Greetings,
this may be a stupid question for many of you, so please don't flame me :
What happens to the output signal if one alters the playback volume of MP3s/MPCs using the software mixer (OS independent)? I guess on the soundcard there is some type of amplifier, which can be controlled via the software mixer, but is it a good idea to set the master volume to 100% ? I tried this some years ago and it resulted in increased background noise. Perhaps the onboard amp of my old SB Live was of bad quality. Since then I only use a maximum 75% for the master volume. On the other hand, when I just set the WAV volume to 100%, I couldn't detect such an noise increase.

Can someone explain that to me (technical background would be nice) ?

PS: Current soundcard: Creative SB Audigy

If you're talking about changing the Windows volume, then yes, it is using the amplifier inside the sound card. Depending on your OS and your sound card, raising the volume too high can result in a.) too much noise, or b.) clipping, or of course c.) nothing bad. For example, I have a SB Live Value... if I raise the volume to 100% in Linux, I get clipping on loud samples, and it disappears around 90%. I don't have the same problem in Windows (because the volume is slightly lower... maybe the driver takes care of this).

So that's some background for you. I couldn't tell you specifically about your card because I've never used it. If you ask me, results may vary, so if somebody tells you that they have the same OS and sound card as you and they can listen to it at 100%, it may not necessarily work the same on your system. I may be completely wrong, but I have seen people disagree about this before. The best thing to do is try 100% -- if it is noisy, turn it down. If you have one, use your external amplifier (eg. a stereo receiver, or powered computer speakers) to change the volume when you are listening and never change the software volume setting. Hope this helps

Don't set all the mixers at 100% of the volume. Besides that the soundcard won't be able to handle such volumes you have the chance that you will blow up your output of your soundcard. This occurs when you play some sound at your computer which is too hard recorded.
This has happened to me and it made my Sound Blaster Live Player useless. When listening with headphones there was from that moment always noise in the background. So to be on the save side, set your master volume at about 75%, like you said. All the others still stand for 100%.

Thanks for the answers.