In facsimile, a frequency modulationsystem where one frequency represents picture black and another frequency represents picture white[?]. Frequencies between these two limits may represent shades of gray
An intentional frequency change used for modulation purposes
... 1981 Joni Mitchell
1982 Neil Young
1983 Glenn Gould
1986 Gordon Lightfoot
1987 The Guess Who[?]
1989 The Band
1990 Maureen Forrester[?]
1991 Leonard Cohen
...