Soft clipping is the result of a peak of a waveform exceeding the maximum volume that a piece of hardware is able to accurately reproduce. In analogue circuitry, this maximum volume is dictated by the maximum voltage the circuit can put out, now, because the peak cant be reproduced above this maximum level, the waveform gets squared off, which causes distortion and adds some nice warm harmonics to the sound while acting like a limiter.
Ableton Soft Clippers – Ableton has a few effects that are capable of soft clipping but my favorite ones are Glue Compressor, Saturator, and Overdrive. The best way to use them is to drive the signal into them until you feel like the distortion is a bit over the top, and then back off until you find the sweet spot.