1. A speech-based system, comprising: a speaker configured to generate output audio from at least one output signal; a microphone configured to produce an input signal representing user speech and at least a portion of the output audio; an input detector configured to detect a trigger expression in the input signal; at least one output detector configured to detect the trigger expression in the at least one output signal; a trigger expression qualifier configured to qualify the trigger expression detected by the input detector based, at least in part, on the at least one output detector not detecting the trigger expression in the at least one output signal; a speech recognizer configured to recognize speech represented by the input signal, the speech recognizer being responsive to the trigger expression; and a command interpreter configured to receive the input signal that represents the speech, and to interpret commands from recognized speech that follows the trigger expression.
1. A speech-based system, comprising: a speaker configured to generate output audio from at least one output signal; a microphone configured to produce an input signal representing user speech and at least a portion of the output audio; an input detector configured to detect a trigger expression in the input signal; at least one output detector configured to detect the trigger expression in the at least one output signal; a trigger expression qualifier configured to qualify the trigger expression detected by the input detector based, at least in part, on the at least one output detector not detecting the trigger expression in the at least one output signal; a speech recognizer configured to recognize speech represented by the input signal, the speech recognizer being responsive to the trigger expression; and a command interpreter configured to receive the input signal that represents the speech, and to interpret commands from recognized speech that follows the trigger expression. 4. The speech-based system of claim 1 , wherein an output signal of the at least one output signal comprises a digital audio stream.