Ambisonic USB mic from surplus bits

[Tubetec]

Around 15 years ago I experimented using the playstation 3 eye mic array with Voxengo Php-929 phase align plugin to create a beam former , it worked very well ,but the hardware was limited to 16khz/16 bit . The PS4 eye has an OV580 USB camera bridge and AK 5703 A/D , it will do 4 channels at 48khz 24 bit .
Theres a few other Ambisonic type mics around but they cost hundreds or thousands and many still use the same cheap electret capsules like MiniDSP's ambimic .
The first generation Sony PS4 camera can be easily found now second hand for around 20 euros , it has the mics wired in on a header plug making it easy to try out other capsules without having to solder to the board directly . The main issue is the mic is its designed for speech and overloads on loud sounds .
I was thinking , could I use a lorlin 4 pole 3 way switch to make an attenuator to go between the mics and the A/D board ?
Obviously I'd need to supply capsule bias to the input input side of the attenuator ,something like 0, -10, -20db steps would be perfect .
The AK5703 has around 100kohms input impedence and needs around 1.8 volts p-p to be fully driven with minimum gain .
It can be fed unbalanced or balanced signal directly from the capsule as shown below .

I found some 16mm cardioid electret capsules , it looks like there around 10db more sensitive than the usual mini electret .
It has a thread at the back which should make it easy to mount up in the usual tetrahedral config .

Maybe someone could walk me through how to design the attenuator with respect to the impedences involved . Seeing as balanced opperation is possible it might be the best way to go .

Theres a few issues with the Sony camera/mic out of the box , it has a propropreitary Sony connector , but a USB 3 adapter is readily available , theres also a third party firmware that can be loaded up , its open source on github , so there might even be a possibility to customise the firmware to better suit a particular application .

 

[Tubetec]

I picked up a second hand PS4 eye today for 20 euros and I also threw in an Xbox 360 kinect camera for 2 euros just to see whats inside , it also has a microphone array .
The new PS5 camera costs only 39 euros but has no built in mic, its now built into the controler , so Id expect the old PS4 cam to be going for next to nothing in the near future .

I see that Sony is giving out a free AUX to USB connector so users of PS4 software can have VR compatibillity in the PS5 , Its seems Sony want you sign up and they'll send you out the part free , I might try the game shop to see if Sony provide it to them .
https://www.playstation.com/en-us/support/hardware/playstation-camera-adaptor/
I have the camera dismantled now , the board is roughly 11cm long by 22mm wide , would easily fit in a mic body .
All the components on the board are tiny so no chance to rework it , Im not sure if Sony adopted the balanced or unbalanced , but I dont measure any connection between the black wires to each capsule , so I assume its balanced .
For anyone who wants a closer look at the pcb ,
https://www.ifixit.com/Teardown/PlayStation+4+Camera+Teardown/26783

 

[kingkorg]

I've been digging into this a little bitt. The question might be where the clipping happens. And if the capsules have built in fet/what kind of polar pattern capsules are. Some capsules overload easily because of the construction. Some because of the fet/bias or if diodes are used instead of high value resistor.

Do theese Eye cams have built in compressor/limiter? Most of the devices using mems mics these days use compression to protect the ad from overloading.

 

[Tubetec]

Its got regular mini electret capsules , omni patern
It has hardware AVC processing on the Ak5703 , which can be dissabled .
The input to the ADC only takes 1.8 volts max ,so I suspect its the input distorts first .
Maybe an external bias voltage could help also ,as the internal is limited to around 2.5 volts where electret capsules can typically withstand higher supply voltages .
I have the camera already , now I need to source the PSVR> PS5 usb adapter cable to be able to make it work with PC . Sony are giving this accessory out for free but I cant seem to fill out the form on their site , it also requires the serial number of your PSVR , which I dont have .

 

[Tubetec]

The older PS3 cam/mic I used in the test years ago had no means of varying the gain at the front end , the newer mic has the ablility to vary the input gain via driver/ software so it should be much better with regards higher SPL sources .
That being said some extra switchable attenuation up front could extend the useble range further in conjunction with higher bias voltages .

