jats:pIn 1878, at the height of his fame, Helmholtz asked what was objective in perception, declaring that—in contrast to empirical science—it is the “artist [who] has beheld the real.” His lecture sought to show how sensory perception can be law-like, and how the effects of art are ultimately grounded in such law-likeness. Such a claim for an objective measure of perception was not unprecedented, yet it failed to distinguish cleanly between what is objective and what is real, opening up a discursive space regarding what sound “is,” and what its objective perception may be. Its arguments followed calls for “a science of beauty” based on number, and was motivated, in part, by Helmholtz's attempt to distance himself from the “weaknesses of Romanticism.” This articles argues that Helmholtz's bold claims were only possible on the basis of the writings of German materialists during the 1840s and 50s, and because sound had been figured for decades as an ambiguous object.</jats:p> jats:pOn this basis, the article considers the role of sound within epistemological debates over sense perception and concepts of the real during the later nineteenth century. It examines the ways in which sound's abstract character became co-opted within Anglo-German discourse concerning objective perception and the scientifically real, initially through the lens of Helmholtz's 1878 lecture, but later broadening this focus to include the mid-century architects of a philosophical materialism, as well as their detractors. A closing case study, a closely documented wager between a geologist and a philosopher about the “real” of sound ca. 1850, demonstrates the imaginative uses of sound as a metonym for philosophical debate. This raises questions about the relation of sensation and number, the contested affinity between sound and concepts of the absolute, and the underlying desire to possess objects of sensory experience.</jats:p>