Synchronized metronome for bands
A free synchronized metronome that runs in the browser: one phone becomes the leader, picks the BPM, the time signature and the accents, and taps Start session. A QR code and a link appear; everyone in the band, marching band, orchestra or study group points their camera at it, opens the page and taps Play along. From then on every device clicks at the same instant, bar after bar, with no app, no account and no cables.
How to use it
- On the leader's phone, choose the BPM (the −5, −1, +1 and +5 buttons, the field or the slider), the time signature (2/4, 3/4, 4/4, 6/8 or 1 to 12 beats) and, if you like, the accents: tap each beat to cycle through strong, normal, soft and muted.
- Tap Start session. The metronome counts down a few seconds and starts; at the same time the Session link and QR code panel opens.
- Show the QR code to the group or send the link in a group chat. Each person opens the page and taps Play along: the device comes in on the next downbeat, in time with the leader.
- Check the line under the number: Synchronized (±N ms) means the clock was set against the site. If a phone connected to a Bluetooth speaker sounds late, open This device and tap +10 ms until its click lines up with the others.
- To change the tempo, tap New session, adjust the BPM and start again. You get a new link, and the group needs to scan the new QR code.
Help and explanations
There is no live connection between the phones. The link carries the tempo and a start time; each device sets its own clock against the site's clock (a few quick requests, the same way a computer keeps its clock right) and works out where every beat falls. That is why it works with lots of people at once, on weak rehearsal-room Wi-Fi, and even when someone arrives late: the new device waits for the next bar and comes in together.
How the phones stay together without being connected
When a session starts, the page picks a start time a few seconds ahead and writes the BPM, beats and accents into the link. From that instant on there is a fixed time grid: the first click, the second, the third, each exactly 60 divided by the BPM seconds after the previous one. Every device that opens the link knows the same grid and only needs to know the exact time, to the millisecond.
That is where clock sync comes in. A phone's clock is usually a few tenths of a second (sometimes whole seconds) fast or slow. The page asks the site for the time six times, measures how long each answer took to travel there and back, and keeps the fastest one, which is the most reliable. From it the page works out the difference between the phone's clock and the site's, then schedules every click on the device's audio clock, which is far steadier than an ordinary web page timer. The bar number on screen is the same on every phone.
What it is for: bands, marching bands, orchestras and group practice
In a marching band or drum corps the sections stand far apart, and one metronome cannot be heard by everyone. With a phone and a small speaker in each section, everybody hears the same click at the same moment. In school bands and orchestras the teacher puts the QR code on the screen and students follow on their own phones with earphones, keeping the room quiet.
It works for practice too: two friends can work on the same song at home, each on their own phone, at the tempo the teacher chose. For solo practice with tap tempo, subdivisions and a speed trainer, use the online metronome; to speed up gradually, try the progressive metronome.
Accuracy, Bluetooth headphones and other details
On decent Wi-Fi or 4G the difference between devices usually stays under 20 milliseconds, close to the limit of what the ear notices in a band. The screen shows the maximum error of the sync (for example, ±6 ms): it is half the time the fastest answer from the site took to travel there and back, so it grows when the connection is slow. The biggest source of delay is the sound output: Bluetooth speakers and headphones delay audio by 100 to 300 ms, and not every browser can tell how much. That is what the ±10 ms fine adjustment under This device is for, and it is saved on the phone.
If the page cannot reach the site, it says so and uses the phone's own clock, which may not match the others. In that case, turn on automatic time in each phone's settings. And remember that the page listens to nothing: it does not use the microphone and does not send sound anywhere.
Tips
- Use wired earphones or the phone's own speaker whenever you can: Bluetooth usually delays the sound by 100 to 300 ms.
- Calibrate once: with two phones side by side on the same link, tap +10 or −10 ms on the one that is off until the two clicks sound like one. The value is stored on that device.
- Before you start, turn the volume up and keep the page open in front; the metronome asks the screen to stay on while it plays.
- In a marching band, put a phone with a speaker in each section: everyone stays together even far from the drum major.
Frequently asked questions
Do I need internet to use the synchronized metronome?
Only to open the page and set the clock in the first few seconds. After that the timing is calculated on the phone itself; if the connection drops during rehearsal, the click keeps going. With no answer from the site at all, the page warns you and uses the device's own clock, which may be ahead of or behind the others.
How many phones can join the same session?
There is no limit. The link does not open a conversation between devices: each one only asks the site for the time. You can use it with a whole marching band, an orchestra or a classroom.
How accurate is the sync?
On a decent connection the difference between devices usually stays under 20 milliseconds, and the screen shows the maximum error of the sync (±N ms). Bluetooth delay is the main problem; that is what the ±10 ms fine adjustment, saved on each phone, is for.
I changed the BPM: do the other phones follow?
No. Since there is no live connection, the tempo travels inside the link. Tap New session, choose the BPM and start again; then show the new QR code to the group. Anyone still on the old link stays at the old tempo.
Can someone join after the session has started?
Yes. Whoever opens the link midway waits for the next downbeat and comes in with everyone else, with the same bar number on screen.
Does it work on iPhone and with the screen locked?
It works in up-to-date Safari, Chrome and Firefox. While the page is open, the metronome asks the screen to stay on; with the screen locked, each browser decides whether to keep playing. On iPhone, check the volume and the silent switch before rehearsal.
Does the site receive any sound or data from the phones?
No. The page does not use the microphone and nothing is recorded. The only request to the site is for the current time, with no account and no cookie. Sound, volume and fine adjustment are stored only on the device.