mark@mips.UUCP (05/20/87)
I recently read (in Aviation Week & Space Technology) an article about
a noise-cancellation system for military pilots' helmets. Seems that
military cockpits are _very_ noisy, with helicopter blades whooshing,
fighter engines roaring, etc, so the pilot can barely hear his/her radio.
The new system puts a microphone in each earcup, and uses the resulting
signal to measure the "error" at the pilot's ear [error == signal at ear
minus signal from radio] and thus cancel much of the ambient noise
(about 30 dB as I recall). So the pilot hears the radio but not the
loud powerplant. Pretty cool.
If memory serves, the whole system is contained in a cigarette-pack sized
box that goes in the pilot's pocket (so the aircraft isn't modified, just
the helmet). Noise cancellation is done with digital circuitry.
Now, a few questions:
1. Has anybody out there experimented with this sort of thing? How
well did it work?
2. Could a hobbyist-grade version be built on the cheap, using e.g.
analog circuits for the signal processing? Or is the major cost
the modified earpieces with mikes?
3. Can the idea be used "backward" to make a microphone which cancels
ambient cockpit noise and only picks up the pilot's voice? For
example, have a 2nd mike that faces _away_ from the pilot, and use
this signal as an approximation of the "error" (ambient noise).
Or is this already available per Scott Dorsey's recommendation of
the "Telex noise-cancelling element"?
Regards,
--
-Mark Johnson **DISCLAIMER: The opinions above are personal.** Hi Max!
UUCP: {decvax,ucbvax,ihnp4}!decwrl!mips!mark TEL: 408-720-1700 x208
USmail: MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086medin@cod.UUCP (Ted Medin) (05/20/87)
Noise cancelling microphones have been around for a long time. I use one
regularly in light planes. I have been flying since 77 or so and they were
in use then.
Tedmarcum@nescorna.UUCP (05/20/87)
In <1027@mips.UUCP> mark@mips.UUCP (Mark G. Johnson) wrote: > ...noise-cancellation system for military pilots' helmets.... > The new system puts a microphone in each earcup, and uses the resulting > signal to measure the "error" at the pilot's ear [error == signal at ear > minus signal from radio] and thus cancel much of the ambient noise > (about 30 dB as I recall).... I read about an experimental system Bose (yes, the speaker folks) was building, in, I think, _Aviation Consumer_. It was an active noise- cancelling system, much as Mark describes. It is apparently VERY comfortable. Also, even without the magic black box the headset did an excellent job of noise attenuation. Alan M. Marcum Sun Microsystems, Technical Consulting marcum@nescorna.Sun.COM Mountain View, California
dralle@lll-lcc.aRpA (Sir Matthew G. Dralle) (05/20/87)
> Noise cancelling microphones have been around for a long time. I use one > regularly in light planes. I have been flying since 77 or so and they were > in use then. The idea behind the noise cancelling mic is really no big deal. In aircraft handheld mics and in the headphone style boom mics there are two "channels" to allow sound to enter. One channel in in the front where you would talk into, and the other is in the BACK of the mic. What happens is noise enters from the front *AND* the from the back. The two signals then subtract in effect because both are trying to vibrate the element together, but from different sides. When you talk into the mic, your sound is applied to one side of the mic only, and has no opposite vibration to subtract from it. Obviously, this system does not work %100, so the mic element is frequency bandwidth is limited to the vocal spectrum only (aprx 200-5000Hz). With the combination of the two cancelling systems, the little jobbers are fairly good at noise cancellation -- at least *I'M* imppressed! :-) Matt Dralle Mild Mannered Tech By Day... ...Pilot By Weekend.
ahv@masscomp.UUCP (Tony Verhulst) (05/21/87)
In article <1027@mips.UUCP> mark@mips.UUCP (Mark G. Johnson) writes: >I recently read (in Aviation Week & Space Technology) an article about >a noise-cancellation system for military pilots' helmets. Seems that >..... >The new system puts a microphone in each earcup, and uses the resulting >signal to measure the "error" at the pilot's ear [error == signal at ear >minus signal from radio] and thus cancel much of the ambient noise >(about 30 dB as I recall). So the pilot hears the radio but not the >loud powerplant. Pretty cool. > I understand that such a system was used on the Voyager flight and was supposed to have prevented the crew from suffering permanent hearing impairment during their flight. I don't know if it worked as advertised or if it is commercially available.
