1. An interactive voice response (IVR) system for providing acknowledgement prompts, the system configured to: receive an input audio stream over a voice channel from a user; identify, from the input audio stream, a keyword, a confidence value associated with the keyword, and an input volume; select an acknowledgement prompt and an output volume for the selected acknowledgement prompt based at least in part on the confidence value and the input volume; and output the selected acknowledgement prompt at the selected output volume to the user.