[HN Gopher] Phased Array Microphone (2023)
___________________________________________________________________
Phased Array Microphone (2023)
Author : bglazer
Score : 555 points
Date : 2024-11-22 17:10 UTC (1 days ago)
(HTM) web link (benwang.dev)
(TXT) w3m dump (benwang.dev)
| amelius wrote:
| Nice. It would be cool if this project could cleanly separate
| sources based on location.
|
| That would be a bit like a lightfield camera, where you can edit
| the focusing parameters after the image has already been taken,
| but now with sound.
|
| https://en.wikipedia.org/wiki/Light_field_camera
| hinkley wrote:
| I'm still sad these didn't become a thing. I don't need a 48MP
| camera phone. No seriously. I do not.
| sitkack wrote:
| If you can get a microlens array infront of that 48MP imager,
| you can have the light field camera you seek.
| hinkley wrote:
| Right. I don't need a 48MP image but a 48MP _sensor_ behind
| a depth of field image would be pretty useful.
|
| The thing about people taking pictures is they interrupt
| the flow of a live experience. My ex specifically bought a
| digital camera with a quiet boot up (low noise focus motor)
| so she could get shots of our friends before they knew she
| was taking pictures.
|
| Being able to take the shot and work on focal length later
| would be less disruptive.
| miloignis wrote:
| I believe it can, there's a demo under the "Directional Audio"
| section, unless I misunderstand you.
| dllu wrote:
| I once did a project to do multilateration of bats (the flying
| mammal) using an array of 4 microphones arranged in a big Y shape
| on the ground. Using the time difference of arrival at the four
| microphones, we could find the positions of each bat that flew
| over the array, as well as identify the species. It was used for
| an environmental study to determine the impact of installing wind
| turbines. Fun times.
| mywacaday wrote:
| I would love to do something like that to track the bats in my
| garden, how feasible would it be for an amateur to do as a
| personal project? Any good references on where to start.
| ryandvm wrote:
| Honestly, that sounds like amazing work. I wish I could afford
| to get out of enterprise software engineering and just do
| academic software development like that.
| jessetemp wrote:
| What were the results of your study? I've heard that bat lungs
| are so sensitive that when they fly across the pressure
| differential of large turbines their capillaries basically
| explode
| dllu wrote:
| Yes basically. Bird lungs are relatively rigid, open at both
| ends like a tube, and have a one-way flow of air, so they are
| less prone to pressure-related injuries. Bat lungs are
| mammalian lungs that expand and contract as they breathe just
| like us, so they are particularly vulnerable to barotrauma
| near wind turbines.
|
| After writing a bunch of MATLAB code to find the bats, I
| handed it off and haven't heard back about whether they
| actually built the wind turbines or not.
| FredPret wrote:
| I had no idea they were mammals until this comment. I thought
| they were furry birds!
| repiret wrote:
| It is not unreasonable to think of bats as flying mice.
| unwind wrote:
| In Swedish that is almost exactly what they are called, bat
| translates to "fladdermus" which is "fladder" (flutter) and
| "mus" (mouse).
| dllu wrote:
| Same in German, die Fledermaus. In fact, in English, the
| word "flittermouse" also means bat [1], although that
| word is rarely used now.
|
| [1] https://en.wiktionary.org/wiki/flittermouse
| bafe wrote:
| I did a similar project at 18. Needless to say I didn't have
| enough HW and SW skills to do much since I implemented the most
| naive form of the TDOA algorithms as well as the most
| inefficient way of estimating the time difference through cross
| correlation. I still learnt a lot and it led me to eventually
| getting a PhD in SAR systems, which are actually beamformers
| using the movement of the platform instead of an array
| isatty wrote:
| > bats (the flying mammal)
|
| As opposed to?
| Rygian wrote:
| Baseball bats?
| bgoated01 wrote:
| Here is a nice article on a study of baseball bats using
| microphones. https://www.acs.psu.edu/drussell/bats/papers/A
| cousticsToday_...
| lscharen wrote:
| Reminds me of Intellectual Venture's Optical Fence developed to
| track and kill mosquitoes with short laser pulses.
|
| As a side-effect of the precision needed to spatially locate
| the mosquitoes, they could detect different wing beat
| frequencies that allowed target discrimination by sex and
| species.
| redblacktree wrote:
| Where can I buy one?
| cyberax wrote:
| I don't think you can. This kind of laser devices is wildly
| dangerous.
| noobface wrote:
| Correct your vision and your mosquito problem in one easy
| purchase.
| antsar wrote:
| You won't see another mosquito - guaranteed!
| dleary wrote:
| This laser mosquito killer is, and always has been, a PR
| whitewashing campaign for Intellectual Venture's
| reputation.
|
| This device has never been built, never been purchasable,
| and it is ALWAYS brought up whenever IV wants to talk about
| how cool they are.
|
| And I say this as someone who loosely knows and was friends
| with a few people that worked there. They brought up this
| same invention when they were talking about their work.
| They eventually soured on the company, once they saw the
| actual sausage being made.
|
| IV is a patent troll, shaking down people doing the real
| work of developing products.
|
| They trot out this invention, and a handful of others, to
| appear like they are a public benefit. Never mind that most
| of these inventions don't really exist, have never been
| manufactured.
|
| They hide the extent of their holdings, they hide the
| byzantine network of shell companies they use to mask their
| holdings, and they spend a significant amount of their
| money lobbying (bribing).
|
| Why do they need to hide all of this?
|
| Look at their front page, prominently featuring the
| "Autoscope", for fighting malaria. Fighting malaria sounds
| great, they're the good guys, right? Now do a bit of web
| searching to try to find out what the Autoscope is and
| where it's being used. It's vaporware press release
| articles going back 8 years.
