A variety of seismic signals representing different physical mechanisms precedes volcanic eruptions. The most meaningful signals are high- and low-frequency earthquakes and volcanic tremor that have tentatively been related to fracturing and magma transport in the volcanic edifice. We provide experimental support for this association by reproducing magma migration while recording seismic signals. Opening fractures emit high-frequency acoustic events, while the switch to low frequency and harmonic tremor accompanies the flow of the melt in the fractures. Discerning between these seismic signals in nature can significantly refine volcanic hazard evaluation.