[Sleep Mode zZ]

  I opened up alsamixer and found the volume is not set at 0db. I changed it to 0db and now it's as loud as in Windows. I don't remember doing anything audio config but for some reason it seems it's using alsa, not Pulseaudio. Actually it's kind of too loud for my efficient HD 558

I was not sure that if the Pulse audio volume control controlled also the ALSA volume level. It seems that it does not. Makes the system a bit more complex than necessary... Now, when you have the ALSA volume settings at 0dB, you can forget it - unless you experience this problem again.
 
You are using Pulse or ALSA depending whichever sound output an application is using. Probably in every application you can change the sound output settings. If you choose in an application to use ALSA directly, you will bypass Pulse audio and its volume controls. You will also reserve the audio hardware exclusively for that application. Other applications will not be able to make any sounds through that device.
 
If you choose Pulse audio, you will still have ALSA working - and its volume settings affects the audio - because Pulse runs on top of ALSA, like RRod wrote. Pulse can take outputs from many applications at the same time and mix them together (and possibly resample some of them).

 

[nepherte]

Pulseaudio will use the drivers that are included with ALSA, but it sounds strange that it is using its mixer as well. You can tell ALSA to always use Pulseaudio:
 

 # /etc/asound.conf # Use PulseAudio by default pcm.!default { type pulse fallback "sysdefault" hint { show on description "Default ALSA Output (currently PulseAudio Sound Server)" } } ctl.!default { type pulse fallback "sysdefault" }

 

[RRod]

  Thanks a lot for your help, folks. I now need to read more about digital volume control and SQ and figure out what setting to use. Everything at 100% is too loud for my HD 558. I have to set my amp at very low to not deafen my ears. Actually I think I don't need an amp for HD 558, but somehow I got one (O2).

 
How low do you have to set the volume in Pulse to where your amp volume is around 50% for your typical music/videos?

 

[Tianming]

   
How low do you have to set the volume in Pulse to where your amp volume is around 50% for your typical music/videos?

Around 70%(-8 db). 

 

[Tianming]

 

Spoiler: Way more than you asked for, OP

Because I have no life:
 
Here** are the results of taking a -0.5dB 10kHz sine wave @ 16/48000 and passing it through Pulseaudio at both 16/48000 and 24/48000 at 35% (-27.29dB) volume. You can see that at 16bits it does appear that PA is dithering the output, and the highest distortion product is about 10dB higher than at 24 bits.
 
**L-to-R: original, 16, 24. dB levels are relative to the max within the file, so subtract 27.29dB from the levels of the volume-controlled files to get an absolute scale.

I am a noob in signal. Does this mean the SQ in the middle one is significantly affected? Also, does player matters? I am now using VLC and Rhythmbox.

 

[RRod]

  I am a noob in signal. Does this mean the SQ in the middle one is significantly affected? Also, does player matters? I am now using VLC and Rhythmbox.

 
It's a bit higher than the one of the right, but I wouldn't call either one bothersome. And this is at 35% volume in Pulse, which is probably lower than you need to push things for your amp's volume knob to be useful. The player would matter if the player uses its own volume instead of making use of Pulse's control, but you can always just use the main volume buttons, which should use Pulse. I'd say find a volume in Pulse where you find your amp volume knob useful, and then enjoy life.

 

[Tianming]

   
It's a bit higher than the one of the right, but I wouldn't call either one bothersome. And this is at 35% volume in Pulse, which is probably lower than you need to push things for your amp's volume knob to be useful. The player would matter if the player uses its own volume instead of making use of Pulse's control, but you can always just use the main volume buttons, which should use Pulse. I'd say find a volume in Pulse where you find your amp volume knob useful, and then enjoy life.

Do you mean the difference made by software volume control is actually very marginal? I haven't notice a big difference in SQ between 100% volume and around 50%, but I did not do strict A/B comparison. (btw I found using 70% volume is actually not enough. When I was testing with 70%, I did not notice the system volume was not at 100%. It turns out I need around 50% to have my amp knob to be useful.)

 

[RRod]

  Do you mean the difference made by software volume control is actually very marginal? I haven't notice a big difference in SQ between 100% volume and around 50%, but I did not do strict A/B comparison. (btw I found using 70% volume is actually not enough. When I was testing with 70%, I did not notice the system volume was not at 100%. It turns out I need around 50% to have my amp knob to be useful.)

 
So in the example above, the distortion products are a bit under 60dB below the signal level, which is already 27dB down from full scale. So we're talking ~90dB down from full scale, which is pretty low. And that's at 35% volume on Pulse; things will look better at 50%. All of this is more complicated of course (you have to consider all frequencies, and the sensitivities of our own hearing to different frequencies), but seeing this output would make me not worry. Indeed, I use Pulse control when I run my PM-3s directly into my laptop, and I have never been bothered by it (except that the jumps using the volume buttons can be a bit too big).

 

[Tianming]

   
So in the example above, the distortion products are a bit under 60dB below the signal level, which is already 27dB down from full scale. So we're talking ~90dB down from full scale, which is pretty low. And that's at 35% volume on Pulse; things will look better at 50%. All of this is more complicated of course (you have to consider all frequencies, and the sensitivities of our own hearing to different frequencies), but seeing this output would make me not worry. Indeed, I use Pulse control when I run my PM-3s directly into my laptop, and I have never been bothered by it (except that the jumps using the volume buttons can be a bit too big).

Thank you very much! I guess I was just worrying too much.