Independent sideband
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Independent sideband (ISB) is an AM single sideband mode which is used with some AM radio transmissions. Normally each sideband carries identical information, but ISB modulates two different input signals — one on the upper sideband, the other on the lower sideband. This is used in some kinds of AM stereo, but is generally otherwise prohibited in the U.S. by the FCC.
ISB is a type of hybrid between double sideband (DSB) and single sideband (SSB) — the other is vestigial sideband (VSB). If the sidebands are out of phase with each other, then phase modulation (PM) of the carrier occurs. AM and PM together then create quadrature amplitude modulation (QAM). ISB may or may not have the carrier suppressed.