[HN Gopher] DIY Acoustic Camera
___________________________________________________________________
DIY Acoustic Camera
Author : tomsonj
Score : 295 points
Date : 2021-10-27 15:35 UTC (7 hours ago)
(HTM) web link (navat.substack.com)
(TXT) w3m dump (navat.substack.com)
| nyanpasu64 wrote:
| Based on my experience building corrscope, I feel this is the
| kind of project that will outgrow Python once you want to
| implement your own low-level algorithms, make it embeddable or
| shippable as an application, or parallelize it. I wonder what's
| the easiest way to port Python DSP code and UIs to a
| compiled/etc. language.
| achn wrote:
| It would be interesting to see how well this could detect non
| incident sounds - for instance detecting reflective/resonant
| hotspots in an audio mixing/recording room.
| kabla wrote:
| Works very well for that! At least on high enough frequencies.
| Source: have done something similar.
| geokon wrote:
| Actual information on how it's done is here:
|
| http://www.acoular.org/literature/index.html
| davidb_ wrote:
| Combining this with Motion Amplification/Video Magnification [1]
| could result in some very interesting visuals and applications
| for factory equipment.
|
| [1] https://www.youtube.com/watch?v=rEoc0YoALt0 Explainer Youtube
| video about Motion Amplification
| 5faulker wrote:
| Thus another surveillance tool is born.
| fragmede wrote:
| It has been rumored that the US military has heartbeat
| sensors (aka real-life minimap) for decades now, would this
| really be a _new_ one?
| runj__ wrote:
| Then put a gun on it and you have something even worse!
| elfchief wrote:
| I don't suppose you have any idea if there are publicly
| available motion amplification tools, yet?
| johndough wrote:
| The authors of the predecessor method released some of their
| code:
|
| https://people.csail.mit.edu/mrub/vidmag/#code
| noodlesUK wrote:
| A starting point for the MIT research in question can be
| found here https://people.csail.mit.edu/mrub/vidmag/
| Wistar wrote:
| That is a great video.
| loxias wrote:
| Interesting. I'm casually familiar with Video Amplification
| (the approach at SIGGRAPH a decade ago IIRC), but have never
| implemented it myself. A really cool result, using the changes
| in the phase of the basis vectors over time to infer motion,
| without having to do dense optic flow.
|
| I'm curious how you would combine acoustic localization in 3
| space with motion amplification. I unreservedly agree that they
| are both "super cool", but don't see how they tie together to
| make something greater than the sum of their parts.
|
| The only thing I thought of is, if two data channels (video,
| audio) are registered accurately enough, one could maybe
| combine the spatially limited frequency information from both
| channels for higher accuracy?
|
| For example: voxel 10,10,10 is determined (by the audio system)
| to have a high amount of coherent sound with a fundamental
| frequency of 2khz. Can that 2khz + 10,10,10 be passed to the
| video system to do something.... cool? useful? If we know that
| sound of a certain spectral profile is coming from a specific
| region, is it useful to amplify (or deaden) video motion with a
| same frequency?
| epmaybe wrote:
| Motion and color amplification from wu et Al are underused in
| my opinion. Maybe because under patent?
| johndough wrote:
| Patents will expire starting from 2035 up to 2040 depending
| on the method used.
| londons_explore wrote:
| I'd like to see this done with a single microphone and a moving
| 'sound mirror' like a fan.
|
| The fan blades should cause doppler shift and changing amplitude
| that varies based on the location of the sound.
|
| I suspect that after just a few seconds, this would give better
| information than an array of 16 microphones.
| jcims wrote:
| That would work for amplitude-based location but this is using
| phase correlation to find time of flight difference to each
| microphone. With a fan idea you would get a lot of phase drop
| outs and smearing that I think would make that difficult.
|
| Not to say wouldn't work, you would get results, but they will
| be based in a different strategy.
| londons_explore wrote:
| But the phase smearing is useful information...
|
| Sure, the maths is complex... But there is only one source
| soundwave and location which causes a given smearing. The
| challenge is to find it...