|
| Look at their "spinouts" page, and try to find any real
| substance at all on these companies. It is all gossamer,
| marketing speak with nothing behind it when you actually go
| looking for it.
|
| Meanwhile, they hold a portfolio of more than 40,000
| patents, and they siphon off billions from the real
| economy. Part of their "licensing agreement" is that you
| can't talk badly about them after they shake you down, or
| else the price goes up.
|
| They are rent-seeking parasites.
| NL807 wrote:
| That sounds like a fun project. Was it part of a research
| grant?
| neumann wrote:
| That sounds super interesting. Is there a write up somewhere of
| the project?
| dllu wrote:
| Here's the report [1], written when I was a second year
| undergrad in 2010.
|
| It's very basic. The species identification is based on
| matching contours of the spectrogram against some template
| contour. The multilateration was, embarrassingly, done by
| brute force by generating a dense 3D grid. At the time, I
| didn't have any knowledge of Kalman filters or anything that
| could have been helpful for actually tracking the bats.
|
| [1] https://daniel.lawrence.lu/public/bat-report.pdf
| belzebalex wrote:
| A nice mention about this is the outstanding and quiet work of
| the Cosys-Lab of the University of Antwerp. They once put a
| microphone array below a scorpio, and showed how bats moved
| their ultrasonic beam to scan for a scorpio. Incredible stuff
| [0].
|
| [0]: https://www.youtube.com/watch?v=57ScSPWhGqU
| crote wrote:
| I'm a bit surprised by those long "arm" PCBs. They are already
| doing calibration to account for some relatively large offsets:
| why not place each sensor on its own PCB, mount them to some
| carrier structure, and let calibration deal with the rest?
| elictronic wrote:
| Pcb manufacturing is cheap. I put 20 parts 1.5 inch by 24 inch
| into pcbway and ended up with final delivered cost of 240
| dollars.
|
| Not having to deal with wiring that many individual boards and
| all days of headaches tracking down issues is well worth it in
| my book.
| crote wrote:
| Huh, you're right. I expected 24-inch-long PCBs to be quite a
| bit more expensive, but even 4-layer boards at those sizes
| are still available at discount prices. I guess such thin
| boards could be used to fill in edges of mixed-order panels?
| It does make me wonder why they say "the array" was $700.
| Maybe assembly was extremely expensive
|
| It doesn't seem they weren't really able to benefit from it
| all that much, though: half of them arrived defective, and
| they had to do quite a lot of debugging to fix them.
| kindiana wrote:
| (OP here) the $700 was for 50 arm boards and 5 hub boards,
| fully assembled and shipped including all the parts (enough
| for 2 full arrays, with some spares). $350 @ qty 2 is
| pretty good, considering just the microphones is ~$100 for
| each array!
|
| Unfortunately the assembly/DFM didn't work out well, but
| with some better design and foresight it should be much
| less work/wiring compared to wiring them manually.
| brunosan wrote:
| Armchair comment. I would LOVE to be a grad student again and try
| to pair it with ultrasound speaker arrays, for medical
| applications. Essentially a super HIFU (High-Intensity Focused
| Ultrasound) with live feedback.
| https://en.wikipedia.org/wiki/Focused_ultrasound
| brudgers wrote:
| Then, why not be a grad student again?
| 01100011 wrote:
| Maybe they want to afford dinner?
| polishdude20 wrote:
| Hey saw your message a while back in a thread talking about
| continuous glucose meters and feeling tired and fatigued
| etc. Mind contacting me? I'd love to chat. My email is in
| my profile
| brudgers wrote:
| TANSTAAFL, but student loans too.
| always_swapping wrote:
| I may be the FUS grad student you seek. Reach out via profile
| email if you want to chat. Cheers!
| etrautmann wrote:
| Medical applications would presumably require contact coupling
| and not through air?
| zipy124 wrote:
| I do my PhD in in-air ultrasound with phased arrays and talk to
| the medical guys at conferences/labs that we talk to and it's
| soooo much harder in solids/liquids. The frequency is
| significantly higher, think 1-10MHz instead of like 40khz, so
| any normal electronics are out the window.
| duped wrote:
| One problem is that the speed of sound is not constant (or
| approximately constant) across the bandwidth you're interested
| in when the sound wave is traveling through solids and liquids.
| proee wrote:
| What is the most practical application for this technology? Could
| you use it to pinpoint sounds coming from a car like a squeak?
| Salmonfisher11 wrote:
| A similar technique is very popular in industrial automation to
| spot leaks in compressed air pipes and their connections from
| far away. These leaks are extremely loud in the ultrasonic
| range. It's overlayed with a camera picture.
|
| That's ultra expensive gear.
| pletnes wrote:
| I'll guess <<ultra expensive>> partly due to very low volumes
| made for a customer that can afford a lot.
| spankalee wrote:
| I've always wanted this for videoconferencing room. A
| microphone array around the screen should be able to
| dynamically focus on the active talkers and cancel out
| background noise and echos to get much better sound quality
| that the muddy crap we usually get.
|
| If there were a speaker array around the screens too, you might
| be able to localize the audio for each person so that it seems
| like the sound is coming from where their head is on the
| screen.
| icegreentea2 wrote:
| Shure sells a variety of array microphones (and the software)
| that handles similar things. I've never used one, but heh.
|
| https://www.shure.com/en-US/products/microphones/mxa710
|
| https://www.shure.com/en-US/products/microphones/mxa920
| Salmonfisher11 wrote:
| Beamforming is standard in modern conference room gear. It's
| being used for making a video focus on the active speaker and
| optimizing his audio.
