  Graph theory is emerging as a new source of tools for time series analysis.
One promising method is to transform a signal into its visibility graph, a
representation which captures many interesting aspects of the signal. Here we
introduce the visibility graph for audio spectra and propose a novel
representation for audio analysis: the spectral visibility graph degree. Such
representation inherently captures the harmonic content of the signal whilst
being resilient to broadband noise. We present experiments demonstrating its
utility to measure robust similarity between harmonic signals in real and
synthesised audio data. The source code is available online.
