Fig. 2From: Musical note onset detection based on a spectral sparsity measureTemporal variation of signal energy per frequency bin and of spectral sparsity for electric guitar (major seventh stopped) excerpt. Note onsets are indicated by vertical lines. (Top and middle) Low- and high-energy log-magnitude spectrograms. (Bottom) Low- and high-energy STFT log-magnitude coefficient vector â„“1-norm variationBack to article page