I want to use an external sound detector/microphone on the STM32F407 (not the MEMS), so how do I pass the audio in via a buffer ? How do I configure the designer to not use the HW input, but a buffer ?
To use a different audio source, you will need to update and recompile the C code in the BSP to access the new audio device. Once you have buffers of audio from this new device, you can interleave it with the existing USB and microphone audio channels to make it available on the HW input pin in Designer. See AudioDriver.c for how this all works.
I am also working on a similar pattern where I have to interface an external condenser microphone to my STM32F407VG board and play the recorded audio through the codec DAC/headphone jack. Please do tell me if you have proceeded further and what could be the correct path to follow. Being a beginner I am through with the block designing and binary file booting into the board.