What is the Virtualizer sound effect in music players and how does it work? I use PlayerPro to play music on my smartphone.

In PlayerPro there are "Sound Effects", which are similar to the DSP manager. One of the sound effects is the Virtualizer.

When I enable the Virtualizer, even at 1%, it really changes the way the music feels. The audio becomes more echoey, and it sounds to me like I'm closer to the music. It gives me a live concert feeling.

When I played with the Virtualizer level I noticed there's a major difference between 0% and 1%. The difference from 1% to 100% is also noticeable, but it's not even close to the drastic difference when the Virtualizer is disabled compared to when it's enabled.

What does the Virtualizer do? What is it for, really?
How does the Virtualizer work?
How does this sound effect simulate a live concert sound (at least that's what it feels like to me)?
In the description of PlayerPro in Google Play this was mentioned: 


  STEREO WIDENING effect (virtualizer)


and a quick search on Wikipedia about what Stereo Widening is:


  Stereo widening
  
  Widening of the stereo image can be achieved by manipulating the
  relationship of the center signal M and the side signal S: M = (L +
  R)/2; S = (L - R)/2. A positive part of the side signal S is now fed
  into the left channel and a part with its phase inverted to the right
  channel. Some boomboxes feature such a process.
  
  Another way of looking at this same effect, without extrapolating a
  center and side signal from the left and right signals, is to simply
  add the left signal, slightly attenuated and phase inverted, into the
  right channel and vice-versa. Taking this a step further, a small
  delay (20-100ms) can be added to the inverted signal before mixing it
  back in to the original for output, adding a slight reverberation to
  the effect.