Compressional waves in air are called sound waves, which are always longitudinal waves with the vibration parallel to the direction of propagation. The result is a propagating wave in which the pressure (and density) of the air varies with distance in a regular way - the pattern is, in fact, exactly the same as the displacement pattern of a transverse wave on a string (see Figure 01 and 02). Here, the air molecules are alternately pressed together and pulled apart by the action of the speaker. In the interest of simplicity, I have loosely used “computer” instead of “sound wave storage device.A compressional wave in air can be set up by the back-and-forth motion of a speaker as shown in Figure 09. Technically, sound synthesis doesn’t rely on a “sound wave stored in a computer.” It simply consists of a “sound wave on a storage device” that is manipulated and/or generated through mechanical means, not by recording. This is not true of analog audio, where sound waves are stored on a medium such as magnetic tape without conversion to digital form. I’m Andy Boyd at the University of Houston, where we’re interested in the way inventive minds work.įor related episodes, see 557, MUSIC: REAL OR FAKE? 1929, SWITCHED ON BACH and 2296, ROBERT MOOG.ĭigital audio, which is now the dominant way in which music is recorded and transferred, stores sound waves as binary files on a computer. But the technology for making and shaping sounds marches steadily forward. Where will it lead? We’ll have to wait and see. With the palate of sounds that can be produced, synthesis is a catalyst for musical creativity. But the timbre of a violin and the nuance of the musician yield an incredibly complex sound wave - a wave so complicated it’s far easier to record a violinist than attempt to synthesize the sound of a violin. In theory, synthesizers can replicate the sound of traditional instruments - for example, a violin. Music synthesis and synthesizers are often associated with strange sounds. Music synthesis can produce almost limitless sounds, including many that we can’t find in nature. They have a multitude of knobs for shaping sound waves - for taking one wave and twisting it into another. Synthesizers are machines or computer programs that create sound waves from scratch, so to speak. Which leads us to ask: rather than record a sound wave and play it back, can’t we just create one on the computer and skip the recording? In fact, we can. And at the center of it all is a sound wave stored in a computer. With just a twenty dollar microphone and a similarly inexpensive clock radio, we recognize music, words, inflections. It’s actually remarkable that this record/playback system works so well. Send a wave to a speaker, and it will vibrate according to the shape of the wave. Just as microphones are recording devices, speakers are playback devices. A close up of the word “Houston’s.” A close up of the letter “O” in “HoustOn’s.” Notice the regular, complex wave pattern “The University of Houston’s College of Engineering presents this series about the machines that make ourĬivilization run, and the people whose ingenuity created them,” as spoken by the author. With a little practice, you can pick out words just by looking at the wave on the screen. There it is - my voice, captured as a picture of a wave. When I record an episode of the Engines of Our Ingenuity, I get to watch the wave drawn in real time on a computer screen. A microphone is really just a sound wave recording device. It’s just like dropping a rock in the water and watching the waves move out in a circle.įor every different sound, there’s a different wave. When someone speaks their vocal chords vibrate. The University of Houston’s College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.
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