If the level of residual noise is smaller than the NMT, the human ear cannot perceive the corrupting noise.In this situation the gain factor is set to unity.

• 相反的，如果残留杂讯比听觉遮蔽阈值大，则人耳听得到该杂讯，因此将增益因子调整小一点，使得干扰杂讯得以被压抑。