DIY Open Source Bluetooth Headphones -- Episode 586

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.

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.

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

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.

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.

Other key features are monitoring the signal levels visually, stereo<->mono routing, USB power, and low audio latency.

To conserve power and save space, the monitoring could be a single LED 'bullet' meter which gets brighter as the input level increases. A bi-colour LED could be used to indicate nearing clipping of the USB input. 

The basic routing just needs the ability to mix the stereo LR output from the USB down to a mono output signal to send to the external analogue device and to take the mono return from the external analogue device and to send it to both the USB LR inputs. These should be individually selectable as you can often end up with a mono mic but stereo speakers type scenario.

Not all computer sound drivers provide appropriate or reliable metering or routing functionality.

Yes, I was wondering what MCUs might be able to do this as it would allow the ability to reconfigure the behaviour of the one hardware device in several ways and make it highly flexible.

with all that I would be a bit worried of either the user interface having to many things to still be simple or with typical "one button designs" be cumbersome to use to get through all options quickly. it is a UX challenge as well.
I thought about having two rows of adressable RGB leds, act as VU meter and indicator for settings.
as long as you do nothing --> VU is show vor in/output
When you move or click a rotary encoder, the leds indicate the setting to adjust. click to enter-> adjust ->click to exit.
so GAIN in , Volume out, mono/Stereo in , mono/stereo out,
Am I missing something?

Speaking of USB mics, another problem-solver device waiting to be discovered is how to mix multiple USB mics down to a single USB mic. A number of web conference applications can only handle a single audio input device so if you have a presenter on a USB microphone and want to take a question from the audience or bring in a guest on another microphone, then you may have to reconfigure the audio input device in you web conference application and then reconfigure it back again. Being able to mix the 2 USB audio devices externally would be useful.

There are a few USB audio type problems out there waiting for solutions.

(Similar with USB web cams, I'm only aware of a single (expensive) product at the moment that allows you to switch between two USB webcams externally to the computer. If they are UVC class compliant webcams, then it should be possible to have a driverless solution.)  

oh thats is a whole different can of worms, but also a very interesting one.
I think with a USB-Host capable MCU one could act as an intermediary to pass on only the data not the USb communications form the PC unlike a switch/hub.
So the PC hosts an MCU via USB
the MCU hosts 2 USB devices
data from USb devices get pased on to the pc.
the PC only ever sees 1 device, so for it its the same device that just passes on different data.

the biggest challenge for that might be latency.

To keep it simple, the mono/stereo could perhaps just be a pair of slide switches.

I was concerned about the power consumption of the addressable LED VU meters but it makes for an interesting UX feature.

I think some dinky 20mA leds would be bright enough, no need for fancy neopixels IMO
since the device could fall under the EU- USB-C recommendetion the power limitations of USB 1.1. don't apply really, but having it all doable with 5V @500mA would of course be preferrable for max compability.

slide switches would be the simplest way for passive routing ,but beeing able to mix them lets say via digital pot would be cool...

Yes, that was intended as a separate project idea.  

( The Inogenie devices do the webcam switching:
https://inogeni.com/product/share2u/  )