| Check | Purpose | Reference | Validity |
|---|---|---|---|
| Microphone level | Each microphone, preamplifier and input reads a known level; re-checked after each session (drift ≤ 0.5 dB). | IEC 60942 calibrator, 94 dB at 1 kHz | 24 h |
| Loop-back | Output-to-input delay, converter clock consistency, dropped-sample detection. | Output-to-input cable | 30 days |
| Microphone matching | The two microphones of a pair respond at the same instant (≤ 1 µs), by swapping positions. | Side-by-side captures, swapped | 24 h |
| Noise floor | Background level per channel before any signal. | Quiet capture | 24 h |
| Environment sensors | Temperature, humidity and pressure against a second instrument. | Reference hygro-thermometer, barometer | 30 days |
| Geometry tools | Rule and calipers against a reference length. | Certified rule or gauge block | 1 year |
Instrument self-checks
Before any science, every instrument proves it reads correctly. Each check produces a sealed calibration record with an expiry; acceptance limits are fixed in the software.