IEC 61672-1: Peak Sound Pressure Level Measurement
TL;DR
Peak sound pressure level (Lpeak) captures the highest instantaneous value of the sound pressure waveform, without any time weighting. IEC 61672-1 Clause 3.12 defines it as Lpeak = 20·log10(ppeak/p0) where ppeak is the maximum absolute instantaneous sound pressure during the measurement. Unlike Fast or Impulse time-weighted levels, Lpeak responds to sub-millisecond transients. C-weighted peak (LCpeak) is the standard form. Peak measurement is critical for hearing damage risk assessment — the EU Directive 2003/10/EC sets exposure limit at LCpeak = 140 dBC.
Definition (Clause 3.12)
Peak sound pressure level is the highest absolute instantaneous sound pressure during the measurement interval, expressed in decibels:
Lpeak = 20 · log₁₀ (|p(t)|max / p₀)
Where p₀ = 20 µPa. Unlike time-weighted levels (F, S, I), peak detection has no time constant — it captures the true waveform peak, including events lasting microseconds.
C-Weighted Peak (LCpeak)
IEC 61672-1 specifies peak measurement with C-weighting, denoted LCpeak. C-weighting is used rather than A-weighting because peak damage risk is related to the physical pressure amplitude, not the perceived loudness. C-weighting is approximately flat, removing only extreme low and high frequency content that may not contribute to mechanical damage.
Some instruments also offer Z-weighted peak (LZpeak) for applications requiring a truly unweighted peak measurement.
Regulatory Thresholds
Peak sound pressure level is a critical parameter in occupational noise regulations:
| Standard | Lower action | Upper action | Exposure limit |
|---|---|---|---|
| EU Directive 2003/10/EC | 135 dBC | 137 dBC | 140 dBC |
| OSHA 1910.95 | — | — | 140 dB (not weighted) |
| UK Control of Noise at Work 2005 | 135 dBC | 137 dBC | 140 dBC |
Exceeding the exposure limit value (140 dBC) is never permitted, regardless of duration or hearing protection.
Peak vs Impulse Weighting
A common confusion exists between Lpeak and Impulse-weighted level (LI). Impulse weighting is an exponential detector with 35 ms attack — it cannot capture true waveform peaks. LCpeak is always greater than or equal to LCI for the same signal. For gunshots, hammering, or explosive events, the difference can exceed 15 dB.
Crest Factor
The ratio of peak to RMS is the crest factor. A pure sine wave has a crest factor of 1.414 (3 dB). IEC 61672-1 requires instruments to handle crest factors up to 23.5 dB (Class 1). Highly impulsive signals like gunshots can have crest factors exceeding 25 dB, which may exceed the instrument's linear operating range.
SonaVyx Peak Measurement
SonaVyx tracks LCpeak continuously in the SPL meter and displays it alongside Leq and time-weighted levels. The noise dose calculator assesses LCpeak against EU and OSHA thresholds and triggers alerts when action levels are approached. For understanding crest factor in the context of system diagnostics, see problem detection where abnormal crest factors indicate clipping or calibration issues.
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Last updated: March 19, 2026