--- title: "ITU-R BS.1770 — The Measurement Underneath Everything" description: "The algorithm every loudness target is defined in terms of. Current revision BS.1770-5 (November 2023), K-weighted and level-gated — and why the gate is the part that matters." canonical_url: "https://elephantaudio.pk/reference/itu-r-bs1770" type: "Article" date_modified: "2026-09-18T13:01:43.380Z" publisher: "Elephant Audio" publisher_url: "https://elephantaudio.pk" source_kind: "published-standard" source_url: "https://www.itu.int/rec/R-REC-BS.1770/en" source_fetched_at: "2026-09-18" entities: - name: "Lahore" type: "City" same_as: - "https://www.wikidata.org/wiki/Q11739" - "https://en.wikipedia.org/wiki/Lahore" - name: "Pakistan" type: "Country" same_as: - "https://www.wikidata.org/wiki/Q843" - "https://en.wikipedia.org/wiki/Pakistan" author: name: "Abu Bakar Zahid" role: "Founder, Managing Director & Music Producer at Elephant Audio" url: "https://elephantaudio.pk/founder" same_as: - "https://www.linkedin.com/in/abubakarzahid94" - "https://www.youtube.com/@AbuBakarZahid" - "https://www.imdb.com/name/nm12369947/" - "https://open.spotify.com/artist/1vsRY1hLmqEBXcx5xeKs0m" - "https://music.apple.com/us/artist/abu-bakar-zahid/1654787374" - "https://www.deezer.com/us/artist/190524117" - "https://on.soundcloud.com/EnpcD" - "https://www.instagram.com/abubakarzahid94/" - "https://www.facebook.com/abubakarzahid9400/" - "https://twitter.com/abubakarzahid94" - "https://soundsofpakistan.com/artist/abu-bakar-zahid/" person: "Abu Bakar Zahid" person_same_as: - "https://www.linkedin.com/in/abubakarzahid94" - "https://www.youtube.com/@AbuBakarZahid" - "https://www.imdb.com/name/nm12369947/" - "https://open.spotify.com/artist/1vsRY1hLmqEBXcx5xeKs0m" - "https://music.apple.com/us/artist/abu-bakar-zahid/1654787374" - "https://www.deezer.com/us/artist/190524117" - "https://on.soundcloud.com/EnpcD" - "https://www.instagram.com/abubakarzahid94/" - "https://www.facebook.com/abubakarzahid9400/" - "https://twitter.com/abubakarzahid94" - "https://soundsofpakistan.com/artist/abu-bakar-zahid/" --- # ITU-R BS.1770 — The Measurement Underneath Everything ## What is ITU-R BS.1770, and why does every spec reference it? ITU-R BS.1770 defines the algorithms that measure audio programme loudness and true-peak level. Every broadcast and streaming target is expressed in its units, which is why LKFS and LUFS are the same measurement under two names. The in-force revision is BS.1770-5, approved November 2023. BS.1770-5 in force (approved November 2023) · Eq. (7) the gate (what makes it foreground loudness) · 1 LU = 1 dB the unit (LKFS and LUFS are identical) · ±0.3 dB true-peak tolerance (per EBU R 128, 20 kHz-limited) One algorithm, two names: Every loudness number on every delivery spec sheet — the European −23, the American −24, the streaming −14 — is a measurement made by the same algorithm. ITU-R BS.1770 defines it, and the regional standards do not redefine the measurement; they only choose a target value to aim it at. That is the whole explanation for the most persistent confusion in the field. ATSC, the North American standard, calls the unit LKFS. The EBU, in Europe, calls it LUFS. They are the same unit, produced by the same computation, and one Loudness Unit equals one decibel. A file measuring −23 LUFS measures −23 LKFS. Nothing converts between them because there is nothing to convert. So the difference between the American target of −24 and the European −23 is not a difference of standards or of units. It is one decibel — small enough that people assume it cannot matter, and large enough that an automated compliance system will reject the file. How EBU R 128 invokes it: > "that measuring audio programme loudness has been defined in ITU-R BS.1770, introducing the measures LU (Loudness Unit) and LUFS (Loudness Units, referenced to Full Scale)" — EBU R 128-2023. clause e) The gate is the part that matters: A plain average of a programme's loudness would be dragged down by every silence and every quiet passage, so a film with long atmospheric stretches would measure quieter than a continuous dialogue piece even if the dialogue in both sat at the same level. The measurement would then be about pacing rather than about loudness. BS.1770 solves this with level gating: passages below a relative threshold are excluded from the integrated figure. EBU R 128 specifies the gated form explicitly and identifies it by equation number, and describes the consequence as measuring foreground loudness — the part an audience actually perceives as the programme, rather than the gaps between it. This is why a quiet, dynamic mix and a dense, compressed one can both deliver at −23 LUFS while sounding nothing alike. The target constrains where the foreground sits. It does not constrain dynamic range, which is measured separately as Loudness Range. > "that the level-gated measurement of Programme Loudness defined in ITU-R BS.1770 Eq.