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Galileo devoted only a few pages to the physical study of acoustics in the Discorsi, his latest book. Yet, his father Vincenzo, a musician and a theorist, had produced several texts on this subject. Galileo thought out the vibrating complexion of sounds, and asserted that the pitch was correlated with the number of vibrations. He was unable to count them, so he did not use the word “frequency,” but the circumlocution “number of vibrations in the same time.” In addition, he imagined two experiments in order to exemplify his theory. The first rested on an analogy between sound vibrations and water waves, the second on the observation of traces on brass plate after a sound scraping with a cutting tool. These traces (or “commas”) were spaced out, and Galileo made a correlation between space variations and sound pitch. This experiment allowed him to demonstrate the relationship that he proposed. Although his analysis of this phenomenon was partially wrong, his theory was correct, nowadays the technical system of phonograph being widespread, we are able, by reproducing this experiment, to understand the reasons, which were the cause of this error. Galileo nevertheless is the precursor of the graphical representation of vibrations, which lies behind the sound recording processes of the late 19th century.