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        <h1>

          Digitizing audio

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        <div id="minitoc"><div class="t"><div class="b"><div><ul id="minitoc-links"><li><p><a href="#WSC9E34A8A-90A9-414d-B104-609C9FA10D81a"><h1 class="topictitle1">Comparing analog and digital audio</h1>

</a></p></li><li><p><a href="#WS2E825A07-11AB-4f2f-A1FD-A1E4D93C3B9Aa"><h1 class="topictitle1">Understanding sample rate</h1>

</a></p></li><li><p><a href="#WSB6F75620-37C3-4f1d-83FF-B13FFFBC11F0a"><h1 class="topictitle1">Understanding bit depth</h1>

</a></p></li><li><p><a href="#WS694562E1-4190-4f6d-A047-5B0E13E4C7A8a"><h1 class="topictitle1">Audio file contents and size</h1>

</a></p></li><li><p><a href="#WSC2942C4F-249F-428e-A194-7F8597B3B06Ca"><h1 class="topictitle1">How Soundbooth digitizes audio</h1>

</a></p></li></ul></div></div></div></div><div><ul class="navlinklist"></ul>

</div>

<div id="WSC9E34A8A-90A9-414d-B104-609C9FA10D81a" class="nochunk"><a name="WSC9E34A8A-90A9-414d-B104-609C9FA10D81a"><!-- --></a><h2 class="topictitle2">Comparing analog and digital audio</h2><div><p>In analog and digital audio, sound is transmitted and

stored in very different ways.</p>

<div class="section"><h4 class="sectiontitle">Analog audio: positive and negative voltage</h4><p>A microphone converts the

pressure waves of sound into voltage changes in a wire: high pressure

becomes positive voltage, and low pressure becomes negative voltage.

When these voltage changes travel down a microphone wire, they can

be recorded onto tape as changes in magnetic strength or onto vinyl records

as changes in groove size. A speaker works like a microphone in

reverse, taking the voltage signals from an audio recording and

vibrating to re‑create the pressure wave. </p>

</div>

<div class="section"><h4 class="sectiontitle">Digital audio: zeroes and ones</h4><p>Unlike analog storage media such

as magnetic tape or vinyl records, computers store audio information

digitally as a series of zeroes and ones. In digital storage, the

original waveform is broken up into individual snapshots called <dfn class="term">samples</dfn>.

This process is typically known as <dfn class="term">digitizing</dfn> or <dfn class="term">sampling</dfn> the

audio, but it is sometimes called <dfn class="term">analog‑to‑digital conversion</dfn>.</p>

<p>When

you record from a microphone into a computer, for example, analog-to-digital

converters transform the analog signal into digital samples that computers

can store and process. </p>

</div>

</div></div>

<div id="WS2E825A07-11AB-4f2f-A1FD-A1E4D93C3B9Aa" class="nochunk"><a name="WS2E825A07-11AB-4f2f-A1FD-A1E4D93C3B9Aa"><!-- --></a><h2 class="topictitle2">Understanding sample rate</h2><div><p>Sample

rate indicates the number of digital samples taken of an audio signal each

second. This rate determines the frequency range of an audio file.

The higher the sample rate, the closer the shape of the digital

waveform is to that of the original analog waveform. Low sample

rates limit the range of frequencies that can be recorded, which

can result in a recording that poorly represents the original sound. </p>

<div xmlns:fn="http://www.w3.org/2005/xpath-functions" xmlns:fo="http://www.w3.org/1999/XSL/Format" xmlns:xs="http://www.w3.org/2001/XMLSchema" class="fignone"><img alt="" id="da06" src="images/da06.png" /><div class="figdesc">Two sample rates</div><br /><dl><dt class="dlterm">A.</dt>

<dd>Low sample rate that distorts the original sound wave</dd><p class="dlseparator"></p><dt class="dlterm">B.</dt>

<dd>High sample

rate that perfectly reproduces the original sound wave</dd><p class="dlseparator"></p></dl>

