ccurrie wrote:Does digital mean less,or no "white noise"?

Not sure what you mean ccurrie. All ANR is digital. It's an application of Digital Signal Processing. One turns the sound into zeros and ones like your CD player uses, looks for re-occuring patterns that are noise like in their profile, re orders the data stream to exclude those non wanted patterns and spits it back out as analog so that the ear can use it.
White noise or blur is a result of the imperfections in the algorithms programmed into the device. I used my first ANR device in a ham radio set back in the 90's. There were no commercial products available. I bought a chip set with a ROM that contained a rudimentary set of instructions to operated the Analog to Digital to Analog converter. Like most things electronic, we've come a long way.

Emory Bored wrote:All ANR is digital. It's an application of Digital Signal Processing. One turns the sound into zeros and ones like your CD player uses, looks for re-occuring patterns that are noise like in their profile, re orders the data stream to exclude those non wanted patterns and spits it back out as analog so that the ear can use it.

That's not the way they work. ANR is an analog process using op-amps. It uses little microphones that are usually located inside the earcup. The microphones sense both the desirable sound coming from the speakers in the headset plus they sense the undesirable sound (noise) coming through the walls of the earcup. The signal from the radio is subtracted from the signal coming from the microphones inside the earcups. This yields a signal that just contains noise. This signal is inverted to make anti-noise. This anti-noise is then fed to the speaker along with the radio signal. In a perfect world, the anti-noise from the speaker cancels the noise coming through the earcup, and you only hear the radio.

If you look at Bose's patents, the circuit diagrams will clearly show this.

Ok. I've done this before, but I thought I would do it again this morning. QFR's vs Zulus. C-182.

- Overall noise levels are very similar, subjectively. Zulus have a narrow edge. The difference is comparable to standing next to a household forced air system vs. standing outside the utility room.

- QFR's actually get rid of more wind noise than the Zulus- absolutely, positively. My passenger tried them as well and thought the same thing. Maybe because the seal cups are slightly tighter for the QFR's.

- Zulus are lighter.

- Zulus have lower clamping forces, meaning my jaw joint doesn't act up as easily.

- Zulus fit better, and I can can move them around on my head without letting in the mayhem.

- Zulus offer slightly better suppression of actual engine exhaust noise. You can hear the exhaust substantially more with the QFR's.

- Prop noise is about the same-maybe, just maybe a slight edge with the Zulu's.

Personally, I don't find it worth $650 to upgrade to Zulus, and not worth $900 to me new. $650 buys decent replacement ANR's to replace my remaining passives. Or a round trip to Schaffer to fish for a few days. Or a nice 406 txpndr. Or towards an extended baggage STC. Or.....

I liked the lightness and fit of the Zulu. I can see why that could be a deciding factor for some. For me, cost is a zero sum game with flying, completing a remodel, and parental and family obligations competing for one another. For other folks, not so much.

Kevbert, you are getting closer. The signal from the radio has nadda to do with the noise cancelling function. Hence, the reason the headsets are fully functioning even when not plugged into the aircraft. All the rest you outlined is correct. Creating sound that is out of phase from the noise creates quiet. At least in that tiny space in the earcups. The radio, of course, is not competing with all the ambient noise and sounds better. So does music, or your phone.... or a scanner radio plugged into the aux. connector of the Zulu. Engineers at Lightspeed cancel more of the low freq. noise than high and have a proprietary scale of attenuation. In a pinch, the headset can be used for other purposes. At Caveman ranch event... I even used the Zulu to walk down and take a few shots at the range. They were moderately effective for the purpose.
When I wear them to bed... my wife is suspicious. So I stopped doing that.

Lesuther,
That makes perfect sense.
You can see that at some frequencies the conventional earmuffs outperform the ANR sets:


Source: http://www.aearo.com/pdf/hearingcons/anr.pdf

kevbert wrote:

Emory Bored wrote:All ANR is digital.

