Reverb Decay (RT60)

In-Depth Explanation

What is Reverb Decay?

In audio production and acoustics, Reverb Decay (specifically measured as RT60) is the standard metric used to define how long a reverberation lasts.

When you sing in a large cathedral, the sound doesn't stop immediately when you close your mouth. The sound waves continue to bounce off the stone walls, creating a lingering wash of echoes. That wash is reverb. The decay time measures exactly how long it takes for that lingering sound to drop 60 decibels (dB) below the volume of the original, initial sound. Because a drop of 60 dB essentially renders the sound inaudible to human ears in a normal room, RT60 is the practical measurement of "when the reverb ends."

How Decay Time Affects a Mix

Controlling reverb decay is one of the most difficult skills for a mixing engineer to master.

• Short Decay (0.2s - 0.8s): Creates a small, tight space (like a small drum room or a vocal booth). It adds a sense of realism and "three-dimensionality" to a dry recording without cluttering the mix.
• Medium Decay (1.0s - 2.0s): The standard range for pop vocals, snare drums, and acoustic guitars. It creates a pleasing, musical halo around the instrument.
• Long Decay (3.0s+): Creates massive, ambient spaces (like a concert hall or a canyon). Used heavily in cinematic scores, ambient music, and dream-pop. However, if used improperly, a long decay will completely wash out a mix, turning it into a muddy, undefined soup of sound.

Syncing Reverb to BPM

A common amateur mixing mistake is setting the reverb decay arbitrarily. If a reverb tail lasts too long, it will still be sounding when the next beat hits. The reverb from the previous chord will crash into the new chord, creating dissonant, muddy frequencies.

To fix this, professional engineers calculate their reverb decay times mathematically based on the song's BPM.

The goal is to set the decay time so the reverb tail dies out exactly before the next significant musical event occurs (usually a quarter note, half note, or full bar).

• If a song is fast (e.g., 140 BPM), the decay time must be short, because the next beat is arriving very quickly.
• If a song is slow (e.g., 70 BPM), the decay time can be much longer, because there is more physical space between the beats for the reverb to bloom.

(You can use our Reverb Time Calculator to instantly calculate the mathematically perfect decay times for your specific BPM).

Pre-Delay

When discussing decay, you must also understand Pre-Delay. This is a separate setting on almost all reverb plugins.

Pre-delay is the amount of time (in milliseconds) between the original dry sound and the onset of the reverb. If you set a pre-delay of 40ms on a vocal track, the listener hears the dry vocal immediately, and 40 milliseconds later, the reverb tail begins.

Pre-delay is a magic trick for mixing. It separates the vocal from the reverb, allowing the crisp, intelligible consonants of the lyric to punch through the mix clearly before the wash of the reverb surrounds it.