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Daniele Nicolodi <nicolodi@science.unitn.it> |
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Mon, 05 Dec 2011 16:20:06 +0100 (2011-12-05) |
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<h1 class="title"><a name="f3-12899" id="f3-12899"></a>Resampling a time-series AO</h1>
<hr>
<p>
<p>
Resampling is the process of changing the sampling rate of data. The method <tt>ao/resample</tt></a>
changes the sampling rate of the input AOs to the desired output sampling frequency by performing band-limited
interpolation, or interpolation.
</p>
<p>
If the ratio of the input and the desired output sample rate can be expressed as an integer ratio P/Q where both
P and Q then band-limited interpolation can be performed. In this case, the data-series
is upsampled (by inserting zeros) and then a low-pass filter is applied at the
original Nyquist frequency.
</p>
<p>
The <tt>ao/resample</tt></a> method can be called with the syntax:
</p>
<div class="fragment"><pre>
b = resample(a, pl)
</pre>
</div>
<p>
and can accept the following parameters:
<table cellspacing="0" class="body" cellpadding="2" border="0" width="80%">
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<col width="25%"/>
<col width="75%"/>
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<th class="categorylist">Key</th>
<th class="categorylist">Description</th>
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<!-- Key 'N' -->
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<p><tt>FSOUT</tt></p>
</td>
<td bgcolor="#f3f4f5">
<p>The desired output frequency (must be positive and integer)</p>
</td>
</tr>
<!-- Key 'FILTER' -->
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<td bgcolor="#f3f4f5">
<p><tt>FILTER</tt></p>
</td>
<td bgcolor="#f3f4f5">
<p>The filter to apply in the resampling process</p>
</td>
</tr>
</tbody>
</table>
</p>
<h2>Example 1</h2>
<p>
Here we will resample a sequence of random data from the original sampling rate of 1 Hz to
an output sampling of 50 Hz.
</p>
<div class="fragment"><pre>
pl = plist(<span class="string">'name'</span>, <span class="string">'None'</span>, <span class="string">'tsfcn'</span>, <span class="string">'randn(size(t))'</span>,<span class="string">'nsecs'</span>,100,<span class="string">'fs'</span>,1,<span class="string">'yunits'</span>,<span class="string">'m'</span>);
x = ao(pl)
pl_re = plist(<span class="string">'fsout'</span>, 50);
x_re = resample(x, pl_re); <span class="comment">% resample the input AO (x) to obtain the resampled output AO (y)</span>
iplot(x, x_re, plist(<span class="string">'XRanges'</span>, [10 20], ...
<span class="string">'Markers'</span>, {<span class="string">'o'</span>, <span class="string">'.'</span>}, ...
<span class="string">'LineStyles'</span>, {<span class="string">'-'</span>, <span class="string">'none'</span>})) <span class="comment">% plot original and resampled data</span>
</pre>
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<img src="images/ltpda_training_1/topic2/re1.png" alt="Resample" border="3">
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<td align="left">Upsampling a time-series AO</td>
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<td align="right">Interpolation of a time-series AO</td>
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