Synchronization via out-of-band clock timing signaling

Abstract

Disclosed embodiments include facilitating clock synchronization and/or synchronous playback among multiple playback devices in a group. An individual playback device estimates and/or calculates a clock time at a clock time source (or a time offset/error between the playback device and the clock time source) based on (i) first clock timing received from the clock time source via a primary timing link and (i) second clock timing received from the clock time source via a secondary timing link. In some embodiments, estimating and/or calculating a clock time and/or clock time offset/error comprises estimating and/or calculating the clock time and/or clock time offset/error with a state estimator, such as a Kalman filter, an extended Kalman filter, or other state estimator configured to estimate a clock time and/or clock time error based on clock timing received via two or more communications links.