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.