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¢ Sound The EM spectrum is often compared to sound, since the two phenomena share many of the same features. Sound is comprised of mechanical pressure waves in a compressible medium such as air or water. Put another way, sound is created when an object moves with enough force to displace (compress) the surrounding air (or other medium capable of carrying these waves). We hear many of these waves (air currents) as audible frequencies (sound), because after the air reaches the ear it minutely moves the eardrum—a delicate drum- like membrane—and sends the oscillations to the brain, where they are then decoded into traffic noise, spoken words, music, the barking of a dog, and so on. The waves of sound could be created by a pen dropping on a desk, by someone's vocal cords being moved in speech, or by a violin string being plucked. The frequency of a wave (expressed as cycles per second) that applies to the EM spectrum also applies to music, a subset of sound. The pitch of a note depends on its frequency. A lower frequency, or an oscillation rate of fewer hertz, is slower moving and produces a lower tone. A higher frequency, or an oscillation rate of more hertz, is faster moving and produces a higher tone. Frequency can be more easily understood and perceived with music than with random sound (noise). Noise—as well as some harsh electronic music—is comprised of disorganised waveforms. This disorganisation manifests acoustically as indistinct, muddy pitches. Music, on the other hand, is comprised of organised waveforms. This organisation manifests acoustically as distinct, discernible pitches. The difference between music and noise can be seen on an oscilloscope—a testing device that shows visually what we hear acoustically—with real-time pictures of waveforms (figure 2). Noise, or random sound, on the oscilloscope appears as irregular waveforms, while music, or pure tone, appears as regular waveforms. For most people, the acoustic and the visual correlate: music is more pleasing than noise to the ear, and regular waveforms are more pleasing than irregular waveforms to the eye. In figure 2, in the examples of music, all the instruments are playing the same note. The waveforms of music on an oscilloscope show organisation, with obvious patterns. The waveforms of noise on an oscilloscope show disorganisation, with no discernible patterns. SN SNS” iW yan 3 AN Nt Music — Symmetry 1. Tuning Fork. Very pure sound; prongs vibrate regularly. 2. Violin. Bright sound, angular waveform. Same pitch as tuning fork: peaks of waves are the same distance apart and pass at the same rate as those produced by the tuning fork. 3. Flute. Same note played as the first two. Purer sound than that of the violin, so its waveform is more rounded. Noise — Asymmetry 4. Cymbal. Irregular patterns and jagged, random wave- forms with no discernible pitch. No regular pattern of peaks and troughs. Photo courtesy of, and text adapted from, Dorling Kindersley Encyclopaedia UK. VV AN Nt * Different Shapes of Waves As illustrated in the diagram of notes played by various instruments, waveforms have different shapes. Figure 3 shows some common ones in their simplest form. Figure 3: Waveforms (A) Sine; (B) Triangle; (C) Sawtooth; (D) Square The more complex an object, the more frequencies it contains and also the more complex waveforms it will have. A useful analogy between simple and complex forms is the difference between plucking a single string (which represents a simple organism like an amoeba) and the playing of an entire orchestra (which represents a complex organism like a human being). ¢ Symmetry and Asymmetry: The Language of Mathematics and Music The symmetry of music and the asymmetry of noise can also be described mathematically. Mathematically, Figure 2: Comparing Music and Noise Waveforms onan Oscilloscope 28 * NEXUS JUNE - JULY 2010 www.nexusmagazine.com