LevelAnchor

A Windows VST plugin that holds a live audio source's loudness on a LUFS target, in real time.

LevelAnchor measures programme loudness continuously and modulates output gain to keep it on the target you set. It does not reshape the audio the way a compressor does — it moves the level, slowly enough to stay inaudible, and leaves the dynamics alone. Set a target, leave it running, and the source stays where you put it.

It is built for streamers, primarily OBS Studio, and it is a showcase of LevelAPI — the loudness engine doing the actual work, which is licensed separately (see The engine below).

To just use the plugin, take the signed installer or the VST2 ZIP from the latest release. The LevelAnchor plugin page has the install guide, an OBS setup walkthrough and the free-use terms.

What it does

• One control. A LUFS target, -24 to -8, default -16, set from the 32-LED strip on the left.
• Shows its work. Scrolling deviation trace against a fixed target line, the gain currently being applied, the integrated output level, deviation from target, and a session timer.
• Will not clip. After the gain change, the signal passes through a high-quality EBU-approved limiter with its ceiling at -1 dB, per EBU R 128 — so anchoring a quiet source upward cannot push peaks into clipping.
• Runs unattended. The plugin does its job with the UI closed, which is how it is normally used.
• Entirely local. No network code of any kind: no telemetry, no accounts, no activation, no update check.

Loudness measurement follows the ITU-R BS.1770 / EBU R 128 lineage. The interesting part is not the measurement — free meters are everywhere — it is holding a target in real time, when loudness is only known after the audio has played.

What it is not

• Not a metering suite, and not a mastering chain. It does one job: anchor to a target LUFS level.
• Not a limiter — although it contains one. The -1 dB ceiling exists to keep the gain change from clipping, not to be driven as a loudness tool.

The engine, and why it is not in this repository

The real-time loudness measurement and adjustment core is LevelAPI2, a closed-source library. It is not in this tree and will not be. What is here is the entire plugin around it: the JUCE processor and editor, the pixel-matrix UI, the parameter handling, and — most relevant if you are evaluating the library — the code that loads LevelAPI2 and calls it from an audio callback.

This repository is a working reference integration rather than a sample: the released binary is built from this same source, differing only in which linking configuration was used. If you are here to see how LevelAPI2 is integrated into a real product, start with Source/LevelApiDynamic.h and its .cpp, alongside the LevelAPI2 loudness SDK documentation, which covers the C API those files call.

Distributed files

The released plugin is a complete, working build with LevelAPI2 linked in statically. There is no DLL to install, no key to enter and nothing to configure: drop it in your VST folder and it works.

A build you make from this source uses the dynamic path. It loads LevelAPI2 from its DLL at runtime, so it needs a copy of the library — which is what a LevelAPI license gets you. Without one the plugin still compiles, loads and runs; it simply passes audio through unchanged. The static configurations are published for transparency rather than as a route to take: building that way needs the library as a static lib, which is a separate arrangement.

So: to use LevelAnchor, take the release. To read or extend it, build the source. Or get in touch to put LevelAPI2 in your own project, or to use the LevelAnchor plugin in an organization with an annual revenue over €500k.

Two linking paths

Both paths are permanent and both are expected to build. Which one you get is decided by the __STATIC_LIB__ define, set per build configuration in LevelAnchor.jucer:

Configuration	Path	Notes
Debug, Release	Dynamic — the default	LevelAPI2 is loaded from its DLL at runtime through the C API in Source/LevelAPI2_dynlib.h. This is what you build if you clone the repo.
Debug-static, Release-static	Static (__STATIC_LIB__=1)	How the released binary is built. Needs LevelAPI2 as a static library, which is a separate arrangement.

PluginProcessor holds whichever adjuster the configuration selected behind an identical method surface, so processBlock is shared between the two paths.

Building

Requirements

• Visual Studio 2022, x64
• JUCE 8 (developed against 8.0.4) and the Projucer
• The VST2 SDK 3.6.9. Steinberg no longer licenses VST2, and the SDK is not redistributable, so it is not included here — you need your own copy.
• A LevelAPI2 license for the DSP core.

Steps

1. Open LevelAnchor/LevelAnchor.jucer in the Projucer.
2. Point the JUCE module paths at your own JUCE 8 modules folder.
3. Set a LIBS environment variable such that $(LIBS)vst/VST_SDK369/VST2_SDK resolves to your VST2 SDK. It is concatenated without a separator, so LIBS must end in one — or just edit the header path in the Projucer to point wherever your SDK lives.
4. Save the project to re-export the Visual Studio files, then build Builds/VisualStudio2022/LevelAnchor.sln — Debug or Release, x64.

Note that the configurations carry a post-build step copying the plugin to C:\Program Files\VSTPlugins, which needs an elevated Visual Studio; remove it in the Projucer if you would rather it did not.

Running a build you made yourself

None of this applies to the released plugin, which has the library inside it. A build from this source needs LevelAPI2-x64.dll at runtime (LevelAPI2-x64_d.dll for Debug builds), looked for in this order:

1. The LEVELAPI2_DLL environment variable — either the DLL itself or the folder holding it. A development convenience; nothing in a shipping build depends on it.
2. Next to the plugin binary. This is the deployment answer.
3. The bare filename, which hands the search to Windows.

The LevelAPI2 library expects a certificate. It is taken from LEVELANCHOR_CERTIFICATE_STR if that was defined at build time, otherwise from a certificate.txt sitting next to the plugin.

Getting the library. LevelAPI2 is not a public download. If you want to build and run against it, or you are looking at the library for your own product, get in touch through the LevelAPI2 loudness library site.

In OBS

Add LevelAnchor as a filter on the audio source you want anchored — open the source's pop-up menu and select Filters → + → VST 2.x Plug-in — then set the target and leave it. Correction starts on the first block of audio; there is no warmup to wait through.

Then do the same on every source that makes noise: mic, Desktop Audio, anything else that is live. Leave them all on the same target, and set the balance the way you always did, on the mixer's volume sliders. OBS has no filter slot on the master output, and per-source is the better place for it anyway: it is what keeps the balance between sources steady.

The menu path is not obvious the first time; there is a step-by-step OBS walkthrough with screenshots if you want it.

License

Three layers, and they are not the same thing:

• This source code is MIT licensed — see LICENSE. Read it, copy from it, build it, ship it in your own product. The integration code serves as implementation example.
• LevelAPI2, the engine, is closed source and licensed separately on an annual B2B basis. MIT covers none of it, it is not in this repository, and a build made from this source does nothing useful until you have it. See the LevelAPI2 licence terms.
• The released plugin is free to use, including on monetized streams and channels. Above €500k of annual organization revenue, a LevelAPI license is required — the same license that covers the engine. The threshold is a hard line, not a suggestion; below it, there is nothing to pay and nothing to sign.

Support

One-to-one help requires a LevelAPI license. For feedback, and for anything to do with licensing the engine, go through the contact details on the LevelAPI site.