By representing the seismic quality factor (Q) as a random variable, we use spectral ratios of acoustic emission (AE) signals to approximate its probability distribution. This representation is used to characterize the heterogeneous and anisotropic attenuation response of a shale block subjected to hydraulic fracturing. Attenuation at the start of the experiment correlates with the imposed principal stresses, with higher stress corresponding with less attenuation. During the fracturing, changes in attenuation correlate with the borehole pressure, which supports the notion that the changes captured by the AE signals are mainly related to perturbations to the stress field. The results are also compatible with previous observations in a sandstone block fractured under similar experimental conditions.