Metronome

Why it exists

Because almost every metronome in a browser drifts, and almost none of them say so.

The obvious way to write one is to ask the page to wake you every half second and make a sound. It works for about ten seconds. Then the browser postpones one wake-up because it was drawing something else, postpones another because it was freeing memory, and the click starts to move. It does not break — it slides. At 120 BPM two milliseconds of average delay per click are enough that after three minutes the click lands where a sixteenth should, and by then you are playing against something that is no longer the tempo.

Here the timer makes no sound: it only wakes up. What makes the sound is the sound card’s clock, which is the only clock in a browser that does not drift, and the clicks are scheduled a tenth of a second before they are heard. If a wake-up arrives late, the window it asks for is longer — and the clicks stay where they were.

About the accent

The accent is higher and louder: three and a half decibels over the beat. For a while this tool meant to separate it by pitch alone, for fear that at high volume a louder first beat would stop being an accent and become a thump. Playing along with it, the fear does not hold: pitch on its own is not enough to carry the downbeat through the instrument in your hands, and three and a half decibels are an accent, not a thump.

The three voices — accent, beat, subdivision — sit a fifth apart from each other, which is the one interval that does not produce a sour chord when a subdivision lands next to a beat. And each one is a click, not a note: a scratch of noise over a pitched body that dies in fifty milliseconds. It is the broadband half you hear through a piano, and it is why mechanical metronomes tick rather than ring.

About the volume

The slider starts at seventy and stays where you leave it for the rest of the visit. Seventy and not a hundred because full has to be somewhere to go: anyone who needs it louder has something to pull.

About 6/8

The beat of 6/8 is the dotted quarter: two beats to the bar, not six. That is how it is conducted, that is how it is counted, and it is the only way “100 BPM” means the same pulse speed it means in 4/4 — if the beat were the eighth, moving from 4/4 to 6/8 at the same number would triple the apparent speed.

One consequence is worth knowing before you go looking for it: in 6/8 the subdivision into three gives the metre’s own eighths, the pulse you feel playing it, and the one into two gives a duplet. Both are legitimate figures, but only one of them is the metre. The menu does not rename its options — a menu that changes its entries while you look at it is worse — so a line underneath says it, when it applies.

About changing tempo while it plays

You can, and nothing jumps. What has already been scheduled is already inside the sound card, so it is left alone: the new grid starts from the first click not yet scheduled, and the new tempo applies from there. Changing only the tempo preserves the position inside the bar exactly; changing metre or subdivision restarts from the next beat boundary, because a new grid hooked to the middle of a triplet would put the accent out of place — by a third of a beat, for ever, with nothing looking broken.

About switching tabs

The sound carries on. A metronome exists to play while you do something else: anyone practising switches to the tab with the score, or to their DAW, and finding it stopped on the way back would remove the very thing it was opened for. What stops is the indicator, because a background browser stops drawing; come back and it resynchronises on its own, because it reads the audio clock and not a counter of its own.

About your data

Everything happens in your browser. This site is made of static files and has no server to send anything to, even if it wanted one.