(7) (which hence measures foreground loudness) is advantageous to improve the loudness matching of programmes" — EBU R 128-2023. clause f) What a compliant meter has to do: A spec that names a target is also naming the measurement. EBU R 128 states the requirement on the meter, not only on the number: - Measure to ITU-R BS.1770, including the level-gating method described in equation (7). - Comply with EBU Tech 3341 — the EBU Mode metering specification, currently version 4.0, dated 21 November 2023. - Measure true peak to the same recommendation, with a measurement tolerance of ±0.3 dB for signals bandwidth-limited to 20 kHz. - ⚠️ True peak is not sample peak. A signal can sit at −1 dBFS by sample and exceed it between samples, which is what the true-peak algorithm reconstructs and what a delivery spec is actually limiting. Revision history, and which one your spec means: A spec sheet that cites a revision number is citing one of these. The in-force revision is BS.1770-5: - BS.1770-5 — November 2023. In force. - BS.1770-4 — October 2015. Superseded. - BS.1770-3 — August 2012. Superseded. - BS.1770-2 — March 2011. Superseded. - BS.1770-1 — September 2007. Superseded. - BS.1770-0 — July 2006. Superseded — the original. A timing detail worth knowing: BS.1770-5 and the current EBU R 128-2023 were both approved in November 2023. A spec sheet written before then may cite BS.1770-4, and older delivery paperwork frequently still does. In practice the targets have not moved, so a file that complies under one revision is not suddenly out of compliance under the next — but if a broadcaster's paperwork and your meter disagree about which revision is in play, that is the first thing to check rather than the last. The sources: Both read directly on 2026-09-18: - ITU-R BS.1770 — Algorithms to measure audio programme loudness and true-peak audio level — The recommendation's own page: in-force revision, full revision history, managed by Study Group 6.: https://www.itu.int/rec/R-REC-BS.1770/en - EBU R 128 — Audio loudness normalisation and permitted maximum level — The source for the gating clause, the meter-compliance requirement and the ±0.3 dB true-peak tolerance quoted here.: https://tech.ebu.ch/docs/r/r128.pdf - EBU Tech 3341 — EBU Mode metering — The meter specification R 128 requires compliance with. Version 4.0, 21 November 2023.: https://tech.ebu.ch/publications/tech3341 ## Frequently asked questions ### Is LKFS different from LUFS? No. They are the same unit measured by the same algorithm, ITU-R BS.1770. ATSC calls it LKFS and the EBU calls it LUFS. One Loudness Unit equals one decibel, and a file measuring −23 LUFS measures −23 LKFS. No conversion exists because none is needed. ### Why does my quiet mix measure the same as a loud one? Because the measurement is gated. Passages below a relative threshold are excluded, so the integrated figure describes foreground loudness rather than an average across the whole timeline. Two mixes with very different dynamic ranges can therefore share a target. Dynamic range is measured separately, as Loudness Range. ### Which revision of BS.1770 should I be measuring to? BS.1770-5, approved November 2023, is the in-force revision. Older spec sheets frequently still cite BS.1770-4 from 2015. The targets have not moved between them, so compliance does not usually change — but if your meter and a broadcaster's paperwork disagree on the revision, check that before re-mixing anything. ## Related - [The European broadcast target](https://elephantaudio.pk/reference/ebu-r128/raw) - [What Spotify normalises playback to](https://elephantaudio.pk/reference/spotify/raw) - [Which target applies to your spot](https://elephantaudio.pk/guides/broadcast-loudness-specs/raw) ## Studio - **Studio:** Elephant Audio — Lahore, Pakistan - **Founder:** Abu Bakar Zahid — Founder, Managing Director & Music Producer at Elephant Audio - **Website:** https://elephantaudio.pk - **Contact:** abubakar@elephantaudio.pk