2. Auto panners
It isn’t always necessary to simply “expand” a sound in space. A wide stereo base will do well, but, if you need to add some dynamics to a mix, auto panner plugins will perfectly suit. They smoothly move a sound to the left and right along channels with frequency modulation defined by an engineer. Auto panners are an excellent solution when it is necessary to enliven monotonous percussion background or to add more movement to sounds with larger sustain.
Stereo reverberation is a technique used for widening a narrow signal and is familiar to every music mixing service. For this reason you should create AUX bus with a reverberator adjusted at a minimum length of the reverb tail – 100–200 ms. You may even cut reverberation high frequencies with an equalizer. Then blend little by little the sound from the bus to a clear signal. You may go a lot farther and play with levels of early and late reflections in reverberator settings. You’ll have quite an interesting effect at audio mixing and mastering services if you completely remove late reflections (in this case you won’t need to adjust the reverb tail as you won’t have it) and blend only early reflections.