Ever found yourself staring at terms like LAeq, LCmax, or dB(A) and wondering what on earth they mean? You’re not alone. The world of sound measurement is full of cryptic abbreviations and technical jargon that can feel overwhelming, even to professionals.
Sound level measurement notations in a nutshell
Sound level measurements often appear in notations like LAF, LAS, LAeq, LCeq and are expressed in decibels (dB). These are letter symbols that follow the conventions outlined in the international standard “IEC 61672-1: Electroacoustics – Sound level meters – Part 1: Specifications”. Each letter or suffix provides specific information about how the measurement was captured and processed. Important stuff, because the perception of sound can really differ from person to person. And we need impartial measurement data to be able to discuss the facts.
In this blog, we break down the most common letters and suffixes used in modern sound level measurements, explained in plain language, with helpful background context.
We’ll help you make sense of what those numbers really mean in practical terms. Whether you’re monitoring city noise, evaluating workplace sound exposure, or simply curious about decibels, this guide will help you understand the world of sound more clearly, both literally and figuratively.
A screenshot of the DSS Dashboard, with several readings from a noise monitoring device.
Why we use Decibels instead of raw linear sound pressure? Great question!
The dynamic range of human hearing, from the threshold of audibility to the threshold of pain, spans from 0,00002 to 20 pascal (Pa) in terms of linear sound pressure. This enormous linear range makes direct comparison of raw sound pressure impractical.
The decibel (dB) scale resolves this by compressing the dynamic range logarithmically. Using 20 µPa as the reference value, it sets the threshold of audibility at 0 dB SPL, resulting in a practical scale from 0 to 120 dB.
For example: the Pa value for rustling leaves would be approximately 0.00006325 Pa (10dB), while whispering (ca. 30dB) would be 0.0006325 Pa, and the rock concert would come out around 6.3245553203, or 110dB.
As you can see: This dB scale makes it far more convenient for practical use, comparison, and communication.
Moreover, our perception of loudness aligns more closely with this logarithmic scale. A tenfold increase in sound power corresponds to a 10 dB increase in sound pressure level, which is perceived as approximately twice as loud.
| SPL Increment (dB) | Sound Power (×) | Sound Pressure (×) | Approx. perceived loudness (×) |
| 0 | 1 | 1,00 | 1 |
| 10 | 10 | 3,16 | 2 |
| 20 | 100 | 10,00 | 4 |
| 30 | 1000 | 31,62 | 8 |
| 40 | 10000 | 100,00 | 16 |
| 50 | 100000 | 316,23 | 32 |
| 60 | 1000000 | 1000,00 | 64 |
| 70 | 10000000 | 3162,28 | 128 |
| 80 | 100000000 | 10000,00 | 256 |
| 90 | 1000000000 | 31622,78 | 512 |
| 100 | 10000000000 | 100000,00 | 1024 |
| 110 | 100000000000 | 316227,77 | 2048 |
| 120 | 1000000000000 | 1000000,00 | 4096 |
Decibel (dB), Sound Pressure Level (SPL) and sound level:
The decibel expresses the logarithmic relationship between a measured quantity and a predefined reference.
When this logarithmic relationship involves the time-mean-square of a sound pressure relative to a reference pressure of 20 micropascals (µPa), it is referred to as Sound Pressure Level (SPL), expressed in dB. This can be considered as a raw sound level measurement without any weightings.
When further processing such as time weighting or time averaging and frequency weighting is applied, it is referred to as “sound level” and should be noted by the corresponding letters and/or suffixes.
Interpreting the Letter Notation
The first letter: (L), sound pressure level:
The starting letter is always an L and indicates that it is a sound pressure level measurement.
The second letter: (A/C/Z), frequency weighting:
Frequency weighting adjusts for how human hearing perceives different frequencies. These weightings are derived from equal-loudness-level contours standardized in ISO 226, and reflect perceptual sensitivity across sound levels.
- A-weighting (A): Based on the 40-phon contour. It reflects ear sensitivity at lower levels. Slight peak at 2.5 kHz (+1.3 dB), attenuation above 6.3 kHz and below 1 kHz.
- C-weighting (C): Based on the 100-phon contour. Suitable for high-level sounds. Less attenuation at low and high frequencies.
- Z-weighting (Z): Zero weighting. Flat frequency response, often used for technical analysis and calibration.
| Equal-loudness contour | High frequency characteristics | Low frequency characteristics | |
| A | 40 phon | Slight peak of +1,3 dB at 2,5 kHz, attenuation above 6,3 kHz (approx -3 dB around 11 kHz) | Attenuation below 1kHz (approx -3 dB around 500 Hz) |
| C | 100 phon | Attenuation above 1,25 kHz (-3 dB at 8 kHz) | Attenuation below 200 Hz (-3 dB at 31,5 Hz) |
| Z | None | Flat | Flat |
The third letter (F/S), time weighting:
The human ear does not detect rapid changes in sound energy instantly; it integrates sound energy over a brief period. To replicate this auditory behavior, exponential time weightings are applied. F stands for Fast exponential time weighting with a time constant of 125 ms and S stands for Slow exponential time weighting with a time constant of 1000 ms.
Time weighting additionally improves readability of the data if it is displayed directly and allows for more accurate comparisons.
Suffix: “eq”, time averaging (Equivalent Continuous Sound Level):
Instead of F or S, a notation may end in eq, indicating an equivalent continuous sound level (Leq). This is a time-integrated average of total sound energy, often over a specific duration such as 1 minute or 15 minutes (e.g. LAeq,1min).
The integrating time is often displayed after the letters, for example LAeq,1min for an integrating time of 1 minute. If the integration time is not included in the abbreviation itself, it is displayed separately elsewhere.
Because it is a logarithmic average of sound energy over time, interpreting the equivalent continuous sound level is not entirely straightforward. Unlike a simple arithmetic mean, this averaging method accounts for both the amplitude and the duration within the integration period.
For example, pulsing a signal at between 0 and 30 dB for half of the integrating time, will not result in an average of 15dB. Instead the result will be 27 dB because 50% of the time is 3 dB less than 100% of the time logarithmically.
| Letter/subtext | Type | Time constant / integrating time |
| F | Exponential time weighting | Fixed 125 ms |
| S | Exponential time weighting | Fixed 1000ms |
| eq | Equivalent continuous sound level | Configurable |
Suffix: max / min (Extreme Values)
max or min suffixes denote the highest or lowest value captured during the measurement period. These apply to frequency- and time-weighted levels. For example, LAFmax is the maximum A-weighted Fast value over a specified duration.
Conclusion: From Abbreviations to Action
Decoding terms like LAeq,15min is more than a technical exercise, it’s the key to making informed decisions in a world increasingly shaped by sound. Whether you’re designing smarter cities, improving workplace conditions, or monitoring environmental impact, understanding how sound is measured empowers you to act with clarity and confidence.
As you now know: the before mentioned measurement labeled LAeq,15min decodes as:
L – Sound pressure level
A – A-weighted (reflecting human hearing sensitivity)
eq – Equivalent continuous level (energy-averaged over time)
15min – Averaged over a 15-minute interval
Understanding this structure ensures correct interpretation and enables more effective use of acoustic data in practice.
This matters, because accurate interpretation of sound level indicators is essential in many real-world contexts, including:
- Urban policy and environmental monitoring
- Workplace safety and compliance
- Smart infrastructure and traffic analysis
- Ecological impact studies
So next time you see a jumble of letters and numbers on a noise report, you’ll know exactly what they mean, and more importantly, why they matter.
