Soft clipping is a type of distortion effect where the amplitude of a signal is saturated along a smooth curve, rather than the abrupt shape of hard-clipping. Soft clipping is similar to the type of distortion found in certain analog audio systems. Examples include a vacuum tube amplified and the saturation of magnetic tape.


There are many non-linear functions that can be used to digitally create a soft-clipping distortion effect. One example of soft-clipping distortion is based on using a cubic function. An equation to create soft-clipping is:


output = input - \frac{1}{3} \cdot {(input)}^{3}


By decreasing the scaling coefficient of the cubic term from \frac{1}{3} to 0, the relative amount of distortion is reduced until the function becomes a linear equation.



A different method for creating soft-clipping distortion is based on the arctangent function. The relative amount of distortion can be set by the \alpha coefficient.


output = \frac{2}{\pi} \cdot arctan(\alpha \cdot input)


Typical values of the \alpha coefficient are on the order of \alpha \in [1,10]. For values of \alpha >> 10, the soft-clipping distortion approaches infinite clipping distortion.


Next, let’s look at another approach to creating distortion called bit reduction or bit crushing.

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