That's not the way they work. ANR is an analog process using op-amps. It uses little microphones that are usually located inside the earcup. The microphones sense both the desirable sound coming from the speakers in the headset plus they sense the undesirable sound (noise) coming through the walls of the earcup. The signal from the radio is subtracted from the signal coming from the microphones inside the earcups. This yields a signal that just contains noise. This signal is inverted to make anti-noise. This anti-noise is then fed to the speaker along with the radio signal. In a perfect world, the anti-noise from the speaker cancels the noise coming through the earcup, and you only hear the radio.

If you look at Bose's patents, the circuit diagrams will clearly show this.

You know, I guess I knew the inside outside subtraction part, I just thought they had come farther than that. Doh! If they haven't they should. But thanks for the reminder. It was a slow brain morning.

flightlogic wrote:Kevbert, you are getting closer. The signal from the radio has nadda to do with the noise cancelling function.

Au contraire.

The "noise cancelling function" first has to identify the noise. The microphones inside of the earcups pick up a signal which includes both the sounds of the radio coming from the headphone speaker and noises from outside the earcup. The only way to identify which part of that signal is noise and which part is radio is to use the signal from the radio as an input to the op-amp comparator.

Or, if you prefer an Argumentum ad verecundiam, the following is from Amar Bose's Patent # 4455675, although the actual circuit diagrams convey more technical information:

According to the invention, there is means defining a headphone cavity and electroacoustical transducing means, such as a pressure sensitive microphone, within the cavity for providing a signal corresponding to the sum of external noise and thesound produced by the headphone driver in the same cavity. There is means for combining this transduced signal with the input signal desired to be reproduced to produce an error signal representative of the noise and other differences between the inputsound signal to be reproduced and the output of the headphone driver in that cavity.

Emory, the technique you describe is used in all sorts of modern digital audio noise reduction circuits that don't have feedback loops (playing a cd, recording sounds without simultaneously playing those sounds through a speaker, etc). However, because the technique adds latency to the signal, it can't be used in a digital feedback loop. The ADC conversion, the digital processing, and the final DAC conversion all take some time. In an ANR headset using digital noise reduction, the noise would reach your ear slightly before the anti-noise correction signal reached your ear, and you would instead have twice as much noise. Then, the microphone would pick up the noise, the delayed anti-noise, the radio signal, and every loop would create even more noise.

kevbert wrote:<snip>

Or, if you prefer an Argumentum ad verecundiam <snippy>
However, because the technique adds latency to the signal, <snippity> feedback.

Thanks Kevbert, I'm getting back up to speed here. In the original noise suppression schemes the breakthrough was that noise could be identified by the DSP because it was repetitive. So no feedback loop was required; it was an active filtering device though rather than one designed for ambient suppression. So, I imagine someone has already tried to eliminate the latency by processing the "anti-noise" feedback loop to make it anticipatory? They must have found that there is too much variation in our noise over the very short period to make up for the latency problem. So, in spite of our awareness of strange attractors and Feigenbaum's turbulent flow equations we are still stuck with this cave man op-amp technology. And this, Ladies and Gentlemen is why we still prefer Continentals and Lycomings to all that fancy new stuff we hear so much about. There are limits to our smartness. We've been running around these last 50 years making stuff up to help us cope emotionally with the fundamental conflicts between General Relativity and Quantum Mechanics when we could have been working on a good cheap set of headphones. Lives wasted, opportunities lost. Carry on. What we need is a Copenhagen Convention on headsets. They both work, screw it.

I still want to try the Sennheiser S1.

Kevbert,
The only reason the radio signal is sampled, is to NOT cancel out the radio. That would obviously be counterproductive.
The actual noise cancelling is mostly about sampling what is outside the headset, not inside. (Unless your ears are wired backwards, and are making significant noise.)

flightlogic wrote:Kevbert,
The only reason the radio signal is sampled, is to NOT cancel out the radio. That would obviously be counterproductive.
The actual noise cancelling is mostly about sampling what is outside the headset, not inside. (Unless your ears are wired backwards, and are making significant noise.)

