[Jibbie]

When the D4 is powered by your computer via USB, it only receives 5v of power, whereas it receives all 9v from the battery.  The more power allows the DAC to operate a little bit better, so a slight improvement in sound quality when switching from USB to the battery is expected.  The difference, however, should be extremely small.  I just run it from USB 24/7 as it is easier than constantly switching out batteries.  

 

[hyururi]

Oh ok thx for the help until now