|
| Have a look at the "Meeting Owl" for example.
|
| It works great up to a limit (around 5m) then you will need
| additional microphones closer to the speaker.
| sitkack wrote:
| XMOS targets this space specifically.
|
| https://www.xmos.com/ a descendant of the Transputer.
| markedathome wrote:
| Microsoft Research had papers on speaker arrays that allowed
| speaker focus and noise cancelling a couple of decades ago. I
| think the technology eventually ended up in the Kinect.
|
| I think Cisco had something similar in their large screen
| meeting room video conferencing systems that could do
| positional audio tracking of multiple people. Could be wrong,
| but I think that was at least 10 years or so ago, if not
| more.
| bongodongobob wrote:
| You just need to buy actual video conferencing gear, this is
| par for the course.
| __MatrixMan__ wrote:
| I wish could rent one to figure out which device in my office
| has a squealing capacitor. I can hear it well enough to be
| driven crazy by it, but not well enough to find it. I start
| disconnecting things to narrow it down but then convince myself
| that it's my ears ringing.
|
| I'm unsure if I'll age out of this problem, or if worse hearing
| will just recreate it at different thresholds.
| adrianmonk wrote:
| You might have some luck with a spectrum analyzer app[1]. A
| fixed-pitch whine should show up as a line on the waterfall
| graph. If you move the phone around to differently locations,
| you might see the line getting stronger or weaker. You can
| also try rotating the phone to different orientations to see
| if it is coming from a particular direction.
|
| I used this to locate an annoying squeal coming from some
| equipment at work once. And to confirm that it wasn't
| imaginary.
|
| ---
|
| [1] On Android, I like these two:
|
| Spectroid (https://play.google.com/store/apps/details?id=org.
| intoorbit....). If you use this, consider turning on the
| waterfall display in the settings.
|
| Spectral Audio Analyzer (https://play.google.com/store/apps/d
| etails?id=radonsoft.net....). This has more color options for
| the waterfall display.
| billyjmc wrote:
| Phyphox is a great sensor suite app for undergrad Physics
| experiments, and it includes a spectrum analyzer. Also, it
| supports both iOS and Android.
| hammock wrote:
| The tech is beamforming .. the applications are AV
| conferencing, camera tracking, voice lift, or sound
| reinforcement
| cushychicken wrote:
| This is more or less the same principle of how Amazon Echo
| devices work, but on steroids.
|
| Very neat. I would be surprised if you aren't seeing some
| diminished marginal returns from all those extra mics, but I
| guess you're trying to capture azimuth deltas that Echo devices
| don't really care about.
| Salmonfisher11 wrote:
| If somebody wants to play around with Zynq 7010's - have a look
| at the EBAZ4205 board. They can be bought from Aliexpress
| (20-30EUR). These are former Bitcoin Mining controllers.
|
| Some people reverse engineered the entire thing. It can be found
| in GitHub. And there's an adapter plate available for getting to
| the GPIOs.
|
| For a less complex entry there are also Chinese FPGAs ("Sipeed"
| boards which use a GoWin FPGA. They are quite capable and the IDE
| is free.
| telgareith wrote:
| Xilinx tool chain is also no-cost.
| scottapotamas wrote:
| For some/smaller parts. Once you start going higher than
| Artix or the token Kintex parts you need to pay up.
| gravypod wrote:
| I was just doing research and landed on this exact page last
| night! I was wondering if anyone knows how someone could mic a
| room and record audio from only a specific area. For my use case
| I want to record a couch so I can watch TV with my friends online
| and remove their speech + show noise from the audio. Setting up
| some array of mics and using them for beam steering would
| probably work but there's not a lot of examples I could find on
| GitHub with code that works in real time.
| imbusy111 wrote:
| From the article "The simplest method of beamforming is delay-
| and-sum (DAS)". Measure distance from a point (couch) to each
| microphone, delay the signal in time domain by the time the
| sound takes to travel from point (couch) to microphone, and add
| up the signals. Pretty trivial. Basically you want the
| microphones receive the couch signal at the same time, even
| though they are different distances away.
|
| Make sure there is enough variation in microphone distances for
| this method to be effective.
| crazygringo wrote:
| Loud show noise and your online friends' nearby audio is going
| to be reflected around the room as well as off of your bodies.
|
| What you want isn't microphone or beamforming tech, it's echo
| cancellation the same as every videoconferencing software uses.
|
| You just need to feed the show audio and friend audio in, and
| apply echo cancellation to each.
| aspenmayer wrote:
| You might look into OBS and/or VoiceMeeter to see how streamers
| selectively route audio while livestreaming/recording
| video/audio streams.
|
| https://obsproject.com/
|
| https://voicemeeter.com/
| killjoywashere wrote:
| I wonder how well this would work with laser microphones on a
| pane of glass. Can you infer keystrokes with near infrared laser?
| That is, can you identify the heatmap of keystroke events to
| infer which keyboard they're using, then replay the tape to
| identify the strings of characters being typed? Can you localize
| the turning of pages with UV?
| Salmonfisher11 wrote:
| Didn't Israeli students show that you can recover audio from
| the vibrations of bulb filament with a fast photo diode?
|
| I'd test that with a CCD line sensor plus a wide aperture lens
| and reading it out with 8kHz. Then you have 128 audio pixels
| that can cover an entire city.
| killjoywashere wrote:
| Line of sight might be an issue there. I'm thinking more
| high-end clandestine eavesdropping. Fun fact: curtains are a
| pretty good defeat for laser microphones, but if the building
| is really old and made of solid stone, you can point at the
| rock instead!
