The crossword solution for the term 'Vary, as a tone' is 'MODULATE'. Modulation is a technique used in music to change the pitch or tone of a sound. It is often used to create a more interesting and dynamic sound. Modulation can be done by changing the frequency of the sound, or by adding effects such as vibrato or tremolo. Modulation can also be used to create a sense of movement or tension in a piece of music.