Why convert BPM to milliseconds
Delays, reverbs, compressors and LFOs sound tighter when their times match the tempo of the song. Most hardware and many plugins ask for times in milliseconds, so you need to convert the tempo, given in beats per minute (BPM), into note lengths.
The formula
One minute is 60,000 ms, so a beat, usually the quarter note, lasts:
quarter note (ms) = 60,000 ÷ BPM
Other values follow:
- half note = 2 × quarter; whole note = 4 × quarter
- eighth = quarter ÷ 2; sixteenth = quarter ÷ 4
- dotted notes are 1.5 times the plain note
- triplets are two-thirds of the plain note
Worked example at 120 BPM
| Note | Length |
|---|---|
| Whole note | 2,000 ms |
| Half note | 1,000 ms |
| Dotted quarter | 750 ms |
| Quarter note | 500 ms |
| Quarter-note triplet | 333.3 ms |
| Dotted eighth | 375 ms |
| Eighth note | 250 ms |
| Eighth-note triplet | 166.7 ms |
| Sixteenth note | 125 ms |
In 4/4 time, one bar lasts 2 seconds, and a quarter-note LFO runs at 2 Hz.
Using the values
- Delay: a quarter or eighth note keeps echoes on the grid. A dotted eighth against straight eighths gives the rolling, cascading echo heard in a lot of rock and pop guitar.
- Reverb: set the pre-delay to a short note value, such as a 1/64 or 1/32 note, or simply 10 to 40 ms, so the dry sound stays clear before the tail starts. Some engineers time the decay so the tail fades by the next beat or bar.
- Compression: a release that ends before the next beat lets the compressor breathe with the groove.
- Modulation: an LFO rate in Hz is BPM ÷ 60 for one cycle per beat.
Tips
- If the beat is a dotted quarter, as in 6/8 played “in two”, enter the tempo of the eighth note or adjust the beat count.
- Small offsets of a few milliseconds ahead of or behind the grid can make a delay sit better in a mix; use the values as a starting point.
- Most digital audio workstations can sync effects to the tempo directly; this calculator is most useful for hardware and older plugins.