kludge@gitpyr.gatech.EDU (Scott Dorsey) (05/21/87)
In article <689@cod.UUCP> medin@cod.nosc.mil.UUCP (Ted Medin) writes: > Noise cancelling microphones have been around for a long time. I use one >regularly in light planes. I have been flying since 77 or so and they were >in use then. I have an old T25 noise cancelling mike which is labelled "AUG 1940" inside. It came free with a BCC-525 that I got at a hamfest. -- Scott Dorsey Kaptain_Kludge ICS Programming Lab (Where old terminals go to die), Rich 110, Georgia Institute of Technology, Box 36681, Atlanta, Georgia 30332 ...!{akgua,allegra,amd,hplabs,ihnp4,seismo,ut-ngp}!gatech!gitpyr!kludge
jpexg@mit-hermes.AI.MIT.EDU (John Purbrick) (05/22/87)
Regarding noise-cancelling speakers and mikes, there was an article in the British magazine "New Scientist" a while back about the use of "anti-noise" near large sources of acoustic noise like stationary gas turbine installations. The idea was to put a microphone some way from the device and drive a speaker adjacent to the device; an electronic system would try to null out the resultant signal as measured at the mike. As I recall the system was claimed to work fairly well, but I don't recall the db figures or how they solved the obvious problem of delay from the noise sources to the mike.
davec@mhuxu.UUCP (Dave Caswell) (05/22/87)
In article <1027@mips.UUCP>, mark@mips.UUCP writes: > I recently read (in Aviation Week & Space Technology) an article about > a noise-cancellation system for military pilots' helmets. Seems that > military cockpits are _very_ noisy, with helicopter blades whooshing, > fighter engines roaring, etc, so the pilot can barely hear his/her radio. > > The new system puts a microphone in each earcup, and uses the resulting > signal to measure the "error" at the pilot's ear [error == signal at ear > minus signal from radio] and thus cancel much of the ambient noise > (about 30 dB as I recall). So the pilot hears the radio but not the > loud powerplant. Pretty cool. > > Now, a few questions: > 1. Has anybody out there experimented with this sort of thing? How > well did it work? I got a demonstration of these things in an early prototype version a couple of years ago. The difference between ordinary tight fitting headphones and these things was really dramatic. Apparantly sounds below a certian frequency just aren't stopped by the passive systems. Turning on the active electronics eliminated the rumble noises as well as the hisses and pop's. Bose donated a set of these things to the Voyager flight. Rutan was really skeptical until he tried them out once. If anyone is interested e-mail me and I'll try and get the current spec's for them. --->Dave Caswell {allegra|ihnp4|...}!mhuxu!davec -or- davec@borax.lcs.mit.edu -- --->Dave Caswell {allegra|ihnp4|...}!mhuxu!davec -or- davec@borax.lcs.mit.edu
jackg@tekirl.TEK.COM (Jack Gjovaag) (05/22/87)
In article <1027@mips.UUCP> mark@mips.UUCP (Mark G. Johnson) writes: >I recently read (in Aviation Week & Space Technology) an article about >a noise-cancellation system for military pilots' helmets. > .......stuff deleted....... > 3. Can the idea be used "backward" to make a microphone which cancels > ambient cockpit noise and only picks up the pilot's voice? For > example, have a 2nd mike that faces _away_ from the pilot, and use > this signal as an approximation of the "error" (ambient noise). > Or is this already available per Scott Dorsey's recommendation of > the "Telex noise-cancelling element"? Almost all aircraft boom mikes do this already. The microphone "listens" through two opposed ports. One port is closest to the pilot's mouth and gets most of the voice energy. Both ports (in theory) hear ambient noise equally and cancel it. Listen to the transmissions from other airplanes. You never hear engine noise, only the pilot's voice. To determine the effectiveness of this, I ran a little experiment where I made a transmission to a friend in another aircraft while my outer marker beacon was beeping at full volume. He could NOT hear the beacon but could hear my voice (I was speaking quietly) perfectly. As an historical note, one early solution to the cockpit noise problem in combat aircraft was a "throat mike". It strapped around the neck with the microphone near the voice box. It was pretty well masked from all the engine and airframe noises but it sure did lousy things as far as speech intelligibility because it left out a lot of speech sounds that are made in the mouth without the vocal cords. Jack Gjovaag Tek Labs
brent@terra.UUCP (05/22/87)
