What is a defining feature of brass family instruments?

A defining feature of brass family instruments is their method of sound production, which involves the player buzzing their lips into a mouthpiece. This technique generates vibrations that resonate within the instrument, creating sound. This buzzing action is unique to brass instruments, setting them apart from other families of the orchestra.

To further clarify, other types of instruments produce sound through different mechanisms. For example, string instruments rely on bowed or plucked strings, while percussion instruments create sound primarily through striking or shaking. Similarly, the statement regarding these instruments being the softest in the orchestra is inaccurate as brass instruments can produce powerful and bright sounds. Therefore, the buzzing of lips into a mouthpiece is indeed the characteristic that accurately defines brass family instruments and distinguishes them from others.