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
... is spread out with 18.5% under the age of 18, 4.4% from 18 to 24, 20.6% from 25 to 44, 26.3% from 45 to 64, and 30.2% who are 65 years of age or older. The median ...