ReSpeaker 4-Mic Linear Array Kit for Raspberry Pi support 8 input & 8 output channels in Raspbian system. The first 6 input channel for microphone recording(only first 4 input channels are valid capture data), rest of 2 input channel are echo channel of playback. The first 2 output channel for playing, rest of 6 output channel are dummy.
Seems to be totally at odds with what it says later.
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.
ec_hw for devices with hardware audio loopback
For devices such as ReSpeaker Core V2, ReSpeaker 6 Mic Array for Pi and ReSpeaker Linear 4 Mic Array for Pi, audio output is captured as one of the input channels. The audio stream diagram is simpler.+---------+ +-------+ +------+ | | | | | | | | | | | FILE |Microphones ---------->| |--------> | AEC |-------> | FIFO |----> Audio Input
| ADC | | | | |
| | ±------+ ±-----+
| | /
| |__/
| ±--------+ Loopback Channel
|
| ±--------+
| | |
Speakers <-------------| DAC |<------- Audio Output
| |
±--------+
To use ec_hw:Run ./ec_hw -h to show its command line options
Run arecord -L to get audio input devices’ name
Select the audio input device ./ec_hw -i {input device name} -c {input channels} -l {loopback channel} -m {mic channel list}
terminal #1, run ec
./ec_hw -h
./ec -i plughw:1 -c 8 -l 7 -m 0,1,2,3terminal #3, record
cat /tmp/ec.output > 16k_s16le_4_channels.raw
ec_hw uses channel 7 as playback audio, remove the playback from channels 0,1,2,3 and writes processed audio to the FIFO /tmp/ec.output
Does the Linear 4 mic for Pi have loopback for Aec and what channel are they 7?