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Phased Array Microphone (2023)

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Re: Phased Array Microphone (2023)

#151

Post by NavinF »

quantadev wrote: post #125
adamcharnock wrote: post #21

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 micr…

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…

> 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

Re: Phased Array Microphone (2023)

#152

Post by ssl-3 »

xyzzy_plugh wrote: post #131
CamperBob2 wrote: post #130

Earlier quoted context omitted.

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.

This is true of all speakers

It's true of all dynamic speakers -- the sort with a voice coil and a magnet.

(But not all speakers are dynamic speakers.)

Re: Phased Array Microphone (2023)

#153

Post by amluto »

KennyBlanken wrote: post #110
amluto wrote: post #59

Earlier quoted context omitted.

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 pr…

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.

> 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.)

Re: Phased Array Microphone (2023)

#154

Post by BobbyTables2 »

xyzzy_plugh wrote: post #131
CamperBob2 wrote: post #130

Earlier quoted context omitted.

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.

This is true of all speakers

But not true of all codecs…

Do you think Apple put a hidden microphone in their devices by pure accident?

Re: Phased Array Microphone (2023)

#155

Post by quantadev »

NavinF wrote: post #151
quantadev wrote: post #125

Earlier quoted context omitted.

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…

> 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://git…

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.

Re: Phased Array Microphone (2023)

#156

Post by nick3443 »

nielsole wrote: post #80
Marthinwurer wrote: post #27

Earlier quoted context omitted.

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.

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

Also used in electric motor controllers to monitor winding temperature.

Re: Phased Array Microphone (2023)

#158

Post by dchichkov »

kindiana wrote: post #147
dchichkov wrote: post #75

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…

(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!

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 ;)

Re: Phased Array Microphone (2023)

#159

Post by pletnes »

djmips wrote: post #86
kqr wrote: post #70

Earlier quoted context omitted.

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

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.

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.

Re: Phased Array Microphone (2023)

#160

Post by pletnes »

Salmonfisher11 wrote: post #9
proee wrote: post #6

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

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.

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