| thatsadude wrote:
| Not a single microphone but there is acoustic vector sensor
| which can also give you the sound's direction. Very expensive
| though, several Israel companies use them for detecting
| gunshot's direction.
| https://www.ese.wustl.edu/~nehorai/research/avs/avssensor.ht...
| loxias wrote:
| Do you know anything about these "acoustic vector sensors"?
|
| When I first saw a popular science article about them, I got
| excited about incorporating them into an array, but couldn't
| find any technical details, just a lot of what looked like
| vaporware. Is it anything more than three orthogonal pressure
| sensors? (aka.... 3 microphones?)
| dendrite9 wrote:
| Microflown makes one, it uses very small temperature
| differences. You can look for acoustic particle velocity
| sensor to find more about how they work. I can't remember
| the paper, otherwise I'd provide a better link.
| https://www.microflown.com/products/standard-probes
|
| This PDF may be helpful http://past.isma-
| isaac.be/downloads/isma2010/papers/isma2010...
| loxias wrote:
| _temperature_ differences. Ah. Thanks for that paper,
| it's enlightening.
| cameron_b wrote:
| Somehow I'm imagining doing the inverse kinematic model of
| a Leslie speaker cabinet by measuring a single point of spl
| over time
| [deleted]
| amelius wrote:
| I'd like to see a video with an acoustic mirror.
| maxcan wrote:
| Is it possible to tune this to specific frequencies to detect
| mosquitos? Their audio signal is pretty weak but its also a very
| specific frequency. This would definitely help in the hunting and
| killing of the little bastards.
| potatoman22 wrote:
| If the mosquito frequency is less than half of the sampling
| rate of these mics, then yes. Very basically, these algorithms
| work by looking at the delay between each mic picking up a
| certain frequency, and calculating the direction of the sound
| wave from that.
| dylan604 wrote:
| No need for the hi-tech equipment for finding mosquitoes. Just
| take me to the spot you're looking, and they will find me.
| pmontra wrote:
| A mosquito racket increases efficiency at least 10 times. If
| you direct the output of that camera to a VR visor you can
| chase and zap them in the dark.
| loxias wrote:
| Yes. One surprising result is that weak sounds, even some below
| the threshold of hearing, are easy to detect, provided you have
| clear line of sight and no turbulence.
| wcfields wrote:
| Following Someone1234's comment[1] Stupid idea(?): Attach a
| mid-power laser to zap bugs, could even be a DIY project with
| an arduino and an PTZ mount.
|
| [1] https://news.ycombinator.com/item?id=29015202
| mLuby wrote:
| Just be careful not to blind yourself. Even a narrow
| flashlight cone could be enough for you to find and kill the
| bug by hand.
|
| Link to a previous post about this mosquito turret concept:
| https://news.ycombinator.com/item?id=27552516
| loxias wrote:
| I'm not the original author, however, ages ago I invented what's
| now being called "acoustic camera". (Specifically, the SOTA on
| the math side for precision, accuracy.)
|
| The resolution is fine enough that with COTS parts, I can record
| my signature simply by sketching it out with my fingernail on a
| table.
|
| Every few years I dust this off and play with it, wondering if
| there's some application or other way to "turn this into money"
| (an increasing concern in the coming months...<tiny>PLZ HIRE
| ME</>), but I'm not a "product guy".
|
| I'll answer some questions about the technology, but would really
| love to know if anyone here has advice on somehow using this
| achievement to pay rent. :)
| jbay808 wrote:
| It would be great if I could point something at a noisy machine
| and find out precisely which panel is loose and vibrating!
| loxias wrote:
| Really? Would it be "great" enough that you'd pay for such a
| device? If so how much? (would love to continue over email)
| joshmarlow wrote:
| I have absolutely no knowledge about this domain, so this idea
| 1) might not be viable and 2) is not a full developed product
| idea - but I thought it would be fun to get your thoughts.
|
| Could you put some sound sensors _inside_ of some mechanical
| structure and use the acoustics to figure out where some
| physical contact is happening on the _outside_ of the
| structure?
