The didgeridoo produces its iconic low-frequency drone through the vibration of the player's lips, similar to a brass instrument. However, because the didgeridoo is essentially a non-tapered or slightly conical cylinder, it acts as a 'closed-pipe' resonator. This means it primarily amplifies the odd-numbered harmonics of the fundamental frequency. What makes the didgeridoo unique is the player's ability to use their vocal tract as a secondary resonator. By changing the shape of their mouth, tongue, and throat, the player can create 'formants'—specific frequency peaks—that highlight different overtones over the constant drone. This creates the rhythmic 'wobble' or 'wavering' sound. Advanced players also use vocalizations, barking or shouting into the tube while maintaining the lip vibration, which creates 'interference' patterns that sound like animal calls or rhythmic textures, all without stopping the continuous flow of air.