How Reverb Send Level and Return Level Affect the Processed Signal

In a conventional parallel setup, the source reaches the main mix through its normal channel. A separate branch feeds the reverb, whose output reaches the mix through an auxiliary or return channel. Ableton’s manual confirms that sends determine how much audio enters an associated return and that several tracks can feed the same return. Ableton Live 12: Mixing

The working signal path is: source → send level → reverb → return level → main mix, alongside the source’s direct route. This article uses “return level” to mean the return channel’s output fader, placed after the reverb and its processing chain.

Check control placement when a plug-in also offers input and output gain. Those controls have separate jobs: FabFilter documents Pro-R 2’s input control as acting before processing and its output control as adjusting the final output. A return channel fader may sit farther downstream, after additional effects. FabFilter Pro-R 2: Input and output options

Raising one track’s send supplies more of that track to the reverb. On a shared return, this lets you change one instrument’s contribution while leaving the other send settings alone. For example, you can add more snare to a shared room reverb without increasing the keyboard’s send. This follows directly from the individual-send routing described in Ableton’s mixing manual.

Think of the sends as the balance of the mix entering the effect. Before moving one, identify the source that needs adjustment: is the snare too reverberant, or is the entire room return too loud? That distinction prevents repeated corrections across several tracks.

A send also changes the signal presented to anything downstream of it. With a level-sensitive processing chain, its effect can extend beyond a simple volume change. Keep that possibility in mind when comparing a higher send with a higher return.

The return fader adjusts the processed signal after it has passed through the return’s effects. With several sources feeding one reverb, moving that fader changes their combined reverberation together. Their individual send settings remain in place.

Use this distinction as a decision aid:

What you want to change	First control to try	Reason
One instrument needs more reverb	That instrument’s send	Changes its contribution to the effect
The shared reverb is too prominent	Return fader	Adjusts the combined processed output
One phrase needs a reverb accent	Automate its send	Selects the material entering the reverb
The existing tail needs a fade	Automate the return	Controls the tail already reaching the mix
The reverberation lasts too long	Decay control	Changes the reverb’s decay behavior

These recommendations assume the return fader follows the processing chain. If you adjust a gain control before another processor instead, you are also changing that processor’s input level. Trace the actual order before treating two controls as interchangeable.

Yes, under specific conditions. Consider a fully wet reverb that responds linearly to input level, with fixed settings, no level-dependent processing, and constant send and return gains. In that simplified model, the gains multiply; their decibel values add.

For one source, write the wet output as w(t) = r × R[s × x(t)], where x(t) is the input, s is send gain, R is reverb processing, and r is return gain. If R is linear, this becomes w(t) = r × s × R[x(t)].

The following is an illustrative gain calculation, not a measured plug-in result. It holds the source and reverb settings constant:

Send gain	Return gain	Combined external gain
−18 dB	0 dB	−18 dB
−12 dB	−6 dB	−18 dB
−18 dB	−6 dB	−24 dB
−12 dB	0 dB	−12 dB

The first two combinations both multiply the hypothetical unity-input reverb output by approximately 0.126. They can therefore produce the same wet level under the stated assumptions. These numbers do not predict the wet level relative to the dry source: that also depends on the reverb’s response and the source material.

The equivalence has limits. FabFilter documents saturation and nonlinear behavior in Pro-R 2’s Thickness control, plus input-triggered ducking and gating. Such features give input level a role that downstream attenuation cannot necessarily reproduce. The practical inference is to compare tone and envelope as well as loudness when exchanging send gain for return gain. FabFilter Pro-R 2: Main controls

For the parallel setup described here, set the reverb’s mix control to 100% wet. Both FabFilter’s Pro-R 2 documentation and Ableton’s Hybrid Reverb documentation explicitly recommend this setting for send or return use. FabFilter: Main controls, Ableton: Live Audio Effect Reference

The direct channel already supplies the dry sound. If the auxiliary reverb also outputs dry audio, moving its return changes that extra dry contribution along with the reverberation. A fully wet return makes the balance easier to interpret.

“100% wet” describes the plug-in’s output, not the entire mix. The direct source remains audible through its separate route. Likewise, 0 dB on a send means unity gain at that control; it does not specify a wet percentage or guarantee equal perceived dry and reverb loudness.

A post-fader send follows the source channel’s fader; a pre-fader send takes its signal before that fader. Ableton documents its Pre/Post setting as selecting a point before or after the mixer stage. Ableton Live 12: Mixing

From that routing, a useful consequence follows: lowering a source fader with a post-fader send also reduces its new contribution to the reverb. With a pre-fader send, lowering the direct channel can leave the reverb feed unchanged, making the source relatively wetter.

For a straightforward mixing exercise, begin with post-fader sends so source-level adjustments also affect the reverb feed. Choose pre-fader deliberately when you want independent control. Test the behavior by lowering the source fader while watching the reverb input meter; confirm the routing rather than relying on a label alone.

Reverb continues producing a tail after an input event. Ableton describes its Reverb decay control as setting the time required for the tail to fall by 60 dB from its initial amplitude. Ableton: Live Audio Effect Reference

That behavior, combined with the signal path, explains the automation difference. Closing a send stops new material entering the reverb while allowing an existing tail to continue. Lowering the return attenuates the tail already coming out.

Try an isolated snare hit: raise its send for the hit, then close the send before the next hit. Leave the return steady and listen through the decay. Repeat with a steady send and a falling return fader. The first operation selects what excites the reverb; the second shapes what you hear afterward.

Increasing level alone does not change the decay parameter. It may make a quiet portion of the tail audible for longer. If duration is the problem, adjust decay; if the entire tail is too prominent, adjust its level.

Use a short passage containing both active playing and gaps. The gaps reveal the tail; the active section reveals how the return fits around the sources. The following workflow turns the distinctions above into a repeatable listening exercise:

1. Create one auxiliary return and insert a reverb set to 100% wet.
2. Route the direct sources and return to the intended mix output.
3. Start with sends closed and the return at a known setting, such as 0 dB.
4. Raise one source’s send gradually until its reverberation is easy to judge.
5. Add other sources individually, balancing their contributions with their sends.
6. Adjust the return to place the combined reverb in the full mix.
7. Check the meters throughout the path, then audition the gaps and any automation.

If there is no reverb, follow the signal in order: source playback, send destination, reverb input, wet output, return fader, and output routing. If changing the return unexpectedly boosts the dry sound, inspect the plug-in’s mix setting. If one instrument dominates the ambience, revisit its send before changing the shared return.

Once the individual contributions work together, use the return as the overall ambience control. Reach for the send when choosing how much of a source enters the effect, and reach for the return when balancing the processed sound that comes back.

• Mixing — Ableton Reference Manual Version 12
• Live Audio Effect Reference — Ableton Reference Manual Version 12
• FabFilter Pro-R 2 Help — Main controls
• FabFilter Pro-R 2 Help — Input and output options