Technical Documentation

SPL Metering

Sound pressure level measurement with A/C/Z weighting, configurable integration times, and Leq logging for compliance documentation

Measurement Types

dBFS Peak

Peak level in dB Full Scale. Instantaneous maximum sample value. Use for monitoring digital headroom.

dBFS RMS

RMS level in dB Full Scale. Average power of the signal. Standard for monitoring digital signal levels.

SPL RMS

Calibrated sound pressure level in dB SPL. Requires microphone calibration with a 94 dB reference.

SPL Leq

Equivalent continuous level over a time period. The standard for noise compliance and regulatory documentation.

Frequency Weighting Curves

A-Weighting

Approximates human hearing sensitivity. Strongly attenuates low frequencies and slightly attenuates very high frequencies. The most commonly used weighting for noise regulations.

A-weighting. -26 dB at 63 Hz, -3 dB at 500 Hz, 0 dB at 1 kHz, +1 dB at 2-4 kHz

C-Weighting

Nearly flat response with gentle LF and HF rolloff. Preferred for peak SPL measurements and low-frequency assessment. Better represents perceived loudness at high levels.

-3 dB at 31.5 Hz, flat 63 Hz–8 kHz, -3 dB at 8 kHz

Z-Weighting (Flat)

No frequency weighting applied. Flat response across the entire measurement bandwidth. Use for broadband energy assessment and system calibration.

Unity gain at all frequencies

Time Response

Peak

τ = Instantaneous | 20 Hz update

Catches transient peaks. Updates at 50 ms intervals.

Fast

τ = 125 ms | 10 Hz update

Standard for live monitoring. Responds to rapid level changes.

Slow

τ = 1.0 s | 2 Hz update

Smoothed reading for steady-state levels. Easier to read.

Smoothing Formula

SPL_smooth = (1 - α) × previous + α × new

α = 1 - exp(-dt / τ)

Leq Integration Periods

Equivalent continuous level over fixed time windows. Uses a circular buffer with running linear-power average.

1 sec

10 sec

1 min

5 min

10 min

15 min

30 min

60 min

90 min

120 min

All Leq modes update at 10 Hz. Linear power averaging: dB → power → average → dB

Calibration

SPL readings require calibration to convert digital levels to absolute dB SPL. Use a 94 dB calibrator placed over your measurement microphone.

Per-channel calibration offset stored in dB

Applied only to SPL_RMS and SPL_LEQ modes

See the SPL Calibration Guide for step-by-step instructions

Warning & Limit Levels

Configurable thresholds for visual alerts when SPL exceeds safe levels.

Warning Level

Default: 85 dB — OSHA action level

Limit Level

Default: 100 dB — exceeds safe exposure

Back to Support SPL Calibration Guide