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105 lines
5.4 KiB
HTML
105 lines
5.4 KiB
HTML
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<h1 class="center">Audio Spectrum and Beats</h1>
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<p>Have a play with one, two or three tones at once. </p>
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<link rel="stylesheet" type="text/css" href="../stylejs.css" />
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<script src="images/audio-spectrum-n.js" type="text/javascript"></script>
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<script type="text/javascript">audiospectrumnMain();</script>
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<p> </p>
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<p class="center"><i>(Note: below 20 Hz is called Infrasound, and above 20,000 Hz is Ultrasound.)</i></p>
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<h3>Beats</h3>
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<p>Start with one tone.</p>
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<p>Now add a second tone and bring it close to the first tone.</p>
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<p>You will notice "beats" as the two sounds interfere with each. Try for example 400 and 402. </p>
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<p>Also try things like 800 and 402 etc.</p>
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<p>You can add a third tone for fun, and make weird sci-fi sounds.</p>
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<h3>Why</h3>
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<p>Because the waves interact to create a new more complex wave.</p>
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<p>Here we see how two waves (in this case of very different frequencies) make a new wave:</p>
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<p class="center"><img src="images/wave-superposition.svg" alt="wave superposition"></p>
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<p> </p>
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<p>Now let's see what happens when the tones are <b>really close in frequency.</b></p>
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<p>They will sometimes be "in sync" and make a bigger wave when added together:</p>
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<p class="center"><img src="images/beats-add.svg" alt="beats add"></p>
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<p>Or they can be "out of sync" and cancel each other out:</p>
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<p class="center"><img src="images/beats-sub.svg" alt="beats subtract"></p>
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<p>And we hear that change as beats.</p>
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<p>Have a play with this graph (drag it left and right) to see it better: <a href="../data/function-grapheraaf5.html?func1=sin(8x)&func2=sin(7.9x)&func3=sin(8x)%2Bsin(7.9x)&xmin=-0.7&xmax=9.3&ymin=-3&ymax=3">Beats Graph</a>.</p>
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<p> </p>
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<h3>Note about what we can hear</h3>
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<p>We can't hear all tones. We are most sensitive to sounds between 1,000 and 4,000 Hz. The sounds played here are not an accurate hearing test though!</p>
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<p class="center"> <img src="images/loudness.gif" width="360" height="192" alt="loudness dB vs frequency graph" /><br>
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<b>A Typical
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"Equal Loudness" Curve </b><br>
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(dB and Loudness explained next!) </p>
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<p> </p>
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<div class="related"><a href="waves-sound.html">Sound</a><a href="waves-introduction.html">Introduction to Waves</a><a href="../calculus/fourier-series.html">Fourier Series</a><a href="index.html">Physics Index</a></div>
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