| 0cf8612b2e1e wrote:
| The rock?! That's incredible. I would have guessed it was
| too dense to pick up normal speaking volume. Then again,
| even the window glass vibration seems pretty magical to me.
| quantadev wrote:
| This beamforming effect only works well when each sensor is
| getting a dramatic enough "different angle" on the signal that
| each one can use phase shifting to cancel out other noise, but
| with a laser there's not really any noise to cancel out (i mean
| you're just monitoring a vibrational spot on a window), and you
| also don't have a far enough "different angle" to shine from,
| if you're monitoring from one spot.
|
| However having multiple lasers from multiple different
| locations _might_ be able to create an improved signal if all
| signals are averaged, but it wouldn 't really be due to the
| phase shifting that's used in beamforming.
| frankus wrote:
| "As part of the calibration, the speed of sound is also a
| parameter which is optimized to obtain the best model of the
| system, which allows this whole procedure to act as a
| ridiculously overengineered thermometer."
|
| Reminds me of the electronics adage: "all sensors are temperature
| sensors, some measure other things as well."
| Marthinwurer wrote:
| I love these kind of inadvertent measurements. One of my
| favorite examples is that a sufficiently accurate IMU can get
| you relatively accurate longitude measurements from the
| Coriolis effect.
| emptiestplace wrote:
| https://en.m.wikipedia.org/wiki/Inertial_measurement_unit
| adolph wrote:
| Slight correction, latitude, not longitude.
|
| The earth's surface closer to the poles has less distance to
| travel for any rotation than the surface closer to the
| equator. As a result the inertial navigation systems of long
| distance systems must be adjusted. Iirc, this is also the
| case for artillery firing computations.
|
| https://www.oxts.com/blog/going-round-circles-earth-
| rotation...
|
| https://www.britannica.com/science/latitude
| billyjmc wrote:
| Coriolis corrections are thrown into sniper ballistic
| calculations, too. Not a huge effect in most conditions,
| but not zero, and there have been a lot of long shots in
| the past two decades.
| psunavy03 wrote:
| "Oi! Suzy!"
| 01HNNWZ0MV43FF wrote:
| Is that the same thing where a flat-earther tried to measure
| something with an expensive laser gyro and kept finding that
| Earth was rotating?
| adolph wrote:
| I think the most you can tell from an IMU or gyro is that
| there is a change in velocity in a direction aligning with
| East-West when there is a change in location and that the
| change in velocity is greater when the location changes in
| line with North-South. The change in velocity would be
| greater as one approaches the poles and lesser at the
| equator.
|
| Thought experiment: if I zeroed my IMU at the North pole
| and traveled in a straight line away from the pole along
| longitude zero, following the guidance of the IMU. By the
| time I got to 45deg latitude I'd be traveling Westward at
| 1,180 kph (.95 Mach) to keep the IMU at zero.
| trueshape wrote:
| The flat earther used a fibre optic gyro. You don't
| "zero" it, it continuously outputs a measurement of its
| own angular rate around it's sensitive axis. For a 3-axis
| gyro placed still on earth, it will read about 15
| degree/hour around wherever the axis of earth is
| oriented.
| nielsole wrote:
| Asahi Linux (and likely MacOS too) uses the resistance of the
| speakers coils to detect overheating of same speakers and
| reduces volume.
| derhuerst wrote:
| https://github.com/AsahiLinux/speakersafetyd
| CamperBob2 wrote:
| Interesting. If the voltage across the speaker voice coil
| can be sampled with enough sensitivity at a fast-enough
| rate, you have an undocumented microphone.
| xyzzy_plugh wrote:
| This is true of all speakers
| CamperBob2 wrote:
| Exactly.
| ssl-3 wrote:
| It's true of all dynamic speakers -- the sort with a
| voice coil and a magnet.
|
| (But not all speakers are dynamic speakers.)
| planewave wrote:
| Would this also be true for electrostatic speakers as
| well? Though would probably would require greater
| gain/amplification or, potentially the application of
| some kind of bias voltage for the capacitive diaphragm of
| the speaker.
|
| Just speculation based on the shared operating principal
| with condenser microphones
| BobbyTables2 wrote:
| But not true of all codecs...
|
| Do you think Apple put a hidden microphone in their
| devices by pure accident?
| squarefoot wrote:
| That's the same principle used by cheap solder stations to
| regulate the tip temperature without employing a thermal
| sensor: they measure the heater resistance, presumably
| during the off state of the PWM signal that drives the
| heater. In that case the measurement is less accurate than
| using a real sensor, still good enough for cheap solder
| stations where a few degrees don't make a big difference.
| nick3443 wrote:
| Also used in electric motor controllers to monitor winding
| temperature.
| psunavy03 wrote:
| I believe this is one of the initial steps an aircraft INS
| uses to find north while it is aligning, but it's been too
| long since I had aircraft systems theory in the front of my
| brain.
| t0mas88 wrote:
| Yes, from earth rotation the INS could figure out true
| north if the latitude is known. Or figure out the latitude
| if current heading is known. But normally it's aligned with
| a starting position from pilot input or GPS.
| VBprogrammer wrote:
| If you are at an airport you will sometimes notice large
| signs giving Longitude and Latitude of the individual
| stands at an airport. These are used to give the initial
| position to the INS via the FMS. Of course these are now
| all built into the database these days so are only used
| (if at all) for gross error checking.
| cameldrv wrote:
| Latitude or Longitude?
| sam_dam_gai wrote:
| Do you mean latitude?
| cushychicken wrote:
| > Reminds me of the electronics adage: "all sensors are
| temperature sensors, some measure other things as well."
|
| I wanna say that's a Bob Pease quote but I can't find an
| attribution to it.
