When I listen to an HD song in Youtube using Firefox it sounds like studio quality. But when I play a high quality FLAC version of the same song on Winamp it sounds not as good as Youtube. So I am not sure if it's my soundcard (default from mother board) or just some settings in Winamp.
closed as not a real question by Nifle, Journeyman Geek♦, slhck♦, KronoS, Dennis Jul 16 '12 at 3:29
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First and foremost, most sensible audio folk will tell you sound quality is subjective, and really depends on the person listening to it.
There's a few minor issues in question I'll address, and then talk about stuff you can do that MAY improve sound quality. I'm a foobar user, so I'm afraid I will be referring to other sources heavily when answering your question.
First, the objective parts:
Firstly HD Video != lossless - youtube uses either AAC at 152 kbps for the 'default' h264 video setting or vorbis at 192 kbps, least according to wikipedia. These are generally decent, sensible quality settings to use.
Secondly, most people, myself included will not be able to tell the difference between flac and lossy audio on most onboard sound cards. There are good, cheap addon cards, but the stock audio devices on PCs are not great. You'd also need good speakers or headphones.
While I to some extent, as an audiophile don't exactly agree with the findings (but they are valid when you JUST look at audio formatting options), you might also find this survey by Jeff Atwood (yes, that one) on lifehacker illuminating. He tested 5 samples at different quality levels and found, in a double blind test, that it was very hard to tell the difference between 192 vbr and better.
Now, from this, we can probably rule out the audio file. Now we need to work out how to tell the difference between the two.With an appropriately equipped soundcard, you could presumably record stereo in from both sources, and compare the wave forms somehow.
Now the subjective parts.
It might also be that there's some artefact in the youtube version, maybe different mastering that makes it sound better. Maybe its winamp settings - turn off any graphic equaliser you have set, and any weird 3d effects. Turn off the plugins.
As an alternative, try another player and see if it sounds better. It shouldn't but you never know. I'm a foobar2k user, but there's other options like lilith.
Now for better sound quality? Ditch the built in sound card (I favour the low end m audio DAW bundles for reasonably priced audio), decent headphones, and where possible use WASAPI exclusive mode in windows 7 with any sound card. There's a WASAPI plugin for winamp here