DIY Split EQ: Processing Transients and Tonal Sound Separately with Free Plugins

#Audio#Plugins#Eventide SplitEQ#Transient Designer#Reaper#Mixing#Mastering#Free Software

Plugins like Eventide’s SplitEQ offer powerful ways to process the transient and tonal parts of your audio independently. This allows for surgical adjustments that aren’t possible with traditional EQs or dynamics processors. While SplitEQ uses sophisticated methods for separation, can we achieve similar functionality using simpler tools, perhaps even free ones?

In the video below, I demonstrate a DIY approach to separating and processing transient and tonal content using a standard transient designer and some clever routing:

This post breaks down the method shown in the video, highlighting how you can build your own “Split EQ” style processing chain.

An Alternative Approach, Not a Clone

It’s important to note, as mentioned in the video description, that this method differs significantly from how SplitEQ likely works internally. SplitEQ seems to use a frequency-dependent separation method (perhaps FFT-based, similar to Oeksound Spiff), allowing it to identify transients within specific frequency bands.

My approach uses a traditional, full-bandwidth transient designer. This means if it detects a transient (like a kick drum), any processing applied to the “transient” channel will affect the entire frequency spectrum for the duration of that detected transient event. It’s less nuanced than SplitEQ but still incredibly useful, offering a different flavour of transient/tonal control.

The DIY Method (Reaper Example)

The core idea is to use a transient designer plugin to create two separate audio streams: one containing mostly the tonal parts and one containing mostly the transient parts. The video demonstrates this using Reaper, taking advantage of its flexible routing and built-in features.

  1. Splitting the Signal:
    • Use any standard transient designer plugin (the video uses the free Kilohearts Transient Shaper).
    • Tonal Stream: Turn the ‘Attack’ parameter all the way down. The main output of the plugin now contains primarily the sustained, tonal parts of the signal.
    • Transient Stream: Utilize Reaper’s “Delta Solo” function (Alt-click the Wet/Dry knob). With the Attack still down, Delta Solo outputs the difference between the original signal and the tonal signal – essentially isolating the transients. Other controls on the transient shaper (like ‘Pump’/‘Speed’ on the Kilohearts plugin) can help fine-tune the separation.
  2. Routing (Reaper Multi-channel Setup):
    • To process these streams separately, a multi-channel track setup is used in the video:
    • Duplicate the transient shaper plugin.
    • Instance 1 (Tonal): Runs in normal mode (Attack down), output routed internally to channels 5 & 6.
    • Instance 2 (Transient): Runs in Delta Solo mode (Attack down), output left on channels 1 & 2.
    • Polarity Correction: Since Delta Solo often inverts polarity, a simple utility plugin (like Reaper’s JS: Channel Polarity Control) is added after Instance 2 to flip the polarity of channels 1 & 2 back.
    • Mixing: A mixer plugin (like Reaper’s JS: IX/Mixer) combines the Transient stream (channels 1 & 2) and the Tonal stream (channels 5 & 6) back into a standard stereo output (channels 1 & 2) at the end of the chain.
  3. Applying Processing:
    • Insert any EQ, compressor, reverb, etc., before the final mixer plugin.
    • Route the plugin to process channels 1 & 2 to affect only the Transients.
    • Route the plugin to process channels 5 & 6 to affect only the Tonal parts.
    • The video demonstrates this using two instances of ReaEQ.

Advanced Integration (Optional)

The video also shows a neat trick if you own FabFilter Pro-Q: when inserted on the multi-channel track (before the mixer), Pro-Q recognizes the 6 channels. You can then create EQ bands specifically for the ‘Front Left/Right’ (affecting Transients on channels 1&2) or ‘Surround Left/Right’ (affecting Tonal on channels 5&6) within the single plugin interface, even linking bands for mirrored adjustments.

Why Bother? Use Cases

This technique, while different from dedicated Split EQs, opens up many mixing possibilities:

  • Boost the crack of a snare (transient) without boosting its ring (tonal).
  • Tighten bass guitar (tonal cut) while enhancing its pluck attack (transient boost).
  • Add reverb only to transients for a unique spatial effect, or only to the tonal body.
  • Control cymbal wash (tonal) independently from the stick hits (transient).

Conclusion

While not a direct replacement for sophisticated plugins like SplitEQ, this DIY approach using a standard transient designer and flexible routing provides a powerful and often free way to gain independent control over the transient and tonal elements of your audio. It’s a technique well worth adding to your mixing and sound design toolkit.

As mentioned at the end of the video, exploring DAW-agnostic methods or even an analog hardware version could be interesting future projects! Let me know if those ideas resonate with you.