Any pure tone. The pitch remaining when all harmonics (overtones) are removed from a basic frequency or musical tone, producing a pure tone. An amplifier or audio circuit that can pass a pure tone without adding any harmonics of its own is said to have low harmonic distortion. Musical instruments usually produce tones rich in harmonics, giving each its particular sound or timbre. Small loudspeakers will be heard to reproduce bass instruments even while producing little or no fundamental pitch because the ear and brain reconstruct the sound of the instrument based on prior knowledge of its timbre.