  In deep learning research, many melody extraction models rely on redesigning
neural network architectures to improve performance. In this paper, we propose
an input feature modification and a training objective modification based on
two assumptions. First, harmonics in the spectrograms of audio data decay
rapidly along the frequency axis. To enhance the model's sensitivity on the
trailing harmonics, we modify the Combined Frequency and Periodicity (CFP)
representation using discrete z-transform. Second, the vocal and non-vocal
segments with extremely short duration are uncommon. To ensure a more stable
melody contour, we design a differentiable loss function that prevents the
model from predicting such segments. We apply these modifications to several
models, including MSNet, FTANet, and a newly introduced model, PianoNet,
modified from a piano transcription network. Our experimental results
demonstrate that the proposed modifications are empirically effective for
singing melody extraction.