Latin is a douchebaggy language to bring to an aviation discussion. {Perjorative term in slang, but arguably less harsh than asshole.} according to Amar Google.

flightlogic wrote:

flightlogic wrote:Kevbert,
The only reason the radio signal is sampled, is to NOT cancel out the radio. That would obviously be counterproductive.
The actual noise cancelling is mostly about sampling what is outside the headset, not inside. (Unless your ears are wired backwards, and are making significant noise.)

Latin is a douchebaggy language to bring to an aviation discussion. {Perjorative term in slang, but arguably less harsh than asshole.} according to Amar Google.

WHAT, I CAN'T HEAR YOU, I'M WEARING ANR HEADPHONES!!!

Now that you guys are getting even more into the technical area of these headsets. How come the Cherokee guy hasn't chimed back in??

Interesting thread though!

I got my new blu tooth high bucks noise canceling headset, but I'll be damned if I can figure out how to plug 'em in......


lc

Epic thread.

Zane wrote:Epic thread.

X2

Zulus are worth it solely for how good Rage Against The Machine sounds while rocking through some canyons... right after getting off a work call using Bluetooth. .

I also did the headsets Inc. Conversion on my DC 13.4's and it is quieter with better radio clarity.

Just ordered the Zulu.2s. Tried them in the booth at OK, really looking forward to them. I thought my old Lightspeeds were nice but these seem incredible. In hindsight I should have given the Sennheisers a fair shake when I had the chance since their booth was right across from Lightspeed but I doubt I would have been swayed. On Emmets recommendation I'll make sure I have some Rage on the ipod.

Rob wrote:Which brings up another thing.... How much noise can uber anr handle?

I have the last Bose offering, the 'x'. They are great in the typical Cessna / Beech / Piper... They are WORSE than a passive headset on anything with a round motor, or turbine that is swinging a big prop up close. In a PC 12 / Meridian type, no worries, they're great, put them on in a Ag cat or air tractor, and they are worthless. On take off they will start making noise of their own trying to keep up with the prop noise.

I see the comment about the A20, but am reluctant to try anything else 'Bose' just yet, has anyone with Bose x experience compared the NEW Zulus ?
I love the technology, but am not too crazy about Boses.

I went to OSH last year and had the Zulus on my list to buy, specifically for the Bluetooth and ANR qualities. After a trip to the Bose booth, I came home with a set of the A20's. They are a night and day improvement over the Bose X's. I do get a little rumble in the A20's on takeoff in the Husky, but that can be quickly fixed by tightening them up on my head. The sound fidelity and quality of the Bluetooth interface is second to none for me.

Headsets are very personal and your results may differ. I didn't like the feel of the Zulus on my 7 5/8" head. The Boses feel and wear great. Prior to getting the Boses A20's, I used the Telex Stratus 50 in my Husky and felt it was the best headset for that noisy plane, but now the A20's are my headset of choice in either the Husky or the 206. I wouldn't go back to a passive set if they were free and the Bose A20's were $2,000 a pop. Well worth it in my opinion.

Emory Bored wrote:So, I imagine someone has already tried to eliminate the latency by processing the "anti-noise" feedback loop to make it anticipatory?

Kalman filters are Bayesian. So yes.

But digital ANR's only provide minor to moderate performance improvements over op amps for headsets. Digital filtering techniques can work well in low signal/high noise conditions. Headsets don't really have this problem, and use the digital filtering largely as (1) sales fluff, (2) possibly lower power consumption, (3) potential minor to moderate improvements in performance.

Analog and digital ANR both work, and some folks obviously care about the qualitative difference. The chipsets used in many low-end headsets are nearly identical. You can buy the workhorse from my QFRs and Softcoms on Digikey, and there are a lot of audiophile hacks out there for those with far more spare time than myself. DSP's are easier to tune with less compromise for a person with the right tools.

Kevbert, I gotta say- you passed the sense of humor test on this thread!
Epic indeed. This thread set off a small brush fire and spread from there. Wondering what will be next down the road? EGT vs. Flux Capacitor.....
Everybody have some great flights (wearing whatever pleases you on your head.... including your wife's panties if that rings your bell) and do it safely.
Looking forward to more interesting reading in the future.