Final answer:
A musical sound is defined by having a perceivable pitch and a distinct timbre, which allows us to distinguish between the same note played by different instruments.
Step-by-step explanation:
By definition, a musical sound has several characteristics, but the main ones are perceivable pitch and distinct timbre. The pitch of a sound is our perception of its frequency; as such, most people can discern between sounds when their frequencies differ by about 0.3% or more. For instance, there is a perceptible difference between sounds at 500.0 Hz and 501.5 Hz. On the other hand, timbre, often referred to as tone quality, is the characteristic that enables us to distinguish between the same note played on different instruments, such as a violin versus a piano. Timbre is influenced by the complex interplay of frequency, amplitude, and timing of sound waves and is described using descriptors like dull, brilliant, warm, and rich.