OD Channel Clamper allows you to clamp a single envelope and can be found in the Graph Editor under the modifiers tab:
Options:
Minimum: Defines the minimum value where the clamp (cutoff) occurs
Maximum: Defines the maximum value where the clamp (cutoff) occurs
Scale : After the clamp, you can scale the resulting values
Add To : After the clamp, you can add an additional value to the result
Here's a how-to video showing OD Channel Clamper in action.