In article <2849@mit-hermes.AI.MIT.EDU>, jpexg@mit-hermes.AI.MIT.EDU (John Purbrick) writes: > > Regarding noise-cancelling speakers and mikes, there was an article in the > British magazine "New Scientist" a while back about the use of "anti-noise" > near large sources of acoustic noise like stationary gas turbine installations. > The idea was to put a microphone some way from the device and drive a speaker > adjacent to the device; an electronic system would try to null out the > resultant signal as measured at the mike. As I recall the system was claimed > to work fairly well, but I don't recall the db figures or how they solved > the obvious problem of delay from the noise sources to the mike. Sounds like New Scientist is putting one over you. It's certainly not this easy (possible ?) to do this in an open acoustic field. It reminds me of an Aurthur C. Clarke story in "Tales of the White Hart" where someone invented one of these sound-nulling gadgets and had fun with it. I remember some years ago reading a similar article in New Scientist about an optical element that had just been invented for large telescopes that corrected images that lay at the extremes of the telecopes' field. The developers of this element were reported to be very excited at the commercial possibilities of the element when applied to corrective lenses for people. The human eye can resolve detail sharply over a small area at the center of the visual field. The new element would correct off-axis images so that the high visual acuity would extend over the whole visual field. The amount of eye movement in scanning an extended image would be greatly reduced. As an example they suggested that inspection of posted train timetables would be greatly facilitated. I've seen articles in similar vein in Scientific American. Was it the April 1st issue ? Made in New Zealand --> Brent Callaghan @ Sun Microsystems uucp: sun!bcallaghan phone: (415) 691 6188
randys@mipon3.intel.com (Randy Steck) (05/23/87)
In article <2849@mit-hermes.AI.MIT.EDU> jpexg@mit-hermes.AI.MIT.EDU (John Purbrick) writes: > >Regarding noise-cancelling speakers and mikes, there was an article in the >British magazine "New Scientist" a while back about the use of "anti-noise" >near large sources of acoustic noise like stationary gas turbine installations. >The idea was to put a microphone some way from the device and drive a speaker >adjacent to the device; an electronic system would try to null out the >resultant signal as measured at the mike. As I recall the system was claimed >to work fairly well, but I don't recall the db figures or how they solved >the obvious problem of delay from the noise sources to the mike. The algorithm of adaptive signal processing apparently used in this system was invented by Widrow of Stanford. I audited a class he taught on the subject and he suggested that one of the students try to build something similar to the above for a class project. He wanted to call it a "Cone of Silence" (I hope it works better than Maxwell Smart's!). However, there seems to be a small problem with the application of such a system. It seems to be possible to cancel noise at the microphone if the source of the noise is reasonably periodic. The problem comes in when a person moves away from the microphone since the hearer may no longer be in the "trough" of the waveform, but at a "peak". If the noise was large enough to cancel in the first place, then the resultant additive component would probably blow a person's ears out. This is minimized by putting the speaker near the device, but the area near the device would have many "peak" regions. And if the microphone moves (maybe being worn by someone?) the adaptive filter has to adjust itself. This may take some time depending on the algorithm used, so the user better not move too fast. And if that weren't bad enough, what about the use of more than one microphone? An additive peak will likely result somewhere. It seems that the system described in this mail would be limited to cancelling noise for 1 or 2 people in a stationary position for long periods of time. But, it's really interesting technology! Makes for alot of fun in the lab, too. -- Randy Steck Intel Corp. ...intelca!mipos3!omepd!randys
iwm@doc.ic.ac.uk (Ian W Moor) (05/23/87)
In article <19549@sun.uucp> brent%terra@Sun.COM (Brent Callaghan) writes: >> British magazine "New Scientist" a while back about the use of "anti-noise" >Sounds like New Scientist is putting one over you. It's >Was it the April 1st issue ? New Scientist usually has one column on the back page about the inventions of Deadelaus (sp?) - these are ingenious and often very plausible but not intended seriously although some do turn out to be viable. It's probable that this is what you read. -- Ian W Moor UUCP: seismo!mcvax!ukc!icdoc!iwm ARPA: iwm%icdoc@ucl Department of Computing Whereat a great and far-off voice was heard, saying, Imperial College. Poop-poop-poopy, and it was even so; and the days 180 Queensgate of Poopy Panda were long in the land. London SW7 Uk.
