root@Arduino:/mnt/sda1# amixer contents
numid=1,iface=MIXER,name='Mic Playback Switch'
  ; type=BOOLEAN,access=rw------,values=1
  : values=off
numid=2,iface=MIXER,name='Mic Playback Volume'
  ; type=INTEGER,access=rw---R--,values=1,min=0,max=32,step=0
  : values=23
  | dBminmax-min=0.00dB,max=47.81dB
numid=5,iface=MIXER,name='Mic Capture Switch'
  ; type=BOOLEAN,access=rw------,values=1
  : values=on
numid=6,iface=MIXER,name='Mic Capture Volume'
  ; type=INTEGER,access=rw---R--,values=1,min=0,max=16,step=0
  : values=0
  | dBminmax-min=0.00dB,max=23.81dB
numid=7,iface=MIXER,name='Auto Gain Control'
  ; type=BOOLEAN,access=rw------,values=1
  : values=on
numid=3,iface=MIXER,name='Speaker Playback Switch'
  ; type=BOOLEAN,access=rw------,values=1
  : values=on
numid=4,iface=MIXER,name='Speaker Playback Volume'
  ; type=INTEGER,access=rw---R--,values=2,min=0,max=151,step=0
  : values=150,150
  | dBminmax-min=-28.37dB,max=0.06dB
root@Arduino:/mnt/sda1# amixer scontrols
Simple mixer control 'Speaker',0
Simple mixer control 'Mic',0
Simple mixer control 'Auto Gain Control',0

Set Mic Capture Volume:

amixer sset 'Mic' 10