Version 2 - Now Available

EBU R128 · ATSC A/85 · ITU BS.1770

LEVELAPI 2
PRECISION
LOUDNESS MEASUREMENT

LevelAPI2 is a high-performance C library for EBU R128 and ATSC A/85 loudness measurement and normalization. Integrate broadcast-grade loudness compliance into any environment via standard C FFI. Built by the team behind the R128 standard itself.

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LevelAPI2 - professional loudness measurement library
R128 EBU Compliant
A/85 ATSC CALM Act
C Native Library
FFI Any Language
Standards
Platforms

Origin

THE LIBRARY
THAT HELPED
WRITE R128

In 2006, the ITU published BS.1770 - the measurement standard that would change how the broadcast industry thinks about loudness. Four years later, the European Broadcast Union released R128, the recommendation that put it into practice globally.

The EBU PLOUD committee's work was carried out with the aid of levelapi, then called LMBA1, in close cooperation with the EBU working group. LevelAPI2 is the direct evolution of that original implementation.

LevelAPI is now maintained by tlemon.com. As it continues from BeatRig since 2026. This is not a third-party implementation of the R128 spec - it is the continuation of the reference work that informed the specification itself.

Capabilities

WHAT IT
MEASURES

Integrated Loudness

Full Program Measurement

Integrated, Momentary, and Short-term loudness (LU / LUFS) with gated and ungated variants. Complete compliance with ITU BS.1770.

True Peak

Inter-sample Peak Detection

High-precision TruePeak measurement prevents clipping after D/A conversion. Automatic peak limiter with ~20ms latency included.

Loudness Range

LRA & Dynamic Analysis

LRA, PSR (Peak-to-Short-term Ratio), PLR (Peak Loudness Range), and histogram data for full dynamic range profiling.

Realtime Window

Continuous Stream Metering

Configurable time window for continuous realtime measurements. Multiple independent instances for parallel source monitoring.

Dual Standard

EBU R128 + ATSC A/85

Single convenience call for full EBU or ATSC compliance. Mix and match with manual calibration for custom workflows.

Surround

Up to 16 Channels

Full surround support with SMPTE/ITU, Film Dolby, and DTS channel ordering. Dialog detection and per-channel weighting.

Integration

SIMPLE
TO EMBED

LevelAPI2 ships as a standard C dynamic library. Load it at runtime via your platform's dynamic linking mechanism and you are ready to go. No dependencies on your build system.

Because it exposes a pure C interface, it can be integrated from virtually any language with C FFI support.

  • C / C++
  • Java
  • LUA
  • Python
  • Rust
  • Go
  • .NET / C#
  • Delphi
  • + more
// Load the library at runtime
void* dll = LevelAPI2_LoadDLL(path, &api);
api.SetCertificate(cert, strlen(cert));

// Create instance, configure for EBU R128
LevelAPI2Ptr h = api.Create_LevelAPI2(
    channels, samplerate, bitdepth
);
api.SetPresetEBU_R128(h);

// Feed samples and analyse
api.AnalyseInterleaved(h, samples, numframes);

// Retrieve loudness results
float lu  = api.GetLevel(h, LU,       -1);
float lra = api.GetLevel(h, LRA,      -1);
float tp  = api.GetLevel(h, TruePeak, -1);

// Normalise to target level
api.AdjustInterleaved(h, samples, numframes);

api.Destroy_LevelAPI2(h);

→ Full example + header file available with license

What's Included

THE
OFFERING

Core Library

LevelAPI2

The core loudness measurement and normalization library. A closed-source binary (.dll / .so) with a pure C interface, built for speed and designed to integrate into any production audio pipeline.

  • EBU R128 & ATSC A/85 compliance in one call
  • Full metering suite: LU, LRA, TruePeak, PSR, PLR, PPM, RMS
  • File-based (WAV/AIFF/FLAC) and stream-based processing
  • High-quality automatic peak limiter included
  • Multiple simultaneous instances via handle system
  • Up to 16-channel surround with dialog detection
Windows .dllLinux .sox86 / x64Custom builds

Bundled - Windows Only

LevelShow2

A DirectShow filter wrapping LevelAPI2 for Windows media pipeline integration. Included in the standard license at no extra cost.

  • DirectShow filter for Windows pipelines
  • Graphical properties page + COM interface
  • 1-instance or 2-instance analyze/adjust workflows
  • Included with LevelAPI2 license
WindowsDirectShowCOM / ILevelShow2
⬤  Coming H2 2025

Realtime loudness adjuster

A VST 2.4 plugin for OBS Studio. Real-time loudness-correcting gain adjustment for live streams, powered by LevelAPI2.

Stay informed →

Licensing

READY TO
INTEGRATE?

LevelAPI2 is licensed on an annual basis. The distribution license covers your right to ship software with the binary included - The offer is a transparent turn-key solution. Once distributed the library runs standalone, no call-home, no time locks.

Get in touch to discuss your use case and receive a trial certificate to ensure the integration in your project.

info [at] levelapi [dot] dev