I am the same and presume that is for the USB and 6 mic as ./ec_hw -i plughw:1 -c 8 -l 7 -m 0,1,2,3 doesn’t work.
I can get software ./ec to work as best it can but scratching my head as this does say…
The ReSpeaker Linear 4 Mic Array for Raspberry Pi is a Pi hat with 4 microphones, 2 audio output channels and 2 loopback channels. The 2 loopback channels can be used for Acoustic Echo Cancellation (AEC). It has two parts, the main part and the linear mic array part.
There seems to be no info on the 2 loopback channels and further down the page it gets more confusing.
FAQ
Q1: There are only 4 Mic in the Mic Array, how could it be 8 channels?A1: There are 2 AC108 in this array, and each AC108 chip has 4 channel output. So it comes a total of 8 channels here, 4 of which are for the microphone, two channels for the playback and the the rest 2 channels are not used.
Which is the oppisite of what it says at the top of the page ?!