In this case, we have a progression of two-note chords. Shown is a slice of a two-note chord above. The spectrogram has many uses in science and technology. In speech pathology, it is used for diagnosis and therapy. A little theory will help us understand what we're doing.
Human speech is produced by our lungs and vocal folds.
The lungs acts like a bellows, forcing air through the larynx, causing the vocal folds to vibrate. By changing the length and tension of the vocal folds, we vary the pitch of our voice as we speak. This primary frequency is further modified by the vocal tract and changing positions of the tongue, lips, and by interaction with the nasal cavity and the palate. The basic mechanism for speech. When singing, it can range over two octaves.