</div><p>To reproduce a given frequency, the sample rate must be at least

twice that frequency. (See <a href="WS3A5AB26B-EFEC-4748-91C9-745D84FE6F16a.html">Nyquist frequency</a>.) For example, CDs have a sample rate of 44,100

samples per second, so they can reproduce frequencies up to 22,050

Hz, which is just beyond the limit of human hearing, 20,000 Hz.</p>

<p>The following table lists the most common sample rates for digital

audio:</p>



<div class="tablenoborder"><table border="1" cellpadding="4" cellspacing="0"><thead align="left"><tr><th valign="top" width="NaN%" id="d16e321"><p>Sample rate</p>

</th>

<th valign="top" width="NaN%" id="d16e324"><p>Quality level</p>

</th>

<th valign="top" width="NaN%" id="d16e327"><p>Frequency range</p>

</th>

</tr>

</thead>

<tbody><tr><td valign="top" width="NaN%" headers="d16e321 "><p>11,025 Hz</p>

</td>

<td valign="top" width="NaN%" headers="d16e324 "><p>Poor AM radio (low‑end multimedia)</p>

</td>

<td valign="top" width="NaN%" headers="d16e327 "><p>0–5,512 Hz</p>

</td>

</tr>

<tr><td valign="top" width="NaN%" headers="d16e321 "><p>22,050 Hz</p>

</td>

<td valign="top" width="NaN%" headers="d16e324 "><p>Near FM radio (high‑end multimedia)</p>

</td>

<td valign="top" width="NaN%" headers="d16e327 "><p>0–11,025 Hz</p>

</td>

</tr>

<tr><td valign="top" width="NaN%" headers="d16e321 "><p>32,000 Hz</p>

</td>

<td valign="top" width="NaN%" headers="d16e324 "><p>Better than FM radio (standard broadcast

rate)</p>

</td>

<td valign="top" width="NaN%" headers="d16e327 "><p>0–16,000 Hz</p>

</td>

</tr>

<tr><td valign="top" width="NaN%" headers="d16e321 "><p>44,100 Hz</p>

</td>

<td valign="top" width="NaN%" headers="d16e324 "><p>CD</p>

</td>

<td valign="top" width="NaN%" headers="d16e327 "><p>0–22,050 Hz</p>

</td>

</tr>

<tr><td valign="top" width="NaN%" headers="d16e321 "><p>48,000 Hz</p>

</td>

<td valign="top" width="NaN%" headers="d16e324 "><p>Standard DVD</p>

</td>

<td valign="top" width="NaN%" headers="d16e327 "><p>0–24,000 Hz</p>

</td>

</tr>

<tr><td valign="top" width="NaN%" headers="d16e321 "><p>96,000 Hz</p>

</td>

<td valign="top" width="NaN%" headers="d16e324 "><p>High-end DVD</p>

</td>

<td valign="top" width="NaN%" headers="d16e327 "><p>0–48,000 Hz</p>

</td>

</tr>

</tbody>

</table>

</div>

</div></div>

<div id="WSB6F75620-37C3-4f1d-83FF-B13FFFBC11F0a" class="nochunk"><a name="WSB6F75620-37C3-4f1d-83FF-B13FFFBC11F0a"><!-- --></a><h2 class="topictitle2">Understanding bit depth</h2><div><p>Bit

depth determines dynamic range. When a sound wave is sampled, each sample

is assigned the amplitude value closest to the original wave’s amplitude. Higher

bit depth provides more possible amplitude values, producing greater dynamic

range, a lower noise floor, and higher fidelity. For the best audio

quality, remain at 32‑bit resolution while transforming audio in

Soundbooth, and then convert to a lower bit depth for output.</p>



<div class="tablenoborder"><table border="1" cellpadding="4" cellspacing="0"><thead align="left"><tr><th valign="top" width="NaN%" id="d16e410"><p>Bit depth</p>

