a) This nonlinear distortion is often referred to as “diff gain” or “dG.” It is present if a signal’s chrominance gain is affected by luminance levels. This amplitude distortion is a result of the system’s inability to uniformly process the high-frequency chrominance signals at all luminance levels. The amount of differential gain distortion is expressed in percent. Since both attenuation and peaking of chrominance can occur in the same signal, it is important to specify whether the maximum over all amplitude difference or the maximum deviation from the blanking level amplitude is being quoted. In general, the NTSC measurement standard defines differential gain as the largest amplitude deviation between any two levels, expressed as a percent of the largest chrominance amplitude. When differential gain is present, color saturation has an unwarranted dependence on luminance level. Color saturation is often improperly reproduced at high luminance levels. The Modulated Ramp or Modulated Stair Step signals can be used to test for differential gain. b) The amplitude change, usually of the 3.6 MHz color subcarrier, introduced by the overall circuit, measured in dB or percent, as the subcarrier is varied from blanking to white level.