Insert vs send effects

At a glance

What is an insert effect?

Every channel in a mixer has a row of insert slots. A plug-in in one of those slots sits in the channel's path, so the whole signal goes in one side and comes out the other, and the next plug-in in the row gets the result. The name depends on the DAW: devices on the track in Ableton Live, Audio FX slots in Logic Pro, inserts in Pro Tools and effect slots on a mixer track in FL Studio. In all four the slots come before the channel fader, so the fader turns down whatever the plug-ins put out.

This is where anything goes that should change the whole sound. An EQ cutting 300 Hz from a vocal has to affect all of the vocal, or the mud is still there. A compressor evening out a bass line has to see every note. Because each plug-in feeds the next, the order of the slots changes what you hear, which the effect order lesson covers.

A reverb or delay works on an insert too, through its dry/wet mix knob. The lab's mix knob is a straight crossfade: at 25% the channel keeps 75% of its dry signal, which is 2.5 dB down, and a quarter of what comes out is reverb. Plug-ins use different curves for that knob, and some hold more of the dry level around the middle, but a dry/wet knob at 100% always means no dry sound at all. Step 2 in the lab shows what that does to a lead.

What is a send effect?

A send is a knob on the channel that copies some of its signal to somewhere else in the mixer, without changing the channel itself. The copy goes to a return channel, often called an aux, which has the effect in its insert slot. The return has a fader of its own and goes to the master alongside everything else. The channel's dry sound and the effect reach the master by two separate paths, which is why the setup is called send and return.

Because the dry sound already reaches the master on the channel, the effect on the return should be 100% wet. Then the send sets how much of each track goes into the effect, and the return fader sets the level of the effect as a whole.

Say you set a vocal's send to −10 dB. The vocal on its channel is exactly where its fader left it, and a copy 10 dB quieter goes into the reverb. How loud the reverb ends up also depends on how much level the reverb itself puts out and on the return fader, so the lab measures it: the coach gives each channel's reverb against its dry sound in dB, taken from the sound you're hearing.

The names change between DAWs. In Ableton Live you add a return track (Create, then Insert Return Track) and every track gets a send knob for it, labelled with the return's letter. In Logic Pro you pick a bus in a channel's send slot and Logic creates an aux channel for it. Pro Tools does the same with a send to a bus that feeds an aux input track, Cubase calls the receiving channel an FX channel, and in FL Studio you route one mixer track to another that holds the reverb.

Why reverb and delay usually go on a send

Several tracks share one space

A mix sounds like the players are in the same room when they share the same reverb. With one reverb on a return, the vocal, the snare and the guitar all get the same reflections and the same decay, each at its own send level. With a reverb on each insert, you'd need the same plug-in with the same settings on every track, and any change has to be made several times over. In the lab, step 5 changes the decay once and both channels follow.

The dry sound keeps its level

A send only adds. Turning it up never takes anything away from the track, so you can balance the dry parts with the faders first and add space afterwards without the balance moving. On an insert, every step you take on the mix knob takes some dry level away, and you end up chasing it with the fader.

You can process the effect on its own

Anything after the reverb on the return touches the reverb and nothing else. A common move is a high-pass filter somewhere between 150 and 500 Hz on a reverb return, so the tail doesn't cloud the bass and kick, and often a gentle cut above 8 to 10 kHz so it sits behind the dry sound. You can also put a compressor on the return with its sidechain fed from the vocal, which turns the reverb down while the singer is singing and lets it swell in the gaps. The ducked delay lesson does the same thing to echoes.

It costs less processing

Reverb is one of the heavier effects to run, and a convolution reverb with a long impulse response is often heavier still. One on a return can serve every track that sends to it, so twenty tracks that need the same space cost one instance instead of twenty.

Returns can feed each other

A return has sends like any other channel. Sending a delay return into the reverb return puts reverb on the echoes but not on the dry vocal, which keeps the vocal close while its repeats sit further back. A delay with no feedback in front of a reverb on a return also gives you pre-delay on a reverb that doesn't have the control.

When an insert is the better choice

EQ, compression, saturation, gates, de-essers and pitch correction all belong on inserts, because each one should change the whole sound. On a send each of them would leave the original untouched underneath, so a cut wouldn't cut and a gate wouldn't silence anything.

Reverb and delay belong on an insert when the effect is part of one sound and only that sound. A spring reverb that's part of a guitar tone, a short slapback that's part of a vocal's character, or a delay feeding a distortion pedal on a synth all make sense in the track's own chain, because their place in the chain changes the sound and nothing else needs them. The same goes for a sound you're going to bounce or resample with the effect printed into it.

