I'm building several voice-controlled embedded systems based on a RPi 3B. When complete, it's embedded in an old phone. Details here.
I'm using a generic USB audio dongle to interface to speakers and microphone. When I test using an old computer headset, it performs reasonably well, but when I use the phone handset the speech recognition degrades significantly. I think this is due to the extra noise I'm getting using the phone's original microphone. The headset mic seems to have an impedance of around 500-800 ohms, whereas the old carbon mic in the phone has an impedance of around 5Kohm.
It would seem that I have two options:
A) Build some sort of impedance matching circuit, maybe using a simple transistor circuit. I'm a little out of my depth here.
2) Replace the original microphone with one that has a better impedance match. Would this electret mic or this one be a good candidate?
Thanks for any advice,
-- Mitch