dsp@oakhill.UUCP (DSP Account) (05/24/87)
the very interesting application referenced below is just one of the many uses of adaptive digital signal processing which the DSP56200 chip, a 256 tap cascadable adaptive FIR (finite impulse response) filter(100ns cycle), from Motorola can provide. several companies are using the DSP56200 right now to solve this problem. the DSP56200 has been available since november 1986. literature, etc., can be obtained by calling (512) 440-2030 or you may send mail over the net. motorola salespeople can give you the same info. ask for BR283 and for DSP56200/D. week before last(today is 5/23), Widrow called us here in austin. he had just heard about the chip from one of his former students. he was very happy to see Motorola had implemented his LMS (least mean squares) algorithm in hardware. >From: mark@mips.UUCP (Mark G. Johnson) >I recently read (in Aviation Week & Space Technology) an article about >a noise-cancellation system for military pilots' helmets. Seems that >military cockpits are _very_ noisy, with helicopter blades whooshing, >fighter engines roaring, etc, so the pilot can barely hear his/her radio. >>From: randys@mipon3.intel.com (Randy Steck) >>The algorithm of adaptive signal processing apparently used in this system >>was invented by Widrow of Stanford. I audited a class he taught on the Motorola DSP Operation in oak hill, texas 512 440 2030
6062871@pucc.Princeton.EDU (Raj Manandhar) (05/25/87)
In article <19549@sun.uucp>, brent%terra@Sun.COM (Brent Callaghan) writes: >I remember some years ago reading a similar article in >New Scientist about an optical element that had just been >invented for large telescopes that corrected images that >lay at the extremes of the telescopes' field.... The human >eye can resolve detail sharply over a small area at the >center of the visual field. The new element would correct >off-axis images so that the high visual acuity would extend >over the whole visual field. The amount of eye movement I'm skeptical because, recalling my high-school biology, the human eye's resolution is best for images that are focused on the fovea, a small circle at the center of the retina that has a high density of light-sensitive (and color-sensitive) cone cells. This is the area that permits me to see what I am typing. Outside of this area, the density is lower, so the device won't do much good. (Incidentally, the fovea doesn't have many rod cells, which are black-and-white things good for low light, which is why you can see in the dark better using your peripheral vision). Raj Manandhar '87 6062871@pucc.bitnet {ihnp4,etc.}!psuvax1!pucc.bitnet!6062871 609/734-7368 417 Edwards Hall, Princeton University, Princeton, NJ 08544
iws@rayssdb.RAY.COM (Ihor W. Slabicky) (05/25/87)
In article <1027@mips.UUCP>, mark@mips.UUCP (Mark G. Johnson) writes: > I recently read (in Aviation Week & Space Technology) an article about > a noise-cancellation system for military pilots' helmets. Seems that > military cockpits are _very_ noisy, with helicopter blades whooshing, > fighter engines roaring, etc, so the pilot can barely hear his/her radio. In the book, Inside The Aquarium, Viktor Suvorov says that the earphones of tank crews produce a loud click before the actual firing. This causes the eardrum to react to the click and not to the sound of the firing of the tanks cannon. The click occurs milliseconds before the firing.
unicorn@pnet01.UUCP (05/26/87)
How quickly we decide something technological cannot be done, because it used to be impractical. And in these rapid-moving times too ! I observed the "noise source canceller" in operation on a "News from Science" blurb on CNN or somesuch a couple of months ago. Naturally, you need a whole buncha power, and the key limitation seems to a requirement for a very high periodic component in the sampled signal. Fortunately, much industrial noise is like this. As for spacing, sound travels 1116 feet/sec. Got a tape measure ?
henry@utzoo.UUCP (Henry Spencer) (05/26/87)
> > Regarding noise-cancelling speakers and mikes, there was an article in the > > British magazine "New Scientist" a while back about the use of "anti-noise" > > near large sources of acoustic noise... > > Sounds like New Scientist is putting one over you. It's > certainly not this easy (possible ?) to do this in an > open acoustic field... No, the idea is for real. The key is that the speaker is right at the source, not somewhere out in the acoustic field. Whether it will ever work well enough to bother with is not something I'd put bets on, but it does not appear to be a priori ridiculous. -- "The average nutritional value Henry Spencer @ U of Toronto Zoology of promises is roughly zero." {allegra,ihnp4,decvax,pyramid}!utzoo!henry
donald@warwick.UUCP (05/26/87)
With regards to anti-noise, I read a very detailed article about it in
"Chartered Mechanical Engineer" (the mag. of the British Institute of
Mechanical Engineers). The article was by some researchers at Essex
University (are they on the net? anyone like to confirm?) and described
various projects it had been used in. In fact there research was more
general than anti-noise; it was anti-vibration -- one of their experiments
was with resilient mountings for big diesel engines (like those in ships)
which took the form of hydraulic rams, a bit like active suspension for
cars.
