https://wiki.seeedstudio.com/ReSpeaker_Mic_Array_v2.0/
How to make Raspberry Pi use an external USB sound card as a default
Play sounds
aplay /home/pi/work/debug/audio/piano2.wav
omxplayer /home/pi/work/debug/audio/file_example_MP3_700KB.mp3
Record sounds
cd /home/pi/work/debug/audio/
arecord -D plughw:0,0 -f cd test.wav # record, please use the arecord -l to check the card and hardware first
aplay -D plughw:0,0 -f cd test.wav # play, please use the aplay -l to check the card and hardware first
arecord -D plughw:0,0 -f cd |aplay -D plughw:0,0 -f cd # record and play at the same time
Only do this after pulseaudio has been installed and the ReSpeaker shows up as the default audio device in Volume Control.
https://scribles.net/enabling-equalizer-on-raspberry-pi-using-alsa-equal-plugin/
If there is no sound:
First check if there is power to the amp. Currently, it's being powered by the bench power supply but later, it will be powered by the alim board. 8V from the bench power supply is enough to power the amp.
On the raspberry pi, try running the following command:
aplay /home/pi/work/debug/audio/piano2.wav
aplay -D plughw:0,0 /home/pi/work/debug/audio/piano2.wav
If you don't hear the piano playing, try this:
aplay -D plughw:0,0 /home/pi/work/debug/audio/piano2.wav
If this worked, it means that the raspberry pi isn't using the respeaker as the default audio device.
You can also log into the desktop of the raspberry pi 4 via RDP and check what the default audio device is set to in the Volume Control. If it's set to "Dummy Output", then it's not using Respeaker as the default audio device.
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If the default audio device is set correctly, it should look like this in the Volume Control:
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Solution - Restart the raspberry pi. Usually, this happens after some new sound apps or packages. The raspberry pi loses the default audio device. Restarting it usually resets it.
If that still doesn't work, follow the instructions here for reinstalling pulseaudio: