Hi Frank: Thanks for setting me straight on this. That's how I had remembered things- it was only when I saw another post that I thought differently. Seems like the dedicated ADC (PCM1808) is better than codecs in this regard. I was interested to see you had also used various STM32 MCUs with SDR software. I have a STM32F746 Discovery board which I thought would be great for such projects as it has a beautiful 4.3" capacitive touchscreen and a WM8994 audio codec. I used it for some projects but cannot get the audio line in and audio line out to work simultaneously (microphone in and line out is OK). Others have had the same problem, but I expect someone out there has figured it out.
I've tried to use the STM32Cube IDE but find it very difficult to get used to, but I've been more successful using the Mbed platform- it's somewhat like the Teensy in good support, libraries etc.
I just figured out that the Audio library ADCS component has not yet been ported to the T4.x, so my idea of using the internal dual 12-bit ADC is a non-starter.