  A number of recent advances in neural audio synthesis rely on upsampling
layers, which can introduce undesired artifacts. In computer vision, upsampling
artifacts have been studied and are known as checkerboard artifacts (due to
their characteristic visual pattern). However, their effect has been overlooked
so far in audio processing. Here, we address this gap by studying this problem
from the audio signal processing perspective. We first show that the main
sources of upsampling artifacts are: (i) the tonal and filtering artifacts
introduced by problematic upsampling operators, and (ii) the spectral replicas
that emerge while upsampling. We then compare different upsampling layers,
showing that nearest neighbor upsamplers can be an alternative to the
problematic (but state-of-the-art) transposed and subpixel convolutions which
are prone to introduce tonal artifacts.
