Parallel processing
The untreated signal stays audible, and a processed copy is mixed in beside it. Sends do this in the mixer. Splitter and Merger do it between devices.
Parallel processing keeps the untreated signal audible and mixes a processed copy in beside it.
Heavy compression on the only copy of a drum kit evens the hits and takes the attack with them. The same compression on a copy, blended under the untreated drums, adds density and leaves the original hits. The same shape works for a distorted copy under a clean bass, or a bright filtered copy beside a dull one.
Sends are the mixer’s version. The channel stays dry, the send feeds the processed chain, and the return level is the blend.
In the Studio, Splitter and Merger do it between devices. Split the signal, process one branch, merge it with the branch you left alone. BandSplitter is the frequency version: highs and lows take different paths, then meet again.