I am working on the Raspberry Pi versions both the 2Mic and 4Mic HATs and so far the 2Mic version is going well. But I am having problems with the 4Mic version software drivers. I have followed the procedures in the Seeed wiki: http://wiki.seeed.cc/ReSpeaker_4_Mic_Array_for_Raspberry_Pi/
up to installing audacity (Install driver Step 5). All previous steps went ok including step 4 where I verified that the sound card ( 4mic-voicecard) was detected. I was also able to record using 'arecord -Dac108 --duration=20 -f S32_LE -r 16000 -c 4 hello.wav' and terminated that process with 'CTR C'. The problem is that 'aplay hello.wav' is unable to play back the recording and gave me an error message: 'aplay: set_params:1299: Sample format non available. Available formats:- U8 - S16_LE'. I also tried with all valid parameters that the installed aplay did recognise but it did not play back. Audicity also did not record but did recognise the reSpeaker voicecard. Both Steps 5 & 6 did not work.
I also checked the configuration with 'arecord -L' and it recognised the reSpeaker voicecard but 'aplay -L' did not. I saved the alsa settings in /etc and activated SPI for LEDs. These worked correctly with the python demo software. I was able to go beyond this with the 2Mic HAT version but I have not completed google assistant yet.
The question is: I have followed everything in the wiki up to Step 4 and explored beyond with debugging the problem and I repeated the whole process on a separate Raspberry Pi but with the same result. Looks like the 4mic voicecard driver was not installed correctly and the only thing that is different from the wiki is that my Raspberry Pi OS (Stretch) may be more recent that Seeed's version? Perhaps the voicecard driver is not compatible with the latest OS (Stretch)? I also used Stretch with the 2Mic version and everything so far is ok with it. Has anyone else reported a problem with the 4mic driver installation using Stretch? I would also suggest that Step 4 is inadequate for verifying that the sound card was correctly installed. One good thing about the install procedure is that it has test points to check out if a step was correctly followed.