if you analize in adobe audition for example in frecuency spectrum view and look for de lowpass limit, for q4 (128kbps) is 18000hz
Not necessarily, saratoga? How precisely defined is Ogg Vorbis decoding? I hear it is very carefully defined for MP3 - compliant decoders giving the same output, within rounding tolerances...
Using Sony Sound Forge:Zooming at the graphs in the basic sound editor, they look very very similar.Now, trying stuff with the spectrum analyser, keep the same settings and switching for one version of a track to the other, I see differences, but I have no idea what they mean of if they are meaninful.
But actually, since it comes from a tape, ... what are the highest frequencies possible on a tape ?