bash-3.1$ xfce4-mixer 
alsa: error: master control not found. I even tried to guess wildly, but to no avail.
alsa: info: developer information follows: (send E-Mail to Developer with that)
alsa: * Headphone,0
alsa: * Front,0  <--- hint hint
alsa: * Front Mic,0  <--- hint hint
alsa: * Front Mic Boost,0  <--- hint hint
alsa: * Surround,0  <--- hint hint
alsa: * Center,0  <--- hint hint
alsa: * LFE,0  <--- hint hint
alsa: * Side,0  <--- hint hint
alsa: * Line,0  <--- hint hint
alsa: * CD,0  <--- hint hint
alsa: * Mic,0  <--- hint hint
alsa: * Mic Boost,0  <--- hint hint
alsa: * PC Speaker,0  <--- hint hint
alsa: * Capture,0
alsa: * Capture,1
alsa: * Channel Mode,0
alsa: * Input Source,0
alsa: * Input Source,1
alsa: info: end of developer information
alsa: error: master control not found. I even tried to guess wildly, but to no avail.
alsa: info: developer information follows: (send E-Mail to Developer with that)
alsa: * Headphone,0
alsa: * Front,0  <--- hint hint
alsa: * Front Mic,0  <--- hint hint
alsa: * Front Mic Boost,0  <--- hint hint
alsa: * Surround,0  <--- hint hint
alsa: * Center,0  <--- hint hint
alsa: * LFE,0  <--- hint hint
alsa: * Side,0  <--- hint hint
alsa: * Line,0  <--- hint hint
alsa: * CD,0  <--- hint hint
alsa: * Mic,0  <--- hint hint
alsa: * Mic Boost,0  <--- hint hint
alsa: * PC Speaker,0  <--- hint hint
alsa: * Capture,0
alsa: * Capture,1
alsa: * Channel Mode,0
alsa: * Input Source,0
alsa: * Input Source,1
alsa: info: end of developer information
alsa: error: master control not found. I even tried to guess wildly, but to no avail.
alsa: info: developer information follows: (send E-Mail to Developer with that)
alsa: * Headphone,0
alsa: * Front,0  <--- hint hint
alsa: * Front Mic,0  <--- hint hint
alsa: * Front Mic Boost,0  <--- hint hint
alsa: * Surround,0  <--- hint hint
alsa: * Center,0  <--- hint hint
alsa: * LFE,0  <--- hint hint
alsa: * Side,0  <--- hint hint
alsa: * Line,0  <--- hint hint
alsa: * CD,0  <--- hint hint
alsa: * Mic,0  <--- hint hint
alsa: * Mic Boost,0  <--- hint hint
alsa: * PC Speaker,0  <--- hint hint
alsa: * Capture,0
alsa: * Capture,1
alsa: * Channel Mode,0
alsa: * Input Source,0
alsa: * Input Source,1
alsa: info: end of developer information