By now we all know that MP3 is a lossy format, meaning that to get a smaller file size some data must be thrown away. But what exactly is discarded? I’ll show you how you can see and hear what is lost when converting to a 320 kbs MP3 and a 56 kbs MP3. I’ll do it in steps so you can follow along at home.
First what you need to do is rip a song from cd to wav, then rip it again/convert to 320 and 56 kbs mp3. 320 kbs is about as good as you can get for sound quality using mp3, and 56 kbs is extremely bad, anyone should be able to hear the difference, while you may not hear the difference in 320 kbs.
Now create a new 16/44.1 session in Protools or whatever you use.
Drag all 3 files into the Editor/sequencer/arrange window/whatever your host calls it. You will notice that the start of the converted files will not line up with the original wav. You will have to zoom in and line up the waveforms sample accurate to get this to work.
Set the outputs of the 3 tracks to a stereo bus (ex bus 1-2).
You need to flip the phase of the 2 mp3 tracks, in protools use a Trim plugin.
Create an additional stereo audio track and set it’s input to the same as the output of the other tracks (ex bus 1-2). Record enable this track.
Mute the 56kbs track and record on the 4th track, you will see and hear the difference between the two files after the conversion. If they were identical the out-of-phase output would be perfectly silent.
(click images for full size screenshot)
Now try it again muting the 320 track and unmuting the 56 track. Much bigger difference this time.
As you can see MP3 loses quite a lot of information, what is more amazing is how this is perfectly acceptable to most people and they even pay for this sort of lowered quality. Correct me if I’m wrong but the iTunes store is only 192 kbs mp3s. It goes back to the quantity vs quality argument I guess.
Thanks to Jesse who pointed out that iTunes sells 128kbit AAC, soon they’ll be offering 256AAC without DRM but at $1.29 each. AAC is better than mp3 but it still has similar problems. At best 128kbit AAC might be as good as 160mp3. So it still sucks.
He also linked me to a geeky neat article about how bad the frequency response of an iPod is: http://www.hometheaterhifi.com/volume_14_1/ipod-bench-tested-3-2007-part-2.html