Delay line

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The term delay line has multiple meanings:

• In electronics and derivative fields such as telecommunications, a delay line is a device where the input signal reaches the output of the device after a known period of time has elapsed. It is rigorously defined as a single-input-channel device, in which the output channel state at a given instant, t, is the same as the input channel state at the instant t−n, where n is a number of time units, i.e., the input sequence undergoes a delay of n time units, such as n femtoseconds, nanoseconds, or microseconds. (The delay line may have additional taps yielding output channels with values less than n.) Specific devices and approaches:
  • A transmission line or equivalent device (such as an analog delay line) used to delay a signal.
  • In computer simulation it can be used as a numerical technique, also called a bi-directional delay line or transmission line modelling (TLM) method.
  • In digital logic and digital signal processing, a delay line or digital delay line refers to a sequential logic element in which the output state at a given time n (in samples) is the same as the input was at the time n−L. Delay lines are generally expressed as z^-L, where L is the length of the delay in samples. A unit delay (a delay of one sample) is therefore expressed as z^-1.
  • In computing, delay line often refers to delay line memory.
• In Optics : cavity delay lines or trombone delay lines e.g. [1]
• In sound reinforcement, delay lines refer to systems of additional loudspeakers used to supplement the main loudspeaker system in areas where it does not reach effectively, such as the back of a large (deep) room or underneath a balcony. The delay line loudspeakers are sent a signal that has been delayed by an amount of time corresponding to the speed of sound in air over the distances involved, roughly one millisecond per foot or 3 ms per meter.
• In neurobiology, delay lines can refer to neurons, the cells that transmit electrical information in the brain. Electrical conduction in neurons is not instantaneous; it is delayed depending on the length of the axon and other properties of the neuron (e.g. myelination). This delay can be used for time sensitive calculations; the canonical example is the calculation of inter-aural time differences in the pons, used for sound localization.

An earlier version of this page came from Federal Standard 1037C and from MIL-STD-188.