what is reverb
what reverb actually is, how a space turns one sound into thousands of reflections, and what that means for your mix. direct sound, early reflections, and the late tail explained.
the sound after the sound
clap your hands in a stairwell. you hear the clap, then you hear the building: a wash of sound that hangs in the air for a second or two after the clap itself is gone. that wash is reverb. it is not one sound. it is thousands of copies of your clap, bouncing off concrete, arriving at your ears from every direction, each one slightly later and slightly quieter than the last.
every sound you have ever heard in a physical space came with reverb attached. your brain is so used to it that a truly dry signal (recorded in an anechoic chamber, or generated inside a computer) sounds wrong. uncomfortable, even. people describe anechoic rooms as oppressive. silence is fine. sound without a space is not.
this is why reverb is not an effect in the way a flanger is an effect. it is the restoration of something your ear expects to be there.
key takeaway
reverb is thousands of reflections fused into one perceived sound. your brain uses it to decide how big the space is, how far away the source is, and how much it should trust what it hears. a mix without deliberate reverb decisions is still making reverb decisions: just bad ones.
three arrivals: direct, early, late
when a sound happens in a room, it reaches you in three stages.
the direct sound travels in a straight line from source to ear. it arrives first, it is the loudest, and your brain uses it to decide where the sound came from. this is the precedence effect: whichever arrival comes first wins localization, even if later arrivals are nearly as loud.
early reflections arrive over the next 5 to 80 milliseconds or so. these are the first few bounces: floor, nearest wall, ceiling. they are sparse enough that they have not yet fused into a wash, but too fast for you to hear them as separate events. instead, your brain reads them as information. their timing and direction tell you the size and shape of the room. (this is the part most tutorials skip, and it is the part that does most of the work. the character of a space lives in the early reflections.)
the late tail is everything after. by now the sound has bounced dozens of times, the reflections have multiplied into the thousands, and they arrive so densely and from so many directions that no individual reflection is audible. the tail is statistical: a smooth, decaying wash with no direction and, ideally, no pitch of its own. how long it takes to fade tells you how big and how hard-surfaced the space is.
a reverb plugin recreates this whole sequence artificially. some do it by sampling a real space, some by simulating one from scratch. that split is stage 2 of this path.
the sabine equation
the decay time of a room was first formalized by wallace sabine around 1900: RT60 ≈ 0.161 × V / A, where V is the room volume in cubic meters and A is the total absorption in sabins (surface area × absorption coefficient). the equation says exactly what your intuition says: bigger rooms ring longer, softer rooms ring shorter. sabine worked this out by measuring how long an organ pipe note hung in a harvard lecture hall, using only his ears and a stopwatch.[^1]
what reverb does in a mix
here is the thing about reverb in a mix: it is not really about making things sound nice. it is about position.
your brain places sounds on a front-to-back axis using the ratio of direct sound to reverberant sound. lots of direct, little reverb: the source is close. little direct, lots of reverb: the source is far. this is not a metaphor. it is how you survive crossing a street without looking.
which means reverb is a trade. every dB of reverb you add pushes a sound further back and glues it more convincingly into the space, and at the same time costs you clarity, intimacy, and transient definition. a dry vocal sits in your face. a wet vocal sits at the back of a hall. neither is correct. they are different positions, and you choose one.
you know the move: a mix feels disconnected, so you reach for reverb, and twenty minutes later everything is further away and nothing is clearer. the fix is rarely more reverb. it is deciding, element by element, what belongs close and what belongs far, and setting the dry/wet balance to match the decision.
a few practical anchors:
use sends, not inserts. instruments sharing one reverb sound like they are in one room. ten instruments with ten insert reverbs sound like ten photographs taped together.
pre-delay buys you both. 20-40 ms of pre-delay separates the dry sound from the tail, so a vocal can stay upfront and intelligible while still living in a space. your ear hears the direct sound clean, then the room arrives.
shorter than you think. a tail that sounds glorious on a soloed snare is usually a wash of mud in the full mix. set decay times in context, with everything playing.
note
the fastest way to learn what reverb is doing to your mix: mute the dry signal and listen to the reverb return alone. if the tail has a pitch, a metallic ring, or a frequency build-up, that coloration is being added to everything you send there. stage 3 of this path covers exactly why that happens.
i am building an algorithmic reverb called OPEN, made for synths and drum machines rather than another plate emulation. it opens for beta soon, and if you want first access you can tick “i want to beta test future plugins” on the signup at /#signup.
frequently asked questions
frequently asked questions
what is reverb in audio?
reverb is the sum of thousands of reflections a space adds to a sound. when you clap in a room, the direct sound reaches your ears first, then reflections off the walls, floor, and ceiling arrive over the next fraction of a second, getting denser and quieter until they fade. a reverb plugin recreates this process artificially so you can place a dry recording in a virtual space.
what is the difference between reverb and echo?
echo is a reflection you can hear as a separate event: a distinct repeat, like shouting at a cliff face. reverb is what happens when reflections arrive so fast and so densely that your ear fuses them into one continuous wash. the technical threshold is around 30-50 ms: reflections closer together than that merge perceptually, reflections further apart start to read as discrete echoes.
what does RT60 mean?
RT60 is the time it takes the reverb tail to decay by 60 dB, which is roughly the point where it disappears under the noise floor. a bedroom might have an RT60 of 0.3 seconds, a concert hall 2 seconds, a cathedral 8 or more. when a reverb plugin has a decay or length control, RT60 is what it is setting.
what is pre-delay on a reverb?
pre-delay is the gap between the dry sound and the first reflection. in a real room, this gap is set by how far the nearest wall is. in a mix, pre-delay is one of the most useful controls you have: 20-40 ms of pre-delay lets a vocal stay upfront and intelligible while the tail still places it in a space.
should reverb go on a send or an insert?
usually a send. a send lets several instruments share one space, which is how real rooms work and how mixes stay coherent. it also lets you process the reverb itself (EQ it, compress it) without touching the dry signal. inserts make sense for sound design or when a single element needs its own private space.
references
a note from the developer
i ignored reverb for years. i treated it as the thing you add at the end so the mix does not sound naked: pick a preset called “vocal hall”, set it to taste, move on. then i started reading the actual research on how artificial reverberation works, and it rearranged how i hear mixes. the front-to-back axis was the part that got me. i had spent years panning things left and right while leaving the depth axis to chance.
now it is the first spatial decision i make, not the last. what is close, what is far, and only then: what space are they all in.
if anything here does not match your experience, or you have a reverb habit that took years to figure out, i want to hear it. jonas@kernaudio.io. i read every email.