Fig. 1. Mt. Etna Volcano. Waveform (detail) obtainined
resampling 200 times the original digitalized waveform
(linear interpolation)
Fig. 2. Mt. Etna
Volcano. Spectrum (DFT) of the waveform in fig. 1, as
calculated by the Java program
As it is possible
to observe in fig. 5 and fig. 6, the resampled signals
taken by the seismograph close to an eruption event, shows
a clear variation in the time evolution of both the
spectrum and the waveform profile. A strong increase of the
amplitude and an enrichment of the spectrum thanks to the
very low-frequency components (made visible and audible
bythe resampling procedure) is clearly
observable in the two figures and clearly recognizable if
listened to.
Fig. 3. Mt. Etna Volcano. Waveform obtainined resampling 10
times the original digitalized waveform, using Sample and
Hold method for interpolation
Fig. 4. Mt. Etna Volcano. Waveform obtained using a linear
interpolation
among digital samples
Fig. 5. Mt. Etna Volcano. Detail of a waveform (after a
pitch shift 200x) showing the beginning of an eruption
phenomenon
Fig. 6. Mt. Etna Volcano. Sonogram of the waveform reported
in fig. 5 the resampling procedure) is clearly observable
in the two figures and clearly recognizable if listened to.