Literature in "Physics Education" has shown that students encounter many difficulties in understanding wave propagation. Such difficulties lead to misconceptions also in understanding sound, often used as context to teach wave propagation. To address these issues, we present in this paper a module in which the students are engaged in computer-based activities dealing with sounds produced by a tuning fork and the Sun. The main reason underlying such choice is to show how the same measurement technique (spectral analysis) can be used to obtain information about very different phenomena. The activities build on a formal analogy to determine the fundamental frequency of sounds emitted by the two sources (tuning fork and Sun). Using a digital audio editor, the sounds are analyzed using three types of graphs: intensity versus time (waveform), intensity versus frequency (spectrum), and frequency versus time (spectrogram). The aim of the activities is to address students' alternative conceptions about the frequency and propagation of mechanical waves using a multi-representation of the same phenomenon. Examples of frequency measurements for the analyzed sounds are reported, as well as paper-and-pencil tasks to determine velocity of sound in the two phenomena. Implications for the teaching of waves and sound are finally discussed.