 

[Tubetec]

I talked to a girl at the game store who told me Sony were still sending out the cables free , but again the same issue of difficulty on the website.
Sony has an office here in Ireland I might try calling them and seeing if they send me it out .

I had a casual look at whats on the market in terms of ambisonics , on the lower end its more or less all geared towards internet voice communication mainly mems , there a few measurement mics usually electret , then the high end studio gear which cost huge money , often they require there own outboard preamp/mixer/signal conditioner to go along with it .

Ambisonic capsule arrangements come in a couple of forms , some mount omni mics on the surface of a sphere a bit like the M50. Others omni or directional mics on their own limb from a central point .
First order, second order depending on the number of mics in the array .
The better audio mics seem to use traditional mylar dual sided capsules suspended at their edges with free air behind .
I know from experience with the linear array and VST you are actually combining pairs of omni sources with various degrees of phase to steer the beam , how does it work with counter poised or linear figure 8 elements ?

In the 4 channel circuit below , can I use two acoustically coupled 16mm directional electret capsules back to back across each channel? If the backside capsule in each opposing pair was powered by the AK5703's internal switchable mic supply and outer powered permanently it would be possible to switch either pair of elements in the array from cardioid to figure 8 ,note it has independantly switchable A and B mic power circuits .



In this example the guy places two electret capsules side by side and arranges a switch to add the second capsule both in and out of phase giving omni cardioid and figure of 8 . I like the idea , his implementation could do with improvement .
https://audioimprov.com/AudioImprov/Mics/Entries/2016/7/8_A_Three-Pattern_Electret_Mic.html

 

[cyrano]

The most common setup is four microphones pointing in four directions, like the Core Sound Tetra.

I built one like that a few years ago, using AT854 hanging mics. Worked well, but I only did one real recording with it. Due to unfortunate circumstances, I forgot to note directions for the four channels, so it was a bit of a learning experience...

Now, the plan is to build one with 8 capsules, to get to HOA. But I haven't recorded anything since COVID started, so I'm not in a hurry.

I'm still learning the ins and outs of ambisonics. When it comes to plugins, there's a lot of good free stuff around, but all DAWs seem to have some disadvantages. I use Reaper, but it lacks an ambi panner. That's being worked upon atm.

 

[Tubetec]

Voxengo PH-979 gave me all I needed in terms of processing , I hate the needless graphics on most ambisonic USB kit now , close your eyes, listen and adjust to taste , disconnect the visual senses from the process entirely .

Id still highly reccomend the PS3 eye for experimental purposes in microphone array processing via VSt/daw before commiting more than ten bucks if you want to be sure of the sonic value .

 

[Tubetec]

Two Ps4 cams with adapter cables on a USB 3 hub should get you 8 audio channels and four eyes

 

[cyrano]

Yes, but the mics are in a different order. Are you sure that will work? Or are you counting on replacing and moving the mics?

I actually considered the PS3 mic before I started my experiment, but abandoned the idea. I can't remember exactly why. Maybe I couldn't find the PS3 mic at that time?

When I started experimenting, having precisely controllable gain on the mic preamp and selected capsules (same freq curve) seemed very important. It is, but I'm a bit less anal about it.

In fact, the first try I did was with four electrets from a comparable setup that came from a directional mic from an early teleconferencing system. But these did not match well.

Anyhow, the plugins I prefer:

https://plugins.iem.at/
Another good set is the SPARTA set:

https://leomccormack.github.io/sparta-site/

 

[Tubetec]

The Ambisonic tool kit has a native Reaper plugin that might be worth a look .
Im really glad to see plenty of open source processing , its really come a long way since the last time I looked

Im just looking at the Xbox 360 kinect now , as far as audio is concerned it only does 16bit 16khz
but its quite a substantial box of tricks , not only does it have the 4 mic array but also motorised pan and tilt ,
The mic capsules are standard directional electret mounted in a rubber boot with a port front and back , everything is wired nicely with two core screened cable back to the board , it looks like really usable stuff in conjunction with the Sony board .
A PZM style mic with the four elements might be an interesting use for these capsules , the spacing could be accounted for in software The usual benefits of PZM's would apply with the addition of beamforming





teardown here
https://www.ifixit.com/Teardown/Xbox+360+Kinect+Teardown/4066
The mems although compact typically have the worst performance , the mini electret is a little better ,
16mm electrets appear to improve things a bit further in terms of frequency response, sensitivity and directionality ,
They can be had for less than 5 euros each , which keeps the cost in reasonable proportion with the other components .
I wasnt worried about calibration of the PS3 eye for use as an ambience recording mic , I made any nessesary compensation on the DAW/VST end after .

