Podcast Loudness Normalizer LUFS Calculator

Loudness Units relative to Full Scale measure perceived loudness rather than electrical peak level. The measurement applies a two-stage K-weighting filter, a high-shelf boost approximating head diffraction plus a high-pass roll-off, then takes the mean square of each channel, sums the channels with fixed weights and converts the result to a logarithmic value. A gating stage discards silence: an absolute gate at -70 LUFS and a relative gate 10 LU below the ungated mean stop pauses between speech from dragging the reading down. One LU equals one decibel, so the gain change required to hit a target is simply target minus measured, which is why normalization is a single static gain move rather than a compression pass. Targets differ by delivery route. Podcast platforms cluster around -16 LUFS for stereo, streaming video around -14 LUFS, while broadcast uses -23 LUFS under EBU R128 and -24 LKFS under ATSC A/85. True peak is a separate constraint: inter-sample peaks falling between digital samples can exceed the sample peak by 1 to 3 dB, and lossy encoding to MP3 or AAC can push them higher still, so -1.0 dBTP is the usual ceiling and -2.0 dBTP is safer for heavily compressed delivery. When the required gain would carry true peak past that ceiling, the options are a limiter or accepting a quieter result. Loudness range much above 12 LU tends to make speech unintelligible in a car or on a train, while under about 4 LU the result sounds flat and fatiguing.

The measurement algorithm was standardized by the International Telecommunication Union as Recommendation ITU-R BS.1770 in 2006, drawing on listening tests coordinated through the ITU and on work by Gilbert Soulodre at the Communications Research Centre Canada, which showed that a simple K-weighted mean-square measure predicted subjective loudness about as well as far more elaborate psychoacoustic models. The original recommendation had no gating, so quiet passages pulled programme readings downward; the relative gate was added in BS.1770-2 in 2011 after the European Broadcasting Union demonstrated the problem with real programme material. Adoption was driven by complaints about loud commercials. The EBU published R128 in August 2010, setting -23 LUFS as the programme target and introducing the loudness range and maximum true peak descriptors, with the accompanying EBU Tech 3341 to 3343 documents defining meter behaviour. In the United States the CALM Act was signed in December 2010 and took effect in December 2012, making the ATSC A/85 recommended practice and its -24 LKFS target legally enforceable for television advertising. Streaming services applied the same idea to playback normalization later in the decade, and podcast publishers converged informally on -16 LUFS for spoken-word stereo, a level that survives platform normalization by being turned down slightly rather than turned up with its noise floor amplified.