Slapback delay in plain English
A slapback is the shortest kind of echo you can still hear as an echo. The delay plays the sound back once, a tenth of a second or so after the original, with no trail of repeats fading away behind it, because the feedback is at or near zero.
Your ear treats a repeat that close in a particular way. It knows there are two events, but they're so near each other that they seem attached, so a sung word gets a little kick of extra size right behind it. A delay at 400 ms sounds like a second voice answering the first; a slapback at 110 ms sounds like the first voice in a bigger, harder space.
Slapback is the sound of a lot of 1950s rock and roll and rockabilly, and it never went away. You'll hear it on vocals that need to stay at the front of a mix, on electric guitars that would sound thin bone dry and on snares that need a bit of room. The general delay lesson covers every control on a delay; this page stays with the one setting and goes into why it works.
The history of slapback
Slapback started as a side effect of tape. A tape recorder writes the sound with a record head, and the tape then carries on past a playback head a short way along. If you listen to the playback head, you hear the sound a fraction of a second after it was recorded. Mix that playback in with the live signal and you get one short echo.
The time of that echo came from two things: the distance between the heads and the speed of the tape. Suppose the heads are 1.5 inches apart. At 15 inches per second, a standard studio speed, the tape takes a tenth of a second to cover that gap, so the echo arrives 100 ms late. Run the same machine at 7.5 inches per second and it arrives after 200 ms. There was no time knob: the machine and the speed it ran at set the echo.
Sam Phillips used this at Sun Studio in Memphis, and it's all over Elvis Presley's early Sun recordings. Feed some of the playback back into the record head and you get more repeats, which is how a tape echo with feedback works. The tape delay lesson follows that side of the story.
The name describes the sound. A clap in front of a hard, flat wall comes back as one sharp reflection, which acousticians call a slap echo. Sound travels at about 343 metres a second, so a reflection 100 ms late has covered about 34 metres, out to a wall 17 metres away and back.
Reading the lab
The lab is the same delay as the main delay lesson, set up for slapback. Sync is off, so you set the time in milliseconds with the Time knob, and the Duck control is locked because it does nothing useful for a single quiet repeat.
On the echo timeline at the top, a slapback with no feedback is a single bar just after the white bar of the original. The top lane is the left speaker and the bottom lane is the right. Add feedback and a second, shorter bar appears; turn on ping-pong and the repeat moves into the left lane only. The Right now panel reads the settings back to you with numbers measured from the delay itself, including how far under the dry sound the repeat sits.
Start with the vocal, because slapback on a voice is easy to hear. The guitar, the acoustic guitar and the drums show what it does to a picked part or a snare. Press A/B to switch the delay off at the same loudness, which is the quickest way to hear what the slap adds.
Slapback delay time
Delay time decides whether you get a slapback at all. The same single repeat can blend into the sound, sit right behind it or stand apart from it, depending only on how long it waits.
| Delay time | What you hear | Usual name |
|---|---|---|
| Under 30 ms | One sound, thicker and coloured in tone | Doubling, the Haas effect, comb filtering |
| 30 – 80 ms | A tight, slightly rough thickening | Short slap or doubling |
| 80 – 150 ms | A quick echo attached to each note | Slapback |
| 150 – 200 ms | A slap that starts to separate | Long slap |
| Over 200 ms | A separate echo after each note | Echo or delay |
Below about 30 ms, your ear stops hearing two events and hears one. That's the precedence effect, which the Haas effect lesson covers. The two copies also add up at some frequencies and cancel at others, which gives the hollow, slightly metallic tone of comb filtering. It's a useful effect in its own right, but you hear it as a change of tone and never as an echo.
Past about 200 ms, each repeat clearly stands on its own. On a vocal, every word gets a second, quieter syllable after it, and on a busy part the echoes start to blur the rhythm. That's a perfectly good delay, but it has lost the tight, attached feel of a slapback.
Between the two, the repeat is late enough to have its own attack and early enough that it seems tied to the note. Shorter times in that range sound tighter and suit fast parts. Longer ones sound more obviously like an echo and work in slower songs and sparse arrangements.
Should slapback follow the tempo?
Usually not. Slapback is one of the few delays that works better with sync off. A run of echoes that's slightly off the beat drifts further out with every repeat, so long delays need to be locked to the tempo, but a single repeat lands once, at the same short distance behind each note, and has nothing to drift away from.
If you'd like a starting point from the tempo, work out a 1/16 note. One beat lasts 60,000 divided by the BPM in milliseconds, and a 1/16 is a quarter of that. At 120 BPM a beat is 500 ms, so a 1/16 is 125 ms. At 150 BPM a beat is 400 ms and a 1/16 comes to 100 ms. Both land in the slapback range, which is one reason faster songs tend to suit a shorter slap. Then move the time by ear until it sits right, and don't worry if that's a few milliseconds off the note. The tempo-synced delay lesson has the full maths for longer delays.
