Metronome

How to use the metronome

1. Set the tempo: type it, drag the slider, use −5, −1, +1, +5, or tap Tap tempo along with a song.
2. Pick a time signature, or type your own beats per bar and beat note under Custom and press Use.
3. Tap a beat square to cycle it through accent, normal and muted. Beat one starts accented, and compound signatures such as 6/8 accent each group of three.
4. Add a subdivision (eighths, triplets or sixteenths) and, for a shuffle feel, raise Swing.
5. Press Start (or Space). Turn on the speed trainer to speed up by itself, or gap practice to drop the click for some bars.

How the clicks stay on time

A metronome built on a JavaScript timer drifts, because browsers run timers late whenever the page is busy, by 4 to 50 ms and by up to a whole second in a background tab. This page uses the timer only to wake up a scheduler. Every 25 ms it looks 0.1 s ahead and books each click due in that window on the Web Audio clock, which runs on the sound card's own sample counter. A click booked for 2.500 s starts on the sample for 2.500 s: at 48,000 samples a second that is within 0.02 ms, however busy the page is. When the tab is hidden the scheduler books 1.5 s ahead instead, so the throttled timer still keeps up; a change you make then can take up to 1.5 s to be heard.

The beat squares are drawn from the same clock, so they light when the click plays rather than when the timer fired. The test for this page renders 4 bars at 120 BPM offline, finds every click in the sound itself, and checks they are 0.500 s apart to within 1 ms.

Beats, signatures and what the BPM counts

The BPM always counts the bottom note of the signature. In 4/4 at 120 BPM each quarter note is 0.5 s and a bar is 2 s. In 6/8 at 120 BPM each eighth note is 0.5 s; 6/8 is felt in two beats of three eighths, so if a piece says dotted quarter = 60, set 180. The default accents follow the usual grouping: 6/8, 9/8 and 12/8 in threes (accents on 1 and 4 in 6/8), 5/4 as 3 + 2 and 7/8 as 2 + 2 + 3. If your piece groups 7/8 as 3 + 2 + 2, tap the beat squares to move the accents to 1, 4 and 6 (one tap turns an accent into a normal beat, two taps turn a normal beat into an accent). Muted beats stay lit so you can count through them.

Swing worked out: at 120 BPM a beat is 0.5 s. Straight eighths (50 %) put the off-beat 0.25 s after the beat; at 66 % it comes 0.33 s after, and the second eighth is only 0.17 s long, the lilt of a swung or shuffle rhythm. With sixteenths, each pair inside the eighth is swung the same way. Triplets are already uneven to the eighth, so swing does not change them.

Speed trainer and gap practice

The speed trainer starts at the tempo you set and adds a fixed number of BPM after every so many bars, then holds at the target. From 100 BPM, +5 every 4 bars up to 120 plays bars 1–4 at 100, bars 5–8 at 105, and reaches 120 at bar 17. The tempo now playing shows beside the tempo name. Gap practice plays some bars and mutes others in a loop: with 2 and 2 you hear bars 1–2, then 3–4 are silent, then it repeats. If you come back in with the click, your inner pulse held.

What it cannot do

• Phones may stop the sound when the screen locks or you switch apps, and an iPhone with its silent switch on may play nothing. Keep the page on screen while you practise.
• Bluetooth headphones and speakers add a delay, often 100 to 300 ms, that the page cannot remove. The clicks stay evenly spaced but come late against the beat squares; use wired headphones or the built-in speaker when that matters.
• It does not listen to you. It cannot tell whether you are on time, and it cannot find the tempo of a song by itself: tap tempo is as steady as your taps.
• The tempo is a whole number from 20 to 300 BPM, and a custom signature has 1 to 32 beats.
• The beat squares are drawn at your screen's refresh rate, so a flash can show up to one frame (about 17 ms at 60 Hz) after its click; the sound is the reference.

Privacy

The clicks are made in this page with Web Audio; no sound files are downloaded and nothing you set is sent anywhere. Your settings are saved in this browser's local storage only, and Clear saved settings deletes them. The page counts an anonymous page view and, the first time you press Start or Tap tempo, the fixed words metronome-start or metronome-tap, never the tempo or any setting.

Questions

How do I set the metronome for 6/8?

Tap 6/8. It clicks six eighth notes per bar with accents on 1 and 4, and the BPM counts those eighth notes. Music in 6/8 is usually felt in two dotted-quarter beats, so for dotted quarter = 60 set 180 BPM (three eighths per beat).

What are subdivisions on a metronome?

Extra, quieter clicks between the beats: eighths (2 per beat), triplets (3) or sixteenths (4). They show where the off-beats fall, which keeps slow tempos steady and exposes rushing in fast passages. Swing lengthens the first of each pair, so eighths at 66 % fall two thirds of the way through the beat.

How does tap tempo work?

Tap Tap tempo (or press T) at least twice in time with the music. The page uses your last nine taps: the median gap between them finds the beat, so one early or late tap does not throw it off, and a straight line fitted through the taps averages out the small wobble in each one. The BPM is set as you tap. Stop tapping for 2 seconds and the next tap starts a fresh count.

How do I find the BPM of a song?

Play the song and tap along with the beat you would clap to, for eight or more taps; the BPM shows as you go. Then press Start and check the clicks stay with the song. If it reads half or double what you expected, you tapped every other beat or the eighth notes; both are valid ways to count the same song.