Historical sourceHistorical source is an original source that contains important historical information. These sources are something that inform us about history at the most basic level, and are used as clues in order to study history. Historical sources can include coins, artefacts, monuments, literary sources, documents, artifacts, archaeological sites, features, oral transmissions, stone inscriptions, paintings, recorded sounds, images and oral history. Even ancient relics and ruins, broadly speaking, are historical sources.
Noise (signal processing)In signal processing, noise is a general term for unwanted (and, in general, unknown) modifications that a signal may suffer during capture, storage, transmission, processing, or conversion. Sometimes the word is also used to mean signals that are random (unpredictable) and carry no useful information; even if they are not interfering with other signals or may have been introduced intentionally, as in comfort noise. Noise reduction, the recovery of the original signal from the noise-corrupted one, is a very common goal in the design of signal processing systems, especially filters.
Signals intelligenceSignals intelligence (SIGINT) is intelligence-gathering by interception of signals, whether communications between people (communications intelligence—abbreviated to COMINT) or from electronic signals not directly used in communication (electronic intelligence—abbreviated to ELINT). Signals intelligence is a subset of intelligence collection management. As classified and sensitive information is usually encrypted, signals intelligence in turn involves the use of cryptanalysis to decipher the messages.
