On Jan 23, 11:05*am, Dick Pierce wrote:
Mark wrote:
--
Rich
You cannot just stick a microphone and invert the signal and hope it
will cancel noise. You need to match the amplitudes at different
frequencies and this requires an adaptive filter.
hardy
oh really?
Really.
are you sure?
Yes. So are a number of professional, experienced
practitioners in the field of active noise cancellation.
have you tried it?
Yes. So have a number of professional, experienced
practitioners in the field of active noise cancellation.
Have you? Are you professional, experienced practitioner
in the field of active noise cancellation? If so, and if
you are claiming something to the contrary, please present
it so that the other professional, experienced practitioners
can evaluate your claims.
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+--------------------------------+
+ * * * * Dick Pierce * * * * * *|
+ Professional Audio Development |
+--------------------------------+
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there are 3 classes of noise reduction methods
1) passive
2) active / non-adaptive (this is the case we are talking about)
a feedback
b feedforward
3) active / adaptive...
a feedback
b feedforward
all three methods are viable...
#1 passive is most effective against higher frequencies.
#2 active / non- adaptive is simple and most effective against lower
frequencies in a limited space (such as headphones)
#3 is also effective but more complex
consumer noise reduction earphones make use of a combination of
methods #1 and #2
do you think all noise reducing headphones use complex DSP #3 adaptive
techniques?
here is some literature discussing active non adaptive (#2) as well
as active adaptive noise reduction applicable to the context of
headphones...
http://www.ind.rwth-aachen.de/filead...humacher11.pdf
this device is designed to easily implement active but NOT adaptive
noise reduction headphones
http://ics.nxp.com/products/interfac...et/ne58633.pdf
Note, this is a NON ADAPTIVE system. It is LTI.
This system is like an acoustical op-amp where the mic is the summing
junction. The amplitude and phase of the anti-noise is adjusted
automatically (non adaptively) by the negative feedback just like an
op-amp creates a virtual ground. And just like an op-amp if the loop
gain is increased too far, the system will become unstable.
This supports my contention that noise cancellation can be effective
without ADAPTIVE techniques.
And YES I have tried this and YES it works
a comparison of our credentials is irrelevant at this point
thanks
Mark