| frankus wrote:
| I first encountered it in Elecia White's book Making Embedded
| Systems, but the attribution is anonymous and whom it's
| attributed to may have heard it elsewhere.
| user_7832 wrote:
| Is there one saying "All electronic devices are smoke machines,
| some can compute too"?
| frabert wrote:
| "All diodes are light-emitting if you try hard enough"
| gavinsyancey wrote:
| "All diodes are light-emitting at least once"
| dmoy wrote:
| Hahaha yea
|
| I've seen that in electronics lab a few times. The
| "temporarily light emitting diode"
| Moru wrote:
| I have a Temporarily light-emitting harddrive cable.
| Really old 40 MB hdd connected to an old computer with a
| cheap power supply that most likely couldn't handle the
| slightly lower than standard power in a friends house.
| sitkack wrote:
| All diodes are also light SENSING is you try hard enough.
| immibis wrote:
| You don't have to try hard. Just use it as a photodiode
| and it magically works. However, if it's inside a plastic
| case that blocks light, it doesn't.
|
| Due to some law about entropy, efficient processes are
| necessarily reversible. That's why electric motors - some
| of the most efficient machines ever invented - are also
| generators.
| biot wrote:
| > However, if it's inside a plastic case that blocks
| light, it doesn't.
|
| You want an ordinary diode to allow current to flow
| easily when it senses light? Simple: shine a powerful
| laser at the plastic-encased diode and it will melt the
| plastic and liquify the metal, fusing it together and
| allowing current to flow again. See? You just needed to
| try harder.
| Moru wrote:
| Or if the hammer don't work, the sledgehammer is over
| there.
| sitkack wrote:
| All diodes are photodiodes, one has to be esp careful of
| glass encapsulated diodes. I have had that bite me
| before.
| slow_typist wrote:
| Especially true for LEDs, tried that in the lab once with
| a flood light, got a few mA out of the LED shortened with
| the multimeter. Did that with 8th graders, we did other
| experiments mainly with pv, LEDs and bipolar transistors
| as well.
|
| The logical question came up more than once: "can we use
| photovoltaic cells as a light?". Pretty sure that'll
| work, too, but didn't try because stuff was expensive
| then and we didn't have any broken parts of cells at the
| time. They probably learned a few things on that day.
| hawski wrote:
| Steve Mould of Youtube fame did this:
|
| Why all solar panels are secretly LEDs (and all LEDs are
| secretly solar panels) -
| https://www.youtube.com/watch?v=6WGKz2sUa0w
| bsder wrote:
| Ah, the light emitting resistor. The moment when you
| realize why it's called Ohm's _Law_.
| jaggederest wrote:
| Similarly, diesel engines come with a reserve fuel supply
| that you can accidentally use once. (diesel engines will
| happily run on engine oil when warm)
| TheSpiceIsLife wrote:
| This happened to me once in a Peugeot 306 2L turbo diesel.
|
| Over filled it and kinda had to do one 1600m trip.
|
| Fortunately it was manual so I was able to stall it fairly
| swiftly in third gear with my foot on the break.
|
| Didn't seem to have any impact on the engine as far as
| normal operating and how it sounded. I didn't do any
| internal inspection.
| qingcharles wrote:
| "All electronics are hand-warmers if miscalibrated correctly
| enough."
| ChuckMcM wrote:
| "Inside every amplifier is an oscillator trying to get out."
| qskousen wrote:
| The one I've heard is "Every machine is a smoke machine, if
| you operate it wrongly enough."
| Bearsilber wrote:
| I just learned how the Duracell Powercheck(c) worked, which was
| done with temperature.
|
| https://youtu.be/zsA3X40nz9w?si=oGg2wdUlLXSDxpsN
| entropicdrifter wrote:
| It does act as a thermometer, if and only if the altitude
| remains constant. The speed of sound fluctuates with both
| temperature and altitude
| _0ffh wrote:
| Right, it gets even worse: Air pressure in not _only_
| altitude-dependent but fluctuates even at constant altitude.
| The pressure (altitude) dependence is comparatively weak,
| though.
| KeplerBoy wrote:
| one might say air pressure changes constantly as we speak.
| adammarples wrote:
| Isn't air pressure the only thing that microphones
| actually measure?
| sojsurf wrote:
| Air pressure differentials, to be precise!
| KeplerBoy wrote:
| By definition, sure. But one always needs some effect
| which changes some electrical property. We can't just
| hook up an ADC (analog digital converter) to thin air and
| hope for the best.
|
| In practice most microphones measure the displacement of
| microscopic membranes, which are deformed by the air
| pressure. The next question then becomes how to measure
| microscopic movements of a tiny membrane. Turns out the
| membrane forms part of a capacitor and the electrical
| characteristics of capacitors depend on their geometry.
| jpc0 wrote:
| That is not necessary true.
|
| There are at least 4 different types of microphones.
| Condenser which does in fact form part of a capacitor,
| dynamic which is effectively a linear generator (coil
| attached to membrane), ribbon which is a change in
| resistance as a small ribbon flexes and piezoelectric
| which is some black magic witg crystals
| KeplerBoy wrote:
| Sure, that's why I wrote most microphones.
|
| There are also some exotic principles like laser or radar
| microphones using interferometry.
|
| https://en.m.wikipedia.org/wiki/Laser_microphone
|
| https://ieeexplore.ieee.org/document/7808865
| jpc0 wrote:
| I think popular is very situational though.
|
| For me I see a lot more dynamic than condensers but I
| guess if you are talking about what is in like every
| single IOT thingamabob then you might be right there.
| sanderjd wrote:
| Fascinating. Is there a book about the history of
| microphones?
|
| I find this to all be in the realm of "I don't believe
| you that any of this works at all" if I didn't have a
| lifetime of experience with the fruits of successfully-
| functioning microphones.
| immibis wrote:
| Many types measure the derivative of air pressure. One
| that measures absolute air pressure can be used for
| calibration.
| amluto wrote:
| I'm not sure how the speed of sound could depend on altitude,
| even in principle. The air doesn't know where it is!
|
| Putting that aside, in an ideal gas, the speed of sound
| depends on the composition of the gas and the temperature
| and, interestingly, does not depend on pressure, and pressure
| is the main way that the altitude would affect the speed of
| sound. So measuring the speed of sound in air actually makes
| for a pretty good thermometer.
|
| https://en.wikipedia.org/wiki/Speed_of_sound
| pants2 wrote:
| In liquids the speed of sound is related to the density, I
| would have thought similar for air but I see your point.
| Very insightful!
| adolph wrote:
| Can an ideal gas of same volume, mass and temperature be
| brought to different pressures?
|
| https://courses.lumenlearning.com/suny-
| physics/chapter/13-3-...
| amluto wrote:
| Not unless you change the average mass of the molecules.
|
| An ideal gas' pressure is a function of number of
| particles per unit volume, its temperature, and nothing
| else. If you do anything involving adding or removing
| heat or _changing_ the volume or pressure, you probably
| also need to know the specific heat at constant volume
| and the specific heat at constant pressure or, frequency,
| their ratio. That ratio is called the adiabatic index or
| the heat capacity ratio, it's written as gamma, and it's
| the last parameter in the speed of sound of an ideal gas.
| Interestingly, it doesn't vary all that much between
| different gasses.
| KennyBlanken wrote:
| From your own link:
|
| "The speed has a weak dependence on frequency and pressure
| in ordinary air, deviating slightly from ideal behavior."
|
| "The speed of sound is raised by humidity. The difference
| between 0% and 100% humidity is about 1.5 m/s at standard
| pressure and temperature, but the size of the humidity
| effect _increases dramatically with temperature_. "
|
| "Slight" can matter significantly in an application like
| this.
| amluto wrote:
| > the size of the humidity effect increases dramatically
| with temperature.
|
| This has little do with the behavior of sound. The
| fraction of the air that consists of water vapor at 100%
| relative is very small at cool temperatures and increases
| to 100% at 100 degrees C.
|
| (Yes, water boils at the temperature at which air that is
| saturated with water vapor is all water vapor.)
| t0mas88 wrote:
| The speed of sound fluctuates with density. Altitude and
| temperature both change density.
| kqr wrote:
| Oh yeah. I realised this the day I discovered my fancy digital
| SLR was a thermometer: https://entropicthoughts.com/does-my-
| dslr-have-dead-pixels
| djmips wrote:
| A lot of people like myself consider heat a form of light but
| I guess a photographer would be just thinking visible light.
| They say that about 50% of the sun's light emissions comes in
| the infrared frequencies.
| kqr wrote:
| That seems like a mistake since heat can transfer e.g. via
| contact without any electromagnetic emission. In fact, that
| is what I think happens with the sensor also, given that
| there is an IR filter in front of it.
|
| But I may misunderstand your comment.
| pletnes wrote:
| Visible light from the sun, or incandescent lights, is also
| emitted due to heat. Planck's law is the mathematical
| relation if you want to know more.
| glitchc wrote:
| Yup, it's called dark noise. Random generation of electrpns
| which sometimes find their way into the depletion region.
| danielheath wrote:
| Back in high school, I built (with some parental assistance) an
| apparatus to measure how quickly the pressure would drop (in a
| pressurized cylinder) when a very small hole allowed air to
| leak out.
|
| Turns out, not only can you measure temperature that way, but
| can extrapolate the graph out to find absolute zero (IIRC my
| result was out by about 20 kelvin, which I think is pretty damn
| good for a high-school-garage project).
| Horffupolde wrote:
| No, there you are measuring R, assuming the air inside the
| cylinder was an ideal gas.
| analog31 wrote:
| >>>> Reminds me of the electronics adage: "all sensors are
| temperature sensors, some measure other things as well."
|
| A corollary that's one of my rules to live by: Never measure
| anything over time without also measuring the ambient
| temperature.
| mastersummoner wrote:
| Not really related, but the way you chose to indicate a
| comment here immediately made me think you had merge
| conflicts.
| mnky9800n wrote:
| a colleague of mine spent months analysing fluctuations in
| narrow band signal from a geophone only for a more senior
| colleague to get fed up with it and demonstrated that actually
| the fluctuations simply correlate with the air temperature and
| do so within the spec sheets reported temperature tolerance.
| adamcharnock wrote:
| I would love to see this come to our various mobile devices in a
| nicely packaged form. I think part of what is holding back
| assistants, universal-translators, etc, is poor audio. Both
| reducing noise and being able to detect direction has a huge
| potential to help (I want to live-translate a group conversation
| around a dining table, for example).
|
| Firstly it would be great if my phone + headphones could combine
| the microphones to this end. But what if all phones in the
| immediate vicinity could cooperate to provide high quality
| directional audio? (Assuming privacy issues could be addressed).
| hatsunearu wrote:
| It's already kind of implemented.
| abecedarius wrote:
| For the hard of hearing like me the killer application would be
| live transcription in a noisy setting like a meetup or party,
| with source separation and grouping of speech from different
| speakers. Could be life-changing.
|
| (Android's Live Transcribe is very good now but doesn't even
| try to separate which words are from different speakers.)
