1. A system comprising: a computer-readable memory storing executable instructions; and one or more physical computer processors in communication with the computer-readable memory, wherein the one or more physical computer processors are programmed by the executable instructions to at least: obtain audio data regarding a user utterance, the audio data comprising a sequence of frames; identify, for a current frame of the sequence of frames, (1) one or more speech recognition decoding graph states corresponding to the current frame, and (2) a window of frames preceding the current frame in the sequence of frames; generate, for a first state of the one or more speech recognition decoding graph states, a parameter of a probability density function, wherein the parameter is generated using an artificial neural network, and wherein input into the artificial neural network comprises data regarding the first state and a plurality of feature vectors corresponding to the window of frames; generate, for the first state of the one or more speech recognition decoding graph states, a first score using a feature vector corresponding to the current frame and the parameter of the probability density function generated using the first state; and select at least one state to add to the speech recognition decoding graph based at least partly on the first score and the first state.
3. The system of claim 1 , wherein the first score corresponds to a probability that the current frame is observed, given the first state.