On a bus send or a volume meter, post fader refers to the fact that the signal strength is proportional to the fader position, meaning that it will be louder if the fader is higher and quieter if the fader is lower. Most effects sends are post fader, so that, for example, the amount of reverb or delay is always proportional to the original dry , whenever the mix engineer wants to create a totally independent mix, pre fader sends are more useful. For instance, when using pre fader sends to create a cue mix, the engineer can change the control room mix, say to check the sound of a particular track, without changing what the musicians in the room are hearing. Also, pre fade sends are sometimes used to create bizarre reverb effects, where the reverb is not proportional to the signal. There is usually a pre/post button on the bus send that lets the engineer select one of the two choices.