When you generate a basic sound in Tone.js, you use an oscillator. An oscillator creates a repeating waveform, which you hear as a musical tone. The shape of this waveform strongly influences the sound's character. The most common oscillator waveforms are sine, square, triangle, and sawtooth.

A sine wave produces a smooth, pure tone. It contains only the fundamental frequency, making it sound mellow and clear. By contrast, a square wave alternates sharply between two levels, resulting in a hollow, woody sound with a strong presence of odd harmonics. A triangle wave has a shape between sine and square, producing a softer tone than square but brighter than sine, with fewer harmonics. The sawtooth wave ramps upward and drops sharply, giving it a buzzy, bright sound rich in both odd and even harmonics.

Each waveform gives you a unique timbre, or sound quality. Sine waves are often used for simple tones or soft basses, while sawtooth and square waves are popular in electronic music for their rich, edgy sounds. By choosing different oscillator types in Tone.js, you can create a wide range of musical textures.