The term "lookahead" in the context of dynamic signal processor effects refers to how an audio software plugin will delay the signal e.g., 0.1 to 1 ms or more, for the sake of implementing the process of analyzing the incoming audio material. And once a brickwall limiter analyzes the input signal the plugin will know what to do and will process the sound accordingly to programmed algorithms and also taking into account user-defined settings.

Audio latency and lookahead limiters​

When you use some look-ahead limiters you might not hear the sound directly after you have hit play in your DAW (i.e., digital audio workstation). Well, this is because of a term called "latency" where the brickwall limiter tells the DAW to wait a little bit whilst it's analyzing the signal before real-time processing takes place.

This so-called latency delay is usually affected by the amount of look-ahead time that is either defined by the user or an already pre-defined setting because some brickwall limiters don't have the option where users can adjust the look-ahead time.

N.B. Automatic Delay Compensation is often used so that the mastering brickwall limiter tells the DAW software how much look-ahead time went into processing. Eventually, everything in that particular session will of course "automatically" sync back together and play at the same time.
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