 

[Tubetec]

https://en.wikipedia.org/wiki/AmbisonicsThe basics are well laid out there ,
It seems the better Ambisonic mics use figure 8 patern capsules , electret come mainly in either omni or cardioid .


Lets say we have a balanced input as shown below in the AK5703 diagram ,
can I mount two electret/fet capsules acoustically coupled, back to back , grounding the case of both and apply mic power to both positive terminals of the capsules and derive a figure 8 polar patern ?

The AK chip allows balanced or unbalanced input to be selected via software , it also allows mic power to be set on or off on two lines . That could give the possibility of remote capsule switching .

When you mix ambisonic channels to stereo typically the vertical axis sound is not needed . The tetra array has its own shortcomings , like time of arrival difference and all kinds of defrations of the sound wave that software cant un-do .

I like the idea of the horizontal point source with four capsules mounted in a line vertically , its basically dual XY stereo mics .
There is of course time of arrival difference from sounds in the vertical plane but the figure 8 null takes care of that very nicely . It reduces the need for processing compared to the tetra and likely better resolves localisation through time of arrival difference at least horizontally ,which is the axis were interested in when we listen to music or trying to locate a ground based sound source .

I see a company called Brahma do a modified Zoom handheld with ambisonic , the newer Zoom mini appears to have both X-Y and M-S ,
hmmmm thats a nice idea, and easy to arrange in a vertical stack for time alignment without resorting to dsp ,
Probably just as easy to do it with four pairs of electrets and figure out a way of dropping the back element on the on M channel .

 

[cyrano]

I know some of that. I've known about Brahma's mics for years nows. I do need height information. Brahma's designer has been on the sursound mailing list since like, forever.

The first mic array I tried was 3 horizontal and 1 for height info (small electrets). That didn't work for me, so I tried a four mic Soundfield-like setup. That works.

What I learned was that you need mics that are very close in level and frequency curve. Gain can be easily adjusted, of course, but you can't EQ frequency curve differences. Or maybe I just haven't found the right EQ. Could be it needs to be linear phase?

I've never tried the double MS setup, since I don't have two figure-of-eight mics at hand. I don't think it's the easiest way to go either. At least, that's what I hear from people who've been using it for classical music recording, usually with Sennheiser MKH mics. Not a cheap setup either...

My first and only real recording with my four mic setup worked pretty well. Unfortunately, the mic was too close to the public, so a lot of their comments slipped into the recording.

Next I will be experimenting with an eight mic setup. Whenever time allows...

 

[Tubetec]

I got the USB adapter cable for the PS4 eye finally , should allow access to the 4 audio streams as independant chanells in any DAW , requires a third party driver for windows for the video ,but the audio may well be plug and play.
I might give an initial check to see if the audio is recognisned without the video plugin ,rtaher than install some spurious 3rd party software

 

[Tubetec]

Ive tried various approaches to installing a driver for the cam but on my system I cant get it to work properly .
The drivers have to be installed seperatey ,first the boot loader , then the driver gets loaded into memory , last the computer uploads a file to the device and updates the flash memory .

Theres a video here where the guy goes through everything , he uses device manager , usb tree and his own driver , I'm using the Sony adapter ,but I get the error he demonstrates via USB2 socket , even though my device shows up as USB 3 in USBTREE viewer .
It can be hard to remove the rementants of older drivers from windows , and sometimes the whole USB stack ends up messed up for that device , Ive tried installing from a fresh install , still other errors , dll components missing etc ,
I'm pretty sure if it was Win 11 if would load right up , I think I'm missing an add-on component in my version of Windows .



All the software is available from the links ,