Cross posted from tpavelka post:

While browsing the VoxForge site I have come across this experiment:

http://www.voxforge.org/home/dev/mp3-compare

The results were kind of surprising, because there is no difference in the files that I could hear, so I figured that it should be the same for MFCC parametrisation (which can be viewed as an extremelly lossy compression and thus should throw away any differences between wav and mp3).

To get some insight I have generated some spectrograms using HCopy's filterbank analysis (which can be viewed as part of the MFCC process) to see if there is any difference. Although they are some visible differences, the most important finding is that the mp3 copression (or maybe the encoding back into wavs, I do not know which one) throws away parts of the recordings, namely the end parts. This part may be up to half a second long and may affect not just the ending silence, but in some cases (com_4311.wav) even the speech. Could this be the reason for the difference in the test?

The spectrograms can be downloaded here, the included Perl scripts may not work under Unix(due to the use of some Windows only commands).