The linear amplifier is a summing amplifier with three separate input channels. The amplifier multiplies the input to each channel by that channel's gain parameter (in value or decibels), and then adds the three products to produce the output.
Since you cannot take the log of a negative number, if you are converting a negative gain (in value) to decibels, the amplifier inverts the gain value to make it positive before converting to decibels. The check box Invert is selected automatically alerting you to the fact that the gain value has been inverted.