One point which might convince the sceptics, their work was mainly to
do with cancelling cyclic noises (i.e. a diesel engine at constant rpm)
so they could use a computer to predict what the noise would be like based
on what it had been like before.
Hope that casts a bit of light... I read it a loooong time ago.
--
/*
* Tim Bissell ... the six million donald man ...
* donald@uk.ac.warwick
* {..seismo}!mcvax!ukc!warwick!donald
*/bob@pedsgo.UUCP (05/28/87)
In article <537@ubu.warwick.UUCP> donald@warwick.UUCP (Tim Bissell) writes: >With regards to anti-noise, I read a very detailed article about it in >"Chartered Mechanical Engineer" (the mag. of the British Institute of > ... I believe a system like this was used on the Voyager around the world airplane. I think it was developed by Bose. As I understand it, the noise within the cockpit would have been unbearable without it, and was endurable, but not pleasent, with it. Bob Weiler
kr@ken.UUCP (Ken Robinson) (06/01/87)
In article <2780@pucc.Princeton.EDU> 6062871@pucc.Princeton.EDU writes: > >In article <19549@sun.uucp>, brent%terra@Sun.COM (Brent Callaghan) writes: > >>I remember some years ago reading a similar article in >>New Scientist about an optical element that had just been >>invented for large telescopes that corrected images that >>lay at the extremes of the telescopes' field.... The human >>eye can resolve detail sharply over a small area at the >>center of the visual field. The new element would correct >>off-axis images so that the high visual acuity would extend >>over the whole visual field. The amount of eye movement > >I'm skeptical because, recalling my high-school biology, the human >eye's resolution is best for images that are focused on the fovea, >a small circle at the center of the retina that has a high density >of light-sensitive (and color-sensitive) cone cells. This is the >area that permits me to see what I am typing. Outside of this area, >the density is lower, so the device won't do much good.> In fact large astronomical telescopes are used to record on *film*, so that your comment on the small angular field of view of the eye, while true, is not relevant. Schmidt telescopes do indeed have a correcting lens before a spherical mirror. This gives good accuracy over a very wide field of view. Ken Robinson kr@uk.ac.rl.vd Informatics Division Rutherford Appleton Laboratory Chilton Didcot Oxon OX11 0QX
ender@mtuxo.UUCP (e.ayanoglu) (06/03/87)
> Regarding noise-cancelling speakers and mikes, there was an article in the > British magazine "New Scientist" a while back about the use of "anti-noise" > near large sources of acoustic noise... This is an application of a well-known method of noise cancellation, the Least Mean Squares (LMS) algorithm. See, for example, Widrow et al., ``Adaptive Noise Cancelling: Principles and Applications,'' Proc. IEEE, Vol. 63, pp. 1692-1716, 1975, or Widrow and Stearns, ``Adaptive Signal Processing,'' Prentice-Hall, Englewood Cliffs, NJ, 1985. As pointed by others, the method does not work as well when the noise spectrum widens. -- Ender Ayanoglu ..!ihnp4!mtuxo!ender (201) 957-3734
RAJ@pucc.UUCP (06/03/87)
Arrgghh! Sorry about the previous edition of this followup. The editor slipped it onto the net. I canceled, but no doubt some of you already have received it. Anyway. In article <429@rlvd.UUCP>, kr@ken.UUCP (Ken Robinson) writes: >In article <2780@pucc.Princeton.EDU> 6062871@pucc.Princeton.EDU writes: [regarding a lens that would improve the off-axis resolution of telescopes and the human eye] >>I'm skeptical because... the human eye's resolution is best for images >>that are focused on the fovea, a small circle at the center of the >>retina that has a high density of... cone cells. Outside of this area, >>the density is lower, so the device won't do much good. >In fact large astronomical telescopes are used to record on *film*, >so that your comment on the small angular field of view of the eye, >while true, is not relevant. Schmidt telescopes do indeed have a This is what I get for quoting too little of the original article in my posting (from account 6062871). Your point about telescopes is quite correct, but the speculation was about correcting the peripheral vision of an otherwise unaided human eye, in which case I think my original objection stands. Interesting note on this, recalled from a Scientific American from a year or so ago: to improve the realism of aircraft flight simulators without overtaxing the computer driving the simulator, they track the pilot's eye, and a detailed picture is projected only in the direction the pilot happens to be looking in. The rest of the picture is left rough, because the pilot can only see that with his low-resolution peripheral vision. I think these are experimental simulators for fighter pilots.