Disclaimer: As far as this sort of electronics goes I would describe myself as a hobbyist at best. Ask me about computers/servers and I’ll give you a professional opinion but here I’m just feeling in the dark hoping that someone more skilled will get some inspiration!
It’s far less complicated than it looks and the component list is literally what I had lying around:
2 x Microphones with amps:
https://www.flyingtech.co.uk/fpv-camera-gimbals/mini-microphone-fpv-racing-drones
1 x USB connector:
https://www.amazon.co.uk/gp/product/B07PQPGZ9T
1 x 0.1uF Capacitor
1 x 3.5 mm stereo audio jack:
https://www.amazon.co.uk/SiYear-Headphone-Replacement-Adapter-Connector/dp/B07WZT7QGL
1 x Phonak TV Connector v2
The USB connector just supplies 5V to each microphone and the signal and ground wires are then connected to the audio jack. The whole thing is powered by a USB battery pack and is therefore portable.
I added the capacitor as without it there was some noise coming from the power supply. I just randomly grabbed one and didn’t perform any calculations or use a scope.
I did try this with a Bluetooth transmitter and the delay is just too much, especially if you can hear the original sound. With the TV Connector the delay is acceptable and the whole thing works quite well.
The issue with the gain is that the microphones pick up the smallest of sounds and amplifies them. The volume isn’t uncomfortable but reducing the gain would probably help focus more on voices than rustling paper. The volume controls on the TV connector do reduce the volume but don’t do much for the actual gain of the mics.
I don’t know too much about Roger but I do know that licenses need to be enabled in the aids to get it to work so there’s a reasonable cost barrier. It is also a proprietary technology, I’m sure that someone more clever than me could reverse engineer it but I don’t know how happy Phonak would be.
I’ve had a quick look around and it’s definitely possible to cheaply get some quite sophisticated audio processors to provide noise cancellation, dynamic range compression, automatic gain etc.
https://www.st.com/content/st_com/en/products/audio-ics/audio-processors.html