Editing Frequency modulation (section)

===Magnetic tape storage===
FM is also used at [[Intermediate frequency|intermediate frequencies]] by analog [[Video cassette recorder|VCR]] systems (including [[VHS]]) to record the [[Luminance (video)|luminance]] (black and white) portions of the video signal. Commonly, the [[chrominance]] component is recorded as a conventional AM signal, using the higher-frequency FM signal as [[Tape bias|bias]]. FM is the only feasible method of recording the luminance ("black-and-white") component of video to (and retrieving video from) [[magnetic tape]] without distortion; video signals have a large range of frequency components – from a few [[hertz]] to several [[megahertz]], too wide for [[Equalization (audio)|equalizers]] to work with due to electronic noise below −60&nbsp;[[decibel|dB]]. FM also keeps the tape at saturation level, acting as a form of [[noise reduction]]; a [[audio level compression|limiter]] can mask variations in playback output, and the [[FM capture]] effect removes [[print-through]] and [[pre-echo]]. A continuous pilot-tone, if added to the signal – as was done on [[V2000]] and many Hi-band formats – can keep mechanical jitter under control and assist [[timebase correction]].

These FM systems are unusual, in that they have a ratio of carrier to maximum modulation frequency of less than two; contrast this with FM audio broadcasting, where the ratio is around 10,000. Consider, for example, a 6-MHz carrier modulated at a 3.5-MHz rate; by [[Bessel function|Bessel]] analysis, the first sidebands are on 9.5 and 2.5&nbsp;MHz and the second sidebands are on 13&nbsp;MHz and −1&nbsp;MHz. The result is a reversed-phase sideband on +1&nbsp;MHz; on demodulation, this results in unwanted output at 6 – 1 = 5&nbsp;MHz. The system must be designed so that this unwanted output is reduced to an acceptable level.<ref>"FM Systems Of Exceptional Bandwidth" Proc. IEEE vol. 112, no. 9, p. 1664, September 1965</ref>