I am planning to use an external Microphone "ReSpeaker 4Mic Hat" from Seeed-Studio on my RPi3 B+ Stretch OS. However, when I run alsamixer, my external Mic is not the default capture device. It seems like bcm2835 is the default soundcard, which means as default I don't have any capture device.
If I launch audacity, I can successfully record sound with the external microphone.
So, where I can set the default setting for Alsa like: Default Input: "hw1,0", default output: "hw0,0"?
If you have not resolved this, check here: http://wiki.seeedstudio.com/ReSpeaker_4_Mic_Array_for_Raspberry_Pi/
It says: "If we want to change the alsa settings, we can use sudo alsactl --file=ac108_asound.state store to save it. And when we need to use the settings again, copy it to: sudo cp ~/seeed-voicecard/ac108_asound.state /var/lib/alsa/asound.state"