visus
/
teensy-audio


			
				
					
						
						
							
							
	<h3>Summary</h3>
	<p>Compute a 1024 point Fast Fourier Transform (FFT) frequency analysis,
		with real value (magnitude) output.  The frequency resolution is
		43 Hz, useful detailed for audio visualization.</p>
	<h3>Audio Connections</h3>
	<table class=doc align=center cellpadding=3>
		<tr class=top><th>Port</th><th>Purpose</th></tr>
		<tr class=odd><td align=center>In 0</td><td>Signal to convert to frequency bins</td></tr>
	</table>
	<h3>Functions</h3>
	<p class=func><span class=keyword>available</span>();</p>
	<p class=desc>Returns true each time the FFT analysis produces new output data.
	</p>
	<p class=func><span class=keyword>read</span>(binNumber);</p>
	<p class=desc>Read a single frequency bin, from 0 to 511.  The result is scaled
		so 1.0 represents a full scale sine wave.
	</p>
	<p class=func><span class=keyword>read</span>(firstBin, lastBin);</p>
	<p class=desc>Read several frequency bins, returning their sum.  The higher
		audio octaves are represented by many bins, which are typically read
		as a group for audio visualization.
	</p>
	<p class=func><span class=keyword>averageTogether</span>(number);</p>
	<p class=desc>This function does nothing.  The 1024 point FFT always
		updates at approximately 86 times per second.
	</p>
	<p class=func><span class=keyword>windowFunction</span>(window);</p>
	<p class=desc>Set the window function to be used.  AudioWindowHanning1024
		is the default.  Windowing may be disabled by NULL, but windowing
		should be used for all non-periodic (music) signals, and all periodic
		signals that are not exact integer division of the sample rate.
	</p>
	<h3>Examples</h3>
	<p class=exam>File &gt; Examples &gt; Audio &gt; Analysis &gt; FFT
	</p>
	<p class=exam>File &gt; Examples &gt; Audio &gt; Analysis &gt; SpectrumAnalyzerBasic
	</p>
	<h3>Notes</h3>
	<p>The raw 16 bit output data bins may be access with myFFT.output[num], where
		num is 0 to 511.</p>
	<p>TODO: caveats about spectral leakage vs frequency precision for arbitrary signals</p>
	<p>Window Types:
		<ul>
		<li><span class=literal>AudioWindowHanning1024</span> (default)</li>
		<li><span class=literal>AudioWindowBartlett1024</span></li>
		<li><span class=literal>AudioWindowBlackman1024</span></li>
		<li><span class=literal>AudioWindowFlattop1024</span></li>
		<li><span class=literal>AudioWindowBlackmanHarris1024</span></li>
		<li><span class=literal>AudioWindowNuttall1024</span></li>
		<li><span class=literal>AudioWindowBlackmanNuttall1024</span></li>
		<li><span class=literal>AudioWindowWelch1024</span></li>
		<li><span class=literal>AudioWindowHamming1024</span></li>
		<li><span class=literal>AudioWindowCosine1024</span></li>
		<li><span class=literal>AudioWindowTukey1024</span></li>
		</ul>
	</p>
	<p>1024 point FFT has a peak CPU usage of approx 52% on Teensy 3.1.
		Average usage is much lower.  Future versions might distribute the
		load more evenly over time....
	</p>