noise canceling headphones

--
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?

are you sure?

have you tried it?

On Jan 23, 11:05 am, Dick Pierce<dpie...@cartchunk.org> 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.

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+

=======================================
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/fileadmin/publications/schumacher11.pdf


this device is designed to easily implement active but NOT adaptive
noise reduction headphones

http://ics.nxp.com/products/interface/datasheet/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

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.

--
+--------------------------------+
+         Dick Pierce            |
+ Professional Audio Development |
+--------------------------------+

On 1/19/2012 11:20 PM, RichD wrote:
A noise canceling headphone consists of a headphone,
plus an external microphone fed to an inverting input,
right?

Well, not quite.

It also includes some signal processing, mixing
capability to properly blend the processed mic
signal with the incoming music signal, amplifiers
to power the headphone drivers themselves, the
mechanical packaging to hold it all together, etc.

Why does that cost $40 extra?

It costs extra because of the signal processing,
mixing capability to properly blend the processed
mic signal with the incoming music signal, amplifiers
to power the headphone drivers themselves, the
mechanical packaging to hold it all together, etc.

On 1/23/2012 3:39 PM, Mark wrote:
On Jan 23, 11:05 am, Dick Pierce<dpie...@cartchunk.org> 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.

--
+--------------------------------+
+ Dick Pierce |
+ Professional Audio Development |
+--------------------------------+

======================================>> 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/fileadmin/publications/schumacher11.pdf


this device is designed to easily implement active but NOT adaptive
noise reduction headphones

http://ics.nxp.com/products/interface/datasheet/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

Hi,

Is it possible to make active noise cancelling headphones without using
a separate microphone? I was thinking it could be possible to use the
headphones speaker elements as a microphone and sample them, and change
the drive signals accordingly, that could allow normal headphones to be
used as all the electronics would be in the signal source (ie. mp3
player).

cheers,
Jamie

Not to be too much of a jerk, but just exactly how to you disambiguate the

RichD wrote:
On Jan 20, Les Cargill<lcargil...@comcast.com> wrote:
A noise canceling headphone consists of a headphone,
plus an external microphone fed to an inverting input,
right?

Why does that cost $40 extra?

2) Because that is what people will pay for them.

Guy I went to college with went to work for Evil Corporation "X", and
basically lived on the road for like ten years. Wasn't married, so
he was able to save almost everything he made. The point is that these
are a "travel" item and people who burn through a corporation's travel
budget can offset salary& bonus with such purchases, and the
resulting value to them is higher than for those of us who don't.

That is why the Sky Mall magazine is like it is...


Sky Mall magazine?

--
Rich


I gather you don't fly much?

http://www.skymall.com/shopping/homepage.htm?pnr=ING

Where does the energy for all that processing and mixing come from?

On Fri, 20 Jan 2012 13:10:59 -0500, Dick Pierce <dpierce_at_cartchunk.org
wrote:

On 1/19/2012 11:20 PM, RichD wrote:
A noise canceling headphone consists of a headphone,
plus an external microphone fed to an inverting input,
right?

Well, not quite.

It also includes some signal processing, mixing
capability to properly blend the processed mic
signal with the incoming music signal, amplifiers
to power the headphone drivers themselves, the
mechanical packaging to hold it all together, etc.

Why does that cost $40 extra?

It costs extra because of the signal processing,
mixing capability to properly blend the processed
mic signal with the incoming music signal, amplifiers
to power the headphone drivers themselves, the
mechanical packaging to hold it all together, etc.

Where does the energy for all that processing and mixing come from?

?-)

Not to be too much of a jerk, but just exactly how to you disambiguate the
received noise signal from the reflected corrective signal?

"josephkk" <joseph_barrett_at_sbcglobal.net> wrote in message
news:5nhsh79fof4la03uog0ama3t8247kaf7fq_at_4ax.com...
Where does the energy for all that processing and mixing come from?

Most commonly, batteries.

Trevor.

And could you explain to me how all the battery power gets to headphone

On 1/23/2012 10:03 PM, josephkk wrote:
Not to be too much of a jerk, but just exactly how to you disambiguate the
received noise signal from the reflected corrective signal?


Hi,

Turn off the drive signal and listen periodically, like a sensorless
BLDC motor maybe?

cheers,
Jamie

On Wed, 25 Jan 2012 17:12:40 -0800, Jamie M<jmorken_at_shaw.ca> wrote:

On 1/23/2012 10:03 PM, josephkk wrote:
Not to be too much of a jerk, but just exactly how to you disambiguate the
received noise signal from the reflected corrective signal?


Hi,

Turn off the drive signal and listen periodically, like a sensorless
BLDC motor maybe?

cheers,
Jamie


Think that through really carefully. What would be the user response to
that?

?-)

On Mon, 23 Jan 2012 16:19:03 -0800, Jamie M <jmorken_at_shaw.ca> wrote:

Not to be too much of a jerk, but just exactly how to you disambiguate the
received noise signal from the reflected corrective signal?