

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.