An oscilloscope is an electronic device that converts sound into a graphic representation of the qualities of that sound. The picture it creates can be thought of as a cross-section through the sound wave.
No musical instrument produces a pure sound of only one frequency. Every musical sound is made up of a principal frequency (the note we hear most clearly) and a unique combination of partial, or harmonic frequencies. A pure frequency can be produced electronically, however, and this creates a pure sine wave on the oscilloscope.
Comparing the sine wave with waves produced by the other sounds can demonstrate pictorially the complex of sounds that make up one instrumental or vocal note. Notice the relationship between a note and its octave. Also the different patterns produced by different vowels, even though they are sung on the same note. The smaller spikes in the wave pattern represent the partial notes present in any one sound.
