My ears are not really too great at picking out if a file has been compressed which is why I am okay with MP3's. I understand that if one has a wav file that has been previously compressed then re-expanded, the quality of the wav is no better than the compressed file. If one were to recompress to a lossy format, the resultant file would be of poor quality. I was just wondering if there was a way to determine if a wav file may have been previously compressed to a lossy format such as MP3. Thanks.

Can we assume that you have the original WAV for comparison? Or that you have the CD and can re-rip the track?

Most mp3 encoders apply a lowpass filter before encoding the audio. This means that you could have a look at the spectral view in whatever which audio editor (EAC's built-in one will do) and look for a lowpass frequancy. Many popular encoders use 16kHz lowpass @ 128kbps bitrate.

A lot of real cd's also cut off at 16khz.

I was just in a discussion about MusicMatch's encoder cutting off at 16khz and I had to look at several cd's & songs before I found some that had substantial music about 16khz.

A few had a very clear cut-off at 16khz. Just what the producer & artist wanted.

The point is, the freq spectrum isn't a reliable indicator.

You can outfilter freqencies, and then listen to the wav. I think this can be done with cooledit, maybe matlab. You can also use analogue filter after the sound comes from soundcard.
This way you should be able to recognise the watery noise that comes hearable when frquencies are removed.

I also know a much easier method of revealing mp3s or other compressed files, but it only works for joint stereo or "channel coupled" compressed files.
This way you can hear even a 320kbit/s encoded joint stereo mp3. I know many people won't belive it, and call me stupid, but it's true. It has to do with how you connect your speakers to your soundcard, or to your speakers.
If the cables are put in a special way, the speaker jack will work as a filter. What it sounds like: Much of the sound that is present in both channels, is very quiet, example bass and much of the lead singer.
What comes clear is sounds that is not in the same degree in both channels, or only in one channel. One can clearly hear the watery effect, because frequencies are removed. In addition the 50Hz noise is very clear.
I know it will work on many soundcards but not all. It will probably NOT ruin your speakers, but use it at your own risk.