|
| Specific Application: prosthetics devices that can - with only
| a few acoustic sensors - determine where the 'touch' was on the
| outside of the device.
|
| If viable, it may be similarly useful for robots - or any
| machine in general - that needs a low-hardware (and thus low
| cost) method of getting course tactile information around it's
| boundary.
| cameron_b wrote:
| Videoconferencing applications are implementing this in
| conjunction with face detection to "steer" wide angle cameras
| into "talking head" shots.
|
| The current tech is spooky trash, parlor trick-quality from
| what I've used. Every time we use some of the automatic gizmos
| in conference rooms, we get tickets to make it stop.
|
| Pick your favorite top video conferencing platform or camera
| maker and they'll want to improve what they have. The Creepy -
| "Just works" jump is a big one.
|
| PS., the industry trade show is happening RIGHT NOW at
| https://www.infocommshow.org/
| robmiller wrote:
| I am an acoustics consultant who designs buildings with
| architects, then sees them through construction. Doors intended
| to isolate noisy rooms regularly underperform, whether due to
| manufacturing or installation problems. Lots of fingerpointing
| when we call it out on project sites, and having a camera show
| the weaknesses due to the perimeter gasketing, frame, door
| leaf, or wall construction surrounding the door would provide
| the necessary visual for contractors to see the problems we are
| pointing out.
| _spduchamp wrote:
| You want to pay the rent? Don't make a product, make a service,
| mainly, "WHERE IS THAT ANNOYING SOUND COMING FROM? SERVICE".
| People will pay you to locate sources of irritating sounds.
| loxias wrote:
| I have "inverse aptitude" at knowing what should be a
| product. :) Never trust me to know what would sell or not. In
| fact, "bet against whatever I think". ;)
|
| In my ideal (and in the best jobs I've had in the past),
| someone finds me (or I find someone) who I can share a list
| of "cool things I've figured out how to do, but don't know
| the usefulness of", and that person then tells me what to
| build.
|
| For your "where is that annoying sound coming from?" service,
| what sort of scale do you imagine, and what form factor?
|
| A handheld consumer device with a range of ~10m which points
| in the direction of the loudest thing?
|
| How much would you pay for such a device? (would love your
| thoughts in email)
| _trampeltier wrote:
| In industrial maintenace are such cameras in use to find air
| leaks in pneumatic. The model from Fluke is something like 20k
| USD. Because of this super high price, I don't know anybody who
| has a such model. So ask another company, if they are
| interested.
| paulirwin wrote:
| Not saying it's exactly the same thing, as I don't think a
| video overlay was involved, but I know someone that got their
| PhD in this area in the 1970s and had a long career working for
| a U.S. military contractor doing this. The U.S. military has a
| significant interest in acoustic beamforming, both in the air
| and underwater, for obvious reasons.
| loxias wrote:
| Oh absolutely! Sorry, I was excited in my typing. It's not
| every day you see "your baby" on HN :) Everything I built was
| on the shoulders of giants, and lol, I didn't invent
| beamforming itself (of course).
|
| The problem I have trying to find the niche application is
| that there's not much (at least, that I could think of) where
| you can have high quality audio data, but where a simple
| camera wouldn't work. Also, full imaging (as opposed to just
| tracking the largest/loudest source via TDOA) is quite
| different math, stupendously more computationally intensive.
| R0b0t1 wrote:
| Industrial automation monitoring is a major commercial
| application. I was going to look at
| https://www.minidsp.com/products/usb-audio-
| interface/uma-16-... for doing it. Do you know what limits
| of detection you could get, and on what equipment?
|
| Monitoring structural vibrations is also useful, and I
| think is an ongoing research area. I mention this because
| it's possible to sell it _and_ research it at the same
| time.
|
| What about synchronized cameras in different locations?
| nyanpasu64 wrote:
| How does this compare with commercial ultrasonic flaw detection
| systems for physical objects?
