How to play the same song on several phones at once, in sync

Everybody has tried it. Four friends open the same song, somebody counts to three, everyone taps play, and for about two seconds it sounds almost right. Then it turns into an echo, then into mush, and one by one the phones go quiet until only the loudest one is left.

That is not bad luck, and it is not your phones. It is a timing problem, and it has a proper fix. This guide shows you how to get every phone in a room playing the same song at the same instant, with nothing more than the phones and an internet connection.

Why tapping play together never works

Your ear is very good at hearing when two copies of a sound arrive at different moments. If two phones are more than roughly 30 milliseconds apart, you stop hearing one song and start hearing an echo. Below that, the two copies blend into one fuller sound.

Thirty milliseconds is far quicker than any thumb. When people react to a spoken “three”, the gap between the fastest and slowest person is usually a couple of hundred milliseconds. On top of that, each phone takes its own time to load the track and start the audio. So even a perfect count gives you phones that are a fifth of a second apart, which is exactly the range that sounds worst.

BeatBuddies never sends a “play now” message, because messages reach each phone at a different time. Instead every phone keeps measuring how far its own clock is from a shared clock on the server. When the song starts, each phone is told the moment it began, and it works out where the music should be right now. A phone that joins four minutes late does not start from the beginning. It starts four minutes in, on the beat.

What you need

• Two or more phones. Android or iPhone. Android can use the app from Google Play; any phone can use the browser at beatbuddies.online/app.
• An internet connection on each phone. Wifi or mobile data. The phones do not need to be on the same wifi network.
• One account, for the person starting the party. New accounts get three days free. Everyone else joins without paying anything.

Step 1: start a party

Step 2: get everyone in

Step 3: add music

Step 4: press play

How to check it is really in sync

The small pill at the top of the party screen says in sync in green when this phone is where it should be. Tap it to open Sync & settings, which tells you in milliseconds how far this phone is from the rest of the party. Anything in single figures is well below what an ear can pick up.

If one phone sounds a little behind

Every phone takes a slightly different time to push sound out of its speaker, and a Bluetooth speaker or Bluetooth earbuds add much more. The clock cannot see that part. So in Sync & settings there is a Nudge this phone slider. If one phone lags, drag its slider to the right a little at a time until the beats land together.

If an iPhone makes no sound at all

On an iPhone, the silent switch on the side can mute the sound a web app plays. Turn on Force sound on iPhone in the same sheet. It sends the music through the channel that ignores the silent switch. Play a test sound is there so you can check the speaker works before the party starts.

Small things that make it sound better

• Spread the phones out. Six phones bunched on one table sound like one loud phone. Six phones around a room sound like the room is playing music.
• Stay below full volume. Phone speakers distort at the very top. Around three quarters is usually cleaner and just as loud in a room.
• Keep the speaker end clear. Face down on a sofa cushion is the quietest place a phone can be.
• Short on data? Turn on Low data mode. The phone then fetches only the current song and the next one, instead of looking three ahead.

For the full living room setup, read how to run a house party with no speaker.