Clock Source and Drift Correction in Audio MIDI Setup

Before you start

Drift correction applies to a local audio configuration in macOS Audio MIDI Setup. The setting is mainly relevant when more than one digital audio device is available, or when an input and output device use separate clock circuits. It does not require an online service or an account.

Before changing settings, connect the audio interfaces to the Mac and confirm that each device appears in Audio MIDI Setup. Note the sample rate shown for each device and keep it consistent across devices you plan to use together.

What drift correction means

Drift is a gradual timing difference between two digital audio devices. Even when both devices are set to the same sample rate, small clock differences can cause audio to fall behind or ahead over time. Drift correction lets one device follow another device from within a multi-device audio configuration.

The clock source is the device that provides the timing reference. If a device is not the clock source and its timing drifts, enabling drift correction on that device may help it stay aligned with the reference device.

Step-by-step instructions

• Open Audio MIDI Setup from the Utilities folder inside Applications.
• Choose Window, then Show Audio Devices if the audio device list is not visible.
• Select the aggregate or multi-output device you want to inspect.
• In the right pane, look at the Clock Source setting and note which device is selected.
• If one of the subdevices has a Drift Correction checkbox, select it only when that subdevice is not the clock source.
• Stop playback in any audio application before changing the setting.
• Close Audio MIDI Setup and reopen the audio application so the revised device configuration is loaded.

The exact placement of these controls can vary between macOS versions. In some versions, drift correction is shown only for devices added to an aggregate device. If the checkbox is absent, the device or the current configuration may not expose the feature.

Check the output

A practical check is to play a steady tone or a known recording through the multi-device setup and listen to whether both outputs stay aligned for several minutes. A growing echo, flanging effect, intermittent glitch, or progressive delay can indicate remaining timing drift.

Do not judge quality by the absence of an error message. Audio MIDI Setup does not always provide a live accuracy measurement or a sample-accurate drift display, so audible behavior is the basic confirmation available.

Common problems and next steps

• The device disappears when changing the sample rate: confirm that all connected devices use a supported sample rate and that one clear clock source is set.
• The audio application does not show the new setup: close and reopen the application after saving changes in Audio MIDI Setup.
• Two interfaces remain noticeably out of sync: choose a different clock source for the aggregate device, then test again.
• Recordings have clicks or short dropouts: check the input device clock source and reduce unnecessary simultaneous input and output device combinations.

Background noise is not a symptom of drift correction by itself. If you hear noise only after changing interfaces, first check input level, cable routing, and whether the unintended device is being monitored.

Changes in Audio MIDI Setup are reversible. Deselect drift correction or return the clock source to its previous value if the setup sounds worse or becomes unstable. If a device exposes its own control software or driver utility, verify whether that utility overrides the selection made in Audio MIDI Setup.