YEMV but as far as I can tell, recordings with more distortion/noise reveal MP3's artifacts most readily. This is assuming of course that you know the CD *very* well, otherwise you can't tell what's from the source vs the compression. I heard this for myself before I knew much about how MP3 works, but it makes even more sense now.
It's analogous to video compression really. On a DVD, when the image is static and simple, it looks very crisp and detailed. However during a big explosion and/or when the camera is panning over a complex scene, that is when you will see the artifacts. Ignoring for a moment how the mp3 encoding process decides what to keep and what to discard, the file itself is at the end of the day a small number of frequency components representing each tiny unit of time (a frame). A really clean studio recording will have simpler waveforms that can be more accurately reconstructed from a small set of frequency components. However when you add background noise, audience noise, disortion from tubes and guitar amps etc you get an extremely complex signal. Also drums and cymbals especially can have a wide freuency content and fast transitions which mp3 has trouble with. You generally won't hear the most artifacts in the main, loudest element of the program, because that's where mp3's psychoacoustic model can get the most perceived quality per bit. The best example I can think of is on one of the DMB live albums (sorry forget which one) during the into to "two step". They're getting into the intro and the audience is clapping in unison. On each clap, with mp3 the clapping sounds like an "envelope" of noise but on the CD it actually sounds like lots of hands coming together. The thing is you'd have to really be familiar with the CD in order to know that you're missing something. But this one example where I can repeatably tell the difference blind (at 160K anyway). A good experiment would be to make a few encodings starting at a very low bit rate, say 32kbps. What the artifacts sound like and what kind of complexity causes them will then be obvious. From there work up to higher bit rates. Above 128kbps it will be get tougher quickly, especially with VBR, as this allows any complex section to use the max 320kbps when needed. Also frankly, don't overlook the bit between your ears either. Knowing that you're getting all the data is important too! Sucks to be listening to something that you only have in mp3 and wonddering if it might sound better otherwise. -- seanadams _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
