How this calculator works
A note value is a fraction of the beat, so its length in milliseconds comes from the tempo. At 120 BPM a quarter note is 500 ms, an eighth note is 250 ms, and a dotted eighth is 375 ms because the dot adds half the value. A triplet takes two thirds of the plain value, so an eighth-note triplet is about 166.7 ms. Setting a delay to one of these values makes the echoes land on the beat grid. The feedback field sets how much of each echo returns; each pass multiplies the level by the feedback fraction, so the number of audible repeats follows a decaying geometric series.
Formula
quarter note (ms) = 60,000 / BPM. delay (ms) = quarter note x quarter-note multiple, where a whole note is 4, a half is 2, a quarter is 1, an eighth is 0.5 and so on. A dotted value is 1.5 times the plain value and a triplet is 2/3. Repeat rate (Hz) = 1000 / delay in ms. Repeats until 1 percent = ln(0.01) / ln(feedback).
Worked example
At 120 BPM a quarter note is 60,000 / 120 = 500 ms, so a dotted eighth delay is 500 x 0.75 = 375 ms. The repeat rate is 1000 / 375 = 2.67 Hz. With 35 percent feedback, each echo is 35 percent of the last, and it takes ln(0.01) / ln(0.35) = 4.36 repeats for the level to fall below one percent, so the tail lasts about 4.36 x 375 = 1,635 ms.
Advertisement
Frequently asked questions
Why use tempo-synced delay?
Echoes that land on the beat grid sound intentional, while arbitrary delays can sound sloppy or create rhythmic clashes. Many plug-ins have a sync button that does this calculation, but the milliseconds are useful when setting a hardware pedal or a reverb pre-delay.
What is the pre-delay in a reverb?
Pre-delay is the gap before the reverb starts. A short pre-delay keeps the dry sound clear and separates it from the tail. Setting it to a note value, often 1/32 or 1/16, fits the ambience to the groove.
Does feedback change the delay time?
No. Feedback controls how much of each echo returns, not how far apart the echoes are. Higher feedback gives more repeats and a longer tail, but the spacing stays at the delay time. Values close to 100 percent can build up and clip.
How long should the reverb decay be?
It depends on the space you want to suggest. A small room might use 0.8 to 1.2 seconds, a hall several seconds. Matching the delay or reverb tail to the bar length keeps the texture from smearing across chord changes, which is why tempo-synced values are a practical starting point.