  Conformer has achieved impressive results in Automatic Speech Recognition
(ASR) by leveraging transformer's capturing of content-based global
interactions and convolutional neural network's exploiting of local features.
In Conformer, two macaron-like feed-forward layers with half-step residual
connections sandwich the multi-head self-attention and convolution modules
followed by a post layer normalization. We improve Conformer's long-sequence
representation ability in two directions, \emph{sparser} and \emph{deeper}. We
adapt a sparse self-attention mechanism with $\mathcal{O}(L\text{log}L)$ in
time complexity and memory usage. A deep normalization strategy is utilized
when performing residual connections to ensure our training of hundred-level
Conformer blocks. On the Japanese CSJ-500h dataset, this deep sparse Conformer
achieves respectively CERs of 5.52\%, 4.03\% and 4.50\% on the three evaluation
sets and 4.16\%, 2.84\% and 3.20\% when ensembling five deep sparse Conformer
variants from 12 to 16, 17, 50, and finally 100 encoder layers.
