An audio processing system configured to generate, based at least in part on captured sound, an audio signal that includes a speech component corresponding to a user's speech utterance and an audio component corresponding to audio output of another device is described herein. The audio processing system is also configured to receive a reference signal that corresponds to the audio output of the other device. The reference signal may be received as ultrasonic audio output of the other device or from a remote server. The audio processing device then processes the generated audio signal to remove at least a part of the generated audio signal that corresponds to the reference signal.