Setting the slapback level
A slapback is a quiet effect. On an insert, a mix of 20 to 35% is a good range. In the lab the mix is a straight crossfade, so at 30% the dry sound is at 70% of its level and the repeat at 30%, which puts the repeat about 7 dB under the dry sound. The Right now panel gives the exact figure for whatever you set.
On a send, set the delay to 100% wet and use the send level from the track. Bring it up until you can clearly hear the slap, then pull it back down until you'd only notice it if it were muted. With the full mix playing, that's usually lower than it seemed with the track soloed.
Darkening the repeat
A slap that's as bright as the original competes with it. Both copies have the same consonants and the same pick attack, so your ear hears two of everything and the part can sound messily doubled. Darken the repeat and it moves behind the original, where it adds size without drawing attention to itself.
Tape did this on its own. The playback of a tape echo lost some top end and picked up a little hiss and saturation, so the slap was always duller than the live sound. A high cut on the delay between 3 and 6 kHz gets you most of the way. A low cut between 100 and 200 Hz stops the repeat adding weight to the bottom of a vocal or a guitar, which you'll notice more once the bass is playing.
In the lab, both filters sit inside the delay, so with feedback at 0% they act on the single repeat once. Add feedback and each later repeat goes through them again and comes back darker still.
Feedback: one repeat or two
The classic slapback has no feedback at all. Feedback sends part of the echo back into the delay to make another one, and a slapback has just one repeat, so most settings start at 0%.
A small amount is still worth trying. At 15%, the second repeat is 15% of the level of the first, which is about 16.5 dB quieter, and any filtering on the delay takes a little more off it. That's too quiet to hear as a second echo. The tail of each note just seems slightly longer, which can help a sparse part.
Past about 20%, the second and third repeats become easy to hear, and you've moved from slapback into a short echo. That can sound lovely on a guitar, but it's a different effect, and the delay feedback lesson covers what happens as you keep going.
Where to use slapback
Vocals
Slapback is a good alternative to reverb when a vocal needs space but has to stay up front. Reverb pushes a sound back into a room. A slap suggests a hard space around the voice, and because the dry vocal stays clean, the words stay as clear and close as they were. A quiet, darkened slap under a rap or pop vocal often goes unnoticed until you mute it.
For a deliberately retro sound, go the other way: a louder slap of about 100 to 130 ms with less filtering, on a vocal that's otherwise fairly dry. That's the sound of the 1950s records, and it reads as a period style the moment you hear it.
Electric guitar
Rockabilly and country guitar lean on slapback, and it suits any clean or lightly driven part that sounds small without it. The repeat lands tight behind each picked note and makes a single guitar sound fuller without washing it out the way a long reverb can. Shorter times, around 80 to 110 ms, keep fast picking clean.
Snare and drums
A quiet slap on a snare, somewhere around 60 to 120 ms, gives a dry drum a sense of a room around it. The repeat carries the snare's transient, so it adds a second, softer crack, and darkening it keeps that second crack from fighting the real one. Keep it off the kick, where a repeat only clutters the low end.
Panning a slapback
The simplest slap sits in the same place as the original, with the repeat in both speakers. It's the most natural sound and the safest one in mono.
You can also put the repeat on one side. With the dry part in the middle and the slap off to the left, the sound feels wider and the slap is easier to hear at a lower level, because it no longer sits directly on top of the original. Another option is to pan the dry part slightly one way and the slap the other. In the lab, ping-pong with no feedback sends the single repeat to the left speaker only.
A panned slapback holds up well when the mix is folded to mono. Widening a part with the Haas effect uses a delay under about 30 ms panned away from the original, and in mono those two close copies comb-filter and the part goes hollow. At 100 ms the repeat is far enough behind that summing to mono just puts the echo back in the middle. The mono compatibility lesson shows why short delays are the ones that cause trouble.
How to set up a slapback delay, step by step
Any delay plug-in will make a slapback, including the stock ones in Ableton Live, Logic Pro and FL Studio. Logic's Tape Delay and Ableton's Echo both have high and low cut filters on their repeats, which you'll want here. These steps work for a vocal or a guitar on an insert.
- Turn sync offSet the delay time in milliseconds, starting at 110 ms.
- Bring the feedback to zeroYou want one repeat. Add up to 15% later if the tail feels too short.
- Set the mix to about 30%That's loud enough to hear clearly while you set the rest, and you'll bring it down at the end.
- Darken and thin the repeatSet a high cut around 4 to 5 kHz and a low cut around 100 to 150 Hz, so the slap sits behind the dry sound.
