One other weird thing I noticed while testing this is that setting the volume to 0% and/or muting does the controls does not seem to completely mute the sound - it is just really quiet (quiet enough not to be an issue for me). Some observations:
__Speakers__ Master: Mute AND/OR Speakers: Mute --> Speakers are muted.
Master: 0% AND Speakers: 0% --> Sound still comes from speakers, but is very quiet.
Master: 0% --> speaker control affects volume.
__Headphones__ Master: 0% AND/OR Headphones: 0% --> Sound still comes from headphones at low volume (if either control is 0%, the volume of the other control has no effect - both have to be non-zero to raise the volume).
Master: Mute AND/OR Headphones: Mute --> Sound still comes from headphones, though is fairly quiet (much lower than 0%).
Because the driver select the amp at the pin complex of the headphone instead of the amp at the audio output
These amps have different dB min
Node 0x02 [Audio Output] wcaps 0xd043d: Stereo Amp-Out Stripe Device: name="ID 4208 Analog", type="Audio", device=0 Amp-Out caps: ofs=0x7f, nsteps=0x7f, stepsize=0x01, mute=1 Amp-Out vals: [0x7f 0x7f] Converter: stream=8, channel=0 PCM: rates [0x7f0]: 32000 44100 48000 88200 96000 176400 192000 bits [0x1e]: 16 20 24 32 formats [0x3]: PCM FLOAT Power states: D0 D3 EPSS Power: setting=D0, actual=D0 Delay: 13 samples Node 0x03 [Audio Output] wcaps 0xd043d: Stereo Amp-Out Stripe Control: name="Speaker Playback Volume", index=0, device=0 ControlAmp: chs=3, dir=Out, idx=0, ofs=0 Control: name="Speaker Playback Switch", index=0, device=0 ControlAmp: chs=3, dir=Out, idx=0, ofs=0 Amp-Out caps: ofs=0x7f, nsteps=0x7f, stepsize=0x01, mute=1 Amp-Out vals: [0x7f 0x7f] Converter: stream=8, channel=0 PCM: rates [0x7f0]: 32000 44100 48000 88200 96000 176400 192000 bits [0x1e]: 16 20 24 32 formats [0x3]: PCM FLOAT Power states: D0 D3 EPSS Power: setting=D0, actual=D0 Delay: 13 samples
Node 0x10 [Pin Complex] wcaps 0x40058d: Stereo Amp-Out Control: name="Headphone Playback Volume", index=0, device=0 ControlAmp: chs=3, dir=Out, idx=0, ofs=0 Control: name="Headphone Playback Switch", index=0, device=0 ControlAmp: chs=3, dir=Out, idx=0, ofs=0 Control: name="Headphone Jack", index=0, device=0 Amp-Out caps: ofs=0x42, nsteps=0x42, stepsize=0x03, mute=1 Amp-Out vals: [0x42 0x42] Pincap 0x0000001c: OUT HP Detect Pin Default 0x032b401f: [Jack] HP Out at Ext Left Conn = Comb, Color = Green DefAssociation = 0x1, Sequence = 0xf Pin-ctls: 0xc0: OUT HP Unsolicited: tag=01, enabled=1 Power states: D0 D3 EPSS Power: setting=D0, actual=D0 Connection: 1 0x02