| loxias wrote:
| No idea! For a few month's stipend and cost of ultrasonic
| parts, I can find out for you. :)
| jcun4128 wrote:
| That's pretty cool as far as adding to a sensor fusion stack
| xattt wrote:
| Coupled with a VR headset, this would recreate the sound goggles
| that were featured in the halloween Magic School Bus special 30
| or so years ago.
| garyfirestorm wrote:
| wow this is amazing. i directly work in automotive and we use
| super expensive stuff which does exactly this (for 500k) lol
| loxias wrote:
| > $500k
|
| Are you kidding me???! It costs so... so... so... much less. I
| thought automotive might be a good application, considering all
| the doors opened by using more DSP tricks layered in addition
| to source localization. (I can localize coherent sound
| _patterns_ s well as coherent sound)
|
| I would love to chat with you, happy to buy a coffee or beer
| for your time. My email's on my profile.
| dendrite9 wrote:
| Some of these devices for automotive are large enough to
| surround a car on 3-4 sides, with several hundreds of
| microphones and the associated cables and positioning arms.
| Depending on where the devices he mentioned are being used,
| there are things like mannequins with heads and models of how
| humans hear for identifying sources inside a car.
|
| Here's an article about a large installation at Porsche.
| https://www.azom.com/article.aspx?ArticleID=18378
| loxias wrote:
| > there are things like mannequins with heads and models of
| how humans hear for identifying sources inside a car.
|
| HRTF stuff is fun, if that's what you're referring to! :)
| I've worked with some of that stuff before, including the
| stupidly overpriced mannequin heads.
|
| > Some of these devices for automotive are large enough to
| surround a car on 3-4 sides, with several hundreds of
| microphones and the associated cables and positioning arms.
| Depending on where the devices he mentioned are being used,
| there are things like mannequins with heads and models of
| how humans hear for identifying sources inside a car.
|
| Do you work in a field that would benefit from the same
| results, for a fraction of the cost? Or, if not, do you
| have any advice on how to find and talk to these mythical
| industries that could pay me? It looks like Porsche wanted
| to build their own, in house, but I'm hoping if it costs
| less than a tenth as much, maybe more people would want
| one.
| dendrite9 wrote:
| Do you mind if I send you an email later at the address
| in your profile?
| loxias wrote:
| Please do!!! I spent about 10 years of my life obsessed
| with this problem/area of research, and, when I have
| ability to pay rent and eat, it's the problem I'll go
| back to.
| buildsjets wrote:
| These are very commonly used in manufacturing plants to find
| leaks in compressed air lines. I had a Fluke vendor visit the
| ol' airplane factory to see if we could use their tools to find
| air leaks in low-pressure ECS system ducting.
|
| But c'mon, they are not $500k. More like $20K.
|
| https://www.fluke.com/en-us/product/industrial-imaging/sonic...
| loxias wrote:
| How many times cheaper would a competing product need to be
| for you to consider buying one?
|
| Obviously, Fluke, and the positive reputation that brand is
| known for, and reliable product support are worth a LOT, but
| I'm sure there's some $$ divisor beyond which you/someone
| like you would take a risk on something substantially
| cheaper.
| 6gvONxR4sf7o wrote:
| Am I understanding it correctly that this is not using anything
| analogous to a lens? How does this not need a lens when optical
| cameras need them?
| seiferteric wrote:
| Audio is low enough frequency that you can process the signal
| directly. The time delay/phase information between each mic
| allows you to know which direction the sound is coming from.
| This is essentially the opposite of beam forming. Theoretically
| you could do it with visible light and not need a lens if you
| had a computer and sensors that could operate fast enough. But
| optical sensors typically only tell you the amplitude of light
| and not phase for example.
|
| Edit: To clarify, the "opposite" of beam forming means using
| processing you can choose which direction you want to listen at
| any one time, like a beam. Then you can scan the beam across
| x,y and make an image.
| marginalia_nu wrote:
| Wouldn't a light version of this basically just be a fancy
| camera obscura?