- Move the time by earSweep between 80 and 150 ms with the track playing. Stop where the repeat feels attached to the notes and doesn't blur the rhythm.
- Set the level in the full mixPull the mix down until you'd only notice the slap if it were gone, then switch the delay off and on to check it's still doing something you like.
Slapback settings for common sounds
These are starting points, each clearly audible on its own. Expect to lower the mix once everything else is playing.
| Source | Time | Feedback | Mix | Filters |
|---|---|---|---|---|
| Modern lead vocal, for space | 90 – 120 ms | 0% | 15 – 25% | High cut 3 – 4 kHz, low cut 150 – 200 Hz |
| 1950s-style vocal | 100 – 130 ms | 0 – 10% | 25 – 35% | High cut 5 – 6 kHz |
| Rockabilly or country guitar | 80 – 110 ms | 0 – 15% | 25 – 35% | High cut 4 – 5 kHz |
| Clean rhythm guitar | 100 – 140 ms | 0% | 15 – 25% | High cut 4 kHz, low cut 150 Hz |
| Snare | 60 – 120 ms | 0% | 10 – 20% | High cut 4 kHz, low cut 200 Hz |
Slapback compared with doubling and reverb
Doubling uses a shorter delay, roughly 20 to 50 ms, and usually moves the time slightly up and down so the copy sounds like a second performance. The best-known version is ADT, artificial double tracking, which Ken Townsend developed at Abbey Road in 1966 using tape machines. A slapback stays at one fixed time and is long enough to hear as a repeat.
Reverb is the other direction. A room sends back thousands of reflections, and the first handful, the early reflections, arrive in roughly the first 50 to 80 ms. A slapback is like keeping one of those reflections, a little later than the rest, and throwing the others away, which is why it suggests a hard space without filling the mix with a wash. The reverb vs delay comparison goes further into choosing between them.
Common slapback mistakes
Too much feedback
A slapback with 30 or 40% feedback is a short echo with a trail of repeats behind every note, and on a vocal those repeats blur the words. Keep it between 0 and 15%.
A slap as bright as the original
Full-range repeats make a part sound like it was recorded twice, slightly out of time. Put a high cut on the delay before you decide the slap is too loud, because darkening often fixes it.
The wrong time for the song
A 150 ms slap on a fast, busy part puts each repeat on top of the next note. If the rhythm starts to feel smeared, shorten the time before you lower the level.
Setting it with the track soloed
On its own, a vocal with a 30% slap sounds obviously echoed. In the full mix the same slap might be right, or completely buried, so set the final level with everything playing.
Train your ears
The quiz under the lab sets a single repeat and asks which of three it is: a thickening under 40 ms, a slapback between 80 and 150 ms, or an echo past 250 ms. The controls and screens are covered, every round is level-matched and each time is picked at random inside its range, so you can't learn one answer by its number. What you're listening for is whether you can point to a second sound at all and, if you can, whether it's still attached to the note.
To find where slapback begins on your own sound, use the lab directly. Pick the vocal, set the mix to 30% and the feedback to 0%, then close your eyes and sweep the Time knob slowly from 30 to 300 ms. Stop when the repeat first sounds like a separate echo and look at the number. Try it again on the guitar and the drums, and you'll find the point moves for each sound.
Questions people ask
What is a good slapback delay time?
Start at 100 to 120 ms and adjust by ear. Most slapback sits between 80 and 150 ms: shorter sounds tighter and more like a thickening, longer sounds more like a distinct echo. Faster songs usually suit the shorter end.
Should slapback delay be synced to the tempo?
It doesn't have to be. A single repeat can't drift against the beat the way a run of echoes can, so the exact time matters less than how it sits with the part. If you want a number from the tempo, a 1/16 note is 125 ms at 120 BPM and 100 ms at 150 BPM.
How much feedback should slapback have?
Between 0 and 15%. At 0% you get one repeat, which is the classic sound. A little feedback adds a second, much quieter repeat that lengthens the tail slightly. Past about 20% it stops sounding like slapback and starts sounding like a short echo.
Is slapback delay the same as doubling?
No. Doubling uses a much shorter delay, roughly 20 to 50 ms, often with the time wobbling slightly so the copy sounds like a second performance. Slapback is longer, at 80 to 150 ms, and you hear it as a quick echo right behind the original.
Can I use slapback instead of reverb on a vocal?
Yes, when you want a vocal to sound bigger without pushing it back into a room. A quiet, darkened slap adds space while the dry voice stays clean and close. A slap and a short reverb also work well together.
Why is it called slapback?
It sounds like a sound bouncing straight back off a hard wall. In acoustics, one distinct reflection like that is called a slap echo, and a reflection 100 ms late comes from a wall about 17 metres away.