Effects can be inserted into any audio BUS in addition to being inserted into channels.  Sends to effects can be processed (such as making a vocal feed into a reverb less bright so the “sss” sound does not ring out) as can bus assigned groups (such as putting all the drums into a stereo bus instead of the main stereo mix, inserting a compressor into the bus for extra punch, and then feeding the bus back into the main stereo mix) or even the Master Fader.

When effects are placed in Master Fader channels of a mixing board, the entire mix sound can be altered.  Common Master Fader effects include COMPRESSION (so the mix sounds more “mushed together”) and EQ (to keep the mix blend but add a little more clarity or heaviness).

One has to be careful when using Master Fader effects because it is easy to over-process the mix.  Remember that every processor (even digital ones) color sound in a certain way. Some processors add to the sound while others subtract.  It is easy to over-compress or limit and lose dynamics.  If the mix processing has a thin or hard sound, then the whole mix will be given that overall tone.  Choose your Master Fader Effects carefully.

Analog tape compression used to be a commonly relied-upon master fader effect that was used by sending the mix to the tape machine at a higher gain than what the tape could safely hold.  Different tapes saturated at different levels and even in different ways.  For example, Agfa 468 tape would not compress much if you kept your levels at or around 0 to +2 dB (when the machine was set so that 0 was 370 nanowebers per meter), while 3M 996 on a machine set exactly the same would start to compress at around -1 to -2 dB and was heavily compressed by the time the sound level reached +2 dB.

Many people relied on the warm compression that resulted from tape saturation.  Some people did not like the tape to change the sound of what was coming out of the mixing board much and preferred more accurate tapes like 468.  As a side note, although 468 was a clear tape it had the problem of shedding – actually leaving tiny bits of plastic on the tape machine that could be seen on Q-tips used to clean the heads.  One particular engineer that liked 468 and had the budget to do so would print extra copies that were never to be played except when being put on the album master.