ISSUE-85: Oscillator folding considerations
authorcrogers
Mon, 04 Jun 2012 17:25:08 -0700
changeset 72 afb5ef123c50
parent 71 4de4b8263c21
child 73 db8f0473c76f
ISSUE-85: Oscillator folding considerations
webaudio/specification.html
--- a/webaudio/specification.html	Mon Jun 04 17:02:20 2012 -0700
+++ b/webaudio/specification.html	Mon Jun 04 17:25:08 2012 -0700
@@ -2825,6 +2825,28 @@
 
 <p>Oscillators are common foundational building blocks in audio synthesis.  An Oscillator will start emitting sound at the time
 specified by the <code>noteOn()</code> method. </p>
+
+<p>
+Mathematically speaking, a <em>continuous-time</em> periodic waveform can have very high (or infinitely high) frequency information when considered
+in the frequency domain.  When this waveform is sampled as a discrete-time digital audio signal at a particular sample-rate,
+then care must be taken to discard (filter out) the high-frequency information higher than the <em>Nyquist</em> frequency (half the sample-rate)
+before converting the waveform to a digital form.  If this is not done, then <em>aliasing</em> of higher frequencies (than the Nyquist frequency) will fold
+back as mirror images into frequencies lower than the Nyquist frequency.  In many cases this will cause audibly objectionable artifacts.
+This is a basic and well understood principle of audio DSP.
+</p>
+
+<p>
+There are several practical approaches that an implementation may take to avoid this aliasing.
+But regardless of approach, the <em>idealized</em> discrete-time digital audio signal is well defined mathematically.
+The trade-off for the implementation is a matter of implementation cost (in terms of CPU usage) versus fidelity to
+achieving this ideal.
+</p>
+
+<p>
+It is expected that an implementation will take some care in achieving this ideal, but it is reasonable to consider lower-quality,
+less-costly approaches on lower-end hardware.
+</p>
+
 <pre>    numberOfInputs  : 0
     numberOfOutputs : 1
     </pre>