Figure 12.10 shows the sound wave for the note middle C played on a flute, a piano, and a trumpet; this is what you would see on an oscilloscope connected to a microphone when each of these instruments plays the note middle C. The fundamental frequency is the same for each-262ÊHz. The overall, general shape of the sound wave is the same for each instrument in that each sound wave repeats itself 262 times a second. The sound wave from the flute is very smooth and looks like a sine wave from a mathematics textbook. A flute has a strong fundamental frequency of 262 Hz and practically no other harmonics or overtones. A musician might describe a flute as having a very pure tone. The sound waves for the piano and trumpet bear the same the overall, general shape in that they, too, repeat themselves 262 times a second; each still has a fundamental frequency of 262 Hz. But these have more wiggles and are generally more complex. In addition to the fundamental frequency of 262 Hz, they each have additional-and different-harmonics present. Figure 12.11 shows the additional harmonics that are present; this is known as an acoustic spectrum. It is the number and relative strength of these various harmonics that give each instrument its distinctive sound-its quality or timbre or voice. An electronic synthesizer creates (or recreates) different voices by combining a fundamental frequency with various harmonics. By doing this a synthesizer can create a sound that matches an existing instrument or create an entirely new sound.

While loudness, pitch, and quality-or amplitude, frequency, and harmonics-may be the most important characteristics or distinctives of a musical sound, two more characteristics are attack and decay. Attack refers to how a sound begins while decay refers to how a sound ends. Does the sound begin very abruptly and then continue at a constant level? Or does it begin softly and gradually increase in amplitude and loudness? Does the sound continue and then suddenly stop or does it die away gradually. Different instruments behave differently. A synthesizer or keyboard will use various attacks and decays to provide different sounds or voices. We may describe these as the envelope of the sound wave-the overall pattern of the sound wave. Figure 12.12 illustrates different musical sounds played on a keyboard that allows different attack and decay envelopes.