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Updates for release 0.3:
setup.py was extended for pypi. doc/index.html is automatically rewritten by doc/src/Makefile to add SourceForge links. index.html is now the standard homepage for pyalsaaudio. Minor documentation fixes (capitalisation, spelling, etc.). Caspers email is hidden in the documentation. git-svn-id: svn://svn.code.sf.net/p/pyalsaaudio/code/trunk@14 ec2f30ec-7544-0410-870e-f70ca00c83f0
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larsimmisch
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doc/node7.html
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<link rel="prev" href="module-alsaaudio.html" />
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<link rel="parent" href="module-alsaaudio.html" />
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<link rel="next" href="pcm-objects.html" />
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name='aesop' content='information' />
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<title>4.1 PCM Terminology and Concepts</title>
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</head>
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<body>
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<DIV CLASS="navigation">
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<div class="navigation">
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<div id='top-navigation-panel' xml:id='top-navigation-panel'>
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<table align="center" width="100%" cellpadding="0" cellspacing="2">
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<tr>
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<td class='online-navigation'><a rel="prev" title="4 alsaaudio"
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href="module-alsaaudio.html"><img src='previous.png'
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border='0' height='32' alt='Previous Page' width='32' /></A></td>
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<td class='online-navigation'><a rel="parent" title="4 alsaaudio"
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href="module-alsaaudio.html"><img src='up.png'
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border='0' height='32' alt='Up One Level' width='32' /></A></td>
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<td class='online-navigation'><a rel="next" title="4.2 PCM Objects"
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border='0' height='32' alt='Up one Level' width='32' /></a></td>
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<td class='online-navigation'><a rel="next" title="4.2 pcm Objects"
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<td align="center" width="100%">PyAlsaAudio</td>
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<td class='online-navigation'><a rel="contents" title="Table of Contents"
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href="contents.html"><img src='contents.png'
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border='0' height='32' alt='Contents' width='32' /></A></td>
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<td class='online-navigation'><img src='blank.png'
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<td class='online-navigation'><img src='blank.png'
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</tr></table>
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<div class='online-navigation'>
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<b class="navlabel">Previous:</b>
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<a class="sectref" rel="prev" href="module-alsaaudio.html">4 alsaaudio</A>
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<a class="sectref" rel="prev" href="module-alsaaudio.html">4 alsaaudio</a>
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<b class="navlabel">Up:</b>
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<a class="sectref" rel="parent" href="module-alsaaudio.html">4 alsaaudio</A>
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<a class="sectref" rel="parent" href="module-alsaaudio.html">4 alsaaudio</a>
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<b class="navlabel">Next:</b>
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<a class="sectref" rel="next" href="pcm-objects.html">4.2 PCM Objects</A>
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<a class="sectref" rel="next" href="pcm-objects.html">4.2 PCM Objects</a>
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</div>
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<hr /></div>
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</DIV>
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</div>
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<!--End of Navigation Panel-->
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<H2><A NAME="SECTION002410000000000000000">
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4.1 PCM Terminology and Concepts</A>
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</H2>
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<h2><a name="SECTION002410000000000000000">
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4.1 PCM Terminology and Concepts</a>
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</h2>
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<P>
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<p>
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In order to use PCM devices it is useful to be familiar with some concepts and
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terminology.
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<P>
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<DL>
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<DT><STRONG>Sample</STRONG></DT>
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<DD>PCM audio, whether it is input or output, consists at the lowest level
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<p>
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<dl>
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<dt><strong>Sample</strong></dt>
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<dd>PCM audio, whether it is input or output, consists at the lowest level
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of a number of single samples. A sample represents the sound in a single channel in
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a brief interval. If more than one channel is in use, more than one sample is required
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for each interval to describe the sound. Samples can be of many different sizes, ranging
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from 8 bit to 64 bit presition. The specific format of each sample can also vary - they
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can be big endian byte order, little endian byte order, or even floats.
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<P>
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</DD>
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<DT><STRONG>Frame</STRONG></DT>
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<DD>A frame consists of exactly one sample per channel. If there is only one
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<p>
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</dd>
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<dt><strong>Frame</strong></dt>
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<dd>A frame consists of exactly one sample per channel. If there is only one
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channel (Mono sound) a frame is simply a single sample. If the sound is stereo, each frame
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consists of two samples, etc.
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<P>
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</DD>
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<DT><STRONG>Frame size</STRONG></DT>
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<DD>This is the size in bytes of each frame. This can vary a lot: if each sample is
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<p>
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</dd>
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<dt><strong>Frame size</strong></dt>
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<dd>This is the size in bytes of each frame. This can vary a lot: if each sample is
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8 bits, and we're handling mono sound, the frame size is one byte. Similarly in 6 channel audio with
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64 bit floating point samples, the frame size is 48 bytes
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<P>
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</DD>
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<DT><STRONG>Rate</STRONG></DT>
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<DD>PCM sound consists of a flow of sound frames. The sound rate controls how often
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<p>
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</dd>
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<dt><strong>Rate</strong></dt>
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<dd>PCM sound consists of a flow of sound frames. The sound rate controls how often
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the current frame is replaced. For example, a rate of 8000 Hz means that a new frame is played
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or captured 8000 times per second.
