Ableton Link- A technology for synchronization that expands on MIDI timing

The MIDI Association

Ableton Link is a technology that synchronizes musical beat, tempo, phase, and start/stop commands across multiple applications running on one or more devices. Applications on devices connected to a local network discover each other automatically and form a musical session in which each participant can perform independently: anyone can start or stop while still staying in time. Anyone can change the tempo, the others will follow. Anyone can join or leave without disrupting the session.

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Core Ableton Link Concepts

Link is different from other types of synchronization technologies because it t is not as rigid. Link allows apps to each have their own independent timelines, but provides four different ways to align the different apps together in time.

Tempo Synchronization

Tempo is pretty well understood and Tempo can be changed via MIDI. The difference with Link is that link is based on multiple players being connected on the same network. With traditional acoustic ensembles, temps change fluidly and the players adapt quickly to these changes. Link works the same way. Every “player” (or participant in the Link network) adopts the last tempo value proposed on the network. So with multiple participants, one person could be suggesting to speed up the tempo and one could be suggesting to slow down the tempo. However the system quickly adapts just as acoustic players would.

Beat Alignment

For a lot of musical situations, just Tempo Synchronization is not enough. Both devices could be playing at the same tempo, but if their beats are not aligned one could be starting a measure at beat 1 and another could be starting at beat 1.8 .

When a session is in a state of beat alignment, an integral value on any participant’s beat timeline corresponds to an integral value on all other participants’ beat timelines. This property says nothing about the magnitude of beat values on each timeline, which can be different, just that any two timelines must only differ by an integral offset. For example, beat 1 on one participant’s timeline might correspond to beat 3 or beat 4 on another’s, but it cannot correspond to beat 3.5.

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Phase Synchronization

Even with Tempo Synchronization and Beat Alignment, when working with loops and bars lines, you often want the large structure ( 2 bar, 4 bar, 8 bar, etc.) to be aligned. Phase Synchronization is a clever way to do this. Link requires that each application provide a quantum value in beats that specifies the desired unit of phase synchronization.

Specifying the quantum value and the handling of phase synchronization is the aspect of Link integration that leads to the greatest diversity of approaches among developers. There’s no one-size-fits-all recommendation about how to do this, it is very application-specific. Some applications have a constant quantum that never changes. Others allow it to change to match a changing value in their app, such as loop length or time signature. In Ableton Live, it is directly tied to the “Global Quantization” control, so it may be useful to explore how different values affect the behavior of Live in order to gain intuition about the quantum.

In order to maintain phase synchronization, the vast majority of Link-enabled applications (including Live) perform a quantized launch when the user starts transport. This means that the user sees some sort of count-in animation or flashing play button until starting at the next quantum boundary. This is a very satisfying interaction because it allows multiple users on different devices to start exactly together just by pressing play at roughly the same time. We strongly recommend that developers implement quantized launching in Link-enabled applications.

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Start/Stop Synchronization

As of Version 3, Link allows peers to share information on the user’s intent to start or stop transport with other peers that have the feature enabled. Start/stop state changes only follow user actions.