Sound server is a piece of software that “delivers” audio data (signal) from an audio rendering app (multimedia player or any other similar software) to an audio output device such as a sound card. It runs as a system service and works as the “middle man” between the OS audio driver and the physical hardware.
Not that long ago (like 6-5 years ago I think) GNU/Linux had troubles playing simultaneous audio outputs where other platforms such as MS Windows had this capability even as for as with Win 95!. There are few primary sound servers in GNU/Linux such as OSS, ALSA (ALSA is primarily an API for directly accessing audio hardware devices), ESD etc but from this bunch, ALSA was the strongest and was also the first to implement the simultaneous audio playback.
Then few years later came another sound server called Pulse audio but, until recently Pulse audio did have few issues with certain sound cards (as in my case it used to automatically mute the audio output in few older versions of Ubuntu) but these days it seems to be pretty stable.
Update: PulseAudio does not communicate directly with your audio hardware, instead, it relies on other tools such as ALSA for that. So in this regard, it is most probably the communication between PulseAudio and ALSA is the reason for those issues (a thanks goes to ‘Olimp’ -- comments, for pointing that out).
Starting with audio streaming to advanced volume controls, it’s plugin architecture lets you easily expand its features.
Talking about its plugins, “Ear Candy” is a pretty cool (intelligent ?) plugin that smartly fades out your audio outputs depending on the “occasion”.
For instance, let’s say that you were listening to an audio file using Banshee and then few seconds later opened a video file in Totem. Then Ear Candy will fade-out the volume of Banshee’s output and bring up the volume level of video that Totem is playing.
Or another example would be to, say while watching a video or listening to some music suddenly Skype rang the heck out of your speakers :), then again our little Ear Candy will fade out all other “noises” and bring up Skype audio to front. Pretty cool, right?
That’s the basic idea of how this app works but it also lets you adjust few advanced settings such as:
*. Manually change the audio fade levels.
*. Change the output device.
*. Enable volume meter detection.
*. Change application name or client name and Window titles.
*. Run at system start-up (can be disabled).
*. Show/Hide try icon… and many other features according to this Ear Candy home page.
You can install Ear Candy sound level manager in Ubuntu 12.04, 11.10 Oneiric Ocelot, 11.04 Natty Narwhal, 10.10 and 10.04 by simply issuing the below command.
sudo apt-get install earcandy
That should do it. Now go ahead and let our cool Ear Candy girl to handle everything for you ;-).