Definition
Momentary loudness is loudness calculated over a sliding rectangular window of 400 ms, without gating, defined in EBU Tech 3341 based on ITU-R BS.1770-4:
L_M(t) = −0.691 + 10 · log10( Σ_i G_i · (1/0.4) · ∫ y_i(τ)² dτ ), with the integral extending from t − 0.4 s to t and y_i the K-weighted signal of channel i.
The window coincides with the length of the blocks used to calculate integrated loudness: momentary is the loudness of a single block. The measurement must be updated at a rate of at least 10 Hz. The highest value in the song is the maximum momentary (Max M). Momentary reacts to single words, hits and accents, but not to a single transient: a 20 ms snare hit weighs 1/20 of the window.
Parameters and units
- Unit: LUFS; differences in LU.
- Window: 400 ms, rectangular, no gating.
- Update rate: ≥ 10 Hz.
- Max momentary: typically 1–3 LU above the maximum short-term in music, more in speech and film.
- Typical values: EDM drop −6/−4 LUFS M; pop chorus −8/−6 LUFS M; spoken voice at −23 integrated LUFS with momentary peaks at −18/−15 LUFS.
Musical function
Momentary shows rapid variations in loudness: an impact, a crash, a shouted word, a drum entry. It is used to spot elements that stick out of the mix for an instant (transition FX, cymbal hits, ad-libs), to balance dialogue and music in video content and to check the difference between the loudest part of a drop and its average. For setting mix levels it is too jumpy: level decisions are made on short-term.
Practical example
Drop of an EDM track, master at −8.0 integrated LUFS:
| Element | Momentary | Notes |
|---|---|---|
| Drop average | −6.8 LUFS | Short-term of the drop |
| First hit of the drop (kick + crash + sub) | −5.2 LUFS | Expected accent |
| Transition impact FX | −4.1 LUFS | 1.1 LU above the first hit |
The transition impact exceeds the drop itself: the impression is that the drop arrives weaker than what precedes it. Lowering the impact by 2 dB brings the maximum momentary down to −5.2 LUFS, coinciding with the first hit of the drop, which becomes the loudest point again.
Common mistakes
- Adjusting faders while watching momentary: the value swings by 3–6 LU within moments and leads to wrong corrections.
- Confusing the maximum momentary with the peak or the true peak.
- Expecting momentary to coincide with integrated loudness: in music it exceeds it by 2–5 LU in the loud sections.
- Ignoring momentary in video and podcast content, where specifications may also limit the maximum short-duration loudness.
How to check it
- App analysis: the Max momentary (400 ms) row is the highest loudness among the 400 ms blocks (100 ms step) calculated with K-weighting, the same ones used for integrated loudness.
- Quick comparison: if the maximum momentary exceeds the maximum short-term by more than 3 LU, a short element sticks out of the mix; find the spot with a history-graph meter.
- Dedicated meters: Youlean Loudness Meter, FabFilter Pro-L 2, iZotope Insight show momentary in real time and the maximum value.
Starting settings
| Parameter | Value | Why |
|---|---|---|
| Window | 400 ms, rectangular | Definition from EBU Tech 3341. |
| Update rate | ≥ 10 Hz | Continuous meter reading. |
| Max M − Max S (music) | 1–3 LU | Accents stand out without overtaking the section. |
| EDM drop | −6/−4 LUFS M | Typical density of club masters. |
| Pop chorus | −8/−6 LUFS M | Common values in commercial masters. |
| Transition FX | ≤ Max M of the following section | The section that follows must remain the loudest point. |
How to check the result
- Maximum momentary (400 ms) ≤ maximum short-term + 3 LU in music.
- The point of maximum momentary coincides with a loud musical section, not with a transition FX.
- In content with dialogue, shouted words do not exceed the integrated loudness by more than 8–10 LU.
- Mix levels are decided on short-term, not on momentary.