1. A method comprising: receiving, by a computing device, a sequence of speech features that characterize an unknown speech input provided on an audio input channel controlled by an application executing on the computing device; receiving meta-data that characterizes the audio input channel, an audio codec applied when generating the sequence of speech features, and a type of the application; transforming the sequence of speech features using one or more trained mapping functions including a feature-space maximum mutual information (fMMI) mapping function, the one or more trained mapping functions controlled by the meta-data that characterizes the audio input channel, the audio codec applied when generating the sequence of speech features, and the type of the application, the fMMI mapping function using neural network based posterior estimates that use the meta-data as input; and performing automatic speech recognition of the transformed speech features.