Reading the numbers

LoudSense measures per ITU-R BS.1770-4 and EBU R128, the same standards a broadcast meter or your DAW's render statistics use. Here is what each number is and what to do with it.

Peak (dBFS)

The largest single sample in the file, relative to full scale. 0 dBFS is the biggest value the file format can hold. A file with a peak of +0.1 contains samples that were clipped at 0 and rounded back; it does not "go above" 0, it hit the ceiling.

True peak (dBTP)

The waveform between the samples can be higher than any sample. LoudSense reconstructs it at 4× oversampling and reports the highest point. A sine at a quarter of the sample rate, offset by 45°, has samples at −3 dBFS and a true peak at 0 dBTP — the classic case. Platforms and encoders react to the true peak, which is why every target has a dBTP ceiling.

Clips

A run of consecutive samples at full scale counts as one clip; the positions are drawn as red lines. Twenty clipped samples in a row are one clip, not twenty. A handful in a drum hit is often inaudible; hundreds across a podcast mean the limiter or the encoder ran out of headroom.

LUFS-M, LUFS-S, LUFS-I

Loudness in LUFS (loudness units relative to full scale) uses the K-weighting filter — a high-pass at 38 Hz and a high shelf above 1.7 kHz — so the number tracks how loud something sounds, not how big the waveform is.

• LUFS-M (momentary) — a 400 ms window, updated every 100 ms. The orange curve on the panel; the stats row shows its maximum.
• LUFS-S (short-term) — a 3 s window. Smoother; its maximum is what some platforms limit ("short-term max −18").
• LUFS-I (integrated) — one number for the whole file, gated: an absolute gate drops silence below −70 LUFS, then a relative gate drops anything more than 10 LU below the average, so a long quiet intro does not drag a loud song down. This is the number every platform target refers to.

Stereo counts both channels: the same tone on two channels reads 3 LU louder than on one.

LRA (loudness range)

The spread of the short-term loudness over the file, in LU, between the 10th and 95th percentile after gating (EBU Tech 3342). A podcast conversation sits around 3 to 6 LU; a dynamic live recording can reach 15 or more. High LRA is not a fault — it tells you the quiet parts are far below the loud ones, which matters for listening in a car.

RMS and noise floor (audiobooks)

Audible and ACX do not use LUFS. Their spec is plain RMS between −23 and −18 dB (0 dB is a full-scale square wave), peaks no higher than −3 dBFS, and a noise floor below −60 dB RMS. LoudSense reports the RMS of the whole file and estimates the noise floor from the quietest audible 100 ms blocks — the fifth percentile, which stands in for "the RMS of the room tone". A noise floor problem is reported before any level advice, because gain cannot fix it.

The health checks

• Channel balance — RMS of left against right in dB. More than 1.5 dB usually means a pan or a one-sided microphone.
• Correlation — how alike the channels are. Below zero the channels partly cancel when summed to mono; check phase.
• DC offset — a constant shift of the waveform. It wastes headroom and can click at edits; a 20 Hz high-pass removes it.
• Silence at the start and end, gaps over three seconds inside the programme, and dropouts — runs of exact digital zeros of 20 ms or more, the signature of a buffer underrun or a bad edit.

When there is silence at the start or end, a Trim silence → WAV button cuts it to 0.2 s each side and downloads the result; the original is untouched and the trimmed file is analysed as a new row.

Speech and music

The strip under the panel and the "speech / music" line come from a per-100-ms classifier: speech has strong modulation at syllable rate, little energy below 150 Hz and many zero crossings; music is steadier and bass-heavy. Short runs are smoothed away. Each class gets its own gated LUFS-I, so "speech −18.4, music −13.9" tells you the bed is 4.5 LU hotter than the voice. Mixed material (sung vocals over a beat, spoken word with a drone) lands wherever the heuristic tips; the numbers are still correct for whatever it labelled.

Why the MP3 clips

Lossy encoding (MP3, AAC, OGG) does not reproduce the waveform exactly. The reconstruction can overshoot the original peaks by up to about 1 dB. A master that peaks at −0.2 dBFS with zero clips can come out of the encoder at +0.1 dBFS with a hundred clips, and the decoder in every phone will hit the ceiling on each of them.

The fix is headroom: limit the master to −1 dBTP true peak before encoding, then check the encoded file, not only the master. Drop both into LoudSense and read the Compare table.

Reading a verdict

Each row compares LUFS-I with the target window and true peak with the ceiling:

• OK — inside the window, peaks under the ceiling.
• Too loud — above the window. The consequence line says what the platform does ("turned down by 2.3 dB"). Nothing is lost, but your master is louder than it needs to be, and the limiting you used to get there was for nothing.
• Too quiet — below the window. Most music platforms do not turn quiet tracks up, so the file will simply play quieter than everything around it. The fix says how much gain, and adds a limiter when the gain would push peaks over the ceiling.
• Peaks too hot — loudness fine, true peak above the ceiling. Limit first, then re-check.

The targets themselves are on Platform targets.