The one formula
A minute has 60,000 milliseconds, so one beat (a quarter note in 4/4) lasts 60,000 ÷ BPM ms. At 120 BPM, a beat is 500 ms. Every other note value is a simple multiple:
- half note = beat × 2; whole note (one bar of 4/4) = beat × 4
- eighth note = beat ÷ 2; sixteenth = beat ÷ 4; thirty-second = beat ÷ 8
- dotted note = note × 1.5 (a dotted eighth is three sixteenths)
- triplet note = note × ⅔ (three triplet eighths fill one beat)
The chart below applies those rules to 120 BPM. For any other tempo, use the BPM to ms calculator or one of its tempo pages, such as 128 BPM or 90 BPM.
| Note | Straight (ms) | Dotted (ms) | Triplet (ms) | LFO (Hz) |
|---|---|---|---|---|
| 1/1 — Whole note | 2000.0 | 3000.0 | 1333.3 | 0.50 |
| 1/2 — Half note | 1000.0 | 1500.0 | 666.7 | 1.00 |
| 1/4 — Quarter note | 500.0 | 750.0 | 333.3 | 2.00 |
| 1/8 — Eighth note | 250.0 | 375.0 | 166.7 | 4.00 |
| 1/16 — Sixteenth note | 125.0 | 187.5 | 83.3 | 8.00 |
| 1/32 — Thirty-second note | 62.5 | 93.8 | 41.7 | 16.00 |
| 1/64 — Sixty-fourth note | 31.3 | 46.9 | 20.8 | 32.00 |
Choosing a delay time
Most plug-ins have a sync switch that does this maths for you, but hardware pedals, older plug-ins and mixing in a DAW without tempo information still need milliseconds. Even with sync available, knowing the numbers helps you choose musically:
- Quarter note — the obvious echo, repeats on every beat. Good for sparse vocals and lead lines; can clutter busy parts.
- Dotted eighth — the U2/Edge guitar sound and a staple on vocals. Repeats fall between the beats and create a rolling rhythm with the dry part.
- Eighth or eighth triplet — tighter, more rhythmic; triplets add swing to straight parts.
- Short “slapback” — 60–120 ms, not usually synced. Rockabilly vocals and guitars; adds thickness without an audible echo.
Feedback controls how many repeats you hear. Around 20–35 % gives two or three echoes; above 60 % repeats pile up and build washes. Filtering the delay return (cutting lows below 200 Hz and highs above 5–8 kHz) keeps echoes behind the dry sound.
Ping-pong and stereo delays
Stereo delays often use two different note values, one per side — for example a quarter note left and a dotted eighth right. Because the two times come from the same beat length, they stay rhythmically related. Ping-pong delays alternate sides with the same time, so each side repeats at twice the time you set.
Reverb pre-delay and decay
Reverb isn’t usually tempo-synced, but timing it to the beat keeps the mix clear. Two settings matter:
- Pre-delay is the gap before the reverb starts. A small value tied to the tempo — a 1/64 or 1/32 note (8–30 ms at typical tempos) — lets the dry attack through before the tail arrives, so vocals stay intelligible.
- Decay (RT60) is how long the tail takes to fade. A common approach is to have it die just before the next important hit: half a bar for snares in a busy groove, a full bar or two for pads and ballads. Subtract the pre-delay so pre-delay plus decay equals the musical length.
Our tempo pages list a 1/64-note pre-delay with half-bar, one-bar and two-bar decay suggestions computed this way. Treat them as starting points; dense mixes want shorter tails than sparse ones.
Compressor release, gates and sidechain
The same arithmetic sets other time-based processors. A sidechain compressor ducking pads under a kick should release in time for the next kick: at 128 BPM, a release around a quarter note (469 ms) minus the attack pumps once per beat. Gates on drum rooms can close on an eighth or sixteenth. Even a bus compressor “breathes” better when its release is related to the beat.
LFO rates in hertz
Tremolos, auto-pans, filter wobbles and chorus rates are set in hertz. Convert with Hz = 1000 ÷ ms, or equivalently BPM ÷ 60 for one cycle per beat. At 140 BPM, a quarter-note LFO is 2.33 Hz and an eighth-note dubstep wobble is 4.67 Hz.
Loop and sample lengths
When you cut loops in a sampler or audio editor, sample-accurate lengths avoid drift. One beat at 44.1 kHz is 44,100 × 60 ÷ BPM samples: 22,050 at 120 BPM, 20,671.9 at 128 BPM. Fractional values are why loops at some tempos slowly drift if the editor rounds each bar; set the project tempo instead of trimming by hand when you can.
Start from the real tempo
All of this depends on knowing the song’s BPM to a decimal place. A track labelled 128 that is really 127.6 will have delays that drift by about 0.3 % — fine for one echo, audible after a long feedback tail. Drop the track into the BPM detector to get its measured tempo, the delay times shown under the result, and a link to the full chart for that tempo.