It's a popular tool for verifying the quality of music downloaded via P2P platforms. Re-encoding YouTube rips is popular - especially bootleg tracks - and this helps weed them out.
Spectrograms are not always a reliable way to judge audio quality of lossy-encoded files.
Lossy codecs use psycho-acoustic models with are designed to save space by discarding data that's unlikely to be missed by humans. - Often frequencies that would be masked by other sounds.
This process often results in what looks like 'holes' in the spectrogram, if compared to a lossless 'smooth' version.
Most people then (wrongly) assume that he file then sounds bad, when actually the bits saved there may well have been used to better encode part of the spectrum that human ears would notice.
It's quite possible to generate a great looking spectrogram that yields a poor sounding file and vice-versa.
Lossy encodes *always* cause some further degradation of audio-quality with each encode so it's best to leave lossy files as is, and always choose the least processed version. (e.g the 128kbps AAC (.m4a) from youtube will always be better than any MP3 version of the same source).
Audacity, SoX , & FFmpeg are also capable of producing more accurate spectrograms than Spek (with a steeper learning curve of course).
Much more informations on this and related topics at Hydrogen Audio[0]
It's a popular tool for verifying the quality of music downloaded via P2P platforms. Re-encoding YouTube rips is popular - especially bootleg tracks - and this helps weed them out.
[0] http://help.spek.cc/