· Can I increase the quality of an MP3 by decoding and re-encoding it?
Some people think that you can decode a low-bitrate MP3 file (say, 128kbps) file to a WAV file, then re-encode that WAV file at a higher bit rate (say, 192kbps), thereby increasing its quality. Or perhaps they might want to change the format of an audio file, for example converting from low-bitrate MP3 to WMA to improve the sound. If you don't understand the way audio compression works, this might actually seem logical.
But this will not work to increase quality. In fact, you will probably make the file sound even worse in the process.
Compressed audio files such as MP3 and WMA use a lossy method of data compression. This means that you can't get the lost data back by decoding the file.
When you create a WAV file from an MP3 file, you are simply decoding the file as-is. All of the data compression artifacts that existed in the 128kbps MP3 will be audible in the resulting uncompressed WAV file.
If you then re-encode that WAV file, you will be adding even more data compression artifacts (however slight) on top of the existing data compression artifacts. This will result in a file that actually sounds slightly worse than what you started with. Even if you re-encode it at a higher bit rate, you are still adding some artifacts without improving the original track. This is generally a Bad Thing.
Note that some audio-editing software packages will let you do this without properly warning you of the consequences. For example, they will let you do a "File/Open" on an MP3 file, and then do a "File/Save As" to a new file. In many cases, they are decoding the file when it is opened, then re-encoding it when it is saved. (There are a few rare exceptions, such as MP3Trim, but these programs can only can do a very limited set of things to the file.)
This is similar to using a graphics application to open a JPG file and then re-saving again as a JPG. Each time this is done, the image loses some quality because of the lossy JPG compression.
So use caution when editing/saving MP3 files, and edit only the original raw uncompressed WAV files whenever possible.
There are times when have no choice but to re-encode material that's already been data compressed. For example, if you're stuck with files compressed in a certain file format and can't go back to the original source material to re-encode them from scratch. Maybe you need to get an audio book into MP3 format and you're forced to grab it with Total Recorder. If you've got no other choice, then hey, make do with what you've got. Just remember that each lossy conversion increases the amount of compression artifacts.
If you simply want to increase the quality of your existing music collection, your best bet is to re-rip from the original CDs at a higher quality setting.