| adolph wrote:
| * Automatic speech recognition (ASR) systems have progressed
| to the point where humans can interact with computing devices
| using speech. However, the distance between a device and the
| speaker will cause a loss in speech quality and therefore
| impact the effectiveness of ASR performance. As such, there
| is a greater need to have reliable voice capture for far-
| field speech recognition. The launch of Amazon Echo devices
| prompted the use of far-field ASR in the consumer electronics
| space, as it allows its users to interact with the device
| from several meters away by using microphone array processing
| techniques.*
|
| https://assets.amazon.science/da/c2/71f5f9fa49f585a4616e49d5.
| ..
| MVissers wrote:
| I believe modern macbook pro's already have multiple
| microphones that probably do some phase-array magic.
| refulgentis wrote:
| Pretty much every device does, the trick always was if it
| actually worked, which Apple is assuredly great at. (source:
| worked on Google Assistant)
| quantadev wrote:
| In general the position of the microphones in space must be
| known precisely for the phase shifting math to be done well,
| and also the clocks on the phones would need to be in sync at
| high precision like 10x the highest frequency sound you're
| picking up. In other words within 10s of thousands of a second.
| Also if the array mic locations is not a simple straight line,
| circle, or other simple geometry the computer code (ie. math)
| to milk out an improved signal becomes very difficult.
| NavinF wrote:
| > 10s of thousands of a second
|
| 10ms? That's a _very_ long time. Phone clocks are much more
| accurate than that because they 're synced to the atomic
| clocks in cell towers and GPS satellites.
|
| Hell even NTP can do 1ms over the internet. AFAIK the only
| modern devices with >10ms inaccurate clocks by default are
| Windows desktops. I complained about that before because it
| screwed up my one-way latency measurements:
| https://github.com/microsoft/WSL/issues/6310
|
| I solved that problem by RTFM and toggling some settings
| until I got the same accuracy as Linux:
| https://learn.microsoft.com/en-us/windows-
| server/networking/...
|
| Anyway I dunno why the math would be too complicated, GPUs
| are great at this kind of signal processing
| quantadev wrote:
| What I meant by that millisecond order of magnitude was
| that the clocks on the phones would need to be highly
| synchronized, with each other, to high precision, which
| would require pre-planning and special efforts.
|
| In 10ms sound can travel about 3 meters, which is on the
| order of magnitude of a room, and represents the range of
| time offsets we're talking about. This has nothing to do
| with the actual frequencies of the sound itself, or the
| rate of PCM-type sampling you need to record quality sound.
| That's a different issue, and doesn't have to do with
| synchronization of different devices.
|
| Regarding the math: A circular array is better than a grid
| (or random placement) because there's only one single math
| formula that's used to compare any mic to any other mic.
| With a grid array the number of unique formulas involved
| goes up as the square of the size of the array. And the
| mics at the 'center' of a grid are basically worthless, and
| offer no added value.
| spaceywilly wrote:
| This is known as the Cocktail Party Problem. It turns out or
| brains do an incredible amount of processing to allow us to
| understand a person talking to us in a noisy room.
|
| https://en.wikipedia.org/wiki/Cocktail_party_effect?wprov=sf...
| gizajob wrote:
| What about a soundfield microphone? Does about the same thing and
| the electronics can be done in the analogue domain.
| radiowave wrote:
| At a rough guess from the audio samples, that array is
| producing an acceptance angle much narrower than any Soundfield
| mic is capable of. The noise source is only 45 degrees off-
| axis; I'd say any first-order microphone polar pattern (i.e.
| those a Soundfield mic is capable of) would capture more of the
| noise than is demonstrated here.
|
| Of course, you can improve on the rejection of off-axis sound
| by instead using a microphone with a more specialized polar
| patten (e.g. a shotgun mic), but then you lose the property of
| the pattern being steerable merely by signal processing.
|
| Lastly, such an array of dirt cheap pressure sensitive mic
| capsules with some clever computation behind them strikes me as
| the sort of thing you could throw Moore's law at, if you could
| justify the quantity. Whereas, Soundfield mics don't make much
| sense unless you're working with very precisely machined
| pressure-gradient capsules.
|
| Still, I get the feeling it'll be a while yet before this
| technique starts looking viable for audio production work, but
| it's very interesting.
| hinkley wrote:
| Boeing ginned up a spherical version of these and used it on 787
| prototypes to identify candidates for sound deadening material.
|
| Apparently in loud situations like airplanes, audio illusions can
| make a sound appear to come from a different spot than it really
| is. And when you have a weight budget for sound dampening
| material it matters if you hit the 80/20 sweet spot or not.
| jcims wrote:
| Look up acoustic cameras on YouTube, there are some pretty
| impressive demonstrations of their capability. This is one of the
| companies I've been watching for a while, but it looks like FLIR
| and some other big names are getting into it:
| https://www.youtube.com/@gfaitechgmbh
|
| The one use case that is both creepy and interesting to me is
| recording a public space and then after the fact 'zooming in' to
| conversations between individuals.
| sipjca wrote:
| I am very interested in how small these arrays can be. From
| talking with a friend with cochlear implants, I would assume
| this could help dramatically with the right signal processing
| to help him hear.
| pftburger wrote:
| I wonder if there is a meaningful limit to number of listening
| zones. I'm imagining a 3d grid of virtual mics in a space, each
| with an AI behind it
|
| Heck, train the model on the raw sensor data and you get the most
| awesome conference mics
| beambot wrote:
| Starting to see more & more of this with drones. In some cases,
| it's for military to detect drones nearby. In others, it's being
| used by drone delivery companies to detect other planes in the
| sky in a way that is cheaper, works in low-visibility, and
| doesn't use the same power requirements as radar.
| dchichkov wrote:
| I'm curious, why haven't you used TDM I2S microphones for your
| array and used PDM?
|
| I understand that ICS-52000 is a relatively low cost ($2/100pcs)
| and there are even breakout boards available with 4 microphones,
| which can be chained to 8 or 16, like
| https://www.cdiweb.com/datasheets/notwired/ds-nw-aud-ics5200...
|
| Then you can take Jetson (or any I2S capable hardware with DSP or
| GPU on it) and chain 16 microphones per I2S port. It would seem a
| lot easier to assemble and probgam, if comared to FPGA setup.
| morcheeba wrote:
| Not OP, but I looked in to this a few years ago. It was more
| expensive then, and only went to 20 kHz. Higher frequencies are
| helpful if you're listening for the hiss of leaking gas, or
| corona discharge of an electric arc.
|
| The Orin has 6xI2S ports internally, so that would work up to
| 16*6 = 96 microphones, which is a good number. But it looks
| like maybe only 3 are brought out & on different dev board
| connectors [1]? As with a lot of design, the devil is in the
| details. An FPGA could be easier to configure if you need more
| than 96 microphones.
|
| My notes:
|
| ICS-52000 $3.50, 20 kHz
|
| ICS-41350 $1.05, 40 kHz
|
| SPH0641LU4H-1 $1.45, 80 kHz+
|
| [1]
| https://docs.nvidia.com/jetson/archives/r34.1/DeveloperGuide...
| tverbeure wrote:
| I've considered making a phased array myself, but never got
| around to sending out the PCB. But here are two reasons by I2S
| is not the best option:
|
| * I2S requires 3 instead of the 2 pins of PDM. However, in the
| datasheet that you provided, it shows how you can daisy-chain
| microphones which is really cool (even if not standard I2S.) So
| that argument goes away.
|
| * PDM gives you access to way higher sample rates which in
| turns gives you more flexibility in choosing the delay for a
| delay-and-sum operation. For example, if the PDM clock is 2MHz,
| you could theoretically delay with a precision of 0.5us. In
| practice, you'll do that with lower precision, but with I2S,
| the clock will typically max out at 192kHz.
|
| * PDM microphones then do be cheaper.
| belzebalex wrote:
| 1) and 3) are valid, but 2) isn't really. In that sort of
| pipeline, you usually do IQ sampling which allows you to
| phase-shift by any arbitrary value with a complex
| multiplication.
| tverbeure wrote:
| Do you have a link that explains this? I'm definitely a
| beginner about this.
| kindiana wrote:
| (OP here) tverbeure hit most of the main points, but mostly
| cost ($2/mic vs $0.5/mic adds up when there are 192
| microphones), difficulty of finding things with enough i2s
| interfaces (even with 16 way daisy chaining, thats still more
| than most/all things will have). The FPGA/custom hardware was
| part of the fun as well!
| dchichkov wrote:
| Yeah, I've also had difficulty finding something with enough
| I2S. It was a while back and I've used Sprocket carrier for
| Jetson TX2 - it had 6 lanes, so up to 96. It was for a SODAR
| application, so the sampling frequency was not that critical
| and to me it felt like the perfect trick to make an array
| with off-the-shelf hardware. So I was just curious, if this
| was something you've considered.
|
| For something indoors, yes, I can see how low sampling
| frequency gets very limiting. And 192 microphones, that's
| really pushing it. Love it.
|
| The $2/mic vs $0.5/mic argument is a fun one. You've
| obviously poured enormous amount of engineering in there,
| involving PCB design, FPGA and network programming, writing
| custom CUDA kernels, signal processing, PyTorch, the list
| goes on. And you've had 4090 plugged in your PC in 2023.
| Classic hobbit in a mithril vest ;)
| djmips wrote:
| This has been on my to-do list since forever! Nice work Ben Wang.
| cma wrote:
| Could this be combined with a smaller number of high quality mics
| and then machine learning or something else incorporating them to
| boost the overall quality while maintaining all the other
| features?
| markhahn wrote:
| afaik, it really depends on the spatial structure of the audio
| field.
|
| think nyquist sampling rates, applied to space, and you can't
| apply a low-pass filter just because you don't care about
| higher-order signals. that means that for any given audio
| environment, there will be some "spatial spectrum" of signal,
| and you need to sample it densely enough to avoid aliasing.
| jensenbox wrote:
| Why a radial pattern and not a grid?
| quantadev wrote:
| Because the distance between the mics needs to be 1) large and
| 2) consistent. It would work with a grid but the mics near the
| middle would be "underutilized" (not maximally taken advantage
| of), and also in a grid the mathematics is horrendous, but with
| a circle it's simple.
| kindiana wrote:
| (OP here) Primary reason is that you can make a big array with
| only 2 boards, a small board in the middle and a bunch of long
| boards around it.
|
| Radial pattern of linear arrays with exponential spacing should
| also be pretty close to optimal for the distribution of
| pairwise microphone distances to maximize the gain with a fixed
| number of microphones.
| jsharf wrote:
| Wow, you can refocus the direction after the audio is recorded!
|
| This would be cool to mix with VR, so you could hear different
| conversations as you move around a virtual room
| jojobas wrote:
| Using crab rave for demo is top notch.
| holyknight wrote:
| damn, this is so cool
| kindiana wrote:
| OP here, cool to see so many people are interested in this
| project! Happy to answer any questions (and I'll go around to
| reply to any questions already here)
| peter_retief wrote:
| Is this what is used to find direction of sound or where sound is
| coming from. Like gunshots?
| sfelicio wrote:
| Very very cool.
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