17. The computer-readable medium of claim 15 , wherein the operations further comprise, for each frame in the received first audio signal: identifying audio characteristics of the user speaking the trigger phrase and audio characteristics of background noise for the corresponding frame in the received first audio signal; comparing the identified audio characteristics of the user speaking the trigger phrase to predetermined threshold values associated with one or more values for trigger phrase model training; and determining a voice activity detection flag for the corresponding frame in the received first audio signal in response to comparing the identified audio characteristics of the user speaking the trigger phrase to the predetermined threshold values.
17. The computer-readable medium of claim 15 , wherein the operations further comprise, for each frame in the received first audio signal: identifying audio characteristics of the user speaking the trigger phrase and audio characteristics of background noise for the corresponding frame in the received first audio signal; comparing the identified audio characteristics of the user speaking the trigger phrase to predetermined threshold values associated with one or more values for trigger phrase model training; and determining a voice activity detection flag for the corresponding frame in the received first audio signal in response to comparing the identified audio characteristics of the user speaking the trigger phrase to the predetermined threshold values. 18. The computer-readable medium of claim 17 , wherein determining the voice activity detection flag for the corresponding frame in the received first audio signal comprises: generating an accept enrollment flag in response to the identified audio characteristics of the user speaking the trigger phrase being less than the predetermined threshold values; and generating a reject enrollment flag in response to the identified audio characteristics of the user speaking the trigger phrase being greater than the predetermined threshold values.