This is NOT the typical low audio out problem with Realtek chipsets which can be mostly fixed with tweaking level, balance & eq. settings. I researched that. This is on a single PC (tower) with two bootable drives, both running Win 7 from the same original image. The only difference (if you can call it that) is one drive is a SSD, the other a HDD. The 2nd bootable drive is used as a backup. This probalm is a good example why I have this. The MB is Gigabyte and it's the on board audio chipset that is being used. No other audio. This is using software for playing back mp4 files (LA Player, Pot Player & VLC Player). Doesn't matter which software, nor does it matter which mp4 file, one one drive the audio is fine. The other, the level is down anywhere from 10 to 20 db! I have updated the driver, but there as no change. It can only be some hidden O/S issue somewhere, but I have no idea what or where. Since everything is the same, the only differences are the system files, possibly including the registry, but that is a long shot. I have been trying different player softwares and I wonder if one of them made some 'hidden' change to the O/S somewhere that it affects the system globally past the user controls. Any idea here??