Interaction between the air reed and the air column in the body of the instrument excites standing waves in the air column, which determines the pitch of the sound. This oscillation results in the "whistle sound" in ducted flue instruments. See wind instrument and flue pipe. A distinct tone color, determined by the dimensions of the instrument and the voicing mouth, is then slightly modified by the player's technique or embouchure. In instruments such as the recorder, the player can vary the pitch of the resulting musical note by opening or closing finger holes along the bore of the instrument, thus changing the effective length.