Let me preface by saying that users like PMA can provide a more technical answer.
]What exactly is loss? Quality loss? How do you specifically define it?
A wav file, like you might rip directly from a CD, is generally around 10MB per minute. When you use a lossless format like Flac, you squeeze the file down to around 70% its actual size, but you don't lose any info. Thus, converting it back to Wav keeps everything together. Mp3, on the other hand, chucks info when it compresses the file, primarily the higher frequencies.
Now, about quality: If you listen to a mp3-turned-Wav on headsets or on your computer, you may not notice much difference. But whenever I play them on a stereo, they sound very distant and hollow. If you compare a normal wav with one created from mp3, I'm sure you'll notice a difference as well. (I say this with a degree of experience. When I first found Queen boots on the old QZ mp3 section years ago, I turned them into WAV cds, too. Then I figured out the difference and realized how many discs I wasted.)
Imagine someone getting an mp3, turing it into wav, sharing it with others, and then someone else repeating that process, and you get an idea of how quickly the quality of recordings can go downhill.
Also, what program do you recommend? Can i download a codec for that?
If you mean for converting Flac to Wav, I suggest Flac Frontend http://wiki.etree.org/index.php?page=FlacFrontend
That will explain how to use it. Like I mentioned, it's real easy to use and makes perfect lossless copies. The only thing some people new to all this might want to consider is the hard drive space they will need. If you have a 600MB Flac torrent, you'll need another 900MB to creat the wav files. Just FYI.
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