Why Frequency Weighting Exists
Human ears don't hear all frequencies equally. We're most sensitive to mid-range frequencies (1–4 kHz) and much less sensitive to very low bass and very high treble. A 50 Hz hum at 70 dB doesn't sound as loud as a 2 kHz tone at 70 dB, even though they carry the same sound pressure level.
Frequency weighting filters correct for this. They adjust the measurement to reflect either how we perceive sound (A-weighting) or the raw physical reality (Z-weighting), depending on what you need.
The Three Weighting Modes
dBA — A-Weighting
A-weighting is the most common and most important. It applies a filter curve that mimics how the human ear responds to sound at moderate levels — significantly reducing low frequencies below 500 Hz and slightly reducing very high frequencies above 6 kHz.
Use dBA when:
- Measuring general environmental or occupational noise
- Assessing noise complaints (neighbors, traffic, construction)
- Monitoring workplace noise exposure (OSHA and NIOSH both use dBA)
- Comparing readings to published noise level charts — nearly all reference charts use dBA
- You're not sure which to use — dBA is the safe default
Every major noise regulation worldwide — OSHA, NIOSH, the EU Physical Agents Directive, WHO guidelines — specifies dBA as the primary measurement unit.
dBC — C-Weighting
C-weighting has a much flatter frequency response than A-weighting. It still rolls off very low (<30 Hz) and very high (>8 kHz) frequencies, but it captures bass and mid-bass energy much more faithfully.
Use dBC when:
- Measuring bass-heavy sounds (live music, subwoofers, industrial machinery)
- Assessing peak or impulse noise (gunshots, hammering, explosions)
- Evaluating hearing protection — the dBC-dBA difference tells you how much low-frequency energy is present, which affects protector selection
- Checking for low-frequency noise problems that dBA would underestimate
Pro tip: If your dBC reading is more than 10 dB higher than your dBA reading at the same location, there's significant low-frequency noise present. This is common near HVAC systems, generators, and music venues.
dBZ — Z-Weighting (Zero/Unweighted)
Z-weighting applies no filter at all. It measures the raw sound pressure level across the full audible spectrum (and beyond). "Z" stands for "zero" weighting.
Use dBZ when:
- Performing technical acoustic analysis
- Comparing measurements between instruments (removes filter variation)
- Feeding data into further analysis where you'll apply your own frequency processing
- Research and scientific measurement
dBZ is the least commonly used in everyday noise measurement. Most people will never need it, but it's valuable for technical users who want the raw data.
Side-by-Side Comparison
| Aspect | dBA | dBC | dBZ |
|---|---|---|---|
| Low-freq sensitivity | Reduced (mirrors human ear) | Nearly flat | Completely flat |
| Best for | General noise, workplace, complaints | Bass, peaks, hearing protection | Technical analysis, raw data |
| Regulatory standard | OSHA, NIOSH, WHO, EU | Peak measurements (Cpeak) | None (reference only) |
| Matches perception? | Yes — approximates human hearing | Partially | No — purely physical |
| Typical difference | Reference | 0–10 dB higher than dBA | 0–15 dB higher than dBA |
| Chart references | Nearly all published charts | Rare | Very rare |
Which Should I Use?
Follow this simple decision path:
- Measuring how loud something sounds? → dBA
- Checking workplace noise for safety? → dBA
- Measuring bass-heavy music or machinery? → dBC (and dBA for comparison)
- Measuring gunshots or explosions? → dBC (peak)
- Need raw data for analysis? → dBZ
- Not sure? → dBA. Always dBA.
In practice: Start with dBA. If you suspect significant low-frequency content, take a dBC reading too and compare. If dBC is 10+ dB higher than dBA, low-frequency noise is dominant and you may want to investigate further. For a full overview of common noise levels measured in dBA, see our decibel chart.
How Sound Gauge Pro Handles Weighting
Sound Gauge Pro implements all three weighting modes using IEC 61672-compliant digital filters — the same standard used by professional sound level meters. The filters are built from biquad coefficients validated against reference curves, not simplified approximations.
You can switch between dBA, dBC, and dBZ with a single tap while measuring. The app also tracks your noise dose using dBA (the OSHA/NIOSH standard), and writes session averages to Apple Health as Environmental Sound Levels.