dB describes a logarithmic ratio; dBA and dBC identify different frequency weightings applied to acoustic measurements, while dBFS describes a digital signal relative to full scale. Decibel Reader shows Estimated dB from digital RMS plus an offset. It does not implement A or C weighting and is not a certified sound-pressure meter.
The letters matter when comparing a browser number with a handheld meter. Matching numbers do not establish matching measurement methods.
Which reading am I looking at?
| Label | Meaning | In Decibel Reader |
|---|---|---|
| dB | A logarithmic ratio that needs a reference and context | Shown only with the Estimated label for the main reading |
| dBA | Acoustic level with A frequency weighting | Not measured |
| dBC | Acoustic level with C frequency weighting | Not measured |
| dBFS | Digital level relative to full scale | Raw RMS in Settings and frequency-band intensity in the spectrum |
A raw RMS level and a spectrum-band level both use dBFS, but they summarize different quantities. A spectrum bar describes a frequency band; the raw RMS describes the combined digital input over a time window. Do not add the bar labels together to obtain the main reading.
Why can dBA and dBC differ for the same sound?
A and C weighting change how much different frequencies contribute to a sound-level measurement. A weighting attenuates very low frequencies more strongly than C weighting. A bass-heavy sound can therefore produce different A- and C-weighted values on the same instrument.
The OSHA Technical Manual explains the weighting networks and distinguishes them from an unweighted acoustic measurement. An unweighted browser estimate is not automatically a Z-weighted measurement: microphone sensitivity and frequency response still need to be established.
There is no universal number to add to a dBC reading to obtain dBA. The difference depends on the frequency content. Similarly, selecting a display offset in Decibel Reader cannot create an A-weighting filter.
What does the browser display offset do?
Decibel Reader calculates 20 × log10(RMS) from the digital input, then adds the display offset. The uncalibrated default is +94 dB. A hypothetical raw value of −35 dBFS would therefore display 59 Estimated dB. This is an arithmetic example, not a collected measurement or a known microphone sensitivity.
Settings shows the raw value and the adjustment. Reference alignment replaces the default offset using a shared observation with a reference meter. The result remains a browser estimate. Read the measurement method for continuous sampling and its disclosed fallback.
How should I compare with a reference meter?
- Note the reference instrument’s weighting, response setting and calibration status.
- Keep the microphones in a similar sound field with a steady ordinary source.
- Use the reference-alignment sample and the reference reading for the same interval.
- Check another ordinary condition without changing the offset to hide disagreement.
Agreement at one condition only checks the alignment there. A different source or frequency mixture can reveal a new difference. The 10-second alignment guide explains the full workflow.
Common questions about the units
Can I rename Estimated dB as dBA after alignment?
No. Reference alignment changes a constant offset, not the frequency weighting or the device’s acoustic validation.
Does a negative dBFS value mean negative sound?
No. A negative dBFS value means the digital signal is below its full-scale reference. It does not describe negative acoustic pressure or a negative noise source.
Can I compare two phones by their displayed dB number?
Only with care: different microphones, gain and processing can produce different scales. For informal before-and-after checks, use the same device, placement and settings.
Can I use the Estimated dB number in an exposure table?
No. A table specified in measured dBA needs the appropriate acoustic measurement. Decibel Reader’s estimated number, chart reference lines and saved report do not supply that measurement.
Sources & further reading
Source links checked October 11, 2026.