| photonic37 wrote:
| The light version of this would be closer to a light field
| camera [https://en.wikipedia.org/wiki/Light_field_camera]
|
| The major difference between a microphone array and an
| imaging sensor is the availability of phase information for
| the received wave. A microphone oscillates with the sound
| pressure wave, and that oscillation is translated directly
| to a voltage. Your software can see the full time series of
| that wave, so the information about it is 'complete'.
|
| An optical image sensor, essentially, turns photons into
| electrons. The optical wave is too fast to turn into a
| voltage time series, so you only see the wave's amplitude
| at a given sample in time. Therefore, in order to turn it
| into an image, you need to recover some fraction of the
| phase information in some way.
|
| A pinhole is one way to do that. One way to think of a
| pinhole is that it maps every source point to a distinct
| imaging plane point, so the phase of the wave doesn't
| matter as much to the final image. It acts as a filter that
| cuts out ambiguous information that phase would have
| disambiguated.
|
| A lens performs a similar operation by interacting with the
| light wave's phase to bend wavefronts in a way that maps
| points on the object to an imaging plane.
|
| Those approaches don't recover 100% of the phase
| information, but they recover or filter enough to form the
| image you care about. Light field cameras attempt to
| recover more complete phase information through various
| ways better explored in the wikipedia link.
|
| Could you create a sound blocking plane with a pinhole that
| makes an acoustic camera that follows similar principles to
| an optical camera obscura? I bet at some level you could,
| but I also bet it would not be very advantageous. You still
| need a microphone array to act as the imagine plane. The
| size of the pinhole is probably very constrained by sound
| wave diffraction (it's a pretty long wave after all,
| compared to light). Using the directly available acoustic
| phase information is more compact and efficient.
| marginalia_nu wrote:
| I figured if you were to create an optical camera on the
| same principles of an acoustic camera you would get into
| trouble with the very short coherence length of sunlight.
| It's easy enough to build something that can deal with a
| laser, but sunlight has a coherence length of just a
| couple of dozen micrometers. If you are working on a
| larger scale than that, the phase information effectively
| becomes useless.
| 6gvONxR4sf7o wrote:
| Thanks!
| _Microft wrote:
| Fun fact: we manage to record amplitude and phase of
| radiowaves, though. That allows us to record them at
| different points on Earth, ship the recorded data to a
| datacenter and computationally merge them to get a planet-
| wide virtual telescope dish with a much better angular
| resolution that a single telescope dish ever could have.
| ddalex wrote:
| we don't record phase, there is no way to recover the
| phase from a single signal
|
| what we do we make sure that all receivers are
| synchronized, i.e take samples at the exact same time
|
| then you can correlate the signal received between dishes
| (which will arrive at different times due to delays in
| propagation), and find out the time difference of the
| signal which then points out to signal origin (beam
| forming) - this is how phased radar works
|
| once you align the signals you can use the minute
| differences in the signals to compute a synthetic
| aperture, i.e improving the angular resolution
| madengr wrote:
| It is analogous to a lens, in that the lens has a large
| aperture that allows a narrow, columnated beam.
|
| This has smaller elements arrayed over a large aperture, and
| controlling the magnitude and phase of individual elements
| allows you to steer that columnated beam.
|
| A bigger aperture gets you a narrower beam; lens, reflector, or
| array, it's all the same.
| thatsadude wrote:
| There are two main ways to do it: algorithms based on time
| difference of arrival and algorithms based on estimation of
| sound energy on a predefined grid. You can also estimate the
| distance but it will not as accurate as the direction.
| thatsadude wrote:
| In fact, you can use some lens such as parabolic reflector but
| it will make the problem very complicated to solve.
| onion2k wrote:
| This could be really useful for finding birds in trees when I'm
| out with my camera...
| loxias wrote:
| Would work! One of the first applications I made was a
| processing layer returning, in spherical coordinates centered
| at an arbitrary reference point, what the system determined as
| the "primary sound source".
|
| In demo, the two angles drove a pair of servos steering a laser
| pointer. Followed the loudest object around the room :)
|
| IME, finding a way to communicate the information to the user
| is often non-intuitive. That is to say, once a device has
| located birds in trees, how would you like it to inform you?
