The examples and documentation for the Spresense have a lot of very clear information, yet I think there's something missing for using digital mics with the Arduino IDE. Modifications to the extension board for using digital mics are very clearly documented with nice pictures. The Arduino example projects are great, showing you to record, encode, etc. And I've also understood you must tell the recorder to use the digital microphones with the following:
theAudio->setRecorderMode(AS_SETRECDR_STS_INPUTDEVICE_MIC_D);
There are also nice details in the audio documentation explaining that CXD56_AUDIO_MIC_CHANNEL_SEL must be changed from the default value of 0xFFFF4321, which is for analog microphones, to values for digital microphones. I've been able to follow the instructions for rebuilding the Nuttx kernel and spresense SDK with a new value of 0xCBA98765 which should enable eight digital mics. The last piece that is not clear is what nuttx/sdk binary files now need to be copied over to the Arduino environment. I have a Windows PC for use with the Arduino IDE and I have a Linux PC for building Nuttx and those examples. Can you please list which files on the Linux machine that I need to copy over to the Windows PC for the Arduino IDE to use the SDK that enables the digital mics? Sorry if this is documented somewhere and I overlooked it!
The instructions provided by Sony to record using the digital mic work fine! It was a hardware problem with my microphones. I was able to use the nuttx example named audio_recorder. I haven't tried with Arduino and the process of copying files from a nuttx build to the arduino build folders is still not very clear, but that's a separate issue.