{"id":205,"date":"2019-10-22T17:47:20","date_gmt":"2019-10-22T17:47:20","guid":{"rendered":"https:\/\/synthnotes.ucsd.edu\/wp7\/?p=205"},"modified":"2019-10-22T17:47:20","modified_gmt":"2019-10-22T17:47:20","slug":"amplitude-introduction","status":"publish","type":"post","link":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/2019\/10\/22\/amplitude-introduction\/","title":{"rendered":"Amplitude: Introduction"},"content":{"rendered":"\n

Amplitude <\/h2>\n\n\n\n

In digital sound, amplitude is a measurement of the strength of a signal, usually between 0 and 1 (linearly) or between -infinity and 0 in decibels (dB). Colloquially, amplitude can be thought of as the volume of a sound (not<\/em> loudness), also called sound pressure level (SPL). Changing the amplitude of a sound is akin to turning a volume knob up or down on a car stereo. <\/p>\n\n\n\n

The decibel (dB) <\/h4>\n\n\n\n

Since our ear responds logarithmically to the amplitude of sound, amplitude (SPL) is most typically measured in decibels. A decibel is a unit of measurement that expresses the ratio of one quantity to another; that is, in order to express something in decibels, we need a reference value. In the case of SPL, our reference is 0dBspl<\/sub> = 20 microPascals (considered to be the threshold of human hearing) Note the ratio in the logarithm of the equation for calculating the SPL of sound: <\/p>\n\n\n\n

L_{p} = 20 \\log_{10} \\bigg(\\frac{p_{rms}}{p_{ref}}\\bigg) \\text{ dB} <\/span> <\/p>\n\n\n\n

<\/p>\n\n\n\n

In audio, we most often speak of decibels as if it is a relative quantity. For instance, if we consider 0dB the loudest sound in digital audio with an amplitude of 1.0, we obtain the following linear amplitudes. <\/p>\n\n\n\n\n \n \n \n \n \n<\/table>\n\n\n\n

Peak v. RMS <\/h4>\n\n\n\n

When measuring the amplitude of a signal, either the peak or root mean square (RMS) amplitude can be used. (Notice in the equation above that the numerator of the fraction is p<\/em>rms<\/em><\/sub> which is the sound pressure level in root mean square (RMS) amplitude.) <\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

In the graphic above, each number is the following: <\/p>\n\n\n\n

  1. Peak amplitude (\u00db<\/em>) <\/li>
  2. Peak-to-peak amplitude (2\u00db<\/em>)<\/li>
  3. RMS amplitude (\u00db\/\u221a2<\/em>) <\/li>
  4. Period (not a measurement of amplitude) <\/li><\/ol>\n\n\n\n

    In digital audio, we often use both peak and RMS amplitude. Peak-to-peak amplitude is almost never used since signals are typically centered around 0 (if you signal is not, there is a DC component that can be removed LINK TO RELEVANT FILE LATER). <\/p>\n\n\n\n

    What if the peak amplitude exceeds 1? <\/h3>\n\n\n\n

    If the peak amplitude exceeds 1, the result is distortion of the signal in the form of clipping. This can damage certain hardware and is best avoided. If the level above 1 is known, one can simply multiply the signal by 1 minus that value. More likely, however, whether or not the amplitude will exceed 1 is unknown. In this case there are several options: hard clipping. soft clipping, limiters, or compressors.<\/p>\n","protected":false},"excerpt":{"rendered":"

    Amplitude In digital sound, amplitude is a measurement of the strength of a signal, usually between 0 and 1 (linearly) or between -infinity and 0 in decibels (dB). Colloquially, amplitude can be thought of as the volume of a sound (not loudness), also called sound pressure level (SPL). Changing the amplitude of a sound is […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-205","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/wp-json\/wp\/v2\/posts\/205","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/wp-json\/wp\/v2\/comments?post=205"}],"version-history":[{"count":5,"href":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/wp-json\/wp\/v2\/posts\/205\/revisions"}],"predecessor-version":[{"id":211,"href":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/wp-json\/wp\/v2\/posts\/205\/revisions\/211"}],"wp:attachment":[{"href":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/wp-json\/wp\/v2\/media?parent=205"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/wp-json\/wp\/v2\/categories?post=205"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/synthnotes.ucsd.edu\/wp7\/index.php\/wp-json\/wp\/v2\/tags?post=205"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}

dB<\/th>linear amplitude<\/th><\/tr>\n
0<\/td>1<\/td>
-3<\/td>0.707945<\/td>
-6<\/td>0.501187<\/td>
-9<\/td>0.354813<\/td>
-12<\/td>0.251188<\/td>