Wave Calibration Guide
Practical ways to calibrate WAV recordings using field calibrators, embedded metadata, and reference tones.
Field calibrator method (start and end)
The most reliable method is to record a known acoustic calibrator at the beginning and end of your measurement session. A common calibrator level is 94 dB at 1 kHz. You record several seconds of the calibrator tone, then measure the RMS (or A-weighted RMS if required) in that segment. The measured level is used to derive a scale factor for the entire recording.
- Record the calibrator tone at the start (and optionally again at the end).
- Compute the RMS level of the tone in the recorded WAV segment.
- Calculate the gain needed so that segment equals the calibrator value (e.g., 94 dB).
- Apply that gain to the rest of the WAV for absolute SPL readings.
Using both a start and end calibration can reveal microphone drift or accidental gain changes during the session.
How sound level meters embed calibration
Many sound level meters include calibration metadata directly in the WAV file or in a companion log. Common approaches include:
- Storing the applied calibration offset in a WAV
LISTorINFOchunk. - Embedding a reference tone at the start of each file so software can detect it automatically.
- Writing a sidecar file (CSV or XML) with the calibration level, microphone sensitivity, and time stamps.
Always check the meter documentation to see how it stores calibration and whether the WAV samples are already scaled.
Other calibration paths
- Microphone sensitivity: Use the mic's rated sensitivity (e.g., mV/Pa) and the recorder gain to compute an absolute scale.
- Reference tone in post: Inject a known tone in the same signal chain and calibrate later.
- Reference measurement: Compare the WAV level to a trusted SLM reading taken simultaneously at the same location.
Each method should document the reference level, time range, and any weighting or time constants used in the calibration step.
Best practices
- Record at least 5-10 seconds of the calibrator tone for a stable RMS value.
- Keep gain settings locked during the entire session.
- Store calibration values alongside the band results so the analysis is traceable.
FAQ
How do I calibrate a WAV recording with a 94 dB calibrator?
Record the calibrator tone at the start (and ideally again at the end). Measure RMS over the tone segment, compute the gain needed to make that segment equal 94 dB, then apply that gain to the full file. Use the same weighting and time constant that you will use in reporting.
What if my sound level meter stores calibration in the WAV file?
Many meters embed calibration offsets in WAV metadata (LIST/INFO chunks) or a sidecar log. Check the meter documentation and avoid double applying calibration if the samples are already scaled.