Sound Signal Basics

Just as an image can be described as a mixture of colors a sound object can be described as a blend of elementary acoustic vibrations. In the physical definition, sound is defined as changes in air pressure transmitted as vibrations through the air. These vibrations are represented as compression waves, and so are characterized by the common properties of waves including frequency, period, wavelength, and amplitude.

If the pressure of the wave varies in a repeating pattern then the sound has a periodic waveform. Sounds with no intelligible pattern are called noise. Most sounds fall somewhere in between these two extremes. A cycle is one repetition of a periodic waveform. The fundamental frequency is the number of these cycles that occur per second. In acoustical terminology it is usually measured in Hertz (Hz), which is equivalent to ‘cycles per second’. Frequency corresponds to the perceived pitch of the waveform. Wavelength, or period, is the length of the cycle. As wavelength increases, the frequency in Hz decreases. Therefore, sounds with longer wavelengths have a lower frequency (i.e. pitch) than sounds with shorter wavelengths.



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