1. A computer-implemented method 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.