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<P>
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</DD>
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<DT><STRONG>Data rate</STRONG></DT>
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<DD>This is the number of bytes, which must be recorded or provided per second
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<p>
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</dd>
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<dt><strong>Data rate</strong></dt>
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<dd>This is the number of bytes, which must be recorded or provided per second
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at a certain frame size and rate.
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<P>
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<p>
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8000 Hz mono sound with 8 bit (1 byte) samples has a data rate of 8000 * 1 * 1 = 8 kb/s
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<P>
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<p>
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At the other end of the scale, 96000 Hz, 6 channel sound with 64 bit (8 bytes) samples
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has a data rate of 96000 * 6 * 8 = 4608 kb/s (almost 5 Mb sound data per second)
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<P>
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</DD>
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<DT><STRONG>Period</STRONG></DT>
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<DD>When the hardware processes data this is done in chunks of frames. The time interval
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<p>
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</dd>
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<dt><strong>Period</strong></dt>
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<dd>When the hardware processes data this is done in chunks of frames. The time interval
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between each processing (A/D or D/A conversion) is known as the period. The size of the period has
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direct implication on the latency of the sound input or output. For low-latency the period size should
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be very small, while low CPU resource usage would usually demand larger period sizes. With ALSA, the
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periods internally, so each period generates an interrupt and a memory copy, but userspace can be
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slower and read or write multiple periods at the same time.
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<P>
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</DD>
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<DT><STRONG>Period size</STRONG></DT>
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<DD>This is the size of each period in Hz. <em>Not bytes, but Hz!.</em> In <tt class="module">alsaaudio</tt>
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<p>
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</dd>
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<dt><strong>Period size</strong></dt>
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<dd>This is the size of each period in Hz. <em>Not bytes, but Hz!.</em> In <tt class="module">alsaaudio</tt>
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the period size is set directly, and it is therefore important to understand the significance of this
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number. If the period size is configured to for example 32, each write should contain exactly 32 frames
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of sound data, and each read will return either 32 frames of data or nothing at all.
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<P>
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</DD>
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</DL>
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<p>
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</dd>
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</dl>
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<P>
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<p>
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Once you understand these concepts, you will be ready to actually utilize PCM API. Read on.
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<P>
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<p>
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<DIV CLASS="navigation">
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<div class="navigation">
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<div class='online-navigation'>
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<p></p><hr />
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<table align="center" width="100%" cellpadding="0" cellspacing="2">
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<tr>
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<td class='online-navigation'><a rel="prev" title="4 alsaaudio"
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href="module-alsaaudio.html"><img src='previous.png'
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border='0' height='32' alt='Previous Page' width='32' /></A></td>
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border='0' height='32' alt='Previous Page' width='32' /></a></td>
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<td class='online-navigation'><a rel="parent" title="4 alsaaudio"
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href="module-alsaaudio.html"><img src='up.png'
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border='0' height='32' alt='Up One Level' width='32' /></A></td>
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<td class='online-navigation'><a rel="next" title="4.2 PCM Objects"
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border='0' height='32' alt='Up one Level' width='32' /></a></td>
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<td class='online-navigation'><a rel="next" title="4.2 pcm Objects"
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href="pcm-objects.html"><img src='next.png'
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border='0' height='32' alt='Next Page' width='32' /></A></td>
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border='0' height='32' alt='Next Page' width='32' /></a></td>
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<td align="center" width="100%">PyAlsaAudio</td>
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<td class='online-navigation'><a rel="contents" title="Table of Contents"
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href="contents.html"><img src='contents.png'
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border='0' height='32' alt='Contents' width='32' /></A></td>
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border='0' height='32' alt='Contents' width='32' /></a></td>
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<td class='online-navigation'><img src='blank.png'
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border='0' height='32' alt='' width='32' /></td>
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<td class='online-navigation'><img src='blank.png'
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@@ -153,17 +154,17 @@ Once you understand these concepts, you will be ready to actually utilize PCM AP
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</tr></table>
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<div class='online-navigation'>
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<b class="navlabel">Previous:</b>
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<a class="sectref" rel="prev" href="module-alsaaudio.html">4 alsaaudio</A>
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<a class="sectref" rel="prev" href="module-alsaaudio.html">4 alsaaudio</a>
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<b class="navlabel">Up:</b>
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<a class="sectref" rel="parent" href="module-alsaaudio.html">4 alsaaudio</A>
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<a class="sectref" rel="parent" href="module-alsaaudio.html">4 alsaaudio</a>
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<b class="navlabel">Next:</b>
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<a class="sectref" rel="next" href="pcm-objects.html">4.2 PCM Objects</A>
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<a class="sectref" rel="next" href="pcm-objects.html">4.2 PCM Objects</a>
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</div>
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</div>
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<hr />
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<span class="release-info">Release 0.2.</span>
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</DIV>
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<span class="release-info">Release 0.3.</span>
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</div>
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<!--End of Navigation Panel-->
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</BODY>
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</HTML>
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</html>
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