</th>

<th valign="top" width="NaN%" id="d16e413"><p>Quality level</p>

</th>

<th valign="top" width="NaN%" id="d16e416"><p>Amplitude values</p>

</th>

<th valign="top" width="NaN%" id="d16e419"><p>Dynamic range</p>

</th>

</tr>

</thead>

<tbody><tr><td valign="top" width="NaN%" headers="d16e410 "><p>8‑bit</p>

</td>

<td valign="top" width="NaN%" headers="d16e413 "><p>Telephony</p>

</td>

<td valign="top" width="NaN%" headers="d16e416 "><p>256</p>

</td>

<td valign="top" width="NaN%" headers="d16e419 "><p>48 dB</p>

</td>

</tr>

<tr><td valign="top" width="NaN%" headers="d16e410 "><p>16‑bit</p>

</td>

<td valign="top" width="NaN%" headers="d16e413 "><p>CD</p>

</td>

<td valign="top" width="NaN%" headers="d16e416 "><p>65,536</p>

</td>

<td valign="top" width="NaN%" headers="d16e419 "><p>96 dB</p>

</td>

</tr>

<tr><td valign="top" width="NaN%" headers="d16e410 "><p>24‑bit</p>

</td>

<td valign="top" width="NaN%" headers="d16e413 "><p>DVD</p>

</td>

<td valign="top" width="NaN%" headers="d16e416 "><p>16,777,216</p>

</td>

<td valign="top" width="NaN%" headers="d16e419 "><p>144 dB</p>

</td>

</tr>

<tr><td valign="top" width="NaN%" headers="d16e410 "><p>32‑bit</p>

</td>

<td valign="top" width="NaN%" headers="d16e413 "><p>Best</p>

</td>

<td valign="top" width="NaN%" headers="d16e416 "><p>4,294,967,296</p>

</td>

<td valign="top" width="NaN%" headers="d16e419 "><p>192 dB</p>

</td>

</tr>

</tbody>

</table>

</div>

<div xmlns:fn="http://www.w3.org/2005/xpath-functions" xmlns:fo="http://www.w3.org/1999/XSL/Format" xmlns:xs="http://www.w3.org/2001/XMLSchema" class="fignone"><img alt="" id="da07" src="images/da07.png" /><div class="figdesc">Higher bit depths provide greater dynamic range.</div><br /></div></div></div>

<div id="WS694562E1-4190-4f6d-A047-5B0E13E4C7A8a" class="nochunk"><a name="WS694562E1-4190-4f6d-A047-5B0E13E4C7A8a"><!-- --></a><h2 class="topictitle2">Audio file contents and size</h2><div><p>An

audio file on your hard drive, such as a WAV file, consists of a

small header indicating sample rate and bit depth, and then a long

series of numbers, one for each sample. These files can be very

large. For example, at 44,100 samples per second and 16 bits per

sample, a mono file requires 86 KB per second—about 5 MB per minute.

That figure doubles to 10 MB per minute for a stereo file, which has

two channels.</p>

</div></div>

<div id="WSC2942C4F-249F-428e-A194-7F8597B3B06Ca" class="nochunk"><a name="WSC2942C4F-249F-428e-A194-7F8597B3B06Ca"><!-- --></a><h2 class="topictitle2">How Soundbooth digitizes audio</h2><div><p>When

you record audio in Soundbooth, the sound card starts the recording process

and specifies what sample rate and bit depth to use. Through Line

In or Microphone In ports, the sound card receives analog audio

and digitally samples it at the specified rate. Soundbooth stores

each sample in sequence until you stop recording.</p>

<p>When you play a file in Soundbooth, the process happens in reverse.

Soundbooth sends a series of digital samples to the sound card.

The card reconstructs the original waveform and sends it as an analog

signal through Line Out ports to your speakers.</p>

<p>To sum up, the process of digitizing audio starts with a pressure

wave in the air. A microphone converts this pressure wave into voltage

changes. A sound card converts these voltage changes into digital

samples. After analog sound becomes digital audio, Soundbooth can

record, edit, and process it—the possibilities are limited only

by your imagination.</p>

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