Mimicking Post-Fader Inserts in Reaper with a Custom Script

#Reaper#Scripting#JSFX#Post-Fader#Workflow#Mixing#Mastering#DIY#ReaPack

Reaper is an incredibly flexible DAW, but one feature sometimes missed by users coming from other platforms is native post-fader inserts. By default, plugins on a Reaper track process audio before the track’s main volume fader and pan controls. While often fine, certain workflows benefit greatly from having effects react to the final fader level.

Think about plugins like dither (which should be applied at the very final stage after all level changes), console emulation systems (where hitting the “channel” input at different levels matters), specific metering plugins, or even binaural renderers for formats like Dolby Atmos. The standard workaround involves routing tracks to auxiliary buses, which can add complexity.

To address this, I developed a system using a ReaScript and some JSFX plugins that cleverly mimics post-fader insert functionality directly on a track. This video explains and demonstrates the system:

This post provides a summary of the installation and usage.

Why Post-Fader Inserts Matter

Placing effects post-fader means their input level changes as you adjust the track fader. This is crucial for:

  • Dithering: Should always be the absolute last process, applied to the final output level.
  • Console Emulation: The fader acts like a channel’s input trim into the console plugin.
  • Metering: Accurately reflects the post-fader signal level.
  • Format Renderers: Tools like Dolby Atmos binaural renderers often need to process the signal after fader adjustments.
  • Certain Dynamics/Saturation: Applying these post-fader can yield different sonic results compared to pre-fader.

Installation Guide

This system uses the ReaPack package manager.

  1. Install ReaPack: If you haven’t already, install ReaPack from reapack.com. It’s an essential tool for extending Reaper’s capabilities.
  2. Import Repository:
    • Go to Extensions > ReaPack > Import repositories....
    • Paste this URL: https://github.com/AudioIdeas/AudioIdeas-Projects (also available at the AudioIdeas GitHub Repo).
    • Click OK.
  3. Install Package:
    • Go to Extensions > ReaPack > Browse packages....
    • Filter by searching for post fader.
    • Select the script (Script: AudioIdeas_Post Fader volume control.lua) and the three JSFX plugins (JSFX: AudioIdeas Post Fader Start, JSFX: AudioIdeas Post Fader End, JSFX: AudioIdeas Post Fader Helper).
    • Right-click and choose Install/update selected packages.
    • Click Apply or OK.

How to Use the System

  1. Run the Script: Open the Action List (Actions > Show action list...), search for post fader, select Script: AudioIdeas_Post Fader volume control.lua, and click Run. (You only need to run this once per Reaper session; it runs in the background).
  2. Insert Plugins: On the track where you want post-fader effects:
    • Insert the JSFX: AudioIdeas Post Fader Start plugin.
    • Insert the plugin(s) you wish to process the audio post-fader (e.g., your dither, console plugin, VU meter).
    • Insert the JSFX: AudioIdeas Post Fader End plugin after those plugins.

Now, any plugins placed between Post Fader Start and Post Fader End will react as if they were placed after the track’s fader. Adjust the fader, volume automation, or trim automation, and the level going into those plugins will change accordingly.

How it Works (The “Magic”)

This isn’t true post-fader processing, but a clever simulation:

  • The background script constantly monitors the fader/volume/trim level of tracks using this system.
  • It sends this level information to the Post Fader Start plugin. This plugin multiplies the audio signal gain by the current fader value before it reaches your target plugins. (e.g., if the fader is at -6dB, it attenuates the signal by 6dB).
  • The script also sends the level info to the Post Fader End plugin. This plugin applies the inverse gain change after your target plugins, restoring the level. (e.g., if the fader is at -6dB, it boosts the signal by 6dB).

The net result is that the plugins in the middle receive a signal modulated by the fader, while the overall track level remains correct.

Features and Considerations

  • Latency: There’s a small delay (default max 100ms) between moving the fader and the gain change being applied. This balances responsiveness with CPU performance. You can adjust this delay by editing the script (find volume_delay variable) – lower values mean less latency but higher CPU usage.
  • Modulation Helper: Reaper doesn’t allow direct parameter modulation by track volume. The included JSFX: AudioIdeas Post Fader Helper plugin outputs the current fader level as a signal that can be used with Reaper’s parameter modulation system. This allows you to, for example, make an EQ band’s gain follow the track fader.

Conclusion

This script and JSFX plugin suite provides a practical solution for achieving post-fader insert workflows directly within Reaper tracks, avoiding the need for complex routing in many common scenarios. It enhances Reaper’s flexibility for tasks like mastering, console emulation, and immersive audio work.

Give it a try! You can find the repository with the code and any updates here: https://github.com/AudioIdeas/AudioIdeas-Projects. I plan to follow up with videos demonstrating specific use cases for this system.