Quick Reference
| Parameter | Requirement | Notes |
|---|---|---|
| Program loudness | -24 LKFS ± 2 LU | Pass range -26 to -22 LKFS, measured per ITU-R BS.1770-4 |
| Gating | Program (ungated) | Full program measurement, no dialogue gating |
| Max true peak | -2.0 dBTP | Best practice: limit at -2.3 dBTP |
| Sample rate | 48 kHz | Broadcast standard, required |
| Dialnorm metadata | Required in AC-3/E-AC-3 | Must match measured loudness in the encoded stream |
| Legal status | Mandatory (CALM Act) | US broadcasters since December 13, 2012 |
How A/85 Compliance Is Measured
One number for everything on air
The core of A/85 is a single reference: -24 LKFS ±2 LU program loudness, measured over the full content per ITU-R BS.1770-4 without dialogue gating. Programs, promos and commercials all measure against the same target, which is exactly what the CALM Act was written to enforce.
True peak with transmission headroom
The -2.0 dBTP ceiling is measured as oversampled true peak. Broadcast chains add processing after your delivery: transmitter limiting, re-encodes, set-top box DACs. Limiting the master at -2.3 dBTP keeps meter tolerance from ever deciding a compliance check.
The measurement and the metadata must agree
A/85 compliance lives in two places: the measured loudness of the audio itself, and the dialnorm value carried in the AC-3/E-AC-3 metadata, which tells consumer decoders how loud the program is. When the two disagree, playback normalization is wrong even though the audio measured clean. Verify the PCM master first, then confirm dialnorm at the encoding stage.
Same numbers as Prime Video, different reason
Amazon adapted A/85 for Prime Video OTT delivery, so both specs read -24 LKFS ±2 LU / -2 dBTP / 48 kHz. The difference is enforcement: A/85 is federal law for broadcasters, the Prime Video spec is a delivery contract. A master that passes one passes the loudness portion of the other.
FAQ
Is ATSC A/85 actually the law?
The CALM Act (Commercial Advertisement Loudness Mitigation Act, 2010) made compliance with ATSC A/85 legally binding for US broadcast television as of December 13, 2012. The FCC enforces it. Commercials and programs are held to the same -24 LKFS reference so ad breaks stop jumping out.
What is the difference between ATSC A/85 and EBU R128?
Both build on ITU-R BS.1770, but they set different targets and ceilings: ATSC A/85 specifies -24 LKFS with a -2 dBTP maximum, EBU R128 specifies -23 LUFS with -1 dBTP. A US broadcast master is 1 LU quieter and keeps 1 dB more peak headroom than a European one. The measurement algorithm underneath is the same.
What is dialnorm and does a PCM QC check cover it?
Dialnorm is a metadata field in the AC-3/E-AC-3 stream that tells the decoder the program loudness so playback can be normalized. A/85 compliance requires dialnorm to match the actual measured loudness. A PCM-level QC check verifies the measured loudness and true peak of the delivery master; the dialnorm value is set at encoding and has to be verified in the encoded stream.
Does A/85 use dialogue gating like Netflix?
No. A/85 measures full program loudness per BS.1770 without dialogue gating. The confusion comes from history: early A/85 practice anchored on dialogue, but the current standard measures the whole program. Netflix's -27 LKFS dialogue-gated spec is a different measurement and a different number.
Why is the true peak ceiling stricter than music streaming?
Broadcast transmission chains, set-top boxes and legacy consumer hardware clip harder and earlier than streaming playback stacks. The -2.0 dBTP ceiling keeps the signal clean through transmitter processing and downstream re-encodes. Limiting at -2.3 dBTP leaves tolerance for meter differences.