Fig. 4From: Musical note onset detection based on a spectral sparsity measureTemporal variation of signal energy per frequency bin and of spectral sparsity for trumpet (Bach) 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