In telecommunication, a standard test tone is a single-frequency signal with a standardized level generally used for level alignment of single links and of links in tandem.

Note: For standardized test signal levels and frequencies, see MIL-STD-188-100 for DOD use, and the Code of Federal Regulations , Title 47, part 68 for other Government agencies.

Source: from Federal Standard 1037C and from MIL-STD-188