DIY Open Source Bluetooth Headphones -- Episode 586

oh yes that sounds very interesting, to solve the problems i actually have a fully fledged (small) audio mixer with USB interface.
so its quite overkill and big to solve just me wanting to use normal audio gear instead of a dedicated USB microphone which I usually use.
It basically was the reason apart from recommendations that I got a dedicated podcasting mic with USB.

So the  key features are just controlling of levels and gain directly on the device, and instant working without drivers to install.
I wonder if there are MCUS that can directly support WIn/mac/linux audo device types on native usb...

A good DAC and ADC via I2S and a sturdy compact case would do the trick.

I was thinking along the lines of taking the basic functionality of a USB audio interface something along the lines of this:

https://cpc.farnell.com/behringer/uca202/usb-audio-interface-2-in-2-out/dp/CS20448

and enhancing it somewhat to make it more useful as a problem-solving tool.

One scenario I'm faced with is that a lot more people are relying on Zoom / MS Teams for online meetings these days however, such systems often expect a 2ch stereo USB based audio input/output whereas audio equipment is often still analogue based. Issues often encountered are:

• no USB audio connectivity or USB audio connectivity but needs audio device drivers require installing but no admin rights to do so.
• different analogue standards in use +4dBu on XLR vs -10dBV on RCA/phono so different levels and balanced / unbalanced signalling.
• limited gain adjustment range at one or both ends.
• mic level versus line level signals.
• stereo vs mono.signals.
• no visible level metering (is a signal actually present and if so, how hot is it?)

So, you either tend to require an audio mixer with USB interface or end up with a number of problem-solving boxes and cables. 

A single problem-solving tool that can be simply plugged into the USB port and give you immediate indication if there is a signal present or not and at what sort of level and be able to configure it for mono/stereo operation and to be able to adjust the gains into the right ball-park and to deliver it on XLR or RCA/phono, all without needing to install drivers or a configuration app, would be a valuable tool.

I've not seen anything available off-the-shelf that ticks all the boxes, without going over-the-top.

Also, sometimes you want a problem-solving tool to use yourself and sometimes you want a problem-solving tool that you can mostly pre-configure and then hand to someone else and be able to support remotely over the phone.   

In an ideal world it might end up being an audio interface that has a bidirectional USB to I2S stage followed by a I2S DSP stage and then an analogue IO stage for maximum flexibility. However, to start off with I was thinking of something a bit simpler, basically an open-source USB audio interface with some basic signal mixing, level monitoring and gain control ability, all that can be powered off the USB port it is connected to.

If it was a modular design, people could tailor it to their individual requirements e.g. balanced vs unbalanced outputs, different metering scales, different gain ranges etc. and even build their own custom mixer. I expect a number of people will be familiar with creating analogue audio circuits, but adding USB audio may be a bit new.

So there is the question i nthe room:
is i2S actually closer to SPI than to I2c ?
what do you think?

that sounds indeed like a neat problem solving product! would be cool to elaborate on that.

This was another interesting element14 presents project.

Up until now I've been using the likes of Denon or Radial Engineering Bluetooth receivers:  

https://www.denonpro.com/products/view/dn-200br

https://www.radialeng.com/product/bt-pro

to accommodate those pesky mobile device users... Starts to get expensive when you need to pair with multiple devices.

However, this open-source project looks like this could open up some alternatives and experimentation.

USB Audio 'Class Compliant' interfaces would be another interesting area to explore further. It would be great to have some 'problem-solving' adapters that can plug into a computer USB port without needing additional drivers and provide basic channel mixing / splitting type functionality along with basic level control and metering, ideally all within the limited USB power budget to avoid the need for yet another wall wart power supply.

a kind of recondensation then.

Isn't I2CS the plural of I2C though? 

I seem to vaguely recall that Philips originally named it the 'Inter Integrated Circuit' bus back in the 80's, so IIC or I²C.

Here we have 'Inter IC Sound' bus where 'Integrated Circuit' has already been condensed down to 'IC', so IIS or I²S. 

If it had been 'Inter Integrated Circuit Sound' bus, then I²CS may well have won the day...

Seems that is the answer but inter intergrated circuit sound would be I2CS then...

thanks, I expect most cheap headphones to use purpose built MCUS with integrated DACs . I havent taken apart any commercial offerings so I dont actually know.
in my experience with these designs the bare I2S module has a very basic amp built in and that was just enough taht I wiuld consider it good.
about 30% of the board space on my custom board is taken by the actual stereo amplifier (2 caps o nthe back havent even been populated yet).
So it should be a lot louder. I´d rather have power overhead than to little.

"...To this end, we have developed the inter-IC sound (I2 S) bus – a serial link especially for digital audio..."

https://www.nxp.com/docs/en/user-manual/UM11732.pdf