Sidechain Limiter Stereo - Sidechain-Begrenzer Stereo

Sidechain-Begrenzer Stereo

Detailed: LSP Sidechain-Begrenzer Stereo – Sidechain Limiter Stereo (SCB1S)

Formats: LADSPA, LV2, LinuxVST, JACK

Categories: Dynamics, Limiter

Developer: Vladimir Sadovnikov

Description: 

This plugin implements a brick-wall limiter with flexible configuration. It prevents input monosignal from raising over the specified Threshold. Additional sidechain inputs are provided for better use.

Attention: this plugin implements set of limiting modes, most of them are iterative. That means that CPU load may be not stable, in other words: the more work should be done, the more CPU resources will be used. Beware from extreme settings.

The short description how does the limiter work can be explained with this iterative algorithm:

  1. Initializes gain reduction curve as all samples are reduced by 0 dB
  2. Detects peaks of the input signal that was adjusted according to the gain reduction curve
  3. If there are no peaks, it finally applies gain reduction curve to the signal and completes processing of the signal
  4. Eliminates peaks by applying patch to the gain reduction curve
  5. Repeats step 2

Simplified peak processing example is shown on the following picture:

Simplified peak processing example

Of course, the output signal does not repeat the envelope form of input signal because it's amplitude is changed smoothly, so actually the form of output signal is more complicated.

Currently there are three forms of patches applied to the gain curve - hermite (using cubic polynom for interpolation transients), exponential and linear. These forms can be explained with following picture:

Forms of patches applied to signal

Gain reduction patch affects not only the peak sample, but also surrounding samples. The position and form of this interpolation is related to the peak, so there are four different variants of patch envelope - thin, tail, duck and wide. All these forms related to the peak are shown on the following picture:

Envelope forms of the patch

On this image, sloping lines mean the transision part of the patch. The flat cap in the middle before the peak is a half of attack time, the flat cap in the middle after the peak is a half of release time. Also it's obvious that different envelope forms differently affect dynamics of the signal.

Controls:

'Limiter' section:

'Signal' section: