Phased Array Microphone (2023)

https://benwang.dev/2023/02/26/Phased-Array-Microphone.html

by bglazer • 2 years ago

600 187 2 years ago

amelius• 2 years ago

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

hinkley3• 2 years ago

I’m still sad these didn’t become a thing. I don’t need a 48MP camera phone. No seriously. I do not.

sitkack5• 2 years ago

If you can get a microlens array infront of that 48MP imager, you can have the light field camera you seek.

miloignis• 2 years ago

I believe it can, there's a demo under the "Directional Audio" section, unless I misunderstand you.

dllu4• 2 years ago

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• 2 years ago

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• 2 years ago

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• 2 years ago

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

dllu4• 2 years ago

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• 2 years ago

I had no idea they were mammals until this comment. I thought they were furry birds!

repiret• 2 years ago

It is not unreasonable to think of bats as flying mice.

bafe• 2 years ago

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• 2 years ago

bats (the flying mammal)

As opposed to?

Rygian• 2 years ago

Baseball bats?

lscharen• 2 years ago

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• 2 years ago

Where can I buy one?

NL807• 2 years ago

That sounds like a fun project. Was it part of a research grant?

neumann2• 2 years ago

That sounds super interesting. Is there a write up somewhere of the project?

dllu4• 2 years ago

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

belzebalex2• 2 years ago

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

crote2• 2 years ago

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• 2 years ago

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.

crote2• 2 years ago

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.

brunosan• 2 years ago

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

brudgers2• 2 years ago

Then, why not be a grad student again?

01100011• 2 years ago

Maybe they want to afford dinner?

always_swapping• 2 years ago

I may be the FUS grad student you seek. Reach out via profile email if you want to chat. Cheers!

etrautmann• 2 years ago

Medical applications would presumably require contact coupling and not through air?

zipy124• 2 years ago

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• 2 years ago

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• 2 years ago

What is the most practical application for this technology? Could you use it to pinpoint sounds coming from a car like a squeak?

Salmonfisher114• 2 years ago

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.

pletnes2• 2 years ago

I’ll guess «ultra expensive» partly due to very low volumes made for a customer that can afford a lot.

spankalee• 2 years ago

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• 2 years ago

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

Salmonfisher114• 2 years ago

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.

markedathome• 2 years ago

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• 2 years ago

You just need to buy actual video conferencing gear, this is par for the course.

__MatrixMan__• 2 years ago

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• 2 years ago

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/details?id=radonsoft.net....). This has more color options for the waterfall display.

hammock• 2 years ago

The tech is beamforming .. the applications are AV conferencing, camera tracking, voice lift, or sound reinforcement

cushychicken2• 2 years ago

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.

Salmonfisher114• 2 years ago

If somebody wants to play around with Zynq 7010's - have a look at the EBAZ4205 board. They can be bought from Aliexpress (20-30€). 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• 2 years ago

Xilinx tool chain is also no-cost.

scottapotamas• 2 years ago

For some/smaller parts. Once you start going higher than Artix or the token Kintex parts you need to pay up.

gravypod• 2 years ago

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• 2 years ago

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• 2 years ago

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• 2 years ago

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/

killjoywashere2• 2 years ago

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?

Salmonfisher114• 2 years ago

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.

killjoywashere2• 2 years ago

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!

quantadev4• 2 years ago

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.

frankus2• 2 years ago

"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• 2 years ago

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• 2 years ago

https://en.m.wikipedia.org/wiki/Inertial_measurement_unit

adolph4• 2 years ago

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

01HNNWZ0MV43FF• 2 years ago

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?

nielsole• 2 years ago

Asahi Linux (and likely MacOS too) uses the resistance of the speakers coils to detect overheating of same speakers and reduces volume.

psunavy033• 2 years ago

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.

cameldrv• 2 years ago

Latitude or Longitude?

sam_dam_gai• 2 years ago

Do you mean latitude?

cushychicken2• 2 years ago

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.

frankus2• 2 years ago

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• 2 years ago

Is there one saying “All electronic devices are smoke machines, some can compute too”?

frabert• 2 years ago

"All diodes are light-emitting if you try hard enough"

jaggederest• 2 years ago

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)

qingcharles• 2 years ago

"All electronics are hand-warmers if miscalibrated correctly enough."

ChuckMcM• 2 years ago

"Inside every amplifier is an oscillator trying to get out."

qskousen• 2 years ago

The one I've heard is "Every machine is a smoke machine, if you operate it wrongly enough."

Bearsilber• 2 years ago

I just learned how the Duracell Powercheck© worked, which was done with temperature.

https://youtu.be/zsA3X40nz9w?si=oGg2wdUlLXSDxpsN

entropicdrifter2• 2 years ago

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• 2 years ago

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.

amluto3• 2 years ago

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

t0mas882• 2 years ago

The speed of sound fluctuates with density. Altitude and temperature both change density.

kqr2• 2 years ago

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

djmips2• 2 years ago

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.

glitchc• 2 years ago

Yup, it's called dark noise. Random generation of electrpns which sometimes find their way into the depletion region.

danielheath• 2 years ago

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• 2 years ago

No, there you are measuring R, assuming the air inside the cylinder was an ideal gas.

analog31• 2 years ago

>>> 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• 2 years ago

Not really related, but the way you chose to indicate a comment here immediately made me think you had merge conflicts.

mnky9800n• 2 years ago

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.

UltraSane• 2 years ago

The highest grade gauge blocks use laser interferometry from Mitutoyo have a measured coefficient of thermal expansion AND a uncertainty of that coefficient. And they have a size variance of plus or minus 30nm. That is only about 410 oxygen atoms.

adamcharnock• 2 years ago

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• 2 years ago

It's already kind of implemented.

abecedarius• 2 years ago

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.)

adolph4• 2 years ago

* 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• 2 years ago

I believe modern macbook pro’s already have multiple microphones that probably do some phase-array magic.

refulgentis• 2 years ago

Pretty much every device does, the trick always was if it actually worked, which Apple is assuredly great at. (source: worked on Google Assistant)

quantadev4• 2 years ago

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• 2 years ago

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

spaceywilly• 2 years ago

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• 2 years ago

What about a soundfield microphone? Does about the same thing and the electronics can be done in the analogue domain.

radiowave• 2 years ago

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.

hinkley3• 2 years ago

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• 2 years ago

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• 2 years ago

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• 2 years ago

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• 2 years ago

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.

dchichkov2• 2 years ago

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• 2 years ago

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...

tverbeure2• 2 years ago

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.

belzebalex2• 2 years ago

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.

kindiana4• 2 years ago

(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!

dchichkov2• 2 years ago

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 ;)

djmips2• 2 years ago

This has been on my to-do list since forever! Nice work Ben Wang.

cma• 2 years ago

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• 2 years ago

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• 2 years ago

Why a radial pattern and not a grid?

quantadev4• 2 years ago

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.

kindiana4• 2 years ago

(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• 2 years ago

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• 2 years ago

Using crab rave for demo is top notch.

holyknight• 2 years ago

damn, this is so cool

kindiana4• 2 years ago

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• 2 years ago

Is this what is used to find direction of sound or where sound is coming from. Like gunshots?

sfelicio• 2 years ago

Very very cool.

Phased Array Microphone (2023)

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