[David Nebenzahl]

On 6/7/2009 6:39 AM Richard Crowley spake thus:

Mr.T wrote:

"Richard Crowley" wrote ...

dpierce wrote ...

Irrelevant. Take a signal, run it through ANYTHING that inverts
the phase. A transformer, an inverting op amp. No discrete
sampling, no DSP of ANY kind required.

But that's not how noise cancellation works. That method would
merely create acoustic feedback.

You do know the difference between positive and negative feedback
right? *Negative* acoustic feedback is actually what they are trying
to achieve. And Dick specifically said to invert the phase, i.e.
negative feedback.

Easy to do electronically, extraordinarily difficult to do
accoustically at short wavelengths. That is why modern consumer noise
cancelling products depend on inexpensive DSP. You cannot just take
an acoustic signal from a microphone "invert" it and try to cancel
noise with it. You don't have to take my word for it. Try it for
yourself.

Just out of curiosity, why not? And no, not about to do this experiment
myself anytime soon.

Let me guess: it (inverting the signal) would work fine at low
frequencies, but progressively worse at higher frequencies?


--
Found--the gene that causes belief in genetic determinism