[ssamadhi97]

Originally Posted by ffooky

Without a doubt this has been (poorly) upsampled from 22 to 44.1KHz.

Indeed. This mirror image stuff is the infamous aliasing, and the frequency the spectrum is mirrored at is the original sampling frequency / 2. In most cases in this thread the spectrum is mirrored at 11025Hz, so the original sampling frequency was 22050Hz. You can observe the same effect with upsampled 32kHz material, where things get mirrored at 16kHz.

Good resampling filters will apply a not too aggressive lowpass / roll-off around original sampling frequency / 2 or do other tricks to prevent aliasing, which always results in a more or less faint mirroring effect around this frequency in the spectrum of upsampled material.

The characteristic that visually sets resampled material apart from the cutoff introduced by mp3 and other lossy encoders is the steepness of the lowpassing effect and the lack of any mirroring - with lossy encoders, the higher frequencies are usually not lowpassed away but simply *not encoded* which results in a very steep cutoff.