Recognition Questions

Why do my prompts trigger barge-in?

A problem speech developers often have is poor echo cancellation. When this happens, prompts played to callers are heard by the speech application. If the prompt is played back loud enough, the speech application may confuse the prompt echo for speech and trigger barge-in, cutting off the prompt.

This commonly happens for a few reasons:

1. The prompt playing is too loud. If you listen to the entire audio, you can typically hear the echo cancellation start to fail. To remedy this, reduce the volume at which the prompts are played.
2. The prompt has leading silence. The echo cancellation hardware uses the first half-second of a prompt to get to get the timing down. Basically, the hardware looks for sound markers in the prompt in order to perform echo cancellation, and if there is only silence it cannot. It is OK to have trailing silence, but not at the prompt's start.
3. The prompt is text to speech. Text to speech can create problems for echo cancellation because there is actual silence between the words. This can cause the echo cancellation to lose the proper timing. A trick to solve this issue is the introduction of noise into the waveform. Typically a +/- 16 or 32 point wave added to the audio can solve this issue.