A convolutional frontend is a typical downsampling strategy [8, 19] ; however, we leave integrating other layer types into SAN-CTC as future work. Instead, we consider three fixed approaches, from least-to most-preserving of the input data: subsampling, which only takes every k-th frame; pooling, which aggregates every k consecutive frames via a statistic (average, maximum); reshaping, where one concatenates k consecutive frames into one <cite>[27]</cite> .