  The multi-stream paradigm of audio processing, in which several sources are
simultaneously considered, has been an active research area for information
fusion. Our previous study offered a promising direction within end-to-end
automatic speech recognition, where parallel encoders aim to capture diverse
information followed by a stream-level fusion based on attention mechanisms to
combine the different views. However, with an increasing number of streams
resulting in an increasing number of encoders, the previous approach could
require substantial memory and massive amounts of parallel data for joint
training. In this work, we propose a practical two-stage training scheme.
Stage-1 is to train a Universal Feature Extractor (UFE), where encoder outputs
are produced from a single-stream model trained with all data. Stage-2
formulates a multi-stream scheme intending to solely train the attention fusion
module using the UFE features and pretrained components from Stage-1.
Experiments have been conducted on two datasets, DIRHA and AMI, as a
multi-stream scenario. Compared with our previous method, this strategy
achieves relative word error rate reductions of 8.2--32.4%, while consistently
outperforming several conventional combination methods.
