Loudness normalization

Tracks come from many sources and are mastered at very different levels: a recent pop single can sound twice as loud as a 1970s recording or a spoken promo. Loudness normalization plays every track and cart at the same perceived loudness, so the operator does not ride the fader from one track to the next.

It is off by default. Turn it on in Settings → Loudness.

How it works

A fixed gain per track. Each track gets one gain, in dB, decided when the track is loaded and kept until it stops. Nothing is compressed or limited: the whole track is made louder or quieter by the same amount, so its own dynamics stay as they were mastered. The player’s fader works on top of it, as before.

The measurement. The background analysis measures each file once:

• its integrated loudness, in LUFS: how loud the whole file sounds, as ITU-R BS.1770 and EBU R128 define it (quiet passages and silence are gated out, so a long fade-out or a pause does not lower it);
• its true peak, in dBTP: the highest level the signal reaches between samples once it is converted to analogue.

New files are measured with their first analysis. Files added before loudness was measured are measured by a background pass that runs while the normal analysis has nothing to do, without touching their markers. It runs whether normalization is on or off, so the measurements are ready when you turn it on. Re-analyse (in the playlist menu) measures a file again. A file shorter than 0.4 s is never measured, and a silent file has no loudness: both play unchanged.

The gain. The gain brings the measured loudness to the Target, plus the track’s own Trim (see Per track):

gain = target − measured loudness + trim

A track louder than the target is turned down by as much as it needs. A quieter track is turned up, but never by more than the Maximum boost, and never so much that its true peak would go above the True-peak ceiling: there is no limiter, so the ceiling is what keeps a boosted track from clipping. A track whose true peak is already above the ceiling is not boosted at all.

Examples, with the defaults (target −16 LUFS, ceiling −1 dBTP, maximum boost 12 dB):

When the gain is decided. When a track is loaded: prepared as a player’s next, started, loaded paused, pre-listened on CUE, or fired as a cart. A track that is playing or paused keeps its gain until it stops, through seeks and pauses. Changing the settings, a track’s measurement or its trim applies the next time the track is loaded; the next track already waiting on a player is prepared again with the new gain, so it starts with it.

Pre-listen. CUE and cart pre-listen play a track with the same gain it gets on air, so what you hear in the headphones matches the programme.

Meters. The meters and their loudness readout measure after the gain, so they show the normalized level. The meters’ own Loudness target (Settings → Meters) only colours the readout; it does not change any gain.

Bit-perfect outputs

A player or cart whose output is bit-perfect is never normalized: it always plays at unity gain (0 dB), whatever the settings, because any gain would change the samples the device receives. With normalization on, its header shows a grey Not normalized badge whose tooltip says “Bit-perfect output: tracks play unaltered.” The same holds for pre-listen on a bit-perfect Cue device, while the player’s Main output, if it is not bit-perfect, still gets the gain.

A track that is already playing (or paused) when its device is turned bit-perfect keeps the gain it started with, and the BP badge stays off for it. The next track plays at 0 dB and bit-perfect. A DSD track in that situation plays converted to PCM with its gain, never as an unchanged DSD stream.

The gain in the player header

While a player is playing or paused, a badge left of BP shows the gain of the track on air. Hover it for the reason.

The badge shows the gain the player asked for when the track started.

Per track: exclude and trim

Some tracks should not follow the target: a station ID mastered loud on purpose, a test tone, a track whose measurement does not match how it sounds (speech often sounds louder than music at the same LUFS). Each track has two settings for that:

• Exclude from normalization: the track always plays unchanged.
• Trim: dB added to the track’s gain, from − to + the Maximum trim (Settings → Loudness), in 0.5 dB steps. Double-click the slider to put it back to 0. The trim is dimmed while the track is excluded.

Where to change them:

• On a waveform: right-click a player’s waveform (or its CUE window’s) and choose Loudness…. The popup names the track and shows its measurement. It keeps editing that track even when the player moves on to another one; close it with its × button. It closes by itself if the track is removed.
• In the cart editor: Settings → Cartwall, click a cart: the same two controls are under Stop other carts when fired, with the measurement under the label.
• Remotely: PUT /api/v1/tracks/<id>/loudness (see Remote control).

The settings belong to the track and are saved with it. A change applies the next time the track is loaded, like any other change.

The track tooltip of the playlist table shows the measurement (“Loudness: −14.2 LUFS, true peak −0.8 dBTP”, or “Loudness: not measured”) and, when it is not the default, the track’s setting (“Excluded from normalization” or “Trim +1.5 dB”). The trim shown is the one in use: when a lowered Maximum trim limits a trim saved earlier, the line also gives the saved value (“Trim +6.0 dB (saved +10.0 dB, limited by the maximum trim)”). The gain badge’s tooltip and the Trim slider show the trim in use too.

Choosing the settings

• Target. −16 LUFS suits most music programmes on air and online. −23 LUFS (EBU R128) or −24 LUFS (ATSC A/85) leave more headroom, but quiet tracks then need larger boosts, which the ceiling and the maximum boost may hold back. Choose a target close to how loud your material already is.
• True-peak ceiling. −1 dBTP leaves room for the conversion and for lossy encoders downstream. Lower it when a stream encoder clips.
• Maximum boost. Keeps a very quiet recording (or a mostly silent one) from being raised into noise. 0 dB only turns loud tracks down.
• Maximum trim. How far the per-track trim may go. Lowering it limits trims already set without changing them, until you next edit that track’s loudness: the edit then saves the limited trim.