Since MP3 files are already compressed, they cannot be compressed any further. Therefore, the true speed is shown. Do DSL filters affect modem performance? Yes. DSL works by sending an "out-of-band" signal on your regular phone line. 56k Modems operate in the normal voice range of a standard phone line ( ~150 - ~3500hz). DSL adds a signal at much higher frequencies. (That's why not everyone can get DSL - if