| onion2k wrote:
| My first thought is for something like an arrow visible
| through the viewfinder, a bit like a damage indicator in an
| FPS game like Halo.
| loxias wrote:
| Hm. Doable. I think the hard part for that then might be
| getting the real time information about the position and
| orientation of the viewfinder in high enough resolution.
|
| Keep in mind "the black box" can output the position in 3
| space (x,y,z, measured in mm) of coherent sound sources,
| but to know _where_ those are relative to the camera, so
| that once can draw a little arrow, can be hard.
|
| I'd like to try hooking it up to a VR/AR headset, since I
| imagine those already handle the task of knowing precisely
| where my head is and where it's looking.
| zlsa wrote:
| I think this might be possible with a phone that has AR
| support - you'd scan a QR code on the sound camera to
| capture its position relative to the world, then the
| phone could display a 3D view through the camera of where
| the sound source(s) are.
| loxias wrote:
| Oh that's interesting! Is your thinking something like:
|
| 1. mount the array on a tripod somewhere in the frame of
| the camera 2. the array is covered with an assortment of
| fiducials, 3. software uses the known intrinsics and
| extrinsics of the camera to figure out the array position
| relative to the camera 4. do the obvious thing with
| chaining transforms until you get the sound source
| position relative to the camera
|
| If so, I think that would work, but would be a lot of
| coding to do all that CV...
|
| > phone that has AR support
|
| I take it cell phones now do much of this work?
| modeless wrote:
| This is super cool. I was thinking about making a 4x4 mems mic
| array on pcb exactly like that one. I had no idea you could just
| buy one off the shelf these days. Has anyone put four together to
| make a 64 mic 3D acoustic camera?
| Someone1234 wrote:
| Stupid idea(?): Back-project onto some sunglasses (or
| corners/edge for behind), and give deaf people some basic level
| of sound-based situational awareness. Combine with some voice ->
| text tech, and you could have something pretty interesting.
| ampdepolymerase wrote:
| There is a long trail of dead startups attempting this. But
| don't let this dissuade you, please do a Show HN when you
| launch.
| marginalia_nu wrote:
| Probably requires the technology to reach some tipping point.
| It was the same with VR and motion tracking. We've been able
| to do those things for nearly half a century, but it hasn't
| been anywhere near commercially viable until recently.
| fragmede wrote:
| The tipping point is the availability of quality,
| affordable AR glasses. Until recently, AR has been too
| niche, so even if the acoustic camera technology is fine,
| the company also has to build AR glasses to go with the
| other part of the system. Whenever Apple comes out with AR
| glasses, then writing an acoustic camera app is almost
| trivial in comparison to having to also having to design
| some AR glasses. Not having to design the glasses makes
| acoustic camera technology overlay software way more
| commercially viable.
| vdqtp3 wrote:
| > availability of quality, affordable AR glasses
|
| And since Intel, Google, Facebook etc keep buying
| startups that produce cool things and preventing them
| from producing more cool things (North Focals being the
| most recent I'm aware of) it's gonna be a while
| rogerbinns wrote:
| Have a look at Microsoft Research's Seeing AI. It is still
| under development but can describe scenes and objects within,
| plus a bunch of other stuff such as documents, people, light,
| colour, currency, products etc. The app is only on Apple (no
| Android!) but the home page does have videos of each feature.
|
| https://www.microsoft.com/en-us/ai/seeing-ai
| jcims wrote:
| One application for those that I think might be interesting is to
| record a scene and retain all of the raw audio. On playback,
| allow people to click on parts of the image and use beamforming
| to focus on that part of the audio.
|
| Does anyone know if the array used here supports timestamped
| samples and/or clock sync to support multiple arrays? Or is it a
| single 16-channel stream?
|
| Having done some very primitive dabbling with this stuff, the DSP
| programming is always the most interesting part to me. These
| folks are killing it with some really cool 3D scanning
| integration to the acoustic analysis
|
| https://youtube.com/user/gfaitechgmbh
| loxias wrote:
| >On playback, allow people to click on parts of the image and
| use beamforming to focus on that part of the audio.
