This app is useful for experimenting with the phenomenon of Delayed Auditory Feedback (DAF) to disrupt speech.
DAF might have other uses, involving speech therapy or practicing speeches that will be presented in large venues where echoes are a problem.
The app is currently currently targeted for Android devices with built-in echo cancellation abilities, such as smart phones that support speakerphone features. If you run on a tablet, which typically does not implement echo cancellation, use headphones to prevent runaway audio feedback.

Controls include volume and delay. Adjust the volume to prevent runaway feedback. Adjust the delay for optimal disruption of talking. We find that 150 milliseconds works pretty well. For best results, the phone should be placed as close to the subject's head as practical.

No ads, free, fully functional. Voluntary contribution suggested via in-app billing, with no nags.