Measurement accuracy
The built-in iPhone microphone is useful for indicative readings. For reference work, use a compatible external microphone and complete acoustic calibration for the entire input path.
Official app support
Measure with confidence.
Help with measurement, calibration, frequency analysis, noise exposure, reports, purchases and public contributions in SPL Reference.
Start here
Microphone access
If levels do not move, open iOS Settings, find SPL Reference, and enable Microphone access. Then confirm the intended input path in Calibrate.
Restore your purchase
Open Settings in SPL Reference and choose Restore Purchases while signed in with the Apple Account used for the original Lifetime Professional Unlock.
Reports and evidence
Complete a measurement, open it in Sessions, add any notes or photographs, then generate a PDF report from the measurement menu.
Free and Professional
SPL Reference is free to download. The free tier includes the built-in microphone, five active measurement minutes per calendar month, two saved measurements and one project.
Lifetime Professional Unlock removes the free limits and unlocks the complete professional toolset with one purchase. There is no subscription.
Public Measurement Library
Measurements are never uploaded automatically. When you choose to contribute, SPL Reference presents the exact public fields for review and asks for explicit authorisation before submission.
Browse the public measurement library or inspect the open data and source on GitHub.
Important measurement guidance
- Phone microphones and connected hardware vary between devices and configurations.
- An unvalidated device is not a certified sound-level meter.
- Occupational-noise results support assessment and documentation; they do not replace professional judgement or applicable legal requirements.
- Before critical work, verify calibration, input route, gain, sample rate and drift evidence.
Still need help?
Contact Direct Sound Records
Include your iPhone model, iOS version, SPL Reference version and a short description of what happened. Do not send confidential measurement data unless it is necessary for support.