8. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving an audio signal encoding a portion of an utterance; receiving context information associated with the utterance, wherein the context information is not derived from the audio signal or any other audio signal; generating, for input to a neural network of an automatic speech recognition system and based on characteristics of the context information that existed when the context information was received, characteristic data that corresponds to the context information; providing, as input to the neural network of the automatic speech recognition system, data corresponding to the audio signal and the characteristic data that corresponds to the context information; and generating a transcription for the utterance based on at least an output of the neural network.
13. The system of claim 8 , wherein the operations further comprise: receiving a set of data derived from the audio signal, the set of data corresponding to one or more time-independent characteristics of the audio signal; wherein providing, as input to a neural network, data corresponding to the audio signal and the characteristic data that corresponds to the context information comprises providing, as input to the neural network, data corresponding to the audio signal, the characteristic data that corresponds to the context information, and the set of data derived from the audio signal.