Keep the mix low on those inserts. Between 10 and 30% is a usual range for a reverb on a lead or vocal insert, and the lab's coach tells you how far the dry sound has dropped at whatever setting you choose.

Pre-fader vs post-fader sends

A send can take its copy from before the channel's fader or after it, and the difference only shows when you move the fader.

A post-fader send follows the fader. Pull a vocal down 6 dB and the copy going to the reverb drops 6 dB too, so the reverb stays at the same level against the dry vocal. That's what you want while mixing, and it's the default in Ableton Live, Logic Pro and Pro Tools. In Ableton the Pre/Post switch sits on the return track and applies to every send into it; in Logic and Pro Tools you set it per send.

A pre-fader send ignores the fader. Pull the same vocal down 6 dB and its reverb doesn't move, so the reverb is now 6 dB louder against the vocal than it was. Close the fader and you hear the reverb on its own. That's useful in two places: headphone mixes while recording, where each performer's mix shouldn't change when you move the main faders, and effects where the dry sound fades out and leaves its reverb behind.

The trouble with pre-fader sends while mixing is fades. Automate a track down at the end of a song with its reverb send set pre-fader and the reverb carries on at full level after the track has gone.

How to set up a reverb send

1. Make a return channelAdd a return or aux track in your DAW and name it after the effect, such as Plate or Hall. One reverb return and one delay return cover a lot of mixes.
2. Put the reverb on it at 100% wetOpen the plug-in and set its mix to 100%. Some reverbs load at a lower mix, so check every time you add one.
3. Turn up the send on each track that needs itStart with the send right down and bring it up until you can hear the space, then back it off a little. Tracks you want further away get more.
4. Leave the sends post-faderThen the reverb follows each track's fader and its automation.
5. EQ the returnA high-pass on the return at 150 to 500 Hz keeps the low end clear. Listen with the return soloed briefly, then in the mix, because a reverb that sounds thin on its own often sits well behind the dry parts.
6. Balance with the return faderUse it to set the overall amount of space, and mute the return now and then to check you still like the mix with it.

Sends for parallel compression and saturation

Any effect on a return is mixed in parallel with the dry tracks, so sends work for more than reverb and delay. A heavily set compressor on a return gives you parallel compression: the drums on their channels keep their transients, and the squashed copy on the return lifts the quiet detail underneath. A saturator on a return does the same for parallel saturation, adding harmonics while the original stays clean.

Timing needs more care here than with reverb. The dry track and its copy have to arrive at the master at the same moment. DAWs compensate for the delay a plug-in adds, so they line up, but with delay compensation switched off, or a plug-in that reports its latency wrongly, the copy arrives a little late and the two cause comb filtering, a hollow, phasey tone. A reverb or delay hides that because its output looks nothing like the dry sound anyway. A compressed copy looks almost exactly like it, so the comb filtering is easy to hear.

Common mistakes

The effect on a return isn't 100% wet

A reverb on a return with its mix at 50% sends half of what it gets back as dry signal, which lands on top of the track's own dry sound. In step 8 of the lab, with the lead's send at −8 dB, the lead comes out 1.6 dB louder than its fader says, the drums go up too, and the reverb drops 6 dB. Every time you change a send, the dry balance changes with it, and that's hard to notice without a meter.

A reverb at 100% on an insert

This is the opposite mistake, and it usually happens when a reverb preset made for a return is loaded onto a track, and the track turns into nothing but reverb.

A different reverb on every track

Each one is a different room, so the parts stop sounding like they were played together, and the session gets heavier with every track you add. Two or three shared returns, such as a short room and a longer plate or hall, cover most mixes.

Correction on a send

An EQ cut or a de-esser on a return only fixes the copy. If the vocal is harsh, the harshness is still on its channel; fix it on the vocal's insert, before the send.

Sends set pre-fader by accident

If a track's reverb doesn't follow its fader or its fade-out, check whether the send is pre-fader. In Ableton, look at the Pre/Post switch on the return track.

Training your ears to hear what's on a send

On a busy mix it's hard to tell which parts are going to a reverb, because the tail of one part hides under another. The quiz under the lab sends the lead, the drums or both to one reverb, covers the screens and matches the loudness, then asks which. Listen to what rings on in the gaps between hits: a tail that carries pitch belongs to the lead, and a wash after each hit belongs to the drums.

Questions people ask

Keep going