1. The process by which the tone quality of the pipe is regulated (as opposed to tuning, which regulates the pitch). Techniques include adjusting the shape of the tone-producing mouth of a flue pipe, cutting small nicks into the mouth, regulating the shape of the reed in a reed pipe, adjusting the size of the toe hole where air enters the pipe, and others. 2. The process by which the hardness of a felt piano hammer head is adjusted or regulated. Techniques include reshaping the hammer by sanding, pricking the felt with sharp needles, applying chemicals to harden or soften the felt, and others. 3. Term used to describe the loudness, softness, or the harmonic or tone quality of a pipe. For example, calliope whistles have very loud