CX decoders made for LPs could not be used with LDs because the CX companding specifications for LaserDisc were changed, from 20 dB of noise reduction to 14 dB, along with moving the 'threshold' where compression/expansion changes from 2:1 to 1:1 from -40 dB to -28 dB - other minor changes to the decoding time constants were made as well. In addition, some of the LaserDisc's FM audio encoding specifications were modified too, allowing more headroom and better high frequency response at high levels. These changes were made because, at the time of CX's adoption on LaserDisc (1981), the vast majority of program sources used for mastering, such as 35 mm optical and magnetic film soundtracks, as well as the 2-inch IVC-9000 and the 1-inch C-Type video tape formats used for LaserDisc mastering, had signal-to-noise ratios low enough that "undecoded" playback would accentuate their noise to unacceptable levels.