Record sound from USB Tablet microphone with ALSA on Gentoo

Question

I fail at recording sound with a tablets microphone that is connected via USB to my Gentoo Linux.

I checked my settings and see tha USB Microphone is detected.

arecord --list-devices
**** List of CAPTURE Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: AD198x Analog [AD198x Analog]
  Subdevices: 0/2
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
card 1: Device [PrimeSense Device], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: Phone [MT65xx Android Phone], device 0: USB Audio [USB Audio]
  Subdevices: 0/1
  Subdevice #0: subdevice #0

So i assume

arecord -D hw:2,0 -d 5 test.wav

will get me the recordings, but it yields:

arecord: main:722: audio open error: Device or resource busy

Any idea how to find out what causes this? Or am I on the wrong track at all? Do i need a dedicated entry in the asound.conf?

it currently looks like this:

cat /etc/asound.conf
#input device
pcm.AD1989A_inputs {
type multi

slaves.a.pcm "hw:PCH,0,0"
slaves.a.channels 2
slaves.b.pcm "hw:PCH,0,1"
slaves.b.channels 2

bindings.0.slave a
bindings.0.channel 0
bindings.1.slave a
bindings.1.channel 1
bindings.2.slave b
bindings.2.channel 0
bindings.3.slave b
bindings.3.channel 1
}

Maybe the pcm list is also relevant for the solution. So i add it here:

arecord --list-pcms
  sysdefault:CARD=PCH
      HDA Intel PCH, AD198x Analog
      Default Audio Device
  front:CARD=PCH,DEV=0
      HDA Intel PCH, AD198x Analog
      Front speakers
  surround40:CARD=PCH,DEV=0
      HDA Intel PCH, AD198x Analog
      4.0 Surround output to Front and Rear speakers
  surround41:CARD=PCH,DEV=0
      HDA Intel PCH, AD198x Analog
      4.1 Surround output to Front, Rear and Subwoofer speakers
  surround50:CARD=PCH,DEV=0
      HDA Intel PCH, AD198x Analog
      5.0 Surround output to Front, Center and Rear speakers
  surround51:CARD=PCH,DEV=0
      HDA Intel PCH, AD198x Analog
      5.1 Surround output to Front, Center, Rear and Subwoofer speakers
  surround71:CARD=PCH,DEV=0
      HDA Intel PCH, AD198x Analog
      7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
  sysdefault:CARD=Device
      PrimeSense Device, USB Audio
      Default Audio Device
  front:CARD=Device,DEV=0
      PrimeSense Device, USB Audio
      Front speakers
  surround40:CARD=Device,DEV=0
      PrimeSense Device, USB Audio
      4.0 Surround output to Front and Rear speakers
  surround41:CARD=Device,DEV=0
      PrimeSense Device, USB Audio
      4.1 Surround output to Front, Rear and Subwoofer speakers
  surround50:CARD=Device,DEV=0
      PrimeSense Device, USB Audio
      5.0 Surround output to Front, Center and Rear speakers
  surround51:CARD=Device,DEV=0
      PrimeSense Device, USB Audio
      5.1 Surround output to Front, Center, Rear and Subwoofer speakers
  surround71:CARD=Device,DEV=0
      PrimeSense Device, USB Audio
      7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
  iec958:CARD=Device,DEV=0
      PrimeSense Device, USB Audio
      IEC958 (S/PDIF) Digital Audio Output
  sysdefault:CARD=Phone
      MT65xx Android Phone, USB Audio
      Default Audio Device
  front:CARD=Phone,DEV=0
      MT65xx Android Phone, USB Audio
      Front speakers
  surround40:CARD=Phone,DEV=0
      MT65xx Android Phone, USB Audio
      4.0 Surround output to Front and Rear speakers
  surround41:CARD=Phone,DEV=0
      MT65xx Android Phone, USB Audio
      4.1 Surround output to Front, Rear and Subwoofer speakers
  surround50:CARD=Phone,DEV=0
      MT65xx Android Phone, USB Audio
      5.0 Surround output to Front, Center and Rear speakers
  surround51:CARD=Phone,DEV=0
      MT65xx Android Phone, USB Audio
      5.1 Surround output to Front, Center, Rear and Subwoofer speakers
  surround71:CARD=Phone,DEV=0
      MT65xx Android Phone, USB Audio
      7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
  iec958:CARD=Phone,DEV=0
      MT65xx Android Phone, USB Audio
      IEC958 (S/PDIF) Digital Audio Output