Audio Levels, Metering, and Headroom
This page is the house reference for the terms that get mixed up most often in DSP, measurement, and product specs: dBFS, dBu, dBV, sample peak, true peak, LUFS, headroom, and the reporting rules that keep SNR, dynamic range, and THD+N comparable.
State the Reference Before the Number
Decibels are relative units. A number in dB is incomplete until the baseline is clear.
- dBFS means level relative to digital full scale.
- dBu means level relative to 0.775 Vrms.
- dBV means level relative to 1.0 Vrms.
House rule: all digital levels are in dBFS unless noted; all analog levels are in dBu unless otherwise specified.
Common Reference Values
| Reference | Meaning | Voltage |
|---|---|---|
| 0 dBu | professional analog reference | 0.775 Vrms |
| +4 dBu | common pro line nominal | about 1.23 Vrms |
| 0 dBV | consumer voltage reference | 1.0 Vrms |
| -10 dBV | common consumer line nominal | about 0.316 Vrms |
Conversion shortcut: dBV = dBu - 2.21.
dBFS: RMS, Sample Peak, and True Peak
dBFS needs a convention, not just a label. This reference treats 0 dBFS as full-scale sine RMS unless explicitly stated otherwise. Sample peak and true peak are separate measurements and should be reported separately when they matter.
- RMS describes signal power over time.
- Sample peak describes the highest stored digital sample.
- True peak describes the reconstructed waveform peak after interpolation.
True peak can exceed sample peak because the reconstructed analog waveform can overshoot between samples. That is why a system can avoid sample clipping and still clip a DAC or encoder downstream.
Headroom Must Reference a Ceiling
Headroom is the remaining margin between the operating level and a named limit. Do not say "1 dB of headroom" by itself.
Preferred phrasing: 1 dB headroom relative to -1 dBTP.
Use true-peak headroom for delivery and encoding chains. If a spec uses sample peak instead, say sample-peak explicitly.
True Peak for Real Delivery Safety
dBTP is the meter that matters when reconstruction or encoding can overshoot. A good default ceiling for general music delivery is -1 dBTP.
- sample-peak meters help avoid raw digital clipping
- true-peak meters help avoid downstream overs after reconstruction, resampling, or encoding
LUFS and Program Loudness
Use LUFS or LKFS for perceived program loudness, not RMS. LUFS is built from the ITU loudness model and uses gating so silence and very low-level passages do not bias the long-term number the same way a simple RMS meter would.
| Meter | Use it for | Do not confuse it with |
|---|---|---|
| LUFS / LKFS | program loudness | sample peak or RMS power |
| dBTP | delivery ceiling safety | integrated loudness target |
| dBFS RMS | signal power reference | perceptual loudness |
For practical work, loudness and true peak should be paired. One answers "how loud does the program average out?" and the other answers "will this overshoot the route or codec?"
SNR, Dynamic Range, and THD+N Are Not Interchangeable
| Metric | What it means | What must be stated |
|---|---|---|
| SNR | signal relative to noise floor | reference level, weighting, bandwidth |
| Dynamic Range | usable level span between floor and ceiling or criterion | method, weighting, bandwidth, criterion |
| THD+N | harmonic distortion plus noise under a specific test condition | test level, bandwidth, weighting, frequency, method |
Do not compare these numbers casually across products unless the measurement method matches. A-weighted and unweighted results are not interchangeable, and numbers collected under different standards or different bandwidth limits often look comparable when they are not.
Measurement Procedure Rule
Every published performance number should state the standard or clearly named custom method behind it. In pro and semipro digital audio measurement work, that often means AES17 or IEC 61606-3 style language. The key is not memorizing every clause. The key is naming the method so comparisons stay honest.
Contributor Pitfalls
- Wrong: "The output is +6 dB." Right: "+6 dBu", "-6 dBFS", or "+6 dB relative to the previous setting."
- Wrong: "It has 1 dB headroom." Right: "It has 1 dB headroom relative to -1 dBTP."
- Wrong: "Peak is safe." Right: "Sample peak is safe, but true peak still needs checking."
- Wrong: "LUFS is just RMS." Right: "LUFS is loudness with defined weighting and gating behavior."
- Wrong: "This converter has 118 dB dynamic range." Right: "118 dB dynamic range, A-weighted, measured by [method]."
Related
- Reading DSP Levels, Q, and Headroom for the beginner workflow that ties references, filter width, and delivery margin together.
- Glossary D for
dBFS,dBu,dBV, dither, and dynamic range. - Glossary H for headroom.
- Glossary L for LUFS and latency.
- Glossary Q for Q and bandwidth terminology.
- Glossary T for true peak and THD+N.
- dB Reference Converter for dBu, dBV, and Vrms checks.
- Q and Bandwidth Converter for filter-width translation.
- True Peak and Headroom Planner for export-margin planning.
- Parametric EQ Biquad Coefficients for filter implementation math.