Some strange errors pop now and then and this particular glitch is a real travesty lol
Firstly, let me describe the problem in more detail so that you can figure out if this problem is currently affecting you. Audio in both music and video files are heard with proper background or theme, ambience sound, however vocal/voice sound is almost completely absent in certain areas and can be heard faintly,with fading in and out in other areas during playback. This effect glitch occurred completely by surprise in files that you may have already played before with no problem, and now effects certain files only while others of the same format play perfectly fine. This problem may also occur after installing a new media player, but is not exclusive to new program installations. and the most telling factor is if you have a stereo or 2.1 speaker system only or other non-surround speaker system.
Okay lets get down to it.if you did install a new media playing program uninstalling the program, will with a 90% certainty, NOT solve the problem ! reverting to previous restore points will also prove fruitless. The root of this glitch lies in the way audio systems installed on your PC interact and in particular codec configurations.
Step 1 - inspect the Sound Device tab in control panel, no matter which version of windows you have their will be a tab in control panel for sound devices. Open it up and check in there for a Speaker Setup tab that will allow you to define what type of speaker system you have connected to your audio output port, set it to headphone, stereo, or 2.1 , whichever applies. This is the speaker definition that WINDOWS uses only.
Step 2 - Codec configuration, whichever codec package you have installed there will be a console where you can define your speaker configuration, and now of course set it to headphone, stereo, or 2.1 , whichever applies. this speaker configuration is what your CODEC will use only.
Step 3 - is not universal to this problem, however certain media players have their own internal configurations that ALSO have speaker configuration options, again set it to what you have.
Those 3 steps would have fixed your problem for you.
The root cause for this glitch is that the files that have no vocals have in fact more than the standard stereo channels in them, in particular , AC3 class 6 channel (5.1) audio streams. what happened is that somewhere along the way, 1 of the 3 Above areas speaker configurations switched to, or was set to a 5.1 or higher configuration. thus the interaction between those layers created a bottleneck where at 1 layer all 6 channels were rendered but were output to only stereo or 2.1 by the other 2 layers. those dropped channels is where your vocals went and also explains the fade in/out as the faulty layer attempted to create the surround effect on merely 2 channels.
The biggest culprit is your codecs, which is where the problem usually comes up in.
Now, some codec packages DO NOT have specialised configuration console or the damn thing is so complicated you'd rather not try, i would recommend simply reinstalling the entire package, make sure to revert to their default settings when installed.
Hope that helps anyone who is having issues with this problem.