Ableton Link

showstack / protocols / ableton-link

Also called Link.

Ableton's peer-to-peer protocol for sharing tempo, beat and phase between music applications on a local network. There is no master and no clock owner: any peer can change the tempo and everyone else follows within a beat.

Timecode and syncOpenAbleton AGVerified

Clock and sync Tiny, ruthlessly regular

Almost no bandwidth. Carries no content at all, only agreement about when. Its value is entirely in its regularity.

What kills it. Jitter, an unaware switch delaying the timestamps it was meant to correct, and two devices both convinced they are the master.

The four flows, and why the model is worth having →

Ports

udp/20808 Link discovery and session state messages
The same port is used for the IPv4 and the IPv6 multicast endpoints in the reference implementation.

Multicast

224.76.78.75 (IPv4)
ff12::8080 (IPv6)
Taken from multicastEndpointV4() and multicastEndpointV6() in the Ableton Link source. Peers announce and discover each other on this group, so anything that blocks local multicast makes Link look broken.

What goes wrong

There is no master. Any peer joining a session adopts the session tempo, and any peer can then change tempo for everyone. If someone nudges a tempo control on the wrong machine, the whole room moves.

Discovery is multicast on 224.76.78.75 port 20808. Client isolation on guest wifi, a VPN client, or a firewall silently blocking multicast all produce the same symptom: zero peers found and no error message.

Link does not work over a VPN or over Bluetooth. Ableton state this directly. A tethered phone or a corporate VPN left running is the usual reason one machine cannot see the others.

On recent macOS versions the local network permission must be granted to each application. If it is not, the app finds nothing and gives no clue why.

Link carries tempo, beat and phase only. Start/stop sync is an optional feature that applications must opt into, so do not assume pressing play on one device starts the others.

It is not timecode. There is no absolute position and no relationship to SMPTE, so Link will keep a band in time with each other but will not lock them to a video playback or a show timeline.

What speaks Ableton Link (3)

Product	Direction	Notes
Ableton Live Ableton AG	bidirectional	Peer-to-peer tempo, beat and phase sync over the local network. There is no master: any peer can change the session tempo. Tempo Follower and External Sync are mutually exclusive.
Chataigne Ben Kuper	bidirectional	Listed among the built-in protocol modules.
Max Cycling '74	bidirectional	Through Max for Live and Link-aware objects.

Open source implementations

Ableton Link — C++, GPL-2.0-or-later

Typical use

Keeping laptops and tablets running different music software on one tempo
DJ software and a live performance rig sharing a grid
Lighting and VJ software following a musical tempo rather than timecode
Ad-hoc jam setups where nobody wants to nominate a master clock

Sources

Ableton Link source — multicast endpoints (224.76.78.75 and ff12::8080, port 20808) — Ableton AG primary
Link Troubleshooting (port 20808, multicast, no VPN, no Bluetooth, macOS local network permission) — Ableton AG primary
Ableton Link repository and licence — Ableton AG primary

Understand the mechanism

How it all runs together How a one gets down a wire

Something wrong, or missing?

Known gaps on this entry: first_published. If you can source one of them, that is a ten minute pull request.

Edit this entry on GitHub — one file, editable in your browser, and your handle goes on it permanently.

Work at Ableton AG? Confirm or correct this entry — it is free, it stays free, and nothing about it is for sale.