|
| You _can_ do that, but the gain isn 't as pronounced as you'd
| like. A 12-16dB gain doesn't sound that dramatic.
|
| Now, combined with some other newfangled math, like neural
| source separation, you might be able to do something
| spectacular...
| acjohnson55 wrote:
| That would be a lot of data. Instead of a few bytes of color
| data per pixel per frame, you'd need a thousands of samples per
| second per unit of spatial resolution.
|
| Another approach to this is the Ambisonics method of capturing
| the directional soundfield at a point. But you'd need to use a
| high degree multipole expansion to get resolution anywhere
| closer to video.
|
| https://en.m.wikipedia.org/wiki/Ambisonics
| awinter-py wrote:
| finally hardware to nail the guy who leans on his car horn
| outside my place
| IshKebab wrote:
| FYI if you put your microphones in a random pattern you can
| reduce aliasing artefacts. It's basically the same as dithering /
| noise shaping.
| loxias wrote:
| This took me years to figure out. :) Even cooler is that you
| can put them in a random pattern AND have the system determine
| its own geometry w/o measurements.
| [deleted]
| supermatt wrote:
| Are there any inexpensive microphone arrays?
|
| I was interested in making my own alexa-like device, but it seems
| mic arrays are sooooo expensive - more than the cost of an alexa
| device for the least expensive one i can find :/
| loxias wrote:
| > Are there any inexpensive microphone arrays?
|
| Not that I can find! Building the array is way more expensive
| than it needs to be.
|
| I have limited EE knowledge, so have been stumbling through it
| on my own, building my first array out of reference
| microphones, another with $10 omnis from guitar center, and one
| with 8x, cheap, repurposed webcams.
|
| Right now, my limiting factor on driving the cost of a future
| array down is that I haven't figured out how to get a lot (at
| least 8) I2S inputs to a micro-controller. If that were solved,
| it would be easier.
| rasz wrote:
| https://www.hackster.io/sandeep-mistry/create-a-usb-
| micropho...
|
| main limitation is USB 1.1 IO, so ~1MB/s. Pico itself can
| interface 15 microphones with no sweat.
| adolph wrote:
| The mike hardware used in the UMA-16 USB mic array [0] is the
| Knowles SPH1668LM4H-1 which runs about a buck and a quarter
| [1]. The DSP, SHARC ADSP21489, is pricier as an eval board
| >$500 [2].
|
| 0. https://www.minidsp.com/products/usb-audio-
| interface/uma-16-...
|
| 1.
| https://www.digikey.com/en/products/detail/knowles/SPH1668LM...
|
| 2. https://www.digikey.com/en/products/detail/analog-devices-
| in...
| thatsadude wrote:
| UMA-16 main audio processor is XMOS though.
| ghostly_s wrote:
| The post links to an inexpensive array at the end. I don't
| really get why the 16-mic one he used is so expensive, those
| smd mics can't be more than $1 or so each...
| supermatt wrote:
| Yeah, the respeaker ones i have looked at - but at $25+ they
| still feel very expensive to me. Are they that
| complicated/expensive to make?
| qazxcvbnmlp wrote:
| It's probably a niche enough product that the engineering /
| marketing work that goes into it is a higher fraction of
| the cost than the raw components.
| Anechoic wrote:
| _those smd mics can 't be more than $1 or so each_
|
| The actual mic capsules are likly far cheaper than $1 a piece
| (probably closer to $0.10 than $1) but the mics in an array
| need to be phased-matched. The two approaches to getting
| phased microphones are 1) building them using precision
| techniques so they are phased-match from the start (which is
| expensive and why pro phase-matched mics are around $1,000
| each), or 2) get a whole pile of cheap mic, test them one-by-
| one (or really, pair-by-pair) and select the mics that are
| best phased-match to use them in the array. The #2 approach
| is cheaper, but does add cost.
| loxias wrote:
| IME, the array only needs phased matched mics if you're
| doing SDB, or something else that cares _deeply_ about
| audio fidelity.
