9. A system, comprising: at least one hardware processor; and at least one computer readable storage medium storing processor-executable instructions that, when executed by the at least one hardware processor, cause the at least one hardware processor to perform: obtaining first data comprising audio data processed by a natural language understanding (NLU) system at least in part by using a first NLU model, a first N-best list of word sequences generated by using a first speech recognition model to recognize at least a portion of the audio data, and associated NLU data indicating how the audio data was understood by the NLU system; and modifying the first speech recognition model and the first NLU model based at least in part on the first data, including using the first N-best list of word sequences, to obtain a second speech recognition model and a second NLU model.
9. A system, comprising: at least one hardware processor; and at least one computer readable storage medium storing processor-executable instructions that, when executed by the at least one hardware processor, cause the at least one hardware processor to perform: obtaining first data comprising audio data processed by a natural language understanding (NLU) system at least in part by using a first NLU model, a first N-best list of word sequences generated by using a first speech recognition model to recognize at least a portion of the audio data, and associated NLU data indicating how the audio data was understood by the NLU system; and modifying the first speech recognition model and the first NLU model based at least in part on the first data, including using the first N-best list of word sequences, to obtain a second speech recognition model and a second NLU model. 12. The system of claim 9 , wherein the modifying comprises jointly modifying the first speech recognition model and the first NLU model by using a performance metric indicative of accuracy of the natural language understanding system.