Stepping back from ANR

Andrey,

If I remember correctly, there was a frequency/attenuation chart on the
back of some foam earplugs carton I saw once in a drug store. I'm sure
ANR manufacturers have plenty of charts for their products. So, data is
obtainable, at least theoretically.

A chart alone means nothing. It all depends on how you measure that chart.

But that doesn't mean much, since
noise perception is a very psychological thing (think of all those crazy
psycho-acoustic models for Hi-Fi audio noise reduction),

Not sure about that.

--
Thomas Borchert (EDDH)

Not all ANR headsets work on the same principle.

I understand that most of them are digital, in that they look for
repetitive noise & then use digital algorithims to s-l-o-w-l-y cancel
out the repetitive components of any noise signal. This has the
advantage that they can work to higher frequencies, but limited in that
they only work with repetitive (i. e. cyclic) signals. They are unable
to cancel random noise.

Some (the Headsets Inc version and maybe others) are a broad band
analog bucking system. They do not cancel just a repetitive
excitation, but can also cancel most of any random noise sensed by the
internal microphone system. The disadvantage of this type is that it
can work only at frequencies below typically about 300 Hz. Above this,
and they must rely on the passive noise rejection of the headset cups -
which is pretty good at high frequencies. It is low frequencies that
passive systems have the poorest atenuation.

Anyone else with more of the puzzle?

"nrp" wrote in message
oups.com...
Not all ANR headsets work on the same principle.

I understand that most of them are digital, in that they look for
repetitive noise & then use digital algorithims to s-l-o-w-l-y cancel
out the repetitive components of any noise signal.

I've never heard of an ANR headset that doesn't just use digital signal
processing as Roger describes.

Perhaps you could direct us to documentation of one that does the sort of
analysis you're talking about. That would help provide some context for the
discussion.

Pete

From Wikipedia on "Psychoacoustics":
---
In many applications of acoustics and audio signal processing it
is necessary to know what humans actually hear. Sound, which consists
of air pressure waves, can be accurately measured with sophisticated
equipment. However, understanding how these waves are received and
mapped into thoughts in the human brain is not trivial.

Recognizing features important to perception enables scientists and
engineers to concentrate on audible features and ignore less important
features of the involved system. It is important to note that the
question of what humans hear is not only a physiological question
of features of the ear but very much also a psychological issue.
---

There's more in that article if you're interested.


noise perception is a very psychological thing (think of all those crazy
psycho-acoustic models for Hi-Fi audio noise reduction),

Not sure about that.

On inquiry, I was told by technical people (I suspect it is a garage
shop operation) at Headsets Inc that their rejection system is all
analog. Being somewhat familiar with analog and digital noise
cancelling systems, I can verify that from the HI system that I have.
Oddly enough the performance seems somewhat similar.

On inquiry, I was told by technical people (I suspect it is a
near-garage shop operation) at Headsets Inc that their rejection system
is all analog. Being somewhat familiar with analog and digital noise
cancelling systems, I can verify that from the HInc system that I have.
Oddly enough the final performance seems somewhat similar.

It is easy to talk about a 180 degree cancelling pressure waveform
generator (per Roger above), but that is an over-simplification of the
problem that isn't acheiveable from a real control loop stability
standpoint.

Digital systems get around this by a slow optimization in the frequency
domain over a wide (i. e. hi) frequency range at the expense of being
able to cancel random noise, whereas analog does it in the time at the
expense of bandwidth, limiting it to a few hundred Hz, but making
analog better at random uncorrelated noise rejection. The Headsets inc
website posted the rejection capability of their system At low
frequencies it is about as good as the best digital system.

At high frequencies (above say 300 Hz), the passive rejection
capability of a good headset (mine is a David Clark H10-40) is more
than adequate to the task for my ears.

I've been trying to get HI interested in random motorcycle helmet noise
cancellation (generally under 100 Hz) but they don't seem interested -
or they may know why the analog control system can't be made stable.

From my engineering experience, a 300 Hz analog response loop is an
impressive acheivement.

"nrp" wrote in message
oups.com...
On inquiry, I was told by technical people (I suspect it is a
near-garage shop operation) at Headsets Inc that their rejection system
is all analog.

So the answer to my question is "no", you do not have first-hand knowledge
of any headset that uses a predictive cancelling algorithm such as you
describe. Okay, thanks.

Peter Duniho wrote:

So the answer to my question is "no", you do not have first-hand knowledge
of any headset that uses a predictive cancelling algorithm such as you
describe. Okay, thanks.

According to:

http://www.telex.com/aircraft/produc...ratus50Digital

that's what they do. Never used one - I have no idea how well it
works, if at all. I have a Bose, a Lightspeed 15XL, and a Clarity Aloft.

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006

So the answer to my question is "no", you do not have first-hand knowledge
of any headset that uses a predictive cancelling algorithm such as you
describe. Okay, thanks.

I do have 25 years ystem engineering experience with error cancellation
techniques in the frequency domain.

So the answer to my question is "no", you do not have first-hand knowledge

of any headset that uses a predictive cancelling algorithm such as you
describe. Okay, thanks.

I do have 25 years of system engineering experience with error
cancellation
techniques in the frequency domain, as well as analog error
minimization techniques.