Loudness Meter

About Loudness Meter

This professional loudness meter measures audio levels in real-time, displaying RMS (Root Mean Square) and peak levels. Perfect for audio engineers, musicians, podcasters, and content creators who need to monitor and analyze audio loudness to ensure optimal levels and prevent clipping.

What does a loudness meter measure that a regular volume meter does not?

A traditional VU or peak meter shows electrical signal strength — it tells you how hot your file is but not how loud it sounds to a listener. A loudness meter measures perceived loudness using a psychoacoustic model defined by ITU-R BS.1770-4 and EBU R128, weighting different frequencies by how the human ear responds to them (the K-weighting curve). The result, expressed in LUFS (Loudness Units relative to Full Scale), correlates with human perception across genres and program types in a way that peak or RMS never can. A heavy metal track and a piano sonata can both peak at -1 dBFS but differ by 15+ LUFS — only a loudness meter tells you the second will sound dramatically quieter. Loudness meters are now mandatory for broadcast and streaming compliance worldwide.

What is LUFS and how does it differ from dB or dBFS?

LUFS stands for Loudness Units relative to Full Scale. One LUFS equals one dB on the K-weighted, gated psychoacoustic scale defined by ITU-R BS.1770-4. The unit was harmonised with LKFS (Loudness K-weighted, Full Scale) used in US broadcast and they are numerically identical. Unlike dBFS, which only describes the digital amplitude of a single sample, LUFS integrates frequency weighting and time gating to model how a human listener actually perceives loudness. Lower LUFS values mean quieter perceived loudness: -23 LUFS (EBU R128 broadcast target) sounds notably quieter than -14 LUFS (Spotify streaming target). LU (Loudness Unit) without the FS suffix expresses relative differences without an absolute reference — useful for level changes (e.g., "reduce by 3 LU").

What is the K-weighting curve and why does it matter?

K-weighting is a two-stage filter defined in ITU-R BS.1770-4 that approximates the frequency sensitivity of human hearing for loudness perception. The first stage is a high-shelf boost of about +4 dB above 2 kHz (modelling the ear canal resonance), and the second is a high-pass filter rolling off below 100 Hz at 12 dB/octave (modelling the ear's reduced bass sensitivity at moderate levels). This makes mid-high frequencies count more toward the loudness measurement and very low frequencies count less — matching how listeners actually perceive program loudness. Without K-weighting, a bass-heavy track would measure louder than it sounds, and a treble-bright track would measure quieter. K-weighting is the reason a properly mixed pop track at -14 LUFS sounds about as loud as a classical recording at the same number.

What is the difference between integrated, short-term, momentary, and true peak readings?

These are four complementary measurements specified by EBU R128. Momentary loudness (M) uses a 400 ms sliding window — catches brief peaks and short loud events. Short-term loudness (S) uses a 3-second window — reflects what a listener calls "loud sections" or "quiet sections." Integrated loudness (I) measures the whole program in one gated number, excluding silence below -70 LUFS absolute and -10 LU relative threshold — the standard for delivery compliance. True peak (TP) shows the maximum analog level after digital-to-analog reconstruction in dBTP, predicting clipping risk on lossy codecs. Together they describe a program completely: I says how loud it is overall, S/M reveal dynamic shape, TP guards against intersample clipping. Modern meters display all four simultaneously.

What target should I use for streaming, broadcast, podcast, and film?

Standards vary by destination. Streaming: Spotify, YouTube, Tidal, Amazon Music use -14 LUFS integrated with max -1 dBTP. Apple Music uses -16 LUFS. Broadcast: EBU R128 (Europe) requires -23 LUFS integrated, max -1 dBTP, LRA below 20 LU. ATSC A/85 (US TV) uses -24 LKFS with max -2 dBTP. Podcast: Apple Podcasts -16 LUFS mono / -19 LUFS stereo, Spotify -14 LUFS. Audiobook (Audible ACX): -23 to -18 LUFS, max -3 dBTP, noise floor below -60 dBFS. Cinema (theatrical): typically mixed for dialogue around -31 to -27 LKFS in a calibrated reference room at 85 dBSPL. When in doubt, normalize for the loudest destination (-14 LUFS) and trust that platforms with stricter targets will turn your file down rather than up — the latter could cause clipping.

What is Loudness Range (LRA) and how do I use it?

Loudness Range (LRA) measures the statistical distribution of short-term loudness across a program, reported in LU. It quantifies the dynamic spread between the quietest and loudest sustained sections, computed as the difference between the 10th and 95th percentile of gated short-term values, ignoring momentary peaks and silences. A heavily compressed pop track might have LRA of 4-6 LU (consistently loud); a classical symphony recording can reach 20+ LU (huge dynamic swings between pianissimo and fortissimo). Broadcast targets often cap LRA at 20 LU to prevent inaudible dialogue alternating with explosive effects. For podcasts and audiobooks, aim for 6-10 LU for comfortable listening in cars or earbuds. LRA is a quality target alongside LUFS, not a replacement — they describe different aspects of the same program.

What is the K-system metering scale and how does it differ from LUFS?

The K-system, proposed by mastering engineer Bob Katz in 1999, was an earlier attempt to standardise perceived-loudness metering with three reference scales: K-20 (20 dB headroom above 0 dBFS reference, for film and audiophile mastering), K-14 (14 dB headroom, for pop and rock CDs), and K-12 (12 dB headroom, for broadcast). It used a 2 kHz pink noise calibration to set 0 dB on the meter to 83 dBSPL in a calibrated room. While the K-system never displaced peak metering during the loudness wars, its goals were later realised by the more rigorous BS.1770/EBU R128 LUFS standard, which uses real psychoacoustic weighting instead of fixed-band pink noise. Modern mastering rooms calibrate to LUFS targets directly; the K-system is now mostly of historical interest, though some legacy plugins still display it.

Why does the same file measure differently on different loudness meters?

All meters claiming ITU-R BS.1770-4 / EBU R128 compliance should agree within ±0.5 LU on integrated loudness for a given file. Larger differences usually indicate one of: meter using an older revision (1770-2 lacks the gating refinement of 1770-4 and can give different results on dynamic material), incorrect input channel weighting (5.1 and stereo files use different channel coefficients), file having a long lead-in silence below the gate (some meters include silence, others don't), or true-peak oversampling differences (4x is standard but some meters use 8x for tighter accuracy). When archiving a master, always document the meter and standard version used. For broadcast delivery, the playout chain's reference meter is the final arbiter — your studio measurement is a prediction, not a guarantee.