audiomixer breaks the audio when trying to downmix
gst-launch-1.0 audiotestsrc ! audio/x-raw,format=F32LE,channels=6 ! audiomixer ! audio/x-raw,channels=2,format=S16LE ! autoaudiosink
produces just noise
gst-launch-1.0 audiotestsrc ! audio/x-raw,format=F32LE,channels=6 ! audiomixer ! audio/x-raw,channels=2,format=S16LE ! autoaudiosink
produces just noise