Sound mass has been an influential trend in music since the 1950’s and yet many questions about its perception remain unanswered. Approaching sound mass from the perspective of auditory scene analysis, we define it as a type of auditory grouping that retains an impression of multiplicity even as it is perceived as a perceptual unit. Sound mass requires all markers of the individual identities of sounds to be deemphasized to prevent them from splitting off into separate streams. Seeking to determine how consistent listeners are in their perception of sound mass, and whether it is possible to determine sound parameters and threshold values that predict sound mass perception, we conducted two perceptual studies on Ligeti’s Continuum . This piece consists of an extremely rapid, steady stream of eighth-note dyads with no tempo changes. We addressed the claim by Ligeti and others that the fusion into a continuous texture or sound mass occurs at ca. 20 attacks/s, hypothesizing that other factors such as pitch organization, emergent rhythm, timbre, and register would affect this value. A variety of factors were found to affect sound mass perception, suggesting that the threshold value is not absolute but varies according to principles of auditory scene analysis.