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Thread: INVERTE THE WAVE
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picon face BY : Brandon, Tom email (remove spam text)



Basic principal is to produce the same wave 180 degrees out of phase. Thus
the sound waves cancel in energy. http://www.headwize.com/ has some stuff on
Active Noise Reduction. In particular the article titled "Adaptive Active
Noise Control for Headphones Using the TMS320C30 DSP" is quite good. In this
article they describe the basic theory of Active Noise Reduction examine the
current (at the time) systems which are generally passive (non-adaptive)
algorithms and present an algorithm for Adaptive Noise Reduction. This is
basically a passive noise reduction system that looks at how much noise got
through (error) and uses this to adapt the algorithm. There system also
allows for selective Noise reduction (i.e. eliminate the jackhammer but keep
your coworker telling you you're about to be hit by a truck) but I don't
know that the algorithms for this are discussed in detail.

This article provides the DSP algorithms used by the system.

Tom.

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