Online metronome

Why a browser metronome usually drifts, and why this one does not

The obvious way to build a metronome in a web page is a timer that fires every beat and plays a sound. It does not keep time. Browser timers are only a request: when the page is busy, or you switch tabs, or the phone is saving battery, the timer fires late, and the beat stutters by whatever it was late by. Over a few minutes that is easy to hear, and it is the worst possible fault in a tool whose only job is to be steady.

This one uses the audio hardware's clock instead. A timer still runs, but all it does is look a tenth of a second ahead and hand the sound card the exact times of the next clicks. The sound card plays them at those times to the sample, however late the timer was. The page was measured in a headless browser, and the gap between one scheduled click and the next was exactly one beat, with no error, at every tempo tried. When the tab is in the background, it looks further ahead, a second and a half, so even a throttled timer cannot open a gap.

Time signatures and subdivisions

The tempo counts quarter notes, as every DAW and most printed music does, and the beat is the note under the time signature. In 3/4 at 90 there are three clicks a bar, two thirds of a second apart. In 6/8 at 90 there are six clicks a bar, and only the first of each group of three gets the full beat sound. That is how 6/8 is actually felt, in two, and hearing all six as equal beats makes a jig sound like a march. 9/8 and 12/8 work the same way, in three and four.

Subdivisions fill in eighths, triplets or sixteenths at a quieter level. Practising with sixteenths on is the fastest way to hear whether a run is even, because a rushed note lands audibly early against the fill. Turn beat one's accent off for pieces where the bar line should not be heard, or when you want to practise feeling the downbeat yourself.

Tap tempo

Tap the button, or press T, along with a song you are listening to. After three taps the tempo is set from the median gap between them, which ignores one sloppy tap in a way a simple average does not. Stop for two seconds and the next tap starts a fresh count. For a recording, the BPM finder reads the tempo from the file itself, to within a fifth of a BPM on material with a clear beat.

The speed trainer

The standard advice for a difficult passage is to play it slowly until it is clean, then speed up a little, over and over. The trainer does the speeding up. Pick how many BPM to add, how many bars to play at each tempo and where to stop, and it steps up on the bar line so the change never lands in the middle of a phrase. Starting at 80 and adding 5 every 4 bars up to 120 is nine steps and 36 bars, about two minutes of focused work. If it gets away from you, stop, knock the tempo back down with the −5 button and start again.

Keyboard

Space starts and stops, T taps, and the up and down arrows move the tempo by one. The tempo you last used is remembered in this browser. A link can set it too: /metronome?bpm=132 opens at 132.

Practising with recordings

Want to play along with a song, not a click? The speed tool slows a recording down without changing its pitch, which is how most people learn a fast solo. For recording yourself in time, the audio editor has the same kind of click built in, a one- or two-bar count-in, and a bar-and-beat grid your takes line up against. It also keeps the click out of what you export.

What it cannot do

There is no tempo map, so a piece that changes tempo mid-way needs you to change it by hand. The sound comes out of your device's speaker or headphones, and Bluetooth headphones add a delay of their own, often 150 ms or more. That delay is constant, so the beat is still steady, but tapping or playing along to a visual cue will feel late. Wired headphones or the speaker avoid it.