A working tool for composers and arrangers who need the exact length of any note value, or who are planning a tempo change via metric modulation rather than a simple tempo marking.
How it works
Every note value has an absolute duration that depends only on the tempo and the note the tempo counts (the time-signature denominator):
beat duration = 60 / BPM (one denominator note)
whole note = beat duration × denominator
note value = whole note / (relative value)At 120 BPM with a quarter-note beat (denominator 4): the beat is 0.5 s, the whole note is 0.5 × 4 = 2 s, a quarter is 2 / 4 = 0.5 s, and an eighth is 0.25 s. Triplets divide the whole note into 12 (triplet eighths) or 6 (triplet quarters), and dotted values multiply the base by 1.5.
Metric modulation
A metric modulation changes the tempo by re-interpreting the pulse. Suppose the music is in quarter notes at 90 BPM and you want the triplet-eighth to become the new quarter. The new tempo scales by the ratio of the two pulse note values:
BPM_new = BPM_old × (new pulse value / old pulse value)The tool reports the old pulse duration, the new tempo, and the new pulse duration so you can write an exact ”♩ = ♪” equivalence in the score.
Why note durations matter for composers and producers
Knowing the exact duration of a note value in seconds is useful in several situations that pure rhythmic notation does not address directly.
Synchronising music to picture. In film, television, and game audio, the composer needs specific events to land on specific video frames. If a cue begins at 00:01:42:00 (one minute, 42 seconds, frame zero) at 120 BPM and a hit point lands 12 frames later at 24 fps, that is 0.5 seconds. Knowing that a quarter note at this tempo is exactly 0.5 seconds means the hit point falls precisely on the next beat. A dotted quarter would be 0.75 seconds — three frames short of the next beat, potentially workable or not depending on context.
Setting DAW parameters. Many digital audio workstations allow you to set delay plugin times, reverb pre-delays, and LFO rates in milliseconds as well as note values. Dialling in a reverb pre-delay of exactly one sixteenth note in milliseconds (for example 125 ms at 120 BPM) creates a tempo-synced ambience that reinforces the rhythm. This tool gives you those millisecond values directly.
Recording with a click track. If a live recording session uses a variable tempo that will later be time-stretched to fit a fixed grid, knowing the intended note durations helps you evaluate whether the performance landed close enough to the target. A recording that is 15 ms early on every downbeat may work after correction; one that is 80 ms off is likely unusable without expensive tempo editing.
The denominator and why it matters
The time-signature denominator tells you which note value equals one beat, and therefore what the metronome is counting. A tempo of 120 BPM with a denominator of 4 (a quarter note beat) gives you 120 quarter notes per minute, each lasting 0.5 seconds. The same 120 BPM with a denominator of 8 (an eighth-note beat) gives you 120 eighth notes per minute — the whole note is now 8 times the beat duration rather than 4 times, which doubles every note value compared to the quarter-note interpretation.
This matters when working across time signatures. A piece that changes from 4/4 to 12/8 may intend the dotted quarter of 12/8 to equal the quarter of 4/4 (a common “compound subdivision” change) or it may intend the eighth note to remain constant (a different musical effect). The denominator field lets you specify which interpretation is in play.
Tips and notes
- Choose the denominator that matches how your conductor or DAW counts the beat — it determines which note equals one click.
- Dotted and triplet values are included because they are where timing errors most often creep in; the table gives them to four decimal places.
- For polyrhythms, look for note durations whose ratio is a simple fraction (3:2, 4:3) — those are the ones that lock cleanly within a bar.
- Metric modulation notation typically appears in the score as an equation between two note values: the old pulse note value equals the new pulse note value. Write this at the tempo change so performers and conductors understand whether the beat continues or re-starts.
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