limiter

A limiter is a device or algorithm that enforces an upper bound on a value, such as a signal level or a rate of activity, to prevent it from exceeding a predefined limit. Limiting is used to protect equipment, ensure regulatory compliance, or manage system behavior.

In audio engineering, a limiter is a type of dynamics processor designed to prevent signal peaks from exceeding a chosen ceiling, thereby reducing distortion from clipping. A brickwall limiter imposes an abrupt ceiling, while a lookahead limiter uses information from future samples to optimize control. Common parameters include threshold, attack and release times, ceiling, and makeup gain. Limiters are widely used in mastering and live sound to preserve headroom.

In electronics, current or voltage limiters cap the output to protect circuits from overcurrent or overvoltage conditions. Implementations include current-limiting circuits in power supplies, fuses, and thermistors. They respond to abnormal conditions by constraining output, often providing fast-acting protection to prevent damage.

In computing, rate limiters control how often an action can be performed within a given time window to prevent abuse or overload. Common approaches include token bucket, leaky bucket, and fixed-window techniques. Rate limiting is used for API gateways, login attempts, and message queuing to maintain service quality and security.

In transportation, speed limiters restrict the maximum speed of a vehicle, typically via the engine control unit or related systems, to comply with laws and enhance safety. The concept also applies to other automated processes that require adherence to preset constraints.