|
| I've never used phased matched mics in my arrays (can't
| afford it!) and also have never needed to "bin" them.
| ("pair-by-pair" testing).
| bytK7 wrote:
| I don't know enough about this so maybe dumb question, but
| couldn't you use DSP to correct phase between microphones
| if you knew their relative differences?
| loxias wrote:
| Yes you can. Another problem though is that the
| microphones need to have a common timebase, unless you
| have More Magic.
| 323 wrote:
| Couldn't one instead record at a higher sample rate (192
| KHz+) and then align in software instead of phase matching
| the mics?
| atoav wrote:
| The mics are probably cheap but 16x ADC in decent quality
| with decent power supply and low time offset between
| channels? How much is a 16chn audio interface with 16 mic
| preamps these days?
| loxias wrote:
| It can be done w/o phase locked ADCs :D it just takes...
| More Cleverness.
|
| I made a 16 mic array out of a bunch of trash-picked and
| cheap 4ch ADCs.
| thatsadude wrote:
| You can estimate 2D direction with 2 microphones (most of
| phones and laptops have at least 2 mic).
| causi wrote:
| I feel like there has to be a cheaper way to do this than a $275
| acoustic array. It's only 16 elements. You couldn't do this with
| 16 cheap microphones?
| fragmede wrote:
| How cheap do you want them? $275/16 = $17 per microphone, or
| $15 per + $35 worth of additional materials to make it into an
| array. Or $10 mics + $115 of metal and plastic.
|
| $275 doesn't really seem exorbitant for niche hardware given
| than you need 16 decently high quality microphones. I eagerly
| await a ShowHN using $2 mics and cardboard instead!
| loxias wrote:
| > given that you need 16 decently high quality microphones...
|
| But... you don't. :) The challenge I find is getting the data
| into the computer. That's what always costs the most. I've
| done it with 8x $1 mics and a used $100 sound card.
| cozzyd wrote:
| Can't you buy a bunch of i2s microphones and use a cheap
| FPGA dev board with a USB interface?'
|
| I may just order a bunch of i2s microphones...
| jack_pp wrote:
| Is this sensitive enough to find flying insects in a room?
| davidb_ wrote:
| I think with some filtering it definitely could be.
| mshockwave wrote:
| visualize that would be super cool
| dghughes wrote:
| They usually find me.
| loxias wrote:
| Not speaking to OP's device, but yes, I was able to track a
| loud fly buzzing through a room in real-time. ~cm accuracy, but
| that can be improved on.
| herval wrote:
| I imagine this + AR glasses can become quite the lifesaver for
| deaf folks. Throw in some voice recognition and you can have
| real-life speech bubbles!
| awinter-py wrote:
| fwiw they did this in world war I with microphone arrays +
| seismometer tape (picture of tape on p5)
|
| https://acousticstoday.org/wp-content/uploads/2020/06/Battle...
| CamperBob2 wrote:
| Awesome article. Deserves a spot on the front page by itself!
| Makes me want to learn a lot more about W. L. Bragg's physics
| exploits, along with those of his father.
| transistor-man wrote:
| Awesome work! How computationally intensive is Acoular / how
| complex would doing this from a live feed instead of recorded
| files be? Thanks for posting your project.
| loxias wrote:
| I'm not familiar with Acoular*, but the math involved in
| computing the sound coherence function over a large space is
| quite involved!
|
| In my implementation, there are multiple stages using a
| dataflow approach with lots of compile time optimization. In
| 2011 I could image a roughly 2m^3 space using 8 microphones at
| ~10fps in real time on 3 desktop computers, 2015 I was able to
| do 12mics, 3m^3 space, on 2 laptops, but that involved a LOT of
| custom numeric programming to shave cycles.
|
| If I had access, I'd love to see what could be done given a
| well tuned implementation and modern GPUs. An efficient scatter
| gather OP (like what AVX3 has) would increase performance by an
| order of magnitude.
|
| *OK, I've skimmed Acoular.
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