APU Dynamics Optimizer

The APU Dynamics Optimizer is a dynamics optimization tool designed to support modern loudness types (LUFS, True Peak). Underneath the hood, the optimizer uses the same compression engine as the APU Loudness Compressor, but benefits from the full audio waveform instead of real-time measurements. This allows the gain envelope to be meticulously optimized across the entire waveform.

The design of this tool allows you to very precisely target a specific average LUFS and dynamic range. Once the gain envelope has been optimized, you can playback the result in real-time while adjusting the character of the sound with the same collection of parameters from the compressor plug-in.

Walkthrough

When you first open an audio file, the optimizer will analyze the audio file’s loudness timeline. You’ll then be presented with a pair of histograms. On the left, you’ll see the audio file’s current loudness distribution. On the right, you’ll see a target distribution. The optimizer’s job is to dynamically compress and expand the audio throughout the entire audio file strategically to match the target distribution.

Before continuing to the next step, you can make adjustments to the source percentiles. This allows you to exclude any unwanted audio from the optimization process. By default, the percentiles are set to match the LRA standard from LUFS. This generally does a good job capturing the main body of the audio.

Once you’re happy with the source percentile range, you can then press the right arrow to continue to the next step.

Once optimization is complete, you can play the result in real-time while adjusting the character of the sound with the same collection of parameters from the compressor plug-in. Use the play/stop buttons and seek slider to navigate the audio while making any adjustments you’d like.

Once you’re happy with the result, you can export the optimized audio to a new file. This file is always stored with the same samplerate as the original audio, using 32-bit floating point wave format. This ensures the highest quality audio is preserved. This format also allows samples over 0 dBFS, which ensures no clipping occurs.

You can listen and export with or without limiting. The built-in limiter can be configured in the Limiter tab, or you can bypass the limiter entirely and use your own external limiter after export.

Dynamics shaping

The dynamics optimizer allows you to reshape the full dynamics spectrum of your audio file. You can choose between Uniform or Normal distribution, with the ability to skew the latter toward the top or bottom of the distribution. This allows you to shape the dynamics of your audio in a variety of ways. The optimizer takes this information and uses it to make many tiny adjustments to the compress/expand ratio over time. Something you’d never be able to do with a traditional compressor.

The optimizer can be configured to use the following distribution types:

Uniform

Uniform distribution type is a flat distribution across the entire loudness range. This is a good starting point for most audio files, as it doesn’t favor any particular loudness range. The result is an extremely balance loudness profile.

Normal

Normal distribution type is a bell curve distribution which can be skewed toward the top or bottom of the distribution. This allows you to dial in a very particular shape of your choosing, whether it’s to more closely match the original audio or for creative effect.

Loudness flavors

One of the key features of this optimizer is its support for a variety of loudness types. The optimizer’s detection circuitry can be configured to use either LUFS or traditional measurement units (RMS, Peak). You can also choose to split or link channels, which is particularly useful for multi-channel audio formats such as Dolby Atmos®.

The optimizer’s detection circuitry can be configured to use any of the following loudness types:

Momentary

Momentary is a short duration LUFS measurement (400ms), which is useful for processing the audio’s moment-by-moment dynamics. This mode is responsive but also transparent, making it an appropriate default for the optimizer. K-weighting and channel weighting are applied to the optimizer’s detection circuitry, improving perceptual accuracy.

Short-Term

Short-Term is a longer duration LUFS measurement (3 seconds), which is useful for processing the audio’s large scale dynamics. Given the longer duration, this mode is less responsive than momentary, but it can be useful for adjusting the bigger picture of the audio’s dynamics. K-weighting and channel weighting are applied as with momentary.

RMS

RMS loudness types use a rolling time interval of 300ms. RMS is a traditional loudness measurement, which is a good first-order approximation of perceived loudness. This mode doesn’t apply K-weighting or channel weighting to the optimizer’s detection circuitry, giving it a more traditional character.

True Peak

True Peak loudness types are similar to traditional peak measurements, but they are more accurate as they take into consideration inter-sample peaks. These measurements use a time interval equal to the configured block size (1ms by default). This mode is extremely responsive, making it suitable for very fast attack and release times.

Peak

Peak loudness types are a standard peak circuit, operating on a time interval equal to the configured block size (1ms by default). This is another traditional compressor style measurement. Technically, this mode is even slightly more responsive than True Peak, but it is less accurate as it doesn’t take into consideration inter-sample peaks.

Credits

This software was developed by APU Software, LLC and is available as a standalone application (windows x64/x86, macOS universal). The software libraries below are utilized for portions of the software:

• JUCE (cross-platform audio and user interface framework)
• Boost (header-only algorithms)
• libebur128 (loudness measurements)

Demo video song credits:

• Dan Phillipson - Feel The Drama, licensed via PremiumBeat.