Loudness targets · Broadcast
ATSC A/85: −24 LKFS, −2 dBTP
ATSC A/85 is the recommended practice behind US television loudness. Programmes and commercials are expected to measure −24 LKFS, and the CALM Act gave it legal teeth for commercials. LKFS is the same thing as LUFS, so any BS.1770 meter can check it.
What ATSC A/85 is
ATSC A/85 is a recommended practice from the Advanced Television Systems Committee, the body behind US digital TV standards. It describes how to measure and control loudness for television so that programmes, adverts and channels sit at a consistent level. Its target is −24 LKFS integrated.
MixOutpost checks A/85 with a tolerance of ±2 dB (−26 to −22 LKFS) and a true-peak ceiling of −2 dBTP, in line with typical US network delivery specs. Your network's or distributor's spec sheet may differ, and it takes precedence.
LKFS and LUFS are the same unit
You'll see both abbreviations, often on the same job. They name the same measurement:
- Loudness, K-weighted, relative to Full Scale (LKFS) is the ATSC and ITU term.
- Loudness Units relative to Full Scale (LUFS) is the EBU term.
Both come from ITU-R BS.1770: K-weighting filter, gated integration, and the same scale. A meter that reads −24 LUFS is reading −24 LKFS. MixOutpost labels the ATSC spec in LKFS to match the paperwork, but the meter is the same one it uses for everything else.
The CALM Act
For years the most common viewer complaint about US television audio was adverts that were much louder than the show. The Commercial Advertisement Loudness Mitigation (CALM) Act addressed that. Under the FCC's rules implementing it, broadcasters and pay-TV operators are expected to follow A/85 for commercials.
The practical effect for mixers: if you deliver spots for US television, the −24 LKFS target isn't optional in the way a streaming reference is. Programme deliveries are usually held to the same target through the network's own specs.
What to aim for
- Land the integrated reading inside the window, ideally near −24 rather than at the edge. Conversions, stems and re-edits can drift a dB.
- Keep true peak under −2 dBTP. Broadcast chains encode audio again downstream, and the extra headroom helps.
- For short spots, loudness is easy to overshoot. A 30-second commercial has no quiet stretches to pull the average down, so every section counts.
- Follow the spec sheet for anything not covered here: measurement of dialogue versus full mix, channel formats, and tolerance.
Specs vary by network
A/85 has been revised since it was first published, and networks and distributors layer their own requirements on top. The figures here match the ATSC A/85 target built into MixOutpost at the time of writing. For a delivery, follow the spec you were given.
Checking ATSC A/85 with MixOutpost
MixOutpost measures on your iPhone, from exactly what your Mac sends, while the timeline plays.
- 01
Stream the output
Insert the MixOutpost plugin last on the master bus, or use the Mac app to send all Mac audio from an editor. Pair your iPhone once with a QR code.
- 02
Open Loudness and pick ATSC A/85
Under TV and film delivery, choose ATSC A/85 (US broadcast). The app shows within spec, or too loud or too quiet and by how many dB outside the tolerance.
- 03
Reset and play the whole spot or programme
Integrated loudness builds from the reset. The reading is taken before Listen as, Dim, Mute or phone volume.
ATSC A/85 compared with other delivery specs
| Spec | Integrated | Tolerance | True peak |
|---|---|---|---|
| EBU R128 (Europe broadcast) | −23 LUFS | ±1 LU | −1 dBTP |
| ATSC A/85 (US broadcast) | −24 LKFS | ±2 dB | −2 dBTP |
| Netflix (dialogue-gated) | −27 LKFS | ±2 dB | −2 dBTP |
See every target, including music streaming and podcasts, on the loudness targets page.
Questions
Is LKFS the same as LUFS?
Yes. Both mean loudness measured to ITU-R BS.1770: K-weighted, gated, relative to full scale. ATSC and many US delivery specs write LKFS; the EBU writes LUFS. A reading of −24 LUFS on MixOutpost is −24 LKFS.
What tolerance does ATSC A/85 allow?
MixOutpost uses ±2 dB around −24 LKFS, which matches common US network delivery specs. Individual networks and distributors publish their own requirements, sometimes tighter, so check the spec sheet you were given.
What is the CALM Act?
The Commercial Advertisement Loudness Mitigation Act is a US law aimed at stopping TV commercials from being louder than the programmes around them. The FCC's rules under it point to ATSC A/85, which is why US broadcast commercials are held to the −24 LKFS target.
Why is the US target −24 and Europe −23?
They're separate standards from different bodies, developed around the same time on the same measurement. In practice a 1 dB difference is small, but it's enough to fail a tight tolerance, so mix to the spec for the market you're delivering to.
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