8. A non-transitory computer readable storage device storing instructions that, when executed by one or more processors, cause the one or more processors to perform operations comprising: receiving, by a mobile device, an audio signal; determining, by the mobile device and using a model that is trained to detect a presence of a synthesized voice and a model that is trained to detect a presence of a user's voice, that the audio signal likely includes both the synthesized voice and the user's voice; in response to determining, by the mobile device and using a model that is trained to detect a presence of a synthesized voice and a model that is trained to detect a presence of a user's voice, that the audio signal likely includes both the synthesized voice and the user's voice, suppressing, by the mobile device, operation of a speech synthesis module implemented by the mobile device; after suppressing operation of the speech synthesis module, obtaining, by the mobile device, a transcription corresponding to the audio signal from an automated speech recognizer; and providing, by the mobile device, the transcription for output.
8. A non-transitory computer readable storage device storing instructions that, when executed by one or more processors, cause the one or more processors to perform operations comprising: receiving, by a mobile device, an audio signal; determining, by the mobile device and using a model that is trained to detect a presence of a synthesized voice and a model that is trained to detect a presence of a user's voice, that the audio signal likely includes both the synthesized voice and the user's voice; in response to determining, by the mobile device and using a model that is trained to detect a presence of a synthesized voice and a model that is trained to detect a presence of a user's voice, that the audio signal likely includes both the synthesized voice and the user's voice, suppressing, by the mobile device, operation of a speech synthesis module implemented by the mobile device; after suppressing operation of the speech synthesis module, obtaining, by the mobile device, a transcription corresponding to the audio signal from an automated speech recognizer; and providing, by the mobile device, the transcription for output. 14. The computer readable storage device of claim 8 , wherein each of the model that is trained to detect a presence of a synthesized voice and the model that is